Merging 'master' into 'wrap'

wrap/pybind11/.appveyor.yml

@@ -19,7 +19,7 @@ install:
     if ($env:PLATFORM -eq "x64") { $env:PYTHON = "$env:PYTHON-x64" }
     $env:PATH = "C:\Python$env:PYTHON\;C:\Python$env:PYTHON\Scripts\;$env:PATH"
     python -W ignore -m pip install --upgrade pip wheel
-    python -W ignore -m pip install pytest numpy --no-warn-script-location
+    python -W ignore -m pip install pytest numpy --no-warn-script-location pytest-timeout
 - ps: |
     Start-FileDownload 'https://gitlab.com/libeigen/eigen/-/archive/3.3.7/eigen-3.3.7.zip'
     7z x eigen-3.3.7.zip -y > $null

wrap/pybind11/.clang-format

@@ -0,0 +1,19 @@
+---
+# See all possible options and defaults with:
+# clang-format --style=llvm --dump-config
+BasedOnStyle: LLVM
+AccessModifierOffset: -4
+AlwaysBreakTemplateDeclarations: Yes
+BinPackArguments: false
+BinPackParameters: false
+BreakBeforeBinaryOperators: All
+BreakConstructorInitializers: BeforeColon
+ColumnLimit: 99
+IndentCaseLabels: true
+IndentPPDirectives: AfterHash
+IndentWidth: 4
+Language: Cpp
+SpaceAfterCStyleCast: true
+Standard: Cpp11
+TabWidth: 4
+...

wrap/pybind11/.clang-tidy

@@ -1,13 +1,66 @@
 FormatStyle: file
 
 Checks: '
+*bugprone*,
+cppcoreguidelines-init-variables,
+cppcoreguidelines-slicing,
+clang-analyzer-optin.cplusplus.VirtualCall,
+google-explicit-constructor,
 llvm-namespace-comment,
-modernize-use-override,
+misc-misplaced-const,
-readability-container-size-empty,
+misc-non-copyable-objects,
-modernize-use-using,
+misc-static-assert,
-modernize-use-equals-default,
+misc-throw-by-value-catch-by-reference,
+misc-uniqueptr-reset-release,
+misc-unused-parameters,
+modernize-avoid-bind,
+modernize-make-shared,
+modernize-redundant-void-arg,
+modernize-replace-auto-ptr,
+modernize-replace-disallow-copy-and-assign-macro,
+modernize-replace-random-shuffle,
+modernize-shrink-to-fit,
 modernize-use-auto,
+modernize-use-bool-literals,
+modernize-use-equals-default,
+modernize-use-equals-delete,
+modernize-use-default-member-init,
+modernize-use-noexcept,
 modernize-use-emplace,
+modernize-use-override,
+modernize-use-using,
+*performance*,
+readability-avoid-const-params-in-decls,
+readability-const-return-type,
+readability-container-size-empty,
+readability-delete-null-pointer,
+readability-else-after-return,
+readability-implicit-bool-conversion,
+readability-make-member-function-const,
+readability-misplaced-array-index,
+readability-non-const-parameter,
+readability-redundant-function-ptr-dereference,
+readability-redundant-smartptr-get,
+readability-redundant-string-cstr,
+readability-simplify-subscript-expr,
+readability-static-accessed-through-instance,
+readability-static-definition-in-anonymous-namespace,
+readability-string-compare,
+readability-suspicious-call-argument,
+readability-uniqueptr-delete-release,
+-bugprone-exception-escape,
+-bugprone-reserved-identifier,
+-bugprone-unused-raii,
 '
 
+CheckOptions:
+- key:             performance-for-range-copy.WarnOnAllAutoCopies
+  value:           true
+- key:             performance-unnecessary-value-param.AllowedTypes
+  value:           'exception_ptr$;'
+- key:             readability-implicit-bool-conversion.AllowPointerConditions
+  value:           true
+
 HeaderFilterRegex: 'pybind11/.*h'
+
+WarningsAsErrors: '*'

wrap/pybind11/.github/CODEOWNERS

@@ -0,0 +1,9 @@
+*.cmake @henryiii
+CMakeLists.txt @henryiii
+*.yml @henryiii
+*.yaml @henryiii
+/tools/ @henryiii
+/pybind11/ @henryiii
+noxfile.py @henryiii
+.clang-format @henryiii
+.clang-tidy @henryiii

wrap/pybind11/.github/CONTRIBUTING.md

@@ -53,6 +53,33 @@ derivative works thereof, in binary and source code form.
 
 ## Development of pybind11
 
+### Quick setup
+
+To setup a quick development environment, use [`nox`](https://nox.thea.codes).
+This will allow you to do some common tasks with minimal setup effort, but will
+take more time to run and be less flexible than a full development environment.
+If you use [`pipx run nox`](https://pipx.pypa.io), you don't even need to
+install `nox`. Examples:
+
+```bash
+# List all available sessions
+nox -l
+
+# Run linters
+nox -s lint
+
+# Run tests on Python 3.9
+nox -s tests-3.9
+
+# Build and preview docs
+nox -s docs -- serve
+
+# Build SDists and wheels
+nox -s build
+```
+
+### Full setup
+
 To setup an ideal development environment, run the following commands on a
 system with CMake 3.14+:
 
@@ -93,7 +120,7 @@ The valid options are:
 * `-DPYBIND11_NOPYTHON=ON`: Disable all Python searching (disables tests)
 * `-DBUILD_TESTING=ON`: Enable the tests
 * `-DDOWNLOAD_CATCH=ON`: Download catch to build the C++ tests
-* `-DOWNLOAD_EIGEN=ON`: Download Eigen for the NumPy tests
+* `-DDOWNLOAD_EIGEN=ON`: Download Eigen for the NumPy tests
 * `-DPYBIND11_INSTALL=ON/OFF`: Enable the install target (on by default for the
   master project)
 * `-DUSE_PYTHON_INSTALL_DIR=ON`: Try to install into the python dir
@@ -126,13 +153,26 @@ cmake --build build --target check
 `--target` can be spelled `-t` in CMake 3.15+. You can also run individual
 tests with these targets:
 
-* `pytest`: Python tests only
+* `pytest`: Python tests only, using the
+[pytest](https://docs.pytest.org/en/stable/) framework
 * `cpptest`: C++ tests only
 * `test_cmake_build`: Install / subdirectory tests
 
 If you want to build just a subset of tests, use
-`-DPYBIND11_TEST_OVERRIDE="test_callbacks.cpp;test_pickling.cpp"`. If this is
+`-DPYBIND11_TEST_OVERRIDE="test_callbacks;test_pickling"`. If this is
-empty, all tests will be built.
+empty, all tests will be built. Tests are specified without an extension if they need both a .py and
+.cpp file.
+
+You may also pass flags to the `pytest` target by editing `tests/pytest.ini` or
+by using the `PYTEST_ADDOPTS` environment variable
+(see [`pytest` docs](https://docs.pytest.org/en/2.7.3/customize.html#adding-default-options)). As an example:
+
+```bash
+env PYTEST_ADDOPTS="--capture=no --exitfirst" \
+    cmake --build build --target pytest
+# Or using abbreviated flags
+env PYTEST_ADDOPTS="-s -x" cmake --build build --target pytest
+```
 
 ### Formatting
 
@@ -164,16 +204,42 @@ name, pre-commit):
 pre-commit install
 ```
 
-### Clang-Tidy
+### Clang-Format
 
-To run Clang tidy, the following recipe should work. Files will be modified in
+As of v2.6.2, pybind11 ships with a [`clang-format`][clang-format]
-place, so you can use git to monitor the changes.
+configuration file at the top level of the repo (the filename is
+`.clang-format`). Currently, formatting is NOT applied automatically, but
+manually using `clang-format` for newly developed files is highly encouraged.
+To check if a file needs formatting:
 
 ```bash
-docker run --rm -v $PWD:/pybind11 -it silkeh/clang:10
+clang-format -style=file --dry-run some.cpp
-apt-get update && apt-get install python3-dev python3-pytest
+```
-cmake -S pybind11/ -B build -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy);-fix"
+
-cmake --build build
+The output will show things to be fixed, if any. To actually format the file:
+
+```bash
+clang-format -style=file -i some.cpp
+```
+
+Note that the `-style-file` option searches the parent directories for the
+`.clang-format` file, i.e. the commands above can be run in any subdirectory
+of the pybind11 repo.
+
+### Clang-Tidy
+
+[`clang-tidy`][clang-tidy] performs deeper static code analyses and is
+more complex to run, compared to `clang-format`, but support for `clang-tidy`
+is built into the pybind11 CMake configuration. To run `clang-tidy`, the
+following recipe should work. Run the `docker` command from the top-level
+directory inside your pybind11 git clone. Files will be modified in place,
+so you can use git to monitor the changes.
+
+```bash
+docker run --rm -v $PWD:/mounted_pybind11 -it silkeh/clang:12
+apt-get update && apt-get install -y python3-dev python3-pytest
+cmake -S /mounted_pybind11/ -B build -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy);-fix" -DDOWNLOAD_EIGEN=ON -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=17
+cmake --build build -j 2 -- --keep-going
 ```
 
 ### Include what you use
@@ -186,7 +252,7 @@ cmake -S . -B build-iwyu -DCMAKE_CXX_INCLUDE_WHAT_YOU_USE=$(which include-what-y
 cmake --build build
 ```
 
-The report is sent to stderr; you can pip it into a file if you wish.
+The report is sent to stderr; you can pipe it into a file if you wish.
 
 ### Build recipes
 
@@ -313,6 +379,8 @@ if you really want to.
 
 
 [pre-commit]: https://pre-commit.com
+[clang-format]: https://clang.llvm.org/docs/ClangFormat.html
+[clang-tidy]: https://clang.llvm.org/extra/clang-tidy/
 [pybind11.readthedocs.org]: http://pybind11.readthedocs.org/en/latest
 [issue tracker]: https://github.com/pybind/pybind11/issues
 [gitter]: https://gitter.im/pybind/Lobby

wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.md

@@ -1,28 +0,0 @@
----
-name: Bug Report
-about: File an issue about a bug
-title: "[BUG] "
----
-
-
-Make sure you've completed the following steps before submitting your issue -- thank you!
-
-1. Make sure you've read the [documentation][]. Your issue may be addressed there.
-2. Search the [issue tracker][] to verify that this hasn't already been reported. +1 or comment there if it has.
-3. Consider asking first in the [Gitter chat room][].
-4. Include a self-contained and minimal piece of code that reproduces the problem. If that's not possible, try to make the description as clear as possible.
-    a. If possible, make a PR with a new, failing test to give us a starting point to work on!
-
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist and the template text in parentheses below.*
-
-## Issue description
-
-(Provide a short description, state the expected behavior and what actually happens.)
-
-## Reproducible example code
-
-(The code should be minimal, have no external dependencies, isolate the function(s) that cause breakage. Submit matched and complete C++ and Python snippets that can be easily compiled and run to diagnose the issue.)

wrap/pybind11/.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,45 @@
+name: Bug Report
+description: File an issue about a bug
+title: "[BUG]: "
+labels: [triage]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Maintainers will only make a best effort to triage PRs. Please do your best to make the issue as easy to act on as possible, and only open if clearly a problem with pybind11 (ask first if unsure).
+  - type: checkboxes
+    id: steps
+    attributes:
+      label: Required prerequisites
+      description: Make sure you've completed the following steps before submitting your issue -- thank you!
+      options:
+        - label: Make sure you've read the [documentation](https://pybind11.readthedocs.io). Your issue may be addressed there.
+          required: true
+        - label: Search the [issue tracker](https://github.com/pybind/pybind11/issues) and [Discussions](https:/pybind/pybind11/discussions) to verify that this hasn't already been reported. +1 or comment there if it has.
+          required: true
+        - label: Consider asking first in the [Gitter chat room](https://gitter.im/pybind/Lobby) or in a [Discussion](https:/pybind/pybind11/discussions/new).
+          required: false
+
+  - type: textarea
+    id: description
+    attributes:
+      label: Problem description
+      placeholder: >-
+        Provide a short description, state the expected behavior and what
+        actually happens. Include relevant information like what version of
+        pybind11 you are using, what system you are on, and any useful commands
+        / output.
+    validations:
+      required: true
+
+  - type: textarea
+    id: code
+    attributes:
+      label: Reproducible example code
+      placeholder: >-
+        The code should be minimal, have no external dependencies, isolate the
+        function(s) that cause breakage. Submit matched and complete C++ and
+        Python snippets that can be easily compiled and run to diagnose the
+        issue. If possible, make a PR with a new, failing test to give us a
+        starting point to work on!
+      render: text

wrap/pybind11/.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
 blank_issues_enabled: false
 contact_links:
+  - name: Ask a question
+    url: https://github.com/pybind/pybind11/discussions/new
+    about: Please ask and answer questions here, or propose new ideas.
   - name: Gitter room
     url: https://gitter.im/pybind/Lobby
     about: A room for discussing pybind11 with an active community

wrap/pybind11/.github/ISSUE_TEMPLATE/feature-request.md

@@ -1,16 +0,0 @@
----
-name: Feature Request
-about: File an issue about adding a feature
-title: "[FEAT] "
----
-
-
-Make sure you've completed the following steps before submitting your issue -- thank you!
-
-1. Check if your feature has already been mentioned / rejected / planned in other issues.
-2. If those resources didn't help, consider asking in the [Gitter chat room][] to see if this is interesting / useful to a larger audience and possible to implement reasonably,
-4. If you have a useful feature that passes the previous items (or not suitable for chat), please fill in the details below.
-
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist.*

wrap/pybind11/.github/ISSUE_TEMPLATE/question.md

@@ -1,21 +0,0 @@
----
-name: Question
-about: File an issue about unexplained behavior
-title: "[QUESTION] "
----
-
-If you have a question, please check the following first:
-
-1. Check if your question has already been answered in the [FAQ][] section.
-2. Make sure you've read the [documentation][]. Your issue may be addressed there.
-3. If those resources didn't help and you only have a short question (not a bug report), consider asking in the [Gitter chat room][]
-4. Search the [issue tracker][], including the closed issues, to see if your question has already been asked/answered. +1 or comment if it has been asked but has no answer.
-5. If you have a more complex question which is not answered in the previous items (or not suitable for chat), please fill in the details below.
-6. Include a self-contained and minimal piece of code that illustrates your question. If that's not possible, try to make the description as clear as possible.
-
-[FAQ]: http://pybind11.readthedocs.io/en/latest/faq.html
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist.*

wrap/pybind11/.github/dependabot.yml

@@ -0,0 +1,16 @@
+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    ignore:
+      # Official actions have moving tags like v1
+      # that are used, so they don't need updates here
+      - dependency-name: "actions/checkout"
+      - dependency-name: "actions/setup-python"
+      - dependency-name: "actions/cache"
+      - dependency-name: "actions/upload-artifact"
+      - dependency-name: "actions/download-artifact"
+      - dependency-name: "actions/labeler"

wrap/pybind11/.github/labeler.yml

@@ -0,0 +1,8 @@
+docs:
+- any:
+  - 'docs/**/*.rst'
+  - '!docs/changelog.rst'
+  - '!docs/upgrade.rst'
+
+ci:
+- '.github/workflows/*.yml'

wrap/pybind11/.github/labeler_merged.yml

@@ -0,0 +1,3 @@
+needs changelog:
+- all:
+  - '!docs/changelog.rst'

wrap/pybind11/.github/pull_request_template.md

@@ -0,0 +1,19 @@
+<!--
+Title (above): please place [branch_name] at the beginning if you are targeting a branch other than master. *Do not target stable*.
+It is recommended to use conventional commit format, see conventionalcommits.org, but not required.
+-->
+## Description
+
+<!-- Include relevant issues or PRs here, describe what changed and why -->
+
+
+## Suggested changelog entry:
+
+<!-- Fill in the below block with the expected RestructuredText entry. Delete if no entry needed;
+     but do not delete header or rst block if an entry is needed! Will be collected via a script. -->
+
+```rst
+
+```
+
+<!-- If the upgrade guide needs updating, note that here too -->

wrap/pybind11/.github/workflows/ci.yml

@@ -9,6 +9,13 @@ on:
       - stable
       - v*
 
+concurrency:
+  group: test-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  PIP_ONLY_BINARY: numpy
+
 jobs:
   # This is the "main" test suite, which tests a large number of different
   # versions of default compilers and Python versions in GitHub Actions.
@@ -16,71 +23,42 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        runs-on: [ubuntu-latest, windows-latest, macos-latest]
+        runs-on: [ubuntu-latest, windows-2022, macos-latest]
-        arch: [x64]
         python:
-        - 2.7
+        - '2.7'
-        - 3.5
+        - '3.5'
-        - 3.8
+        - '3.6'
-        - pypy2
+        - '3.9'
-        - pypy3
+        - '3.10'
+        - 'pypy-3.7-v7.3.7'
+        - 'pypy-3.8-v7.3.7'
 
         # Items in here will either be added to the build matrix (if not
         # present), or add new keys to an existing matrix element if all the
         # existing keys match.
         #
-        # We support three optional keys: args (both build), args1 (first
+        # We support an optional key: args, for cmake args
-        # build), and args2 (second build).
         include:
+          # Just add a key
           - runs-on: ubuntu-latest
-            python: 3.6
+            python: '3.6'
-            arch: x64
             args: >
               -DPYBIND11_FINDPYTHON=ON
-          - runs-on: windows-2016
+              -DCMAKE_CXX_FLAGS="-D_=1"
-            python: 3.7
-            arch: x86
-            args2: >
-              -DCMAKE_CXX_FLAGS="/permissive- /EHsc /GR"
           - runs-on: windows-latest
-            python: 3.6
+            python: '3.6'
-            arch: x64
             args: >
               -DPYBIND11_FINDPYTHON=ON
-          - runs-on: windows-latest
-            python: 3.7
-            arch: x64
-
-          - runs-on: ubuntu-latest
-            python: 3.9-dev
-            arch: x64
           - runs-on: macos-latest
-            python: 3.9-dev
+            python: 'pypy-2.7'
-            arch: x64
+          # Inject a couple Windows 2019 runs
-            args: >
+          - runs-on: windows-2019
-              -DPYBIND11_FINDPYTHON=ON
+            python: '3.9'
+          - runs-on: windows-2019
+            python: '2.7'
 
-        # These items will be removed from the build matrix, keys must match.
+    name: "🐍 ${{ matrix.python }} • ${{ matrix.runs-on }} • x64 ${{ matrix.args }}"
-        exclude:
-            # Currently 32bit only, and we build 64bit
-          - runs-on: windows-latest
-            python: pypy2
-            arch: x64
-          - runs-on: windows-latest
-            python: pypy3
-            arch: x64
-
-            # Currently broken on embed_test
-          - runs-on: windows-latest
-            python: 3.8
-            arch: x64
-          - runs-on: windows-latest
-            python: 3.9-dev
-            arch: x64
-
-    name: "🐍 ${{ matrix.python }} • ${{ matrix.runs-on }} • ${{ matrix.arch }} ${{ matrix.args }}"
     runs-on: ${{ matrix.runs-on }}
-    continue-on-error: ${{ endsWith(matrix.python, 'dev') }}
 
     steps:
     - uses: actions/checkout@v2
@@ -89,13 +67,18 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python }}
-        architecture: ${{ matrix.arch }}
 
-    - name: Setup Boost (Windows / Linux latest)
+    - name: Setup Boost (Linux)
-      run: echo "::set-env name=BOOST_ROOT::$BOOST_ROOT_1_72_0"
+      # Can't use boost + define _
+      if: runner.os == 'Linux' && matrix.python != '3.6'
+      run: sudo apt-get install libboost-dev
+
+    - name: Setup Boost (macOS)
+      if: runner.os == 'macOS'
+      run: brew install boost
 
     - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.3
+      uses: jwlawson/actions-setup-cmake@v1.12
 
     - name: Cache wheels
       if: runner.os == 'macOS'
@@ -106,10 +89,11 @@ jobs:
         # for ways to do this more generally
         path: ~/Library/Caches/pip
         # Look to see if there is a cache hit for the corresponding requirements file
-        key: ${{ runner.os }}-pip-${{ matrix.python }}-${{ matrix.arch }}-${{ hashFiles('tests/requirements.txt') }}
+        key: ${{ runner.os }}-pip-${{ matrix.python }}-x64-${{ hashFiles('tests/requirements.txt') }}
 
     - name: Prepare env
-      run: python -m pip install -r tests/requirements.txt --prefer-binary
+      run: |
+        python -m pip install -r tests/requirements.txt
 
     - name: Setup annotations on Linux
       if: runner.os == 'Linux'
@@ -132,6 +116,8 @@ jobs:
       run: cmake --build . --target pytest -j 2
 
     - name: C++11 tests
+      # TODO: Figure out how to load the DLL on Python 3.8+
+      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11-dev' || matrix.python == 'pypy-3.8'))"
       run: cmake --build .  --target cpptest -j 2
 
     - name: Interface test C++11
@@ -141,7 +127,7 @@ jobs:
       run: git clean -fdx
 
     # Second build - C++17 mode and in a build directory
-    - name: Configure ${{ matrix.args2 }}
+    - name: Configure C++17
       run: >
         cmake -S . -B build2
         -DPYBIND11_WERROR=ON
@@ -149,7 +135,6 @@ jobs:
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
         ${{ matrix.args }}
-        ${{ matrix.args2 }}
 
     - name: Build
       run: cmake --build build2 -j 2
@@ -158,8 +143,28 @@ jobs:
       run: cmake --build build2 --target pytest
 
     - name: C++ tests
+      # TODO: Figure out how to load the DLL on Python 3.8+
+      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10' || matrix.python == '3.11-dev' || matrix.python == 'pypy-3.8'))"
       run: cmake --build build2 --target cpptest
 
+    # Third build - C++17 mode with unstable ABI
+    - name: Configure (unstable ABI)
+      run: >
+        cmake -S . -B build3
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=17
+        -DPYBIND11_INTERNALS_VERSION=10000000
+        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+        ${{ matrix.args }}
+
+    - name: Build (unstable ABI)
+      run: cmake --build build3 -j 2
+
+    - name: Python tests (unstable ABI)
+      run: cmake --build build3 --target pytest
+
     - name: Interface test
       run: cmake --build build2 --target test_cmake_build
 
@@ -167,21 +172,105 @@ jobs:
     # MSVC, but for now, this action works:
     - name: Prepare compiler environment for Windows 🐍 2.7
       if: matrix.python == 2.7 && runner.os == 'Windows'
-      uses: ilammy/msvc-dev-cmd@v1
+      uses: ilammy/msvc-dev-cmd@v1.10.0
       with:
         arch: x64
 
     # This makes two environment variables available in the following step(s)
     - name: Set Windows 🐍 2.7 environment variables
       if: matrix.python == 2.7 && runner.os == 'Windows'
+      shell: bash
       run: |
-        echo "::set-env name=DISTUTILS_USE_SDK::1"
+        echo "DISTUTILS_USE_SDK=1" >> $GITHUB_ENV
-        echo "::set-env name=MSSdk::1"
+        echo "MSSdk=1" >> $GITHUB_ENV
 
     # This makes sure the setup_helpers module can build packages using
     # setuptools
     - name: Setuptools helpers test
       run: pytest tests/extra_setuptools
+      if: "!(matrix.python == '3.5' && matrix.runs-on == 'windows-2022')"
+
+
+  deadsnakes:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+        # TODO: Fails on 3.10, investigate
+        - python-version: "3.9"
+          python-debug: true
+          valgrind: true
+      # - python-version: "3.11-dev"
+      #   python-debug: false
+
+    name: "🐍 ${{ matrix.python-version }}${{ matrix.python-debug && '-dbg' || '' }} (deadsnakes)${{ matrix.valgrind && ' • Valgrind' || '' }} • x64"
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup Python ${{ matrix.python-version }} (deadsnakes)
+      uses: deadsnakes/action@v2.1.1
+      with:
+        python-version: ${{ matrix.python-version }}
+        debug: ${{ matrix.python-debug }}
+
+    - name: Update CMake
+      uses: jwlawson/actions-setup-cmake@v1.12
+
+    - name: Valgrind cache
+      if: matrix.valgrind
+      uses: actions/cache@v2
+      id: cache-valgrind
+      with:
+        path: valgrind
+        key: 3.16.1 # Valgrind version
+
+    - name: Compile Valgrind
+      if: matrix.valgrind && steps.cache-valgrind.outputs.cache-hit != 'true'
+      run: |
+        VALGRIND_VERSION=3.16.1
+        curl https://sourceware.org/pub/valgrind/valgrind-$VALGRIND_VERSION.tar.bz2 -o - | tar xj
+        mv valgrind-$VALGRIND_VERSION valgrind
+        cd valgrind
+        ./configure
+        make -j 2 > /dev/null
+
+    - name: Install Valgrind
+      if: matrix.valgrind
+      working-directory: valgrind
+      run: |
+        sudo make install
+        sudo apt-get update
+        sudo apt-get install libc6-dbg  # Needed by Valgrind
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    - name: Configure
+      env:
+        SETUPTOOLS_USE_DISTUTILS: stdlib
+      run: >
+        cmake -S . -B build
+        -DCMAKE_BUILD_TYPE=Debug
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=17
+
+    - name: Build
+      run: cmake --build build -j 2
+
+    - name: Python tests
+      run: cmake --build build --target pytest
+
+    - name: C++ tests
+      run: cmake --build build --target cpptest
+
+    - name: Run Valgrind on Python tests
+      if: matrix.valgrind
+      run: cmake --build build --target memcheck
 
 
   # Testing on clang using the excellent silkeh clang docker images
@@ -194,12 +283,20 @@ jobs:
           - 3.6
           - 3.7
           - 3.9
-          - 5
           - 7
           - 9
           - dev
+        std:
+          - 11
+        include:
+          - clang: 5
+            std: 14
+          - clang: 10
+            std: 20
+          - clang: 10
+            std: 17
 
-    name: "🐍 3 • Clang ${{ matrix.clang }} • x64"
+    name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
     container: "silkeh/clang:${{ matrix.clang }}"
 
     steps:
@@ -214,6 +311,7 @@ jobs:
         cmake -S . -B build
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
+        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build
@@ -252,50 +350,54 @@ jobs:
       run: cmake --build build --target pytest
 
 
-  # Testing CentOS 8 + PGI compilers
+# TODO: Internal compiler error - report to NVidia
-  centos-nvhpc8:
+#  # Testing CentOS 8 + PGI compilers
-    runs-on: ubuntu-latest
+#  centos-nvhpc8:
-    name: "🐍 3 • CentOS8 / PGI 20.7 • x64"
+#    runs-on: ubuntu-latest
-    container: centos:8
+#    name: "🐍 3 • CentOS8 / PGI 20.11 • x64"
-
+#    container: centos:8
-    steps:
+#
-    - uses: actions/checkout@v2
+#    steps:
-
+#    - uses: actions/checkout@v2
-    - name: Add Python 3 and a few requirements
+#
-      run: yum update -y && yum install -y git python3-devel python3-numpy python3-pytest make environment-modules
+#    - name: Add Python 3 and a few requirements
-
+#      run: yum update -y && yum install -y git python3-devel python3-numpy python3-pytest make environment-modules
-    - name: Install CMake with pip
+#
-      run: |
+#    - name: Install CMake with pip
-        python3 -m pip install --upgrade pip
+#      run: |
-        python3 -m pip install cmake --prefer-binary
+#        python3 -m pip install --upgrade pip
-
+#        python3 -m pip install cmake --prefer-binary
-    - name: Install NVidia HPC SDK
+#
-      run: yum -y install https://developer.download.nvidia.com/hpc-sdk/nvhpc-20-7-20.7-1.x86_64.rpm https://developer.download.nvidia.com/hpc-sdk/nvhpc-2020-20.7-1.x86_64.rpm
+#    - name: Install NVidia HPC SDK
-
+#      run: >
-    - name: Configure
+#        yum -y install
-      shell: bash
+#        https://developer.download.nvidia.com/hpc-sdk/20.11/nvhpc-20-11-20.11-1.x86_64.rpm
-      run: |
+#        https://developer.download.nvidia.com/hpc-sdk/20.11/nvhpc-2020-20.11-1.x86_64.rpm
-        source /etc/profile.d/modules.sh
+#
-        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.7
+#    - name: Configure
-        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+#      shell: bash
-
+#      run: |
-    - name: Build
+#        source /etc/profile.d/modules.sh
-      run: cmake --build build -j 2 --verbose
+#        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.11
-
+#        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-    - name: Python tests
+#
-      run: cmake --build build --target pytest
+#    - name: Build
-
+#      run: cmake --build build -j 2 --verbose
-    - name: C++ tests
+#
-      run: cmake --build build --target cpptest
+#    - name: Python tests
-
+#      run: cmake --build build --target pytest
-    - name: Interface test
+#
-      run: cmake --build build --target test_cmake_build
+#    - name: C++ tests
+#      run: cmake --build build --target cpptest
+#
+#    - name: Interface test
+#      run: cmake --build build --target test_cmake_build
 
 
   # Testing on CentOS 7 + PGI compilers, which seems to require more workarounds
   centos-nvhpc7:
     runs-on: ubuntu-latest
-    name: "🐍 3 • CentOS7 / PGI 20.7 • x64"
+    name: "🐍 3 • CentOS7 / PGI 20.9 • x64"
     container: centos:7
 
     steps:
@@ -305,17 +407,17 @@ jobs:
       run: yum update -y && yum install -y epel-release && yum install -y git python3-devel make environment-modules cmake3
 
     - name: Install NVidia HPC SDK
-      run:  yum -y install https://developer.download.nvidia.com/hpc-sdk/nvhpc-20-7-20.7-1.x86_64.rpm https://developer.download.nvidia.com/hpc-sdk/nvhpc-2020-20.7-1.x86_64.rpm
+      run:  yum -y install https://developer.download.nvidia.com/hpc-sdk/20.9/nvhpc-20-9-20.9-1.x86_64.rpm https://developer.download.nvidia.com/hpc-sdk/20.9/nvhpc-2020-20.9-1.x86_64.rpm
 
     # On CentOS 7, we have to filter a few tests (compiler internal error)
-    # and allow deeper templete recursion (not needed on CentOS 8 with a newer
+    # and allow deeper template recursion (not needed on CentOS 8 with a newer
     # standard library). On some systems, you many need further workarounds:
     # https://github.com/pybind/pybind11/pull/2475
     - name: Configure
       shell: bash
       run: |
         source /etc/profile.d/modules.sh
-        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.7
+        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.9
         cmake3 -S . -B build -DDOWNLOAD_CATCH=ON \
                             -DCMAKE_CXX_STANDARD=11 \
                             -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
@@ -340,6 +442,7 @@ jobs:
     - name: Interface test
       run: cmake3 --build build --target test_cmake_build
 
+
   # Testing on GCC using the GCC docker images (only recent images supported)
   gcc:
     runs-on: ubuntu-latest
@@ -349,8 +452,13 @@ jobs:
         gcc:
           - 7
           - latest
+        std:
+          - 11
+        include:
+          - gcc: 10
+            std: 20
 
-    name: "🐍 3 • GCC ${{ matrix.gcc }} • x64"
+    name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
     container: "gcc:${{ matrix.gcc }}"
 
     steps:
@@ -362,10 +470,8 @@ jobs:
     - name: Update pip
       run: python3 -m pip install --upgrade pip
 
-    - name: Setup CMake 3.18
+    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.3
+      uses: jwlawson/actions-setup-cmake@v1.12
-      with:
-        cmake-version: 3.18
 
     - name: Configure
       shell: bash
@@ -373,7 +479,7 @@ jobs:
         cmake -S . -B build
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
-        -DCMAKE_CXX_STANDARD=11
+        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build
@@ -389,6 +495,103 @@ jobs:
       run: cmake --build build --target test_cmake_build
 
 
+  # Testing on ICC using the oneAPI apt repo
+  icc:
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+
+    name: "🐍 3 • ICC latest • x64"
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Add apt repo
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y wget build-essential pkg-config cmake ca-certificates gnupg
+        wget https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS-2023.PUB
+        sudo apt-key add GPG-PUB-KEY-INTEL-SW-PRODUCTS-2023.PUB
+        echo "deb https://apt.repos.intel.com/oneapi all main" | sudo tee /etc/apt/sources.list.d/oneAPI.list
+
+    - name: Add ICC & Python 3
+      run: sudo apt-get update; sudo apt-get install -y intel-oneapi-compiler-dpcpp-cpp-and-cpp-classic cmake python3-dev python3-numpy python3-pytest python3-pip
+
+    - name: Update pip
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        python3 -m pip install --upgrade pip
+
+    - name: Install dependencies
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        python3 -m pip install -r tests/requirements.txt
+
+    - name: Configure C++11
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake -S . -B build-11     \
+        -DPYBIND11_WERROR=ON    \
+        -DDOWNLOAD_CATCH=ON     \
+        -DDOWNLOAD_EIGEN=OFF    \
+        -DCMAKE_CXX_STANDARD=11             \
+        -DCMAKE_CXX_COMPILER=$(which icpc)  \
+        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+
+    - name: Build C++11
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-11 -j 2 -v
+
+    - name: Python tests C++11
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        sudo service apport stop
+        cmake --build build-11 --target check
+
+    - name: C++ tests C++11
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-11 --target cpptest
+
+    - name: Interface test C++11
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-11 --target test_cmake_build
+
+    - name: Configure C++17
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake -S . -B build-17     \
+        -DPYBIND11_WERROR=ON    \
+        -DDOWNLOAD_CATCH=ON     \
+        -DDOWNLOAD_EIGEN=OFF    \
+        -DCMAKE_CXX_STANDARD=17             \
+        -DCMAKE_CXX_COMPILER=$(which icpc)  \
+        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+
+    - name: Build C++17
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-17 -j 2 -v
+
+    - name: Python tests C++17
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        sudo service apport stop
+        cmake --build build-17 --target check
+
+    - name: C++ tests C++17
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-17 --target cpptest
+
+    - name: Interface test C++17
+      run: |
+        set +e; source /opt/intel/oneapi/setvars.sh; set -e
+        cmake --build build-17 --target test_cmake_build
+
+
   # Testing on CentOS (manylinux uses a centos base, and this is an easy way
   # to get GCC 4.8, which is the manylinux1 compiler).
   centos:
@@ -397,11 +600,11 @@ jobs:
       fail-fast: false
       matrix:
         centos:
-          - 7  # GCC 4.8
+          - centos7  # GCC 4.8
-          - 8
+          - stream8
 
     name: "🐍 3 • CentOS ${{ matrix.centos }} • x64"
-    container: "centos:${{ matrix.centos }}"
+    container: "quay.io/centos/centos:${{ matrix.centos }}"
 
     steps:
     - uses: actions/checkout@v2
@@ -413,12 +616,14 @@ jobs:
       run: python3 -m pip install --upgrade pip
 
     - name: Install dependencies
-      run: python3 -m pip install cmake -r tests/requirements.txt --prefer-binary
+      run: |
+        python3 -m pip install cmake -r tests/requirements.txt
 
     - name: Configure
       shell: bash
       run: >
         cmake -S . -B build
+        -DCMAKE_BUILD_TYPE=MinSizeRel
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
@@ -476,7 +681,7 @@ jobs:
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
       working-directory: /build-tests
 
-    - name: Run tests
+    - name: Python tests
       run: make pytest -j 2
       working-directory: /build-tests
 
@@ -493,16 +698,13 @@ jobs:
     - uses: actions/setup-python@v2
 
     - name: Install Doxygen
-      run: sudo apt install -y doxygen
+      run: sudo apt-get install -y doxygen librsvg2-bin # Changed to rsvg-convert in 20.04
-
-    - name: Install docs & setup requirements
-      run: python3 -m pip install -r docs/requirements.txt
 
     - name: Build docs
-      run: python3 -m sphinx -W -b html docs docs/.build
+      run: pipx run nox -s docs
 
     - name: Make SDist
-      run: python3 setup.py sdist
+      run: pipx run nox -s build -- --sdist
 
     - run: git status --ignored
 
@@ -514,6 +716,250 @@ jobs:
     - name: Compare Dists (headers only)
       working-directory: include
       run: |
-        python3 -m pip install --user -U ../dist/*
+        python3 -m pip install --user -U ../dist/*.tar.gz
         installed=$(python3 -c "import pybind11; print(pybind11.get_include() + '/pybind11')")
         diff -rq $installed ./pybind11
+
+  win32:
+    strategy:
+      fail-fast: false
+      matrix:
+        python:
+        - 3.5
+        - 3.6
+        - 3.7
+        - 3.8
+        - 3.9
+        - pypy-3.6
+
+        include:
+          - python: 3.9
+            args: -DCMAKE_CXX_STANDARD=20 -DDOWNLOAD_EIGEN=OFF
+          - python: 3.8
+            args: -DCMAKE_CXX_STANDARD=17
+
+    name: "🐍 ${{ matrix.python }} • MSVC 2019 • x86 ${{ matrix.args }}"
+    runs-on: windows-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup Python ${{ matrix.python }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python }}
+        architecture: x86
+
+    - name: Update CMake
+      uses: jwlawson/actions-setup-cmake@v1.12
+
+    - name: Prepare MSVC
+      uses: ilammy/msvc-dev-cmd@v1.10.0
+      with:
+        arch: x86
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    # First build - C++11 mode and inplace
+    - name: Configure ${{ matrix.args }}
+      run: >
+        cmake -S . -B build
+        -G "Visual Studio 16 2019" -A Win32
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        ${{ matrix.args }}
+    - name: Build C++11
+      run: cmake --build build -j 2
+
+    - name: Python tests
+      run: cmake --build build -t pytest
+
+  win32-msvc2015:
+    name: "🐍 ${{ matrix.python }} • MSVC 2015 • x64"
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python:
+          - 2.7
+          - 3.6
+          - 3.7
+          # todo: check/cpptest does not support 3.8+ yet
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup 🐍 ${{ matrix.python }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python }}
+
+    - name: Update CMake
+      uses: jwlawson/actions-setup-cmake@v1.12
+
+    - name: Prepare MSVC
+      uses: ilammy/msvc-dev-cmd@v1.10.0
+      with:
+        toolset: 14.0
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    # First build - C++11 mode and inplace
+    - name: Configure
+      run: >
+        cmake -S . -B build
+        -G "Visual Studio 14 2015" -A x64
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+
+    - name: Build C++14
+      run: cmake --build build -j 2
+
+    - name: Run all checks
+      run: cmake --build build -t check
+
+
+  win32-msvc2017:
+    name: "🐍 ${{ matrix.python }} • MSVC 2017 • x64"
+    runs-on: windows-2016
+    strategy:
+      fail-fast: false
+      matrix:
+        python:
+          - 2.7
+          - 3.5
+          - 3.7
+        std:
+          - 14
+
+        include:
+          - python: 2.7
+            std: 17
+            args: >
+              -DCMAKE_CXX_FLAGS="/permissive- /EHsc /GR"
+          - python: 3.7
+            std: 17
+            args: >
+              -DCMAKE_CXX_FLAGS="/permissive- /EHsc /GR"
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup 🐍 ${{ matrix.python }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python }}
+
+    - name: Update CMake
+      uses: jwlawson/actions-setup-cmake@v1.12
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    # First build - C++11 mode and inplace
+    - name: Configure
+      run: >
+        cmake -S . -B build
+        -G "Visual Studio 15 2017" -A x64
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
+        ${{ matrix.args }}
+
+    - name: Build ${{ matrix.std }}
+      run: cmake --build build -j 2
+
+    - name: Run all checks
+      run: cmake --build build -t check
+
+  mingw:
+    name: "🐍 3 • windows-latest • ${{ matrix.sys }}"
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { sys: mingw64, env: x86_64 }
+          - { sys: mingw32, env: i686 }
+    steps:
+    - uses: msys2/setup-msys2@v2
+      with:
+        msystem: ${{matrix.sys}}
+        install: >-
+          git
+          mingw-w64-${{matrix.env}}-gcc
+          mingw-w64-${{matrix.env}}-python-pip
+          mingw-w64-${{matrix.env}}-python-numpy
+          mingw-w64-${{matrix.env}}-python-scipy
+          mingw-w64-${{matrix.env}}-cmake
+          mingw-w64-${{matrix.env}}-make
+          mingw-w64-${{matrix.env}}-python-pytest
+          mingw-w64-${{matrix.env}}-eigen3
+          mingw-w64-${{matrix.env}}-boost
+          mingw-w64-${{matrix.env}}-catch
+
+    - uses: actions/checkout@v2
+
+    - name: Configure C++11
+      # LTO leads to many undefined reference like
+      # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -S . -B build
+
+    - name: Build C++11
+      run: cmake --build build -j 2
+
+    - name: Python tests C++11
+      run: cmake --build build --target pytest -j 2
+
+    - name: C++11 tests
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target cpptest -j 2
+
+    - name: Interface test C++11
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target test_cmake_build
+
+    - name: Clean directory
+      run: git clean -fdx
+
+    - name: Configure C++14
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -S . -B build2
+
+    - name: Build C++14
+      run: cmake --build build2 -j 2
+
+    - name: Python tests C++14
+      run: cmake --build build2 --target pytest -j 2
+
+    - name: C++14 tests
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target cpptest -j 2
+
+    - name: Interface test C++14
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target test_cmake_build
+
+    - name: Clean directory
+      run: git clean -fdx
+
+    - name: Configure C++17
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -S . -B build3
+
+    - name: Build C++17
+      run: cmake --build build3 -j 2
+
+    - name: Python tests C++17
+      run: cmake --build build3 --target pytest -j 2
+
+    - name: C++17 tests
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target cpptest -j 2
+
+    - name: Interface test C++17
+      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cmake_build

wrap/pybind11/.github/workflows/configure.yml

@@ -18,7 +18,7 @@ jobs:
       matrix:
         runs-on: [ubuntu-latest, macos-latest, windows-latest]
         arch: [x64]
-        cmake: [3.18]
+        cmake: ["3.21"]
 
         include:
         - runs-on: ubuntu-latest
@@ -55,7 +55,7 @@ jobs:
     # An action for adding a specific version of CMake:
     #   https://github.com/jwlawson/actions-setup-cmake
     - name: Setup CMake ${{ matrix.cmake }}
-      uses: jwlawson/actions-setup-cmake@v1.3
+      uses: jwlawson/actions-setup-cmake@v1.12
       with:
         cmake-version: ${{ matrix.cmake }}
 
@@ -82,57 +82,3 @@ jobs:
       working-directory: build dir
       if: github.event_name == 'workflow_dispatch'
       run: cmake --build . --config Release --target check
-
-  # This builds the sdists and wheels and makes sure the files are exactly as
-  # expected. Using Windows and Python 2.7, since that is often the most
-  # challenging matrix element.
-  test-packaging:
-    name: 🐍 2.7 • 📦 tests • windows-latest
-    runs-on: windows-latest
-
-    steps:
-    - uses: actions/checkout@v2
-
-    - name: Setup 🐍 2.7
-      uses: actions/setup-python@v2
-      with:
-        python-version: 2.7
-
-    - name: Prepare env
-      run: python -m pip install -r tests/requirements.txt --prefer-binary
-
-    - name: Python Packaging tests
-      run: pytest tests/extra_python_package/
-
-
-  # This runs the packaging tests and also builds and saves the packages as
-  # artifacts.
-  packaging:
-    name: 🐍 3.8 • 📦 & 📦 tests • ubuntu-latest
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v2
-
-    - name: Setup 🐍 3.8
-      uses: actions/setup-python@v2
-      with:
-        python-version: 3.8
-
-    - name: Prepare env
-      run: python -m pip install -r tests/requirements.txt build twine --prefer-binary
-
-    - name: Python Packaging tests
-      run: pytest tests/extra_python_package/
-
-    - name: Build SDist and wheels
-      run: |
-        python -m build -s -w .
-        PYBIND11_GLOBAL_SDIST=1 python -m build -s -w .
-
-    - name: Check metadata
-      run: twine check dist/*
-
-    - uses: actions/upload-artifact@v2
-      with:
-        path: dist/*

wrap/pybind11/.github/workflows/format.yml

@@ -19,15 +19,17 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2
-    - uses: pre-commit/action@v2.0.0
+    - uses: pre-commit/action@v2.0.3
       with:
         # Slow hooks are marked with manual - slow is okay here, run them too
-        extra_args: --hook-stage manual
+        extra_args: --hook-stage manual --all-files
 
   clang-tidy:
+    # When making changes here, please also review the "Clang-Tidy" section
+    # in .github/CONTRIBUTING.md and update as needed.
     name: Clang-Tidy
     runs-on: ubuntu-latest
-    container: silkeh/clang:10
+    container: silkeh/clang:12
     steps:
     - uses: actions/checkout@v2
 
@@ -35,7 +37,12 @@ jobs:
       run: apt-get update && apt-get install -y python3-dev python3-pytest
 
     - name: Configure
-      run: cmake -S . -B build -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy);--warnings-as-errors=*"
+      run: >
+        cmake -S . -B build
+        -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy)"
+        -DDOWNLOAD_EIGEN=ON
+        -DDOWNLOAD_CATCH=ON
+        -DCMAKE_CXX_STANDARD=17
 
     - name: Build
-      run: cmake --build build -j 2
+      run: cmake --build build -j 2 -- --keep-going

wrap/pybind11/.github/workflows/labeler.yml

@@ -0,0 +1,16 @@
+name: Labeler
+on:
+  pull_request_target:
+    types: [closed]
+
+jobs:
+  label:
+    name: Labeler
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/labeler@main
+      if: github.event.pull_request.merged == true
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        configuration-path: .github/labeler_merged.yml

wrap/pybind11/.github/workflows/pip.yml

@@ -0,0 +1,108 @@
+name: Pip
+
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+    branches:
+    - master
+    - stable
+    - v*
+  release:
+    types:
+    - published
+
+env:
+  PIP_ONLY_BINARY: numpy
+
+jobs:
+  # This builds the sdists and wheels and makes sure the files are exactly as
+  # expected. Using Windows and Python 2.7, since that is often the most
+  # challenging matrix element.
+  test-packaging:
+    name: 🐍 2.7 • 📦 tests • windows-latest
+    runs-on: windows-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup 🐍 2.7
+      uses: actions/setup-python@v2
+      with:
+        python-version: 2.7
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    - name: Python Packaging tests
+      run: pytest tests/extra_python_package/
+
+
+  # This runs the packaging tests and also builds and saves the packages as
+  # artifacts.
+  packaging:
+    name: 🐍 3.8 • 📦 & 📦 tests • ubuntu-latest
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup 🐍 3.8
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.8
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt build twine
+
+    - name: Python Packaging tests
+      run: pytest tests/extra_python_package/
+
+    - name: Build SDist and wheels
+      run: |
+        python -m build
+        PYBIND11_GLOBAL_SDIST=1 python -m build
+
+    - name: Check metadata
+      run: twine check dist/*
+
+    - name: Save standard package
+      uses: actions/upload-artifact@v2
+      with:
+        name: standard
+        path: dist/pybind11-*
+
+    - name: Save global package
+      uses: actions/upload-artifact@v2
+      with:
+        name: global
+        path: dist/pybind11_global-*
+
+
+
+  # When a GitHub release is made, upload the artifacts to PyPI
+  upload:
+    name: Upload to PyPI
+    runs-on: ubuntu-latest
+    if: github.event_name == 'release' && github.event.action == 'published'
+    needs: [packaging]
+
+    steps:
+    - uses: actions/setup-python@v2
+
+    # Downloads all to directories matching the artifact names
+    - uses: actions/download-artifact@v2
+
+    - name: Publish standard package
+      uses: pypa/gh-action-pypi-publish@v1.5.0
+      with:
+        password: ${{ secrets.pypi_password }}
+        packages_dir: standard/
+
+    - name: Publish global package
+      uses: pypa/gh-action-pypi-publish@v1.5.0
+      with:
+        password: ${{ secrets.pypi_password_global }}
+        packages_dir: global/

wrap/pybind11/.github/workflows/upstream.yml

@@ -0,0 +1,112 @@
+
+name: Upstream
+
+on:
+  workflow_dispatch:
+  pull_request:
+
+concurrency:
+  group: upstream-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  PIP_ONLY_BINARY: numpy
+
+jobs:
+  standard:
+    name: "🐍 3.11 dev • ubuntu-latest • x64"
+    runs-on: ubuntu-latest
+    if: "contains(github.event.pull_request.labels.*.name, 'python dev')"
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Setup Python 3.11
+      uses: actions/setup-python@v2
+      with:
+        python-version: "3.11-dev"
+
+    - name: Setup Boost (Linux)
+      if: runner.os == 'Linux'
+      run: sudo apt-get install libboost-dev
+
+    - name: Update CMake
+      uses: jwlawson/actions-setup-cmake@v1.12
+
+    - name: Prepare env
+      run: |
+        python -m pip install -r tests/requirements.txt
+
+    - name: Setup annotations on Linux
+      if: runner.os == 'Linux'
+      run: python -m pip install pytest-github-actions-annotate-failures
+
+    # First build - C++11 mode and inplace
+    - name: Configure C++11
+      run: >
+        cmake -S . -B .
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=11
+
+    - name: Build C++11
+      run: cmake --build . -j 2
+
+    - name: Python tests C++11
+      run: cmake --build . --target pytest -j 2
+
+    - name: C++11 tests
+      run: cmake --build .  --target cpptest -j 2
+
+    - name: Interface test C++11
+      run: cmake --build . --target test_cmake_build
+
+    - name: Clean directory
+      run: git clean -fdx
+
+    # Second build - C++17 mode and in a build directory
+    - name: Configure C++17
+      run: >
+        cmake -S . -B build2
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=17
+        ${{ matrix.args }}
+        ${{ matrix.args2 }}
+
+    - name: Build
+      run: cmake --build build2 -j 2
+
+    - name: Python tests
+      run: cmake --build build2 --target pytest
+
+    - name: C++ tests
+      run: cmake --build build2 --target cpptest
+
+    # Third build - C++17 mode with unstable ABI
+    - name: Configure (unstable ABI)
+      run: >
+        cmake -S . -B build3
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=17
+        -DPYBIND11_INTERNALS_VERSION=10000000
+        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+        ${{ matrix.args }}
+
+    - name: Build (unstable ABI)
+      run: cmake --build build3 -j 2
+
+    - name: Python tests (unstable ABI)
+      run: cmake --build build3 --target pytest
+
+    - name: Interface test
+      run: cmake --build build2 --target test_cmake_build
+
+    # This makes sure the setup_helpers module can build packages using
+    # setuptools
+    - name: Setuptools helpers test
+      run: pytest tests/extra_setuptools

wrap/pybind11/.gitignore

@@ -41,3 +41,5 @@ pybind11Targets.cmake
 /.vscode
 /pybind11/include/*
 /pybind11/share/*
+/docs/_build/*
+.ipynb_checkpoints/

wrap/pybind11/.pre-commit-config.yaml

@@ -15,12 +15,14 @@
 repos:
 # Standard hooks
 - repo: https://github.com/pre-commit/pre-commit-hooks
-  rev: v3.2.0
+  rev: v4.1.0
   hooks:
   - id: check-added-large-files
   - id: check-case-conflict
+  - id: check-docstring-first
   - id: check-merge-conflict
   - id: check-symlinks
+  - id: check-toml
   - id: check-yaml
   - id: debug-statements
   - id: end-of-file-fixer
@@ -28,54 +30,115 @@ repos:
   - id: requirements-txt-fixer
   - id: trailing-whitespace
   - id: fix-encoding-pragma
+    exclude: ^noxfile.py$
+
+- repo: https://github.com/asottile/pyupgrade
+  rev: v2.31.0
+  hooks:
+  - id: pyupgrade
+
+- repo: https://github.com/PyCQA/isort
+  rev: 5.10.1
+  hooks:
+  - id: isort
 
 # Black, the code formatter, natively supports pre-commit
 - repo: https://github.com/psf/black
-  rev: 20.8b1
+  rev: 21.12b0 # Keep in sync with blacken-docs
   hooks:
   - id: black
-    # Not all Python files are Blacked, yet
+
-    files: ^(setup.py|pybind11|tests/extra)
+- repo: https://github.com/asottile/blacken-docs
+  rev: v1.12.0
+  hooks:
+  - id: blacken-docs
+    additional_dependencies:
+    - black==21.12b0 # keep in sync with black hook
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
-  rev: v1.1.9
+  rev: v1.1.10
   hooks:
   - id: remove-tabs
 
+# Autoremoves unused imports
+- repo: https://github.com/hadialqattan/pycln
+  rev: v1.1.0
+  hooks:
+  - id: pycln
+
+- repo: https://github.com/pre-commit/pygrep-hooks
+  rev: v1.9.0
+  hooks:
+  - id: python-check-blanket-noqa
+  - id: python-check-blanket-type-ignore
+  - id: python-no-log-warn
+  - id: rst-backticks
+  - id: rst-directive-colons
+  - id: rst-inline-touching-normal
+
 # Flake8 also supports pre-commit natively (same author)
-- repo: https://gitlab.com/pycqa/flake8
+- repo: https://github.com/PyCQA/flake8
-  rev: 3.8.3
+  rev: 4.0.1
   hooks:
   - id: flake8
-    additional_dependencies: [flake8-bugbear, pep8-naming]
+    additional_dependencies: &flake8_dependencies
+      - flake8-bugbear
+      - pep8-naming
     exclude: ^(docs/.*|tools/.*)$
 
+- repo: https://github.com/asottile/yesqa
+  rev: v1.3.0
+  hooks:
+  - id: yesqa
+    additional_dependencies: *flake8_dependencies
+
 # CMake formatting
 - repo: https://github.com/cheshirekow/cmake-format-precommit
-  rev: v0.6.11
+  rev: v0.6.13
   hooks:
   - id: cmake-format
     additional_dependencies: [pyyaml]
     types: [file]
     files: (\.cmake|CMakeLists.txt)(.in)?$
 
+# Check static types with mypy
+- repo: https://github.com/pre-commit/mirrors-mypy
+  rev: v0.931
+  hooks:
+  - id: mypy
+    # Running per-file misbehaves a bit, so just run on all files, it's fast
+    pass_filenames: false
+    additional_dependencies: [typed_ast]
+
 # Checks the manifest for missing files (native support)
 - repo: https://github.com/mgedmin/check-manifest
-  rev: "0.42"
+  rev: "0.47"
   hooks:
   - id: check-manifest
     # This is a slow hook, so only run this if --hook-stage manual is passed
     stages: [manual]
     additional_dependencies: [cmake, ninja]
 
+- repo: https://github.com/codespell-project/codespell
+  rev: v2.1.0
+  hooks:
+  - id: codespell
+    exclude: ".supp$"
+    args: ["-L", "nd,ot,thist"]
+
+- repo: https://github.com/shellcheck-py/shellcheck-py
+  rev: v0.8.0.3
+  hooks:
+  - id: shellcheck
+
 # The original pybind11 checks for a few C++ style items
 - repo: local
   hooks:
   - id: disallow-caps
     name: Disallow improper capitalization
     language: pygrep
-    entry: PyBind|Numpy|Cmake
+    entry: PyBind|Numpy|Cmake|CCache|PyTest
     exclude: .pre-commit-config.yaml
 
 - repo: local

wrap/pybind11/CMakeLists.txt

@@ -7,13 +7,18 @@
 
 cmake_minimum_required(VERSION 3.4)
 
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.4...3.22)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.22)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.22)
+endif()
+
+# Avoid infinite recursion if tests include this as a subdirectory
+if(DEFINED PYBIND11_MASTER_PROJECT)
+  return()
 endif()
 
 # Extract project version from source
@@ -73,6 +78,10 @@ if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
     set(CMAKE_CXX_EXTENSIONS OFF)
     set(CMAKE_CXX_STANDARD_REQUIRED ON)
   endif()
+
+  set(pybind11_system "")
+
+  set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 else()
   set(PYBIND11_MASTER_PROJECT OFF)
   set(pybind11_system SYSTEM)
@@ -82,6 +91,9 @@ endif()
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
+set(PYBIND11_INTERNALS_VERSION
+    ""
+    CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR
@@ -98,6 +110,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/descr.h
     include/pybind11/detail/init.h
     include/pybind11/detail/internals.h
+    include/pybind11/detail/type_caster_base.h
     include/pybind11/detail/typeid.h
     include/pybind11/attr.h
     include/pybind11/buffer_info.h
@@ -109,6 +122,7 @@ set(PYBIND11_HEADERS
     include/pybind11/eigen.h
     include/pybind11/embed.h
     include/pybind11/eval.h
+    include/pybind11/gil.h
     include/pybind11/iostream.h
     include/pybind11/functional.h
     include/pybind11/numpy.h
@@ -116,7 +130,8 @@ set(PYBIND11_HEADERS
     include/pybind11/pybind11.h
     include/pybind11/pytypes.h
     include/pybind11/stl.h
-    include/pybind11/stl_bind.h)
+    include/pybind11/stl_bind.h
+    include/pybind11/stl/filesystem.h)
 
 # Compare with grep and warn if mismatched
 if(PYBIND11_MASTER_PROJECT AND NOT CMAKE_VERSION VERSION_LESS 3.12)
@@ -142,22 +157,45 @@ endif()
 string(REPLACE "include/" "${CMAKE_CURRENT_SOURCE_DIR}/include/" PYBIND11_HEADERS
                "${PYBIND11_HEADERS}")
 
-# Cache variables so pybind11_add_module can be used in parent projects
+# Cache variable so this can be used in parent projects
-set(PYBIND11_INCLUDE_DIR
+set(pybind11_INCLUDE_DIR
     "${CMAKE_CURRENT_LIST_DIR}/include"
+    CACHE INTERNAL "Directory where pybind11 headers are located")
+
+# Backward compatible variable for add_subdirectory mode
+if(NOT PYBIND11_MASTER_PROJECT)
+  set(PYBIND11_INCLUDE_DIR
+      "${pybind11_INCLUDE_DIR}"
       CACHE INTERNAL "")
+endif()
 
 # Note: when creating targets, you cannot use if statements at configure time -
 # you need generator expressions, because those will be placed in the target file.
 # You can also place ifs *in* the Config.in, but not here.
 
 # This section builds targets, but does *not* touch Python
+# Non-IMPORT targets cannot be defined twice
+if(NOT TARGET pybind11_headers)
+  # Build the headers-only target (no Python included):
+  # (long name used here to keep this from clashing in subdirectory mode)
+  add_library(pybind11_headers INTERFACE)
+  add_library(pybind11::pybind11_headers ALIAS pybind11_headers) # to match exported target
+  add_library(pybind11::headers ALIAS pybind11_headers) # easier to use/remember
 
-# Build the headers-only target (no Python included):
+  target_include_directories(
-# (long name used here to keep this from clashing in subdirectory mode)
+    pybind11_headers ${pybind11_system} INTERFACE $<BUILD_INTERFACE:${pybind11_INCLUDE_DIR}>
-add_library(pybind11_headers INTERFACE)
+                                                  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
-add_library(pybind11::pybind11_headers ALIAS pybind11_headers) # to match exported target
+
-add_library(pybind11::headers ALIAS pybind11_headers) # easier to use/remember
+  target_compile_features(pybind11_headers INTERFACE cxx_inheriting_constructors cxx_user_literals
+                                                     cxx_right_angle_brackets)
+  if(NOT "${PYBIND11_INTERNALS_VERSION}" STREQUAL "")
+    target_compile_definitions(
+      pybind11_headers INTERFACE "PYBIND11_INTERNALS_VERSION=${PYBIND11_INTERNALS_VERSION}")
+  endif()
+else()
+  # It is invalid to install a target twice, too.
+  set(PYBIND11_INSTALL OFF)
+endif()
 
 include("${CMAKE_CURRENT_SOURCE_DIR}/tools/pybind11Common.cmake")
 
@@ -168,21 +206,18 @@ elseif(USE_PYTHON_INCLUDE_DIR AND DEFINED PYTHON_INCLUDE_DIR)
   file(RELATIVE_PATH CMAKE_INSTALL_INCLUDEDIR ${CMAKE_INSTALL_PREFIX} ${PYTHON_INCLUDE_DIRS})
 endif()
 
-# Fill in headers target
-target_include_directories(
-  pybind11_headers ${pybind11_system} INTERFACE $<BUILD_INTERFACE:${PYBIND11_INCLUDE_DIR}>
-                                                $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
-
-target_compile_features(pybind11_headers INTERFACE cxx_inheriting_constructors cxx_user_literals
-                                                   cxx_right_angle_brackets)
-
 if(PYBIND11_INSTALL)
-  install(DIRECTORY ${PYBIND11_INCLUDE_DIR}/pybind11 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+  install(DIRECTORY ${pybind11_INCLUDE_DIR}/pybind11 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
-  # GNUInstallDirs "DATADIR" wrong here; CMake search path wants "share".
   set(PYBIND11_CMAKECONFIG_INSTALL_DIR
-      "share/cmake/${PROJECT_NAME}"
+      "${CMAKE_INSTALL_DATAROOTDIR}/cmake/${PROJECT_NAME}"
       CACHE STRING "install path for pybind11Config.cmake")
 
+  if(IS_ABSOLUTE "${CMAKE_INSTALL_INCLUDEDIR}")
+    set(pybind11_INCLUDEDIR "${CMAKE_INSTALL_FULL_INCLUDEDIR}")
+  else()
+    set(pybind11_INCLUDEDIR "\$\{PACKAGE_PREFIX_DIR\}/${CMAKE_INSTALL_INCLUDEDIR}")
+  endif()
+
   configure_package_config_file(
     tools/${PROJECT_NAME}Config.cmake.in "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
     INSTALL_DESTINATION ${PYBIND11_CMAKECONFIG_INSTALL_DIR})
@@ -260,8 +295,5 @@ endif()
 if(NOT PYBIND11_MASTER_PROJECT)
   set(pybind11_FOUND
       TRUE
-      CACHE INTERNAL "true if pybind11 and all required components found on the system")
+      CACHE INTERNAL "True if pybind11 and all required components found on the system")
-  set(pybind11_INCLUDE_DIR
-      "${PYBIND11_INCLUDE_DIR}"
-      CACHE INTERNAL "Directory where pybind11 headers are located")
 endif()

wrap/pybind11/MANIFEST.in

@@ -1,4 +1,6 @@
 recursive-include pybind11/include/pybind11 *.h
 recursive-include pybind11 *.py
+recursive-include pybind11 py.typed
+recursive-include pybind11 *.pyi
 include pybind11/share/cmake/pybind11/*.cmake
-include LICENSE README.md pyproject.toml setup.py setup.cfg
+include LICENSE README.rst pyproject.toml setup.py setup.cfg

wrap/pybind11/README.md

@@ -1,145 +0,0 @@
-![pybind11 logo](https://github.com/pybind/pybind11/raw/master/docs/pybind11-logo.png)
-
-# pybind11 — Seamless operability between C++11 and Python
-
-[![Documentation Status](https://readthedocs.org/projects/pybind11/badge/?version=master)](http://pybind11.readthedocs.org/en/master/?badge=master)
-[![Documentation Status](https://readthedocs.org/projects/pybind11/badge/?version=stable)](http://pybind11.readthedocs.org/en/stable/?badge=stable)
-[![Gitter chat](https://img.shields.io/gitter/room/gitterHQ/gitter.svg)](https://gitter.im/pybind/Lobby)
-[![CI](https://github.com/pybind/pybind11/workflows/CI/badge.svg)](https://github.com/pybind/pybind11/actions)
-[![Build status](https://ci.appveyor.com/api/projects/status/riaj54pn4h08xy40?svg=true)](https://ci.appveyor.com/project/wjakob/pybind11)
-
-**pybind11** is a lightweight header-only library that exposes C++ types in
-Python and vice versa, mainly to create Python bindings of existing C++ code.
-Its goals and syntax are similar to the excellent [Boost.Python][] library by
-David Abrahams: to minimize boilerplate code in traditional extension modules
-by inferring type information using compile-time introspection.
-
-The main issue with Boost.Python—and the reason for creating such a similar
-project—is Boost. Boost is an enormously large and complex suite of utility
-libraries that works with almost every C++ compiler in existence. This
-compatibility has its cost: arcane template tricks and workarounds are
-necessary to support the oldest and buggiest of compiler specimens. Now that
-C++11-compatible compilers are widely available, this heavy machinery has
-become an excessively large and unnecessary dependency.
-
-Think of this library as a tiny self-contained version of Boost.Python with
-everything stripped away that isn't relevant for binding generation. Without
-comments, the core header files only require ~4K lines of code and depend on
-Python (2.7 or 3.5+, or PyPy) and the C++ standard library. This compact
-implementation was possible thanks to some of the new C++11 language features
-(specifically: tuples, lambda functions and variadic templates). Since its
-creation, this library has grown beyond Boost.Python in many ways, leading to
-dramatically simpler binding code in many common situations.
-
-Tutorial and reference documentation is provided at
-[pybind11.readthedocs.org][].  A PDF version of the manual is available
-[here][docs-pdf].
-
-## Core features
-pybind11 can map the following core C++ features to Python:
-
-- Functions accepting and returning custom data structures per value, reference, or pointer
-- Instance methods and static methods
-- Overloaded functions
-- Instance attributes and static attributes
-- Arbitrary exception types
-- Enumerations
-- Callbacks
-- Iterators and ranges
-- Custom operators
-- Single and multiple inheritance
-- STL data structures
-- Smart pointers with reference counting like `std::shared_ptr`
-- Internal references with correct reference counting
-- C++ classes with virtual (and pure virtual) methods can be extended in Python
-
-## Goodies
-In addition to the core functionality, pybind11 provides some extra goodies:
-
-- Python 2.7, 3.5+, and PyPy (tested on 7.3) are supported with an implementation-agnostic
-  interface.
-
-- It is possible to bind C++11 lambda functions with captured variables. The
-  lambda capture data is stored inside the resulting Python function object.
-
-- pybind11 uses C++11 move constructors and move assignment operators whenever
-  possible to efficiently transfer custom data types.
-
-- It's easy to expose the internal storage of custom data types through
-  Pythons' buffer protocols. This is handy e.g. for fast conversion between
-  C++ matrix classes like Eigen and NumPy without expensive copy operations.
-
-- pybind11 can automatically vectorize functions so that they are transparently
-  applied to all entries of one or more NumPy array arguments.
-
-- Python's slice-based access and assignment operations can be supported with
-  just a few lines of code.
-
-- Everything is contained in just a few header files; there is no need to link
-  against any additional libraries.
-
-- Binaries are generally smaller by a factor of at least 2 compared to
-  equivalent bindings generated by Boost.Python. A recent pybind11 conversion
-  of PyRosetta, an enormous Boost.Python binding project,
-  [reported][pyrosetta-report] a binary size reduction of **5.4x** and compile
-  time reduction by **5.8x**.
-
-- Function signatures are precomputed at compile time (using `constexpr`),
-  leading to smaller binaries.
-
-- With little extra effort, C++ types can be pickled and unpickled similar to
-  regular Python objects.
-
-## Supported compilers
-
-1. Clang/LLVM 3.3 or newer (for Apple Xcode's clang, this is 5.0.0 or newer)
-2. GCC 4.8 or newer
-3. Microsoft Visual Studio 2015 Update 3 or newer
-4. Intel C++ compiler 17 or newer (16 with pybind11 v2.0 and 15 with pybind11
-   v2.0 and a [workaround][intel-15-workaround])
-5. Cygwin/GCC (tested on 2.5.1)
-6. NVCC (CUDA 11 tested)
-7. NVIDIA PGI (20.7 tested)
-
-## About
-
-This project was created by [Wenzel Jakob](http://rgl.epfl.ch/people/wjakob).
-Significant features and/or improvements to the code were contributed by
-Jonas Adler,
-Lori A. Burns,
-Sylvain Corlay,
-Trent Houliston,
-Axel Huebl,
-@hulucc,
-Sergey Lyskov
-Johan Mabille,
-Tomasz Miąsko,
-Dean Moldovan,
-Ben Pritchard,
-Jason Rhinelander,
-Boris Schäling,
-Pim Schellart,
-Henry Schreiner,
-Ivan Smirnov, and
-Patrick Stewart.
-
-### Contributing
-
-See the [contributing guide][] for information on building and contributing to
-pybind11.
-
-
-### License
-
-pybind11 is provided under a BSD-style license that can be found in the
-[`LICENSE`][] file. By using, distributing, or contributing to this project,
-you agree to the terms and conditions of this license.
-
-
-[pybind11.readthedocs.org]: http://pybind11.readthedocs.org/en/master
-[docs-pdf]: https://media.readthedocs.org/pdf/pybind11/master/pybind11.pdf
-[Boost.Python]: http://www.boost.org/doc/libs/1_58_0/libs/python/doc/
-[pyrosetta-report]: http://graylab.jhu.edu/RosettaCon2016/PyRosetta-4.pdf
-[contributing guide]:  https://github.com/pybind/pybind11/blob/master/.github/CONTRIBUTING.md
-[`LICENSE`]: https://github.com/pybind/pybind11/blob/master/LICENSE
-[intel-15-workaround]: https://github.com/pybind/pybind11/issues/276

wrap/pybind11/README.rst

@@ -0,0 +1,180 @@
+.. figure:: https://github.com/pybind/pybind11/raw/master/docs/pybind11-logo.png
+   :alt: pybind11 logo
+
+**pybind11 — Seamless operability between C++11 and Python**
+
+|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |GitHub Discussions| |CI| |Build status|
+
+|Repology| |PyPI package| |Conda-forge| |Python Versions|
+
+`Setuptools example <https://github.com/pybind/python_example>`_
+• `Scikit-build example <https://github.com/pybind/scikit_build_example>`_
+• `CMake example <https://github.com/pybind/cmake_example>`_
+
+.. start
+
+
+**pybind11** is a lightweight header-only library that exposes C++ types
+in Python and vice versa, mainly to create Python bindings of existing
+C++ code. Its goals and syntax are similar to the excellent
+`Boost.Python <http://www.boost.org/doc/libs/1_58_0/libs/python/doc/>`_
+library by David Abrahams: to minimize boilerplate code in traditional
+extension modules by inferring type information using compile-time
+introspection.
+
+The main issue with Boost.Python—and the reason for creating such a
+similar project—is Boost. Boost is an enormously large and complex suite
+of utility libraries that works with almost every C++ compiler in
+existence. This compatibility has its cost: arcane template tricks and
+workarounds are necessary to support the oldest and buggiest of compiler
+specimens. Now that C++11-compatible compilers are widely available,
+this heavy machinery has become an excessively large and unnecessary
+dependency.
+
+Think of this library as a tiny self-contained version of Boost.Python
+with everything stripped away that isn’t relevant for binding
+generation. Without comments, the core header files only require ~4K
+lines of code and depend on Python (2.7 or 3.5+, or PyPy) and the C++
+standard library. This compact implementation was possible thanks to
+some of the new C++11 language features (specifically: tuples, lambda
+functions and variadic templates). Since its creation, this library has
+grown beyond Boost.Python in many ways, leading to dramatically simpler
+binding code in many common situations.
+
+Tutorial and reference documentation is provided at
+`pybind11.readthedocs.io <https://pybind11.readthedocs.io/en/latest>`_.
+A PDF version of the manual is available
+`here <https://pybind11.readthedocs.io/_/downloads/en/latest/pdf/>`_.
+And the source code is always available at
+`github.com/pybind/pybind11 <https://github.com/pybind/pybind11>`_.
+
+
+Core features
+-------------
+
+
+pybind11 can map the following core C++ features to Python:
+
+- Functions accepting and returning custom data structures per value,
+  reference, or pointer
+- Instance methods and static methods
+- Overloaded functions
+- Instance attributes and static attributes
+- Arbitrary exception types
+- Enumerations
+- Callbacks
+- Iterators and ranges
+- Custom operators
+- Single and multiple inheritance
+- STL data structures
+- Smart pointers with reference counting like ``std::shared_ptr``
+- Internal references with correct reference counting
+- C++ classes with virtual (and pure virtual) methods can be extended
+  in Python
+
+Goodies
+-------
+
+In addition to the core functionality, pybind11 provides some extra
+goodies:
+
+- Python 2.7, 3.5+, and PyPy/PyPy3 7.3 are supported with an
+  implementation-agnostic interface.
+
+- It is possible to bind C++11 lambda functions with captured
+  variables. The lambda capture data is stored inside the resulting
+  Python function object.
+
+- pybind11 uses C++11 move constructors and move assignment operators
+  whenever possible to efficiently transfer custom data types.
+
+- It’s easy to expose the internal storage of custom data types through
+  Pythons’ buffer protocols. This is handy e.g. for fast conversion
+  between C++ matrix classes like Eigen and NumPy without expensive
+  copy operations.
+
+- pybind11 can automatically vectorize functions so that they are
+  transparently applied to all entries of one or more NumPy array
+  arguments.
+
+- Python's slice-based access and assignment operations can be
+  supported with just a few lines of code.
+
+- Everything is contained in just a few header files; there is no need
+  to link against any additional libraries.
+
+- Binaries are generally smaller by a factor of at least 2 compared to
+  equivalent bindings generated by Boost.Python. A recent pybind11
+  conversion of PyRosetta, an enormous Boost.Python binding project,
+  `reported <https://graylab.jhu.edu/Sergey/2016.RosettaCon/PyRosetta-4.pdf>`_
+  a binary size reduction of **5.4x** and compile time reduction by
+  **5.8x**.
+
+- Function signatures are precomputed at compile time (using
+  ``constexpr``), leading to smaller binaries.
+
+- With little extra effort, C++ types can be pickled and unpickled
+  similar to regular Python objects.
+
+Supported compilers
+-------------------
+
+1. Clang/LLVM 3.3 or newer (for Apple Xcode’s clang, this is 5.0.0 or
+   newer)
+2. GCC 4.8 or newer
+3. Microsoft Visual Studio 2015 Update 3 or newer
+4. Intel classic C++ compiler 18 or newer (ICC 20.2 tested in CI)
+5. Cygwin/GCC (previously tested on 2.5.1)
+6. NVCC (CUDA 11.0 tested in CI)
+7. NVIDIA PGI (20.9 tested in CI)
+
+About
+-----
+
+This project was created by `Wenzel
+Jakob <http://rgl.epfl.ch/people/wjakob>`_. Significant features and/or
+improvements to the code were contributed by Jonas Adler, Lori A. Burns,
+Sylvain Corlay, Eric Cousineau, Aaron Gokaslan, Ralf Grosse-Kunstleve, Trent Houliston, Axel
+Huebl, @hulucc, Yannick Jadoul, Sergey Lyskov Johan Mabille, Tomasz Miąsko,
+Dean Moldovan, Ben Pritchard, Jason Rhinelander, Boris Schäling, Pim
+Schellart, Henry Schreiner, Ivan Smirnov, Boris Staletic, and Patrick Stewart.
+
+We thank Google for a generous financial contribution to the continuous
+integration infrastructure used by this project.
+
+
+Contributing
+~~~~~~~~~~~~
+
+See the `contributing
+guide <https://github.com/pybind/pybind11/blob/master/.github/CONTRIBUTING.md>`_
+for information on building and contributing to pybind11.
+
+License
+~~~~~~~
+
+pybind11 is provided under a BSD-style license that can be found in the
+`LICENSE <https://github.com/pybind/pybind11/blob/master/LICENSE>`_
+file. By using, distributing, or contributing to this project, you agree
+to the terms and conditions of this license.
+
+.. |Latest Documentation Status| image:: https://readthedocs.org/projects/pybind11/badge?version=latest
+   :target: http://pybind11.readthedocs.org/en/latest
+.. |Stable Documentation Status| image:: https://img.shields.io/badge/docs-stable-blue.svg
+   :target: http://pybind11.readthedocs.org/en/stable
+.. |Gitter chat| image:: https://img.shields.io/gitter/room/gitterHQ/gitter.svg
+   :target: https://gitter.im/pybind/Lobby
+.. |CI| image:: https://github.com/pybind/pybind11/workflows/CI/badge.svg
+   :target: https://github.com/pybind/pybind11/actions
+.. |Build status| image:: https://ci.appveyor.com/api/projects/status/riaj54pn4h08xy40?svg=true
+   :target: https://ci.appveyor.com/project/wjakob/pybind11
+.. |PyPI package| image:: https://img.shields.io/pypi/v/pybind11.svg
+   :target: https://pypi.org/project/pybind11/
+.. |Conda-forge| image:: https://img.shields.io/conda/vn/conda-forge/pybind11.svg
+   :target: https://github.com/conda-forge/pybind11-feedstock
+.. |Repology| image:: https://repology.org/badge/latest-versions/python:pybind11.svg
+   :target: https://repology.org/project/python:pybind11/versions
+.. |Python Versions| image:: https://img.shields.io/pypi/pyversions/pybind11.svg
+   :target: https://pypi.org/project/pybind11/
+.. |GitHub Discussions| image:: https://img.shields.io/static/v1?label=Discussions&message=Ask&color=blue&logo=github
+   :target: https://github.com/pybind/pybind11/discussions

wrap/pybind11/docs/Doxyfile

@@ -18,5 +18,5 @@ ALIASES               += "endrst=\endverbatim"
 QUIET                  = YES
 WARNINGS               = YES
 WARN_IF_UNDOCUMENTED   = NO
-PREDEFINED             = DOXYGEN_SHOULD_SKIP_THIS \
+PREDEFINED             = PY_MAJOR_VERSION=3 \
-                         PY_MAJOR_VERSION=3
+                         PYBIND11_NOINLINE

wrap/pybind11/docs/advanced/cast/custom.rst

@@ -26,7 +26,9 @@ The following Python snippet demonstrates the intended usage from the Python sid
         def __int__(self):
             return 123
 
+
     from example import print
+
     print(A())
 
 To register the necessary conversion routines, it is necessary to add an
@@ -44,7 +46,7 @@ type is explicitly allowed.
              * function signatures and declares a local variable
              * 'value' of type inty
              */
-            PYBIND11_TYPE_CASTER(inty, _("inty"));
+            PYBIND11_TYPE_CASTER(inty, const_name("inty"));
 
             /**
              * Conversion part 1 (Python->C++): convert a PyObject into a inty

wrap/pybind11/docs/advanced/cast/eigen.rst

@@ -52,7 +52,7 @@ can be mapped *and* if the numpy array is writeable (that is
 the passed variable will be transparently carried out directly on the
 ``numpy.ndarray``.
 
-This means you can can write code such as the following and have it work as
+This means you can write code such as the following and have it work as
 expected:
 
 .. code-block:: cpp
@@ -203,7 +203,7 @@ adding the ``order='F'`` option when creating an array:
 
 .. code-block:: python
 
-    myarray = np.array(source, order='F')
+    myarray = np.array(source, order="F")
 
 Such an object will be passable to a bound function accepting an
 ``Eigen::Ref<MatrixXd>`` (or similar column-major Eigen type).

wrap/pybind11/docs/advanced/cast/overview.rst

@@ -75,91 +75,97 @@ The following basic data types are supported out of the box (some may require
 an additional extension header to be included). To pass other data structures
 as arguments and return values, refer to the section on binding :ref:`classes`.
 
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 |  Data type                         |  Description              | Header file                       |
-+====================================+===========================+===============================+
++====================================+===========================+===================================+
 | ``int8_t``, ``uint8_t``            | 8-bit integers            | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``int16_t``, ``uint16_t``          | 16-bit integers           | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``int32_t``, ``uint32_t``          | 32-bit integers           | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``int64_t``, ``uint64_t``          | 64-bit integers           | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``ssize_t``, ``size_t``            | Platform-dependent size   | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``float``, ``double``              | Floating point types      | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``bool``                           | Two-state Boolean type    | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``char``                           | Character literal         | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``char16_t``                       | UTF-16 character literal  | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``char32_t``                       | UTF-32 character literal  | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``wchar_t``                        | Wide character literal    | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``const char *``                   | UTF-8 string literal      | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``const char16_t *``               | UTF-16 string literal     | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``const char32_t *``               | UTF-32 string literal     | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``const wchar_t *``                | Wide string literal       | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::string``                    | STL dynamic UTF-8 string  | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::u16string``                 | STL dynamic UTF-16 string | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::u32string``                 | STL dynamic UTF-32 string | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::wstring``                   | STL dynamic wide string   | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::string_view``,              | STL C++17 string views    | :file:`pybind11/pybind11.h`       |
 | ``std::u16string_view``, etc.      |                           |                                   |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::pair<T1, T2>``              | Pair of two custom types  | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::tuple<...>``                | Arbitrary tuple of types  | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::reference_wrapper<...>``    | Reference type wrapper    | :file:`pybind11/pybind11.h`       |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::complex<T>``                | Complex numbers           | :file:`pybind11/complex.h`        |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::array<T, Size>``            | STL static array          | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::vector<T>``                 | STL dynamic array         | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::deque<T>``                  | STL double-ended queue    | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::valarray<T>``               | STL value array           | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::list<T>``                   | STL linked list           | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::map<T1, T2>``               | STL ordered map           | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::unordered_map<T1, T2>``     | STL unordered map         | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::set<T>``                    | STL ordered set           | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::unordered_set<T>``          | STL unordered set         | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::optional<T>``               | STL optional type (C++17) | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::experimental::optional<T>`` | STL optional type (exp.)  | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::variant<...>``              | Type-safe union (C++17)   | :file:`pybind11/stl.h`            |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
+| ``std::filesystem::path<T>``       | STL path (C++17) [#]_     | :file:`pybind11/stl/filesystem.h` |
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::function<...>``             | STL polymorphic function  | :file:`pybind11/functional.h`     |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::chrono::duration<...>``     | STL time duration         | :file:`pybind11/chrono.h`         |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``std::chrono::time_point<...>``   | STL date/time             | :file:`pybind11/chrono.h`         |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``Eigen::Matrix<...>``             | Eigen: dense matrix       | :file:`pybind11/eigen.h`          |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``Eigen::Map<...>``                | Eigen: mapped memory      | :file:`pybind11/eigen.h`          |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
 | ``Eigen::SparseMatrix<...>``       | Eigen: sparse matrix      | :file:`pybind11/eigen.h`          |
-+------------------------------------+---------------------------+-------------------------------+
++------------------------------------+---------------------------+-----------------------------------+
+
+.. [#] ``std::filesystem::path`` is converted to ``pathlib.Path`` and
+   ``os.PathLike`` is converted to ``std::filesystem::path``, but this requires
+   Python 3.6 (for ``__fspath__`` support).

wrap/pybind11/docs/advanced/cast/stl.rst

@@ -5,7 +5,7 @@ Automatic conversion
 ====================
 
 When including the additional header file :file:`pybind11/stl.h`, conversions
-between ``std::vector<>``/``std::deque<>``/``std::list<>``/``std::array<>``,
+between ``std::vector<>``/``std::deque<>``/``std::list<>``/``std::array<>``/``std::valarray<>``,
 ``std::set<>``/``std::unordered_set<>``, and
 ``std::map<>``/``std::unordered_map<>`` and the Python ``list``, ``set`` and
 ``dict`` data structures are automatically enabled. The types ``std::pair<>``
@@ -72,6 +72,17 @@ The ``visit_helper`` specialization is not required if your ``name::variant`` pr
 a ``name::visit()`` function. For any other function name, the specialization must be
 included to tell pybind11 how to visit the variant.
 
+.. warning::
+
+    When converting a ``variant`` type, pybind11 follows the same rules as when
+    determining which function overload to call (:ref:`overload_resolution`), and
+    so the same caveats hold. In particular, the order in which the ``variant``'s
+    alternatives are listed is important, since pybind11 will try conversions in
+    this order. This means that, for example, when converting ``variant<int, bool>``,
+    the ``bool`` variant will never be selected, as any Python ``bool`` is already
+    an ``int`` and is convertible to a C++ ``int``. Changing the order of alternatives
+    (and using ``variant<bool, int>``, in this example) provides a solution.
+
 .. note::
 
     pybind11 only supports the modern implementation of ``boost::variant``

wrap/pybind11/docs/advanced/cast/strings.rst

@@ -36,13 +36,13 @@ everywhere <http://utf8everywhere.org/>`_.
         }
     );
 
-.. code-block:: python
+.. code-block:: pycon
 
-    >>> utf8_test('🎂')
+    >>> utf8_test("🎂")
     utf-8 is icing on the cake.
     🎂
 
-    >>> utf8_charptr('🍕')
+    >>> utf8_charptr("🍕")
     My favorite food is
     🍕
 
@@ -80,7 +80,7 @@ raise a ``UnicodeDecodeError``.
         }
     );
 
-.. code-block:: python
+.. code-block:: pycon
 
     >>> isinstance(example.std_string_return(), str)
     True
@@ -114,7 +114,7 @@ conversion has the same overhead as implicit conversion.
         }
     );
 
-.. code-block:: python
+.. code-block:: pycon
 
     >>> str_output()
     'Send your résumé to Alice in HR'
@@ -143,7 +143,7 @@ returned to Python as ``bytes``, then one can return the data as a
         }
     );
 
-.. code-block:: python
+.. code-block:: pycon
 
     >>> example.return_bytes()
     b'\xba\xd0\xba\xd0'
@@ -160,7 +160,7 @@ encoding, but cannot convert ``std::string`` back to ``bytes`` implicitly.
         }
     );
 
-.. code-block:: python
+.. code-block:: pycon
 
     >>> isinstance(example.asymmetry(b"have some bytes"), str)
     True
@@ -229,16 +229,16 @@ character.
     m.def("pass_char", [](char c) { return c; });
     m.def("pass_wchar", [](wchar_t w) { return w; });
 
-.. code-block:: python
+.. code-block:: pycon
 
-    >>> example.pass_char('A')
+    >>> example.pass_char("A")
     'A'
 
 While C++ will cast integers to character types (``char c = 0x65;``), pybind11
 does not convert Python integers to characters implicitly. The Python function
 ``chr()`` can be used to convert integers to characters.
 
-.. code-block:: python
+.. code-block:: pycon
 
     >>> example.pass_char(0x65)
     TypeError
@@ -259,17 +259,17 @@ a combining acute accent). The combining character will be lost if the
 two-character sequence is passed as an argument, even though it renders as a
 single grapheme.
 
-.. code-block:: python
+.. code-block:: pycon
 
-    >>> example.pass_wchar('é')
+    >>> example.pass_wchar("é")
     'é'
 
-    >>> combining_e_acute = 'e' + '\u0301'
+    >>> combining_e_acute = "e" + "\u0301"
 
     >>> combining_e_acute
     'é'
 
-    >>> combining_e_acute == 'é'
+    >>> combining_e_acute == "é"
     False
 
     >>> example.pass_wchar(combining_e_acute)
@@ -278,9 +278,9 @@ single grapheme.
 Normalizing combining characters before passing the character literal to C++
 may resolve *some* of these issues:
 
-.. code-block:: python
+.. code-block:: pycon
 
-    >>> example.pass_wchar(unicodedata.normalize('NFC', combining_e_acute))
+    >>> example.pass_wchar(unicodedata.normalize("NFC", combining_e_acute))
     'é'
 
 In some languages (Thai for example), there are `graphemes that cannot be

wrap/pybind11/docs/advanced/classes.rst

@@ -9,7 +9,7 @@ that you are already familiar with the basics from :doc:`/classes`.
 Overriding virtual functions in Python
 ======================================
 
-Suppose that a C++ class or interface has a virtual function that we'd like to
+Suppose that a C++ class or interface has a virtual function that we'd like
 to override from within Python (we'll focus on the class ``Animal``; ``Dog`` is
 given as a specific example of how one would do this with traditional C++
 code).
@@ -161,6 +161,7 @@ Here is an example:
         def __init__(self, name):
             Dog.__init__(self)  # Without this, a TypeError is raised.
             self.name = name
+
         def bark(self):
             return "yap!"
 
@@ -259,7 +260,7 @@ override the ``name()`` method):
 
 .. note::
 
-    Note the trailing commas in the ``PYBIND11_OVERIDE`` calls to ``name()``
+    Note the trailing commas in the ``PYBIND11_OVERRIDE`` calls to ``name()``
     and ``bark()``. These are needed to portably implement a trampoline for a
     function that does not take any arguments. For functions that take
     a nonzero number of arguments, the trailing comma must be omitted.
@@ -804,7 +805,7 @@ to bind these two functions:
             }
         ));
 
-The ``__setstate__`` part of the ``py::picke()`` definition follows the same
+The ``__setstate__`` part of the ``py::pickle()`` definition follows the same
 rules as the single-argument version of ``py::init()``. The return type can be
 a value, pointer or holder type. See :ref:`custom_constructors` for details.
 
@@ -1153,12 +1154,65 @@ error:
 
     >>> class PyFinalChild(IsFinal):
     ...     pass
+    ...
     TypeError: type 'IsFinal' is not an acceptable base type
 
 .. note:: This attribute is currently ignored on PyPy
 
 .. versionadded:: 2.6
 
+Binding classes with template parameters
+========================================
+
+pybind11 can also wrap classes that have template parameters. Consider these classes:
+
+.. code-block:: cpp
+
+    struct Cat {};
+    struct Dog {};
+
+    template <typename PetType>
+    struct Cage {
+        Cage(PetType& pet);
+        PetType& get();
+    };
+
+C++ templates may only be instantiated at compile time, so pybind11 can only
+wrap instantiated templated classes. You cannot wrap a non-instantiated template:
+
+.. code-block:: cpp
+
+    // BROKEN (this will not compile)
+    py::class_<Cage>(m, "Cage");
+        .def("get", &Cage::get);
+
+You must explicitly specify each template/type combination that you want to
+wrap separately.
+
+.. code-block:: cpp
+
+    // ok
+    py::class_<Cage<Cat>>(m, "CatCage")
+        .def("get", &Cage<Cat>::get);
+
+    // ok
+    py::class_<Cage<Dog>>(m, "DogCage")
+        .def("get", &Cage<Dog>::get);
+
+If your class methods have template parameters you can wrap those as well,
+but once again each instantiation must be explicitly specified:
+
+.. code-block:: cpp
+
+    typename <typename T>
+    struct MyClass {
+        template <typename V>
+        T fn(V v);
+    };
+
+    py::class<MyClass<int>>(m, "MyClassT")
+        .def("fn", &MyClass<int>::fn<std::string>);
+
 Custom automatic downcasters
 ============================
 
@@ -1247,7 +1301,7 @@ Accessing the type object
 
 You can get the type object from a C++ class that has already been registered using:
 
-.. code-block:: python
+.. code-block:: cpp
 
     py::type T_py = py::type::of<T>();
 
@@ -1259,3 +1313,37 @@ object, just like ``type(ob)`` in Python.
     Other types, like ``py::type::of<int>()``, do not work, see :ref:`type-conversions`.
 
 .. versionadded:: 2.6
+
+Custom type setup
+=================
+
+For advanced use cases, such as enabling garbage collection support, you may
+wish to directly manipulate the ``PyHeapTypeObject`` corresponding to a
+``py::class_`` definition.
+
+You can do that using ``py::custom_type_setup``:
+
+.. code-block:: cpp
+
+   struct OwnsPythonObjects {
+       py::object value = py::none();
+   };
+   py::class_<OwnsPythonObjects> cls(
+       m, "OwnsPythonObjects", py::custom_type_setup([](PyHeapTypeObject *heap_type) {
+           auto *type = &heap_type->ht_type;
+           type->tp_flags |= Py_TPFLAGS_HAVE_GC;
+           type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
+               auto &self = py::cast<OwnsPythonObjects&>(py::handle(self_base));
+               Py_VISIT(self.value.ptr());
+               return 0;
+           };
+           type->tp_clear = [](PyObject *self_base) {
+               auto &self = py::cast<OwnsPythonObjects&>(py::handle(self_base));
+               self.value = py::none();
+               return 0;
+           };
+       }));
+   cls.def(py::init<>());
+   cls.def_readwrite("value", &OwnsPythonObjects::value);
+
+.. versionadded:: 2.8

wrap/pybind11/docs/advanced/embedding.rst

@@ -40,15 +40,15 @@ The essential structure of the ``main.cpp`` file looks like this:
     }
 
 The interpreter must be initialized before using any Python API, which includes
-all the functions and classes in pybind11. The RAII guard class `scoped_interpreter`
+all the functions and classes in pybind11. The RAII guard class ``scoped_interpreter``
 takes care of the interpreter lifetime. After the guard is destroyed, the interpreter
 shuts down and clears its memory. No Python functions can be called after this.
 
 Executing Python code
 =====================
 
-There are a few different ways to run Python code. One option is to use `eval`,
+There are a few different ways to run Python code. One option is to use ``eval``,
-`exec` or `eval_file`, as explained in :ref:`eval`. Here is a quick example in
+``exec`` or ``eval_file``, as explained in :ref:`eval`. Here is a quick example in
 the context of an executable with an embedded interpreter:
 
 .. code-block:: cpp
@@ -108,11 +108,11 @@ The two approaches can also be combined:
 Importing modules
 =================
 
-Python modules can be imported using `module::import()`:
+Python modules can be imported using ``module_::import()``:
 
 .. code-block:: cpp
 
-    py::module sys = py::module::import("sys");
+    py::module_ sys = py::module_::import("sys");
     py::print(sys.attr("path"));
 
 For convenience, the current working directory is included in ``sys.path`` when
@@ -122,18 +122,19 @@ embedding the interpreter. This makes it easy to import local Python files:
 
     """calc.py located in the working directory"""
 
+
     def add(i, j):
         return i + j
 
 
 .. code-block:: cpp
 
-    py::module calc = py::module::import("calc");
+    py::module_ calc = py::module_::import("calc");
     py::object result = calc.attr("add")(1, 2);
     int n = result.cast<int>();
     assert(n == 3);
 
-Modules can be reloaded using `module::reload()` if the source is modified e.g.
+Modules can be reloaded using ``module_::reload()`` if the source is modified e.g.
 by an external process. This can be useful in scenarios where the application
 imports a user defined data processing script which needs to be updated after
 changes by the user. Note that this function does not reload modules recursively.
@@ -143,7 +144,7 @@ changes by the user. Note that this function does not reload modules recursively
 Adding embedded modules
 =======================
 
-Embedded binary modules can be added using the `PYBIND11_EMBEDDED_MODULE` macro.
+Embedded binary modules can be added using the ``PYBIND11_EMBEDDED_MODULE`` macro.
 Note that the definition must be placed at global scope. They can be imported
 like any other module.
 
@@ -153,7 +154,7 @@ like any other module.
     namespace py = pybind11;
 
     PYBIND11_EMBEDDED_MODULE(fast_calc, m) {
-        // `m` is a `py::module` which is used to bind functions and classes
+        // `m` is a `py::module_` which is used to bind functions and classes
         m.def("add", [](int i, int j) {
             return i + j;
         });
@@ -162,14 +163,14 @@ like any other module.
     int main() {
         py::scoped_interpreter guard{};
 
-        auto fast_calc = py::module::import("fast_calc");
+        auto fast_calc = py::module_::import("fast_calc");
         auto result = fast_calc.attr("add")(1, 2).cast<int>();
         assert(result == 3);
     }
 
 Unlike extension modules where only a single binary module can be created, on
 the embedded side an unlimited number of modules can be added using multiple
-`PYBIND11_EMBEDDED_MODULE` definitions (as long as they have unique names).
+``PYBIND11_EMBEDDED_MODULE`` definitions (as long as they have unique names).
 
 These modules are added to Python's list of builtins, so they can also be
 imported in pure Python files loaded by the interpreter. Everything interacts
@@ -196,7 +197,7 @@ naturally:
     int main() {
         py::scoped_interpreter guard{};
 
-        auto py_module = py::module::import("py_module");
+        auto py_module = py::module_::import("py_module");
 
         auto locals = py::dict("fmt"_a="{} + {} = {}", **py_module.attr("__dict__"));
         assert(locals["a"].cast<int>() == 1);
@@ -215,9 +216,9 @@ naturally:
 Interpreter lifetime
 ====================
 
-The Python interpreter shuts down when `scoped_interpreter` is destroyed. After
+The Python interpreter shuts down when ``scoped_interpreter`` is destroyed. After
 this, creating a new instance will restart the interpreter. Alternatively, the
-`initialize_interpreter` / `finalize_interpreter` pair of functions can be used
+``initialize_interpreter`` / ``finalize_interpreter`` pair of functions can be used
 to directly set the state at any time.
 
 Modules created with pybind11 can be safely re-initialized after the interpreter
@@ -229,8 +230,8 @@ global data. All the details can be found in the CPython documentation.
 
 .. warning::
 
-    Creating two concurrent `scoped_interpreter` guards is a fatal error. So is
+    Creating two concurrent ``scoped_interpreter`` guards is a fatal error. So is
-    calling `initialize_interpreter` for a second time after the interpreter
+    calling ``initialize_interpreter`` for a second time after the interpreter
     has already been initialized.
 
     Do not use the raw CPython API functions ``Py_Initialize`` and
@@ -241,7 +242,7 @@ global data. All the details can be found in the CPython documentation.
 Sub-interpreter support
 =======================
 
-Creating multiple copies of `scoped_interpreter` is not possible because it
+Creating multiple copies of ``scoped_interpreter`` is not possible because it
 represents the main Python interpreter. Sub-interpreters are something different
 and they do permit the existence of multiple interpreters. This is an advanced
 feature of the CPython API and should be handled with care. pybind11 does not
@@ -257,5 +258,5 @@ We'll just mention a couple of caveats the sub-interpreters support in pybind11:
  2. Managing multiple threads, multiple interpreters and the GIL can be
     challenging and there are several caveats here, even within the pure
     CPython API (please refer to the Python docs for details). As for
-    pybind11, keep in mind that `gil_scoped_release` and `gil_scoped_acquire`
+    pybind11, keep in mind that ``gil_scoped_release`` and ``gil_scoped_acquire``
     do not take sub-interpreters into account.

wrap/pybind11/docs/advanced/exceptions.rst

@@ -43,18 +43,28 @@ at its exception handler.
 |                                      | of bounds access in ``__getitem__``, |
 |                                      | ``__setitem__``, etc.)               |
 +--------------------------------------+--------------------------------------+
-| :class:`pybind11::value_error`       | ``ValueError`` (used to indicate     |
-|                                      | wrong value passed in                |
-|                                      | ``container.remove(...)``)           |
-+--------------------------------------+--------------------------------------+
 | :class:`pybind11::key_error`         | ``KeyError`` (used to indicate out   |
 |                                      | of bounds access in ``__getitem__``, |
 |                                      | ``__setitem__`` in dict-like         |
 |                                      | objects, etc.)                       |
 +--------------------------------------+--------------------------------------+
+| :class:`pybind11::value_error`       | ``ValueError`` (used to indicate     |
+|                                      | wrong value passed in                |
+|                                      | ``container.remove(...)``)           |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::type_error`        | ``TypeError``                        |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::buffer_error`      | ``BufferError``                      |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::import_error`      | ``ImportError``                      |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::attribute_error`   | ``AttributeError``                   |
++--------------------------------------+--------------------------------------+
+| Any other exception                  | ``RuntimeError``                     |
++--------------------------------------+--------------------------------------+
 
 Exception translation is not bidirectional. That is, *catching* the C++
-exceptions defined above above will not trap exceptions that originate from
+exceptions defined above will not trap exceptions that originate from
 Python. For that, catch :class:`pybind11::error_already_set`. See :ref:`below
 <handling_python_exceptions_cpp>` for further details.
 
@@ -67,9 +77,10 @@ Registering custom translators
 
 If the default exception conversion policy described above is insufficient,
 pybind11 also provides support for registering custom exception translators.
-To register a simple exception conversion that translates a C++ exception into
+Similar to pybind11 classes, exception translators can be local to the module
-a new Python exception using the C++ exception's ``what()`` method, a helper
+they are defined in or global to the entire python session.  To register a simple
-function is available:
+exception conversion that translates a C++ exception into a new Python exception
+using the C++ exception's ``what()`` method, a helper function is available:
 
 .. code-block:: cpp
 
@@ -79,29 +90,39 @@ This call creates a Python exception class with the name ``PyExp`` in the given
 module and automatically converts any encountered exceptions of type ``CppExp``
 into Python exceptions of type ``PyExp``.
 
+A matching function is available for registering a local exception translator:
+
+.. code-block:: cpp
+
+    py::register_local_exception<CppExp>(module, "PyExp");
+
+
 It is possible to specify base class for the exception using the third
-parameter, a `handle`:
+parameter, a ``handle``:
 
 .. code-block:: cpp
 
     py::register_exception<CppExp>(module, "PyExp", PyExc_RuntimeError);
+    py::register_local_exception<CppExp>(module, "PyExp", PyExc_RuntimeError);
 
-Then `PyExp` can be caught both as `PyExp` and `RuntimeError`.
+Then ``PyExp`` can be caught both as ``PyExp`` and ``RuntimeError``.
 
 The class objects of the built-in Python exceptions are listed in the Python
 documentation on `Standard Exceptions <https://docs.python.org/3/c-api/exceptions.html#standard-exceptions>`_.
-The default base class is `PyExc_Exception`.
+The default base class is ``PyExc_Exception``.
 
-When more advanced exception translation is needed, the function
+When more advanced exception translation is needed, the functions
-``py::register_exception_translator(translator)`` can be used to register
+``py::register_exception_translator(translator)`` and
+``py::register_local_exception_translator(translator)`` can be used to register
 functions that can translate arbitrary exception types (and which may include
-additional logic to do so).  The function takes a stateless callable (e.g.  a
+additional logic to do so).  The functions takes a stateless callable (e.g. a
 function pointer or a lambda function without captured variables) with the call
 signature ``void(std::exception_ptr)``.
 
 When a C++ exception is thrown, the registered exception translators are tried
 in reverse order of registration (i.e. the last registered translator gets the
-first shot at handling the exception).
+first shot at handling the exception). All local translators will be tried
+before a global translator is tried.
 
 Inside the translator, ``std::rethrow_exception`` should be used within
 a try block to re-throw the exception.  One or more catch clauses to catch
@@ -156,6 +177,57 @@ section.
     may be explicitly (re-)thrown to delegate it to the other,
     previously-declared existing exception translators.
 
+    Note that ``libc++`` and ``libstdc++`` `behave differently <https://stackoverflow.com/questions/19496643/using-clang-fvisibility-hidden-and-typeinfo-and-type-erasure/28827430>`_
+    with ``-fvisibility=hidden``. Therefore exceptions that are used across ABI boundaries need to be explicitly exported, as exercised in ``tests/test_exceptions.h``.
+    See also: "Problems with C++ exceptions" under `GCC Wiki <https://gcc.gnu.org/wiki/Visibility>`_.
+
+
+Local vs Global Exception Translators
+=====================================
+
+When a global exception translator is registered, it will be applied across all
+modules in the reverse order of registration. This can create behavior where the
+order of module import influences how exceptions are translated.
+
+If module1 has the following translator:
+
+.. code-block:: cpp
+
+      py::register_exception_translator([](std::exception_ptr p) {
+        try {
+            if (p) std::rethrow_exception(p);
+        } catch (const std::invalid_argument &e) {
+            PyErr_SetString("module1 handled this")
+        }
+      }
+
+and module2 has the following similar translator:
+
+.. code-block:: cpp
+
+      py::register_exception_translator([](std::exception_ptr p) {
+        try {
+            if (p) std::rethrow_exception(p);
+        } catch (const std::invalid_argument &e) {
+            PyErr_SetString("module2 handled this")
+        }
+      }
+
+then which translator handles the invalid_argument will be determined by the
+order that module1 and module2 are imported. Since exception translators are
+applied in the reverse order of registration, which ever module was imported
+last will "win" and that translator will be applied.
+
+If there are multiple pybind11 modules that share exception types (either
+standard built-in or custom) loaded into a single python instance and
+consistent error handling behavior is needed, then local translators should be
+used.
+
+Changing the previous example to use ``register_local_exception_translator``
+would mean that when invalid_argument is thrown in the module2 code, the
+module2 translator will always handle it, while in module1, the module1
+translator will do the same.
+
 .. _handling_python_exceptions_cpp:
 
 Handling exceptions from Python in C++
@@ -182,13 +254,13 @@ For example:
 
     try {
         // open("missing.txt", "r")
-        auto file = py::module::import("io").attr("open")("missing.txt", "r");
+        auto file = py::module_::import("io").attr("open")("missing.txt", "r");
         auto text = file.attr("read")();
         file.attr("close")();
     } catch (py::error_already_set &e) {
         if (e.matches(PyExc_FileNotFoundError)) {
             py::print("missing.txt not found");
-        } else if (e.match(PyExc_PermissionError)) {
+        } else if (e.matches(PyExc_PermissionError)) {
             py::print("missing.txt found but not accessible");
         } else {
             throw;
@@ -253,6 +325,34 @@ Alternately, to ignore the error, call `PyErr_Clear
 Any Python error must be thrown or cleared, or Python/pybind11 will be left in
 an invalid state.
 
+Chaining exceptions ('raise from')
+==================================
+
+In Python 3.3 a mechanism for indicating that exceptions were caused by other
+exceptions was introduced:
+
+.. code-block:: py
+
+    try:
+        print(1 / 0)
+    except Exception as exc:
+        raise RuntimeError("could not divide by zero") from exc
+
+To do a similar thing in pybind11, you can use the ``py::raise_from`` function. It
+sets the current python error indicator, so to continue propagating the exception
+you should ``throw py::error_already_set()`` (Python 3 only).
+
+.. code-block:: cpp
+
+    try {
+        py::eval("print(1 / 0"));
+    } catch (py::error_already_set &e) {
+        py::raise_from(e, PyExc_RuntimeError, "could not divide by zero");
+        throw py::error_already_set();
+    }
+
+.. versionadded:: 2.8
+
 .. _unraisable_exceptions:
 
 Handling unraisable exceptions

wrap/pybind11/docs/advanced/functions.rst

@@ -17,7 +17,7 @@ bindings for functions that return a non-trivial type. Just by looking at the
 type information, it is not clear whether Python should take charge of the
 returned value and eventually free its resources, or if this is handled on the
 C++ side. For this reason, pybind11 provides a several *return value policy*
-annotations that can be passed to the :func:`module::def` and
+annotations that can be passed to the :func:`module_::def` and
 :func:`class_::def` functions. The default policy is
 :enum:`return_value_policy::automatic`.
 
@@ -50,7 +50,7 @@ implied transfer of ownership, i.e.:
 
 .. code-block:: cpp
 
-    m.def("get_data", &get_data, return_value_policy::reference);
+    m.def("get_data", &get_data, py::return_value_policy::reference);
 
 On the other hand, this is not the right policy for many other situations,
 where ignoring ownership could lead to resource leaks.
@@ -90,17 +90,18 @@ The following table provides an overview of available policies:
 |                                                  | return value is referenced by Python. This is the default policy for       |
 |                                                  | property getters created via ``def_property``, ``def_readwrite``, etc.     |
 +--------------------------------------------------+----------------------------------------------------------------------------+
-| :enum:`return_value_policy::automatic`           | **Default policy.** This policy falls back to the policy                   |
+| :enum:`return_value_policy::automatic`           | This policy falls back to the policy                                       |
 |                                                  | :enum:`return_value_policy::take_ownership` when the return value is a     |
 |                                                  | pointer. Otherwise, it uses :enum:`return_value_policy::move` or           |
 |                                                  | :enum:`return_value_policy::copy` for rvalue and lvalue references,        |
 |                                                  | respectively. See above for a description of what all of these different   |
-|                                                  | policies do.                                                               |
+|                                                  | policies do. This is the default policy for ``py::class_``-wrapped types.  |
 +--------------------------------------------------+----------------------------------------------------------------------------+
 | :enum:`return_value_policy::automatic_reference` | As above, but use policy :enum:`return_value_policy::reference` when the   |
 |                                                  | return value is a pointer. This is the default conversion policy for       |
 |                                                  | function arguments when calling Python functions manually from C++ code    |
-|                                                  | (i.e. via handle::operator()). You probably won't need to use this.        |
+|                                                  | (i.e. via ``handle::operator()``) and the casters in ``pybind11/stl.h``.   |
+|                                                  | You probably won't need to use this explicitly.                            |
 +--------------------------------------------------+----------------------------------------------------------------------------+
 
 Return value policies can also be applied to properties:
@@ -119,7 +120,7 @@ targeted arguments can be passed through the :class:`cpp_function` constructor:
 .. code-block:: cpp
 
     class_<MyClass>(m, "MyClass")
-        .def_property("data"
+        .def_property("data",
             py::cpp_function(&MyClass::getData, py::return_value_policy::copy),
             py::cpp_function(&MyClass::setData)
         );
@@ -182,6 +183,9 @@ relies on the ability to create a *weak reference* to the nurse object. When
 the nurse object is not a pybind11-registered type and does not support weak
 references, an exception will be thrown.
 
+If you use an incorrect argument index, you will get a ``RuntimeError`` saying
+``Could not activate keep_alive!``. You should review the indices you're using.
+
 Consider the following example: here, the binding code for a list append
 operation ties the lifetime of the newly added element to the underlying
 container:
@@ -228,7 +232,7 @@ is equivalent to the following pseudocode:
     });
 
 The only requirement is that ``T`` is default-constructible, but otherwise any
-scope guard will work. This is very useful in combination with `gil_scoped_release`.
+scope guard will work. This is very useful in combination with ``gil_scoped_release``.
 See :ref:`gil`.
 
 Multiple guards can also be specified as ``py::call_guard<T1, T2, T3...>``. The
@@ -251,7 +255,7 @@ For instance, the following statement iterates over a Python ``dict``:
 
 .. code-block:: cpp
 
-    void print_dict(py::dict dict) {
+    void print_dict(const py::dict& dict) {
         /* Easily interact with Python types */
         for (auto item : dict)
             std::cout << "key=" << std::string(py::str(item.first)) << ", "
@@ -268,7 +272,7 @@ And used in Python as usual:
 
 .. code-block:: pycon
 
-    >>> print_dict({'foo': 123, 'bar': 'hello'})
+    >>> print_dict({"foo": 123, "bar": "hello"})
     key=foo, value=123
     key=bar, value=hello
 
@@ -289,7 +293,7 @@ Such functions can also be created using pybind11:
 
 .. code-block:: cpp
 
-   void generic(py::args args, py::kwargs kwargs) {
+   void generic(py::args args, const py::kwargs& kwargs) {
        /// .. do something with args
        if (kwargs)
            /// .. do something with kwargs
@@ -302,8 +306,9 @@ The class ``py::args`` derives from ``py::tuple`` and ``py::kwargs`` derives
 from ``py::dict``.
 
 You may also use just one or the other, and may combine these with other
-arguments as long as the ``py::args`` and ``py::kwargs`` arguments are the last
+arguments.  Note, however, that ``py::kwargs`` must always be the last argument
-arguments accepted by the function.
+of the function, and ``py::args`` implies that any further arguments are
+keyword-only (see :ref:`keyword_only_arguments`).
 
 Please refer to the other examples for details on how to iterate over these,
 and on how to cast their entries into C++ objects. A demonstration is also
@@ -362,6 +367,8 @@ like so:
     py::class_<MyClass>("MyClass")
         .def("myFunction", py::arg("arg") = static_cast<SomeType *>(nullptr));
 
+.. _keyword_only_arguments:
+
 Keyword-only arguments
 ======================
 
@@ -373,6 +380,7 @@ argument in a function definition:
     def f(a, *, b):  # a can be positional or via keyword; b must be via keyword
         pass
 
+
     f(a=1, b=2)  # good
     f(b=2, a=1)  # good
     f(1, b=2)  # good
@@ -392,6 +400,15 @@ feature does *not* require Python 3 to work.
 
 .. versionadded:: 2.6
 
+As of pybind11 2.9, a ``py::args`` argument implies that any following arguments
+are keyword-only, as if ``py::kw_only()`` had been specified in the same
+relative location of the argument list as the ``py::args`` argument.  The
+``py::kw_only()`` may be included to be explicit about this, but is not
+required.  (Prior to 2.9 ``py::args`` may only occur at the end of the argument
+list, or immediately before a ``py::kwargs`` argument at the end).
+
+.. versionadded:: 2.9
+
 Positional-only arguments
 =========================
 
@@ -524,6 +541,8 @@ The default behaviour when the tag is unspecified is to allow ``None``.
     not allow ``None`` as argument.  To pass optional argument of these copied types consider
     using ``std::optional<T>``
 
+.. _overload_resolution:
+
 Overload resolution order
 =========================
 
@@ -540,11 +559,13 @@ an explicit ``py::arg().noconvert()`` attribute in the function definition).
 If the second pass also fails a ``TypeError`` is raised.
 
 Within each pass, overloads are tried in the order they were registered with
-pybind11.
+pybind11. If the ``py::prepend()`` tag is added to the definition, a function
+can be placed at the beginning of the overload sequence instead, allowing user
+overloads to proceed built in functions.
 
 What this means in practice is that pybind11 will prefer any overload that does
-not require conversion of arguments to an overload that does, but otherwise prefers
+not require conversion of arguments to an overload that does, but otherwise
-earlier-defined overloads to later-defined ones.
+prefers earlier-defined overloads to later-defined ones.
 
 .. note::
 
@@ -553,3 +574,42 @@ earlier-defined overloads to later-defined ones.
     requiring one conversion over one requiring three, but only prioritizes
     overloads requiring no conversion at all to overloads that require
     conversion of at least one argument.
+
+.. versionadded:: 2.6
+
+    The ``py::prepend()`` tag.
+
+Binding functions with template parameters
+==========================================
+
+You can bind functions that have template parameters. Here's a function:
+
+.. code-block:: cpp
+
+    template <typename T>
+    void set(T t);
+
+C++ templates cannot be instantiated at runtime, so you cannot bind the
+non-instantiated function:
+
+.. code-block:: cpp
+
+    // BROKEN (this will not compile)
+    m.def("set", &set);
+
+You must bind each instantiated function template separately. You may bind
+each instantiation with the same name, which will be treated the same as
+an overloaded function:
+
+.. code-block:: cpp
+
+    m.def("set", &set<int>);
+    m.def("set", &set<std::string>);
+
+Sometimes it's more clear to bind them with separate names, which is also
+an option:
+
+.. code-block:: cpp
+
+    m.def("setInt", &set<int>);
+    m.def("setString", &set<std::string>);

wrap/pybind11/docs/advanced/misc.rst

@@ -84,7 +84,7 @@ could be realized as follows (important changes highlighted):
         });
     }
 
-The ``call_go`` wrapper can also be simplified using the `call_guard` policy
+The ``call_go`` wrapper can also be simplified using the ``call_guard`` policy
 (see :ref:`call_policies`) which yields the same result:
 
 .. code-block:: cpp
@@ -132,7 +132,7 @@ However, it can be acquired as follows:
 
 .. code-block:: cpp
 
-    py::object pet = (py::object) py::module::import("basic").attr("Pet");
+    py::object pet = (py::object) py::module_::import("basic").attr("Pet");
 
     py::class_<Dog>(m, "Dog", pet)
         .def(py::init<const std::string &>())
@@ -146,7 +146,7 @@ has been executed:
 
 .. code-block:: cpp
 
-    py::module::import("basic");
+    py::module_::import("basic");
 
     py::class_<Dog, Pet>(m, "Dog")
         .def(py::init<const std::string &>())
@@ -223,7 +223,7 @@ avoids this issue involves weak reference with a cleanup callback:
 
 .. code-block:: cpp
 
-    // Register a callback function that is invoked when the BaseClass object is colelcted
+    // Register a callback function that is invoked when the BaseClass object is collected
     py::cpp_function cleanup_callback(
         [](py::handle weakref) {
             // perform cleanup here -- this function is called with the GIL held
@@ -237,13 +237,13 @@ avoids this issue involves weak reference with a cleanup callback:
 
 .. note::
 
-    PyPy (at least version 5.9) does not garbage collect objects when the
+    PyPy does not garbage collect objects when the interpreter exits. An alternative
-    interpreter exits. An alternative approach (which also works on CPython) is to use
+    approach (which also works on CPython) is to use the :py:mod:`atexit` module [#f7]_,
-    the :py:mod:`atexit` module [#f7]_, for example:
+    for example:
 
     .. code-block:: cpp
 
-        auto atexit = py::module::import("atexit");
+        auto atexit = py::module_::import("atexit");
         atexit.attr("register")(py::cpp_function([]() {
             // perform cleanup here -- this function is called with the GIL held
         }));
@@ -284,7 +284,7 @@ work, it is important that all lines are indented consistently, i.e.:
     )mydelimiter");
 
 By default, pybind11 automatically generates and prepends a signature to the docstring of a function
-registered with ``module::def()`` and ``class_::def()``. Sometimes this
+registered with ``module_::def()`` and ``class_::def()``. Sometimes this
 behavior is not desirable, because you want to provide your own signature or remove
 the docstring completely to exclude the function from the Sphinx documentation.
 The class ``options`` allows you to selectively suppress auto-generated signatures:

wrap/pybind11/docs/advanced/pycpp/numpy.rst

@@ -57,11 +57,11 @@ specification.
 
     struct buffer_info {
         void *ptr;
-        ssize_t itemsize;
+        py::ssize_t itemsize;
         std::string format;
-        ssize_t ndim;
+        py::ssize_t ndim;
-        std::vector<ssize_t> shape;
+        std::vector<py::ssize_t> shape;
-        std::vector<ssize_t> strides;
+        std::vector<py::ssize_t> strides;
     };
 
 To create a C++ function that can take a Python buffer object as an argument,
@@ -150,8 +150,10 @@ NumPy array containing double precision values.
 
 When it is invoked with a different type (e.g. an integer or a list of
 integers), the binding code will attempt to cast the input into a NumPy array
-of the requested type. Note that this feature requires the
+of the requested type. This feature requires the :file:`pybind11/numpy.h`
-:file:`pybind11/numpy.h` header to be included.
+header to be included. Note that :file:`pybind11/numpy.h` does not depend on
+the NumPy headers, and thus can be used without declaring a build-time
+dependency on NumPy; NumPy>=1.7.0 is a runtime dependency.
 
 Data in NumPy arrays is not guaranteed to packed in a dense manner;
 furthermore, entries can be separated by arbitrary column and row strides.
@@ -169,6 +171,31 @@ template parameter, and it ensures that non-conforming arguments are converted
 into an array satisfying the specified requirements instead of trying the next
 function overload.
 
+There are several methods on arrays; the methods listed below under references
+work, as well as the following functions based on the NumPy API:
+
+- ``.dtype()`` returns the type of the contained values.
+
+- ``.strides()`` returns a pointer to the strides of the array (optionally pass
+  an integer axis to get a number).
+
+- ``.flags()`` returns the flag settings. ``.writable()`` and ``.owndata()``
+  are directly available.
+
+- ``.offset_at()`` returns the offset (optionally pass indices).
+
+- ``.squeeze()`` returns a view with length-1 axes removed.
+
+- ``.view(dtype)`` returns a view of the array with a different dtype.
+
+- ``.reshape({i, j, ...})`` returns a view of the array with a different shape.
+  ``.resize({...})`` is also available.
+
+- ``.index_at(i, j, ...)`` gets the count from the beginning to a given index.
+
+
+There are also several methods for getting references (described below).
+
 Structured types
 ================
 
@@ -231,8 +258,8 @@ by the compiler. The result is returned as a NumPy array of type
 
 .. code-block:: pycon
 
-    >>> x = np.array([[1, 3],[5, 7]])
+    >>> x = np.array([[1, 3], [5, 7]])
-    >>> y = np.array([[2, 4],[6, 8]])
+    >>> y = np.array([[2, 4], [6, 8]])
     >>> z = 3
     >>> result = vectorized_func(x, y, z)
 
@@ -309,17 +336,17 @@ where ``N`` gives the required dimensionality of the array:
     m.def("sum_3d", [](py::array_t<double> x) {
         auto r = x.unchecked<3>(); // x must have ndim = 3; can be non-writeable
         double sum = 0;
-        for (ssize_t i = 0; i < r.shape(0); i++)
+        for (py::ssize_t i = 0; i < r.shape(0); i++)
-            for (ssize_t j = 0; j < r.shape(1); j++)
+            for (py::ssize_t j = 0; j < r.shape(1); j++)
-                for (ssize_t k = 0; k < r.shape(2); k++)
+                for (py::ssize_t k = 0; k < r.shape(2); k++)
                     sum += r(i, j, k);
         return sum;
     });
     m.def("increment_3d", [](py::array_t<double> x) {
         auto r = x.mutable_unchecked<3>(); // Will throw if ndim != 3 or flags.writeable is false
-        for (ssize_t i = 0; i < r.shape(0); i++)
+        for (py::ssize_t i = 0; i < r.shape(0); i++)
-            for (ssize_t j = 0; j < r.shape(1); j++)
+            for (py::ssize_t j = 0; j < r.shape(1); j++)
-                for (ssize_t k = 0; k < r.shape(2); k++)
+                for (py::ssize_t k = 0; k < r.shape(2); k++)
                     r(i, j, k) += 1.0;
     }, py::arg().noconvert());
 
@@ -343,21 +370,21 @@ The returned proxy object supports some of the same methods as ``py::array`` so
 that it can be used as a drop-in replacement for some existing, index-checked
 uses of ``py::array``:
 
-- ``r.ndim()`` returns the number of dimensions
+- ``.ndim()`` returns the number of dimensions
 
-- ``r.data(1, 2, ...)`` and ``r.mutable_data(1, 2, ...)``` returns a pointer to
+- ``.data(1, 2, ...)`` and ``r.mutable_data(1, 2, ...)``` returns a pointer to
   the ``const T`` or ``T`` data, respectively, at the given indices.  The
   latter is only available to proxies obtained via ``a.mutable_unchecked()``.
 
-- ``itemsize()`` returns the size of an item in bytes, i.e. ``sizeof(T)``.
+- ``.itemsize()`` returns the size of an item in bytes, i.e. ``sizeof(T)``.
 
-- ``ndim()`` returns the number of dimensions.
+- ``.ndim()`` returns the number of dimensions.
 
-- ``shape(n)`` returns the size of dimension ``n``
+- ``.shape(n)`` returns the size of dimension ``n``
 
-- ``size()`` returns the total number of elements (i.e. the product of the shapes).
+- ``.size()`` returns the total number of elements (i.e. the product of the shapes).
 
-- ``nbytes()`` returns the number of bytes used by the referenced elements
+- ``.nbytes()`` returns the number of bytes used by the referenced elements
   (i.e. ``itemsize()`` times ``size()``).
 
 .. seealso::
@@ -376,7 +403,7 @@ In Python 2, the syntactic sugar ``...`` is not available, but the singleton
 
 .. code-block:: python
 
-   a = # a NumPy array
+   a = ...  # a NumPy array
    b = a[0, ..., 0]
 
 The function ``py::ellipsis()`` function can be used to perform the same
@@ -388,7 +415,7 @@ operation on the C++ side:
    py::array b = a[py::make_tuple(0, py::ellipsis(), 0)];
 
 .. versionchanged:: 2.6
-   ``py::ellipsis()`` is now also avaliable in Python 2.
+   ``py::ellipsis()`` is now also available in Python 2.
 
 Memory view
 ===========

wrap/pybind11/docs/advanced/pycpp/object.rst

@@ -20,6 +20,40 @@ Available types include :class:`handle`, :class:`object`, :class:`bool_`,
     Be sure to review the :ref:`pytypes_gotchas` before using this heavily in
     your C++ API.
 
+.. _instantiating_compound_types:
+
+Instantiating compound Python types from C++
+============================================
+
+Dictionaries can be initialized in the :class:`dict` constructor:
+
+.. code-block:: cpp
+
+    using namespace pybind11::literals; // to bring in the `_a` literal
+    py::dict d("spam"_a=py::none(), "eggs"_a=42);
+
+A tuple of python objects can be instantiated using :func:`py::make_tuple`:
+
+.. code-block:: cpp
+
+    py::tuple tup = py::make_tuple(42, py::none(), "spam");
+
+Each element is converted to a supported Python type.
+
+A `simple namespace`_ can be instantiated using
+
+.. code-block:: cpp
+
+    using namespace pybind11::literals;  // to bring in the `_a` literal
+    py::object SimpleNamespace = py::module_::import("types").attr("SimpleNamespace");
+    py::object ns = SimpleNamespace("spam"_a=py::none(), "eggs"_a=42);
+
+Attributes on a namespace can be modified with the :func:`py::delattr`,
+:func:`py::getattr`, and :func:`py::setattr` functions. Simple namespaces can
+be useful as lightweight stand-ins for class instances.
+
+.. _simple namespace: https://docs.python.org/3/library/types.html#types.SimpleNamespace
+
 .. _casting_back_and_forth:
 
 Casting back and forth
@@ -30,7 +64,7 @@ types to Python, which can be done using :func:`py::cast`:
 
 .. code-block:: cpp
 
-    MyClass *cls = ..;
+    MyClass *cls = ...;
     py::object obj = py::cast(cls);
 
 The reverse direction uses the following syntax:
@@ -56,12 +90,12 @@ This example obtains a reference to the Python ``Decimal`` class.
 .. code-block:: cpp
 
     // Equivalent to "from decimal import Decimal"
-    py::object Decimal = py::module::import("decimal").attr("Decimal");
+    py::object Decimal = py::module_::import("decimal").attr("Decimal");
 
 .. code-block:: cpp
 
     // Try to import scipy
-    py::object scipy = py::module::import("scipy");
+    py::object scipy = py::module_::import("scipy");
     return scipy.attr("__version__");
 
 
@@ -81,7 +115,7 @@ via ``operator()``.
 .. code-block:: cpp
 
     // Use Python to make our directories
-    py::object os = py::module::import("os");
+    py::object os = py::module_::import("os");
     py::object makedirs = os.attr("makedirs");
     makedirs("/tmp/path/to/somewhere");
 
@@ -132,6 +166,7 @@ Keyword arguments are also supported. In Python, there is the usual call syntax:
     def f(number, say, to):
         ...  # function code
 
+
     f(1234, say="hello", to=some_instance)  # keyword call in Python
 
 In C++, the same call can be made using:
@@ -196,9 +231,9 @@ C++ functions that require a specific subtype rather than a generic :class:`obje
     #include <pybind11/numpy.h>
     using namespace pybind11::literals;
 
-    py::module os = py::module::import("os");
+    py::module_ os = py::module_::import("os");
-    py::module path = py::module::import("os.path");  // like 'import os.path as path'
+    py::module_ path = py::module_::import("os.path");  // like 'import os.path as path'
-    py::module np = py::module::import("numpy");  // like 'import numpy as np'
+    py::module_ np = py::module_::import("numpy");  // like 'import numpy as np'
 
     py::str curdir_abs = path.attr("abspath")(path.attr("curdir"));
     py::print(py::str("Current directory: ") + curdir_abs);

wrap/pybind11/docs/advanced/pycpp/utilities.rst

@@ -28,7 +28,7 @@ Capturing standard output from ostream
 
 Often, a library will use the streams ``std::cout`` and ``std::cerr`` to print,
 but this does not play well with Python's standard ``sys.stdout`` and ``sys.stderr``
-redirection. Replacing a library's printing with `py::print <print>` may not
+redirection. Replacing a library's printing with ``py::print <print>`` may not
 be feasible. This can be fixed using a guard around the library function that
 redirects output to the corresponding Python streams:
 
@@ -42,20 +42,31 @@ redirects output to the corresponding Python streams:
     m.def("noisy_func", []() {
         py::scoped_ostream_redirect stream(
             std::cout,                               // std::ostream&
-            py::module::import("sys").attr("stdout") // Python output
+            py::module_::import("sys").attr("stdout") // Python output
         );
         call_noisy_func();
     });
 
+.. warning::
+
+    The implementation in ``pybind11/iostream.h`` is NOT thread safe. Multiple
+    threads writing to a redirected ostream concurrently cause data races
+    and potentially buffer overflows. Therefore it is currently a requirement
+    that all (possibly) concurrent redirected ostream writes are protected by
+    a mutex. #HelpAppreciated: Work on iostream.h thread safety. For more
+    background see the discussions under
+    `PR #2982 <https://github.com/pybind/pybind11/pull/2982>`_ and
+    `PR #2995 <https://github.com/pybind/pybind11/pull/2995>`_.
+
 This method respects flushes on the output streams and will flush if needed
 when the scoped guard is destroyed. This allows the output to be redirected in
 real time, such as to a Jupyter notebook. The two arguments, the C++ stream and
 the Python output, are optional, and default to standard output if not given. An
-extra type, `py::scoped_estream_redirect <scoped_estream_redirect>`, is identical
+extra type, ``py::scoped_estream_redirect <scoped_estream_redirect>``, is identical
 except for defaulting to ``std::cerr`` and ``sys.stderr``; this can be useful with
-`py::call_guard`, which allows multiple items, but uses the default constructor:
+``py::call_guard``, which allows multiple items, but uses the default constructor:
 
-.. code-block:: py
+.. code-block:: cpp
 
     // Alternative: Call single function using call guard
     m.def("noisy_func", &call_noisy_function,
@@ -63,7 +74,7 @@ except for defaulting to ``std::cerr`` and ``sys.stderr``; this can be useful wi
                          py::scoped_estream_redirect>());
 
 The redirection can also be done in Python with the addition of a context
-manager, using the `py::add_ostream_redirect() <add_ostream_redirect>` function:
+manager, using the ``py::add_ostream_redirect() <add_ostream_redirect>`` function:
 
 .. code-block:: cpp
 
@@ -92,7 +103,7 @@ arguments to disable one of the streams if needed.
 Evaluating Python expressions from strings and files
 ====================================================
 
-pybind11 provides the `eval`, `exec` and `eval_file` functions to evaluate
+pybind11 provides the ``eval``, ``exec`` and ``eval_file`` functions to evaluate
 Python expressions and statements. The following example illustrates how they
 can be used.
 
@@ -104,7 +115,7 @@ can be used.
     ...
 
     // Evaluate in scope of main module
-    py::object scope = py::module::import("__main__").attr("__dict__");
+    py::object scope = py::module_::import("__main__").attr("__dict__");
 
     // Evaluate an isolated expression
     int result = py::eval("my_variable + 10", scope).cast<int>();

wrap/pybind11/docs/advanced/smart_ptrs.rst

@@ -77,6 +77,7 @@ segmentation fault).
 .. code-block:: python
 
    from example import Parent
+
    print(Parent().get_child())
 
 The problem is that ``Parent::get_child()`` returns a pointer to an instance of

wrap/pybind11/docs/basics.rst

@@ -39,7 +39,7 @@ on various C++11 language features that break older versions of Visual Studio.
 
     To use the C++17 in Visual Studio 2017 (MSVC 14.1), pybind11 requires the flag
     ``/permissive-`` to be passed to the compiler `to enforce standard conformance`_. When
-    building with Visual Studio 2019, this is not strictly necessary, but still adviced.
+    building with Visual Studio 2019, this is not strictly necessary, but still advised.
 
 ..  _`to enforce standard conformance`: https://docs.microsoft.com/en-us/cpp/build/reference/permissive-standards-conformance?view=vs-2017
 
@@ -109,7 +109,7 @@ a file named :file:`example.cpp` with the following contents:
     PYBIND11_MODULE(example, m) {
         m.doc() = "pybind11 example plugin"; // optional module docstring
 
-        m.def("add", &add, "A function which adds two numbers");
+        m.def("add", &add, "A function that adds two numbers");
     }
 
 .. [#f1] In practice, implementation and binding code will generally be located
@@ -118,8 +118,8 @@ a file named :file:`example.cpp` with the following contents:
 The :func:`PYBIND11_MODULE` macro creates a function that will be called when an
 ``import`` statement is issued from within Python. The module name (``example``)
 is given as the first macro argument (it should not be in quotes). The second
-argument (``m``) defines a variable of type :class:`py::module <module>` which
+argument (``m``) defines a variable of type :class:`py::module_ <module>` which
-is the main interface for creating bindings. The method :func:`module::def`
+is the main interface for creating bindings. The method :func:`module_::def`
 generates binding code that exposes the ``add()`` function to Python.
 
 .. note::
@@ -136,7 +136,14 @@ On Linux, the above example can be compiled using the following command:
 
 .. code-block:: bash
 
-    $ c++ -O3 -Wall -shared -std=c++11 -fPIC `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+    $ c++ -O3 -Wall -shared -std=c++11 -fPIC $(python3 -m pybind11 --includes) example.cpp -o example$(python3-config --extension-suffix)
+
+.. note::
+
+    If you used :ref:`include_as_a_submodule` to get the pybind11 source, then
+    use ``$(python3-config --includes) -Iextern/pybind11/include`` instead of
+    ``$(python3 -m pybind11 --includes)`` in the above compilation, as
+    explained in :ref:`building_manually`.
 
 For more details on the required compiler flags on Linux and macOS, see
 :ref:`building_manually`. For complete cross-platform compilation instructions,
@@ -181,7 +188,7 @@ names of the arguments ("i" and "j" in this case).
           py::arg("i"), py::arg("j"));
 
 :class:`arg` is one of several special tag classes which can be used to pass
-metadata into :func:`module::def`. With this modified binding code, we can now
+metadata into :func:`module_::def`. With this modified binding code, we can now
 call the function using keyword arguments, which is a more readable alternative
 particularly for functions taking many parameters:
 

wrap/pybind11/docs/benchmark.py

@@ -1,8 +1,7 @@
 # -*- coding: utf-8 -*-
-import random
-import os
-import time
 import datetime as dt
+import os
+import random
 
 nfns = 4  # Functions per class
 nargs = 4  # Arguments per function
@@ -14,7 +13,7 @@ def generate_dummy_code_pybind11(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -26,14 +25,13 @@ def generate_dummy_code_pybind11(nclasses=10):
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % \
+            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % (fn, cl, fn)
-                (fn, cl, fn)
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <pybind11/pybind11.h>\n\n"
     result += "namespace py = pybind11;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "PYBIND11_MODULE(example, m) {\n"
     result += bindings
     result += "}"
@@ -46,7 +44,7 @@ def generate_dummy_code_boost(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -58,14 +56,16 @@ def generate_dummy_code_boost(nclasses=10):
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n' % \
+            bindings += (
-                (fn, cl, fn)
+                '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n'
+                % (fn, cl, fn)
+            )
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <boost/python.hpp>\n\n"
     result += "namespace py = boost::python;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "BOOST_PYTHON_MODULE(example) {\n"
     result += bindings
     result += "}"
@@ -73,17 +73,19 @@ def generate_dummy_code_boost(nclasses=10):
 
 
 for codegen in [generate_dummy_code_pybind11, generate_dummy_code_boost]:
-    print ("{")
+    print("{")
     for i in range(0, 10):
         nclasses = 2 ** i
         with open("test.cpp", "w") as f:
             f.write(codegen(nclasses))
         n1 = dt.datetime.now()
-        os.system("g++ -Os -shared -rdynamic -undefined dynamic_lookup "
+        os.system(
+            "g++ -Os -shared -rdynamic -undefined dynamic_lookup "
             "-fvisibility=hidden -std=c++14 test.cpp -I include "
-            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so")
+            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so"
+        )
         n2 = dt.datetime.now()
         elapsed = (n2 - n1).total_seconds()
-        size = os.stat('test.so').st_size
+        size = os.stat("test.so").st_size
         print("   {%i, %f, %i}," % (nclasses * nfns, elapsed, size))
-    print ("}")
+    print("}")

wrap/pybind11/docs/changelog.rst

@@ -6,21 +6,697 @@ Changelog
 Starting with version 1.8.0, pybind11 releases use a `semantic versioning
 <http://semver.org>`_ policy.
 
-v2.6.0 (IN PROGRESS)
+Version 2.9.1 (Feb 2, 2022)
+---------------------------
+
+Changes:
+
+* If possible, attach Python exception with ``py::raise_from`` to ``TypeError``
+  when casting from C++ to Python. This will give additional info if Python
+  exceptions occur in the caster. Adds a test case of trying to convert a set
+  from C++ to Python when the hash function is not defined in Python.
+  `#3605 <https://github.com/pybind/pybind11/pull/3605>`_
+
+* Add a mapping of C++11 nested exceptions to their Python exception
+  equivalent using ``py::raise_from``. This attaches the nested exceptions in
+  Python using the ``__cause__`` field.
+  `#3608 <https://github.com/pybind/pybind11/pull/3608>`_
+
+* Propagate Python exception traceback using ``raise_from`` if a pybind11
+  function runs out of overloads.
+  `#3671 <https://github.com/pybind/pybind11/pull/3671>`_
+
+* ``py::multiple_inheritance`` is now only needed when C++ bases are hidden
+  from pybind11.
+  `#3650 <https://github.com/pybind/pybind11/pull/3650>`_ and
+  `#3659 <https://github.com/pybind/pybind11/pull/3659>`_
+
+
+Bug fixes:
+
+* Remove a boolean cast in ``numpy.h`` that causes MSVC C4800 warnings when
+  compiling against Python 3.10 or newer.
+  `#3669 <https://github.com/pybind/pybind11/pull/3669>`_
+
+* Render ``py::bool_`` and ``py::float_`` as ``bool`` and ``float``
+  respectively.
+  `#3622 <https://github.com/pybind/pybind11/pull/3622>`_
+
+Build system improvements:
+
+* Fix CMake extension suffix computation on Python 3.10+.
+  `#3663 <https://github.com/pybind/pybind11/pull/3663>`_
+
+* Allow ``CMAKE_ARGS`` to override CMake args in pybind11's own ``setup.py``.
+  `#3577 <https://github.com/pybind/pybind11/pull/3577>`_
+
+* Remove a few deprecated c-headers.
+  `#3610 <https://github.com/pybind/pybind11/pull/3610>`_
+
+* More uniform handling of test targets.
+  `#3590 <https://github.com/pybind/pybind11/pull/3590>`_
+
+* Add clang-tidy readability check to catch potentially swapped function args.
+  `#3611 <https://github.com/pybind/pybind11/pull/3611>`_
+
+
+Version 2.9.0 (Dec 28, 2021)
+----------------------------
+
+This is the last version to support Python 2.7 and 3.5.
+
+New Features:
+
+* Allow ``py::args`` to be followed by other arguments; the remaining arguments
+  are implicitly keyword-only, as if a ``py::kw_only{}`` annotation had been
+  used.
+  `#3402 <https://github.com/pybind/pybind11/pull/3402>`_
+
+Changes:
+
+* Make str/bytes/memoryview more interoperable with ``std::string_view``.
+  `#3521 <https://github.com/pybind/pybind11/pull/3521>`_
+
+* Replace ``_`` with ``const_name`` in internals, avoid defining ``pybind::_``
+  if ``_`` defined as macro (common gettext usage)
+  `#3423 <https://github.com/pybind/pybind11/pull/3423>`_
+
+
+Bug fixes:
+
+* Fix a rare warning about extra copy in an Eigen constructor.
+  `#3486 <https://github.com/pybind/pybind11/pull/3486>`_
+
+* Fix caching of the C++ overrides.
+  `#3465 <https://github.com/pybind/pybind11/pull/3465>`_
+
+* Add missing ``std::forward`` calls to some ``cpp_function`` overloads.
+  `#3443 <https://github.com/pybind/pybind11/pull/3443>`_
+
+* Support PyPy 7.3.7 and the PyPy3.8 beta. Test python-3.11 on PRs with the
+  ``python dev`` label.
+  `#3419 <https://github.com/pybind/pybind11/pull/3419>`_
+
+* Replace usage of deprecated ``Eigen::MappedSparseMatrix`` with
+  ``Eigen::Map<Eigen::SparseMatrix<...>>`` for Eigen 3.3+.
+  `#3499 <https://github.com/pybind/pybind11/pull/3499>`_
+
+* Tweaks to support Microsoft Visual Studio 2022.
+  `#3497 <https://github.com/pybind/pybind11/pull/3497>`_
+
+Build system improvements:
+
+* Nicer CMake printout and IDE organisation for pybind11's own tests.
+  `#3479 <https://github.com/pybind/pybind11/pull/3479>`_
+
+* CMake: report version type as part of the version string to avoid a spurious
+  space in the package status message.
+  `#3472 <https://github.com/pybind/pybind11/pull/3472>`_
+
+* Flags starting with ``-g`` in ``$CFLAGS`` and ``$CPPFLAGS`` are no longer
+  overridden by ``.Pybind11Extension``.
+  `#3436 <https://github.com/pybind/pybind11/pull/3436>`_
+
+* Ensure ThreadPool is closed in ``setup_helpers``.
+  `#3548 <https://github.com/pybind/pybind11/pull/3548>`_
+
+* Avoid LTS on ``mips64`` and ``ppc64le`` (reported broken).
+  `#3557 <https://github.com/pybind/pybind11/pull/3557>`_
+
+
+v2.8.1 (Oct 27, 2021)
+---------------------
+
+Changes and additions:
+
+* The simple namespace creation shortcut added in 2.8.0 was deprecated due to
+  usage of CPython internal API, and will be removed soon. Use
+  ``py::module_::import("types").attr("SimpleNamespace")``.
+  `#3374 <https://github.com/pybinyyd/pybind11/pull/3374>`_
+
+* Add C++ Exception type to throw and catch ``AttributeError``. Useful for
+  defining custom ``__setattr__`` and ``__getattr__`` methods.
+  `#3387 <https://github.com/pybind/pybind11/pull/3387>`_
+
+Fixes:
+
+* Fixed the potential for dangling references when using properties with
+  ``std::optional`` types.
+  `#3376 <https://github.com/pybind/pybind11/pull/3376>`_
+
+* Modernize usage of ``PyCodeObject`` on Python 3.9+ (moving toward support for
+  Python 3.11a1)
+  `#3368 <https://github.com/pybind/pybind11/pull/3368>`_
+
+* A long-standing bug in ``eigen.h`` was fixed (originally PR #3343). The bug
+  was unmasked by newly added ``static_assert``'s in the Eigen 3.4.0 release.
+  `#3352 <https://github.com/pybind/pybind11/pull/3352>`_
+
+* Support multiple raw inclusion of CMake helper files (Conan.io does this for
+  multi-config generators).
+  `#3420 <https://github.com/pybind/pybind11/pull/3420>`_
+
+* Fix harmless warning on upcoming CMake 3.22.
+  `#3368 <https://github.com/pybind/pybind11/pull/3368>`_
+
+* Fix 2.8.0 regression with MSVC 2017 + C++17 mode + Python 3.
+  `#3407 <https://github.com/pybind/pybind11/pull/3407>`_
+
+* Fix 2.8.0 regression that caused undefined behavior (typically
+  segfaults) in ``make_key_iterator``/``make_value_iterator`` if dereferencing
+  the iterator returned a temporary value instead of a reference.
+  `#3348 <https://github.com/pybind/pybind11/pull/3348>`_
+
+
+v2.8.0 (Oct 4, 2021)
 --------------------
 
+New features:
+
+* Added ``py::raise_from`` to enable chaining exceptions.
+  `#3215 <https://github.com/pybind/pybind11/pull/3215>`_
+
+* Allow exception translators to be optionally registered local to a module
+  instead of applying globally across all pybind11 modules. Use
+  ``register_local_exception_translator(ExceptionTranslator&& translator)``
+  instead of  ``register_exception_translator(ExceptionTranslator&&
+  translator)`` to keep your exception remapping code local to the module.
+  `#2650 <https://github.com/pybinyyd/pybind11/pull/2650>`_
+
+* Add ``make_simple_namespace`` function for instantiating Python
+  ``SimpleNamespace`` objects. **Deprecated in 2.8.1.**
+  `#2840 <https://github.com/pybind/pybind11/pull/2840>`_
+
+* ``pybind11::scoped_interpreter`` and ``initialize_interpreter`` have new
+  arguments to allow ``sys.argv`` initialization.
+  `#2341 <https://github.com/pybind/pybind11/pull/2341>`_
+
+* Allow Python builtins to be used as callbacks in CPython.
+  `#1413 <https://github.com/pybind/pybind11/pull/1413>`_
+
+* Added ``view`` to view arrays with a different datatype.
+  `#987 <https://github.com/pybind/pybind11/pull/987>`_
+
+* Implemented ``reshape`` on arrays.
+  `#984 <https://github.com/pybind/pybind11/pull/984>`_
+
+* Enable defining custom ``__new__`` methods on classes by fixing bug
+  preventing overriding methods if they have non-pybind11 siblings.
+  `#3265 <https://github.com/pybind/pybind11/pull/3265>`_
+
+* Add ``make_value_iterator()``, and fix ``make_key_iterator()`` to return
+  references instead of copies.
+  `#3293 <https://github.com/pybind/pybind11/pull/3293>`_
+
+* Improve the classes generated by ``bind_map``: `#3310 <https://github.com/pybind/pybind11/pull/3310>`_
+
+  * Change ``.items`` from an iterator to a dictionary view.
+  * Add ``.keys`` and ``.values`` (both dictionary views).
+  * Allow ``__contains__`` to take any object.
+
+* ``pybind11::custom_type_setup`` was added, for customizing the
+  ``PyHeapTypeObject`` corresponding to a class, which may be useful for
+  enabling garbage collection support, among other things.
+  `#3287 <https://github.com/pybind/pybind11/pull/3287>`_
+
+
+Changes:
+
+* Set ``__file__`` constant when running ``eval_file`` in an embedded interpreter.
+  `#3233 <https://github.com/pybind/pybind11/pull/3233>`_
+
+* Python objects and (C++17) ``std::optional`` now accepted in ``py::slice``
+  constructor.
+  `#1101 <https://github.com/pybind/pybind11/pull/1101>`_
+
+* The pybind11 proxy types ``str``, ``bytes``, ``bytearray``, ``tuple``,
+  ``list`` now consistently support passing ``ssize_t`` values for sizes and
+  indexes. Previously, only ``size_t`` was accepted in several interfaces.
+  `#3219 <https://github.com/pybind/pybind11/pull/3219>`_
+
+* Avoid evaluating ``PYBIND11_TLS_REPLACE_VALUE`` arguments more than once.
+  `#3290 <https://github.com/pybind/pybind11/pull/3290>`_
+
+Fixes:
+
+* Bug fix: enum value's ``__int__`` returning non-int when underlying type is
+  bool or of char type.
+  `#1334 <https://github.com/pybind/pybind11/pull/1334>`_
+
+* Fixes bug in setting error state in Capsule's pointer methods.
+  `#3261 <https://github.com/pybind/pybind11/pull/3261>`_
+
+* A long-standing memory leak in ``py::cpp_function::initialize`` was fixed.
+  `#3229 <https://github.com/pybind/pybind11/pull/3229>`_
+
+* Fixes thread safety for some ``pybind11::type_caster`` which require lifetime
+  extension, such as for ``std::string_view``.
+  `#3237 <https://github.com/pybind/pybind11/pull/3237>`_
+
+* Restore compatibility with gcc 4.8.4 as distributed by ubuntu-trusty, linuxmint-17.
+  `#3270 <https://github.com/pybind/pybind11/pull/3270>`_
+
+
+Build system improvements:
+
+* Fix regression in CMake Python package config: improper use of absolute path.
+  `#3144 <https://github.com/pybind/pybind11/pull/3144>`_
+
+* Cached Python version information could become stale when CMake was re-run
+  with a different Python version. The build system now detects this and
+  updates this information.
+  `#3299 <https://github.com/pybind/pybind11/pull/3299>`_
+
+* Specified UTF8-encoding in setup.py calls of open().
+  `#3137 <https://github.com/pybind/pybind11/pull/3137>`_
+
+* Fix a harmless warning from CMake 3.21 with the classic Python discovery.
+  `#3220 <https://github.com/pybind/pybind11/pull/3220>`_
+
+* Eigen repo and version can now be specified as cmake options.
+  `#3324 <https://github.com/pybind/pybind11/pull/3324>`_
+
+
+Backend and tidying up:
+
+* Reduced thread-local storage required for keeping alive temporary data for
+  type conversion to one key per ABI version, rather than one key per extension
+  module.  This makes the total thread-local storage required by pybind11 2
+  keys per ABI version.
+  `#3275 <https://github.com/pybind/pybind11/pull/3275>`_
+
+* Optimize NumPy array construction with additional moves.
+  `#3183 <https://github.com/pybind/pybind11/pull/3183>`_
+
+* Conversion to ``std::string`` and ``std::string_view`` now avoids making an
+  extra copy of the data on Python >= 3.3.
+  `#3257 <https://github.com/pybind/pybind11/pull/3257>`_
+
+* Remove const modifier from certain C++ methods on Python collections
+  (``list``, ``set``, ``dict``) such as (``clear()``, ``append()``,
+  ``insert()``, etc...) and annotated them with ``py-non-const``.
+
+* Enable readability ``clang-tidy-const-return`` and remove useless consts.
+  `#3254 <https://github.com/pybind/pybind11/pull/3254>`_
+  `#3194 <https://github.com/pybind/pybind11/pull/3194>`_
+
+* The clang-tidy ``google-explicit-constructor`` option was enabled.
+  `#3250 <https://github.com/pybind/pybind11/pull/3250>`_
+
+* Mark a pytype move constructor as noexcept (perf).
+  `#3236 <https://github.com/pybind/pybind11/pull/3236>`_
+
+* Enable clang-tidy check to guard against inheritance slicing.
+  `#3210 <https://github.com/pybind/pybind11/pull/3210>`_
+
+* Legacy warning suppression pragma were removed from eigen.h. On Unix
+  platforms, please use -isystem for Eigen include directories, to suppress
+  compiler warnings originating from Eigen headers. Note that CMake does this
+  by default. No adjustments are needed for Windows.
+  `#3198 <https://github.com/pybind/pybind11/pull/3198>`_
+
+* Format pybind11 with isort consistent ordering of imports
+  `#3195 <https://github.com/pybind/pybind11/pull/3195>`_
+
+* The warnings-suppression "pragma clamp" at the top/bottom of pybind11 was
+  removed, clearing the path to refactoring and IWYU cleanup.
+  `#3186 <https://github.com/pybind/pybind11/pull/3186>`_
+
+* Enable most bugprone checks in clang-tidy and fix the found potential bugs
+  and poor coding styles.
+  `#3166 <https://github.com/pybind/pybind11/pull/3166>`_
+
+* Add ``clang-tidy-readability`` rules to make boolean casts explicit improving
+  code readability. Also enabled other misc and readability clang-tidy checks.
+  `#3148 <https://github.com/pybind/pybind11/pull/3148>`_
+
+* Move object in ``.pop()`` for list.
+  `#3116 <https://github.com/pybind/pybind11/pull/3116>`_
+
+
+
+
+v2.7.1 (Aug 3, 2021)
+---------------------
+
+Minor missing functionality added:
+
+* Allow Python builtins to be used as callbacks in CPython.
+  `#1413 <https://github.com/pybind/pybind11/pull/1413>`_
+
+Bug fixes:
+
+* Fix regression in CMake Python package config: improper use of absolute path.
+  `#3144 <https://github.com/pybind/pybind11/pull/3144>`_
+
+* Fix Mingw64 and add to the CI testing matrix.
+  `#3132 <https://github.com/pybind/pybind11/pull/3132>`_
+
+* Specified UTF8-encoding in setup.py calls of open().
+  `#3137 <https://github.com/pybind/pybind11/pull/3137>`_
+
+* Add clang-tidy-readability rules to make boolean casts explicit improving
+  code readability. Also enabled other misc and readability clang-tidy checks.
+  `#3148 <https://github.com/pybind/pybind11/pull/3148>`_
+
+* Move object in ``.pop()`` for list.
+  `#3116 <https://github.com/pybind/pybind11/pull/3116>`_
+
+Backend and tidying up:
+
+* Removed and fixed warning suppressions.
+  `#3127 <https://github.com/pybind/pybind11/pull/3127>`_
+  `#3129 <https://github.com/pybind/pybind11/pull/3129>`_
+  `#3135 <https://github.com/pybind/pybind11/pull/3135>`_
+  `#3141 <https://github.com/pybind/pybind11/pull/3141>`_
+  `#3142 <https://github.com/pybind/pybind11/pull/3142>`_
+  `#3150 <https://github.com/pybind/pybind11/pull/3150>`_
+  `#3152 <https://github.com/pybind/pybind11/pull/3152>`_
+  `#3160 <https://github.com/pybind/pybind11/pull/3160>`_
+  `#3161 <https://github.com/pybind/pybind11/pull/3161>`_
+
+
+v2.7.0 (Jul 16, 2021)
+---------------------
+
+New features:
+
+* Enable ``py::implicitly_convertible<py::none, ...>`` for
+  ``py::class_``-wrapped types.
+  `#3059 <https://github.com/pybind/pybind11/pull/3059>`_
+
+* Allow function pointer extraction from overloaded functions.
+  `#2944 <https://github.com/pybind/pybind11/pull/2944>`_
+
+* NumPy: added ``.char_()`` to type which gives the NumPy public ``char``
+  result, which also distinguishes types by bit length (unlike ``.kind()``).
+  `#2864 <https://github.com/pybind/pybind11/pull/2864>`_
+
+* Add ``pybind11::bytearray`` to manipulate ``bytearray`` similar to ``bytes``.
+  `#2799 <https://github.com/pybind/pybind11/pull/2799>`_
+
+* ``pybind11/stl/filesystem.h`` registers a type caster that, on C++17/Python
+  3.6+, converts ``std::filesystem::path`` to ``pathlib.Path`` and any
+  ``os.PathLike`` to ``std::filesystem::path``.
+  `#2730 <https://github.com/pybind/pybind11/pull/2730>`_
+
+* A ``PYBIND11_VERSION_HEX`` define was added, similar to ``PY_VERSION_HEX``.
+  `#3120 <https://github.com/pybind/pybind11/pull/3120>`_
+
+
+
+Changes:
+
+* ``py::str`` changed to exclusively hold ``PyUnicodeObject``. Previously
+  ``py::str`` could also hold ``bytes``, which is probably surprising, was
+  never documented, and can mask bugs (e.g. accidental use of ``py::str``
+  instead of ``py::bytes``).
+  `#2409 <https://github.com/pybind/pybind11/pull/2409>`_
+
+* Add a safety guard to ensure that the Python GIL is held when C++ calls back
+  into Python via ``object_api<>::operator()`` (e.g. ``py::function``
+  ``__call__``).  (This feature is available for Python 3.6+ only.)
+  `#2919 <https://github.com/pybind/pybind11/pull/2919>`_
+
+* Catch a missing ``self`` argument in calls to ``__init__()``.
+  `#2914 <https://github.com/pybind/pybind11/pull/2914>`_
+
+* Use ``std::string_view`` if available to avoid a copy when passing an object
+  to a ``std::ostream``.
+  `#3042 <https://github.com/pybind/pybind11/pull/3042>`_
+
+* An important warning about thread safety was added to the ``iostream.h``
+  documentation; attempts to make ``py::scoped_ostream_redirect`` thread safe
+  have been removed, as it was only partially effective.
+  `#2995 <https://github.com/pybind/pybind11/pull/2995>`_
+
+
+Fixes:
+
+* Performance: avoid unnecessary strlen calls.
+  `#3058 <https://github.com/pybind/pybind11/pull/3058>`_
+
+* Fix auto-generated documentation string when using ``const T`` in
+  ``pyarray_t``.
+  `#3020 <https://github.com/pybind/pybind11/pull/3020>`_
+
+* Unify error messages thrown by ``simple_collector``/``unpacking_collector``.
+  `#3013 <https://github.com/pybind/pybind11/pull/3013>`_
+
+* ``pybind11::builtin_exception`` is now explicitly exported, which means the
+  types included/defined in different modules are identical, and exceptions
+  raised in different modules can be caught correctly. The documentation was
+  updated to explain that custom exceptions that are used across module
+  boundaries need to be explicitly exported as well.
+  `#2999 <https://github.com/pybind/pybind11/pull/2999>`_
+
+* Fixed exception when printing UTF-8 to a ``scoped_ostream_redirect``.
+  `#2982 <https://github.com/pybind/pybind11/pull/2982>`_
+
+* Pickle support enhancement: ``setstate`` implementation will attempt to
+  ``setattr`` ``__dict__`` only if the unpickled ``dict`` object is not empty,
+  to not force use of ``py::dynamic_attr()`` unnecessarily.
+  `#2972 <https://github.com/pybind/pybind11/pull/2972>`_
+
+* Allow negative timedelta values to roundtrip.
+  `#2870 <https://github.com/pybind/pybind11/pull/2870>`_
+
+* Fix unchecked errors could potentially swallow signals/other exceptions.
+  `#2863 <https://github.com/pybind/pybind11/pull/2863>`_
+
+* Add null pointer check with ``std::localtime``.
+  `#2846 <https://github.com/pybind/pybind11/pull/2846>`_
+
+* Fix the ``weakref`` constructor from ``py::object`` to create a new
+  ``weakref`` on conversion.
+  `#2832 <https://github.com/pybind/pybind11/pull/2832>`_
+
+* Avoid relying on exceptions in C++17 when getting a ``shared_ptr`` holder
+  from a ``shared_from_this`` class.
+  `#2819 <https://github.com/pybind/pybind11/pull/2819>`_
+
+* Allow the codec's exception to be raised instead of :code:`RuntimeError` when
+  casting from :code:`py::str` to :code:`std::string`.
+  `#2903 <https://github.com/pybind/pybind11/pull/2903>`_
+
+
+Build system improvements:
+
+* In ``setup_helpers.py``, test for platforms that have some multiprocessing
+  features but lack semaphores, which ``ParallelCompile`` requires.
+  `#3043 <https://github.com/pybind/pybind11/pull/3043>`_
+
+* Fix ``pybind11_INCLUDE_DIR`` in case ``CMAKE_INSTALL_INCLUDEDIR`` is
+  absolute.
+  `#3005 <https://github.com/pybind/pybind11/pull/3005>`_
+
+* Fix bug not respecting ``WITH_SOABI`` or ``WITHOUT_SOABI`` to CMake.
+  `#2938 <https://github.com/pybind/pybind11/pull/2938>`_
+
+* Fix the default ``Pybind11Extension`` compilation flags with a Mingw64 python.
+  `#2921 <https://github.com/pybind/pybind11/pull/2921>`_
+
+* Clang on Windows: do not pass ``/MP`` (ignored flag).
+  `#2824 <https://github.com/pybind/pybind11/pull/2824>`_
+
+* ``pybind11.setup_helpers.intree_extensions`` can be used to generate
+  ``Pybind11Extension`` instances from cpp files placed in the Python package
+  source tree.
+  `#2831 <https://github.com/pybind/pybind11/pull/2831>`_
+
+Backend and tidying up:
+
+* Enable clang-tidy performance, readability, and modernization checks
+  throughout the codebase to enforce best coding practices.
+  `#3046 <https://github.com/pybind/pybind11/pull/3046>`_,
+  `#3049 <https://github.com/pybind/pybind11/pull/3049>`_,
+  `#3051 <https://github.com/pybind/pybind11/pull/3051>`_,
+  `#3052 <https://github.com/pybind/pybind11/pull/3052>`_,
+  `#3080 <https://github.com/pybind/pybind11/pull/3080>`_, and
+  `#3094 <https://github.com/pybind/pybind11/pull/3094>`_
+
+
+* Checks for common misspellings were added to the pre-commit hooks.
+  `#3076 <https://github.com/pybind/pybind11/pull/3076>`_
+
+* Changed ``Werror`` to stricter ``Werror-all`` for Intel compiler and fixed
+  minor issues.
+  `#2948 <https://github.com/pybind/pybind11/pull/2948>`_
+
+* Fixed compilation with GCC < 5 when the user defines ``_GLIBCXX_USE_CXX11_ABI``.
+  `#2956 <https://github.com/pybind/pybind11/pull/2956>`_
+
+* Added nox support for easier local testing and linting of contributions.
+  `#3101 <https://github.com/pybind/pybind11/pull/3101>`_ and
+  `#3121 <https://github.com/pybind/pybind11/pull/3121>`_
+
+* Avoid RTD style issue with docutils 0.17+.
+  `#3119 <https://github.com/pybind/pybind11/pull/3119>`_
+
+* Support pipx run, such as ``pipx run pybind11 --include`` for a quick compile.
+  `#3117 <https://github.com/pybind/pybind11/pull/3117>`_
+
+
+
+v2.6.2 (Jan 26, 2021)
+---------------------
+
+Minor missing functionality added:
+
+* enum: add missing Enum.value property.
+  `#2739 <https://github.com/pybind/pybind11/pull/2739>`_
+
+* Allow thread termination to be avoided during shutdown for CPython 3.7+ via
+  ``.disarm`` for ``gil_scoped_acquire``/``gil_scoped_release``.
+  `#2657 <https://github.com/pybind/pybind11/pull/2657>`_
+
+Fixed or improved behavior in a few special cases:
+
+* Fix bug where the constructor of ``object`` subclasses would not throw on
+  being passed a Python object of the wrong type.
+  `#2701 <https://github.com/pybind/pybind11/pull/2701>`_
+
+* The ``type_caster`` for integers does not convert Python objects with
+  ``__int__`` anymore with ``noconvert`` or during the first round of trying
+  overloads.
+  `#2698 <https://github.com/pybind/pybind11/pull/2698>`_
+
+* When casting to a C++ integer, ``__index__`` is always called and not
+  considered as conversion, consistent with Python 3.8+.
+  `#2801 <https://github.com/pybind/pybind11/pull/2801>`_
+
+Build improvements:
+
+* Setup helpers: ``extra_compile_args`` and ``extra_link_args`` automatically set by
+  Pybind11Extension are now prepended, which allows them to be overridden
+  by user-set ``extra_compile_args`` and ``extra_link_args``.
+  `#2808 <https://github.com/pybind/pybind11/pull/2808>`_
+
+* Setup helpers: Don't trigger unused parameter warning.
+  `#2735 <https://github.com/pybind/pybind11/pull/2735>`_
+
+* CMake: Support running with ``--warn-uninitialized`` active.
+  `#2806 <https://github.com/pybind/pybind11/pull/2806>`_
+
+* CMake: Avoid error if included from two submodule directories.
+  `#2804 <https://github.com/pybind/pybind11/pull/2804>`_
+
+* CMake: Fix ``STATIC`` / ``SHARED`` being ignored in FindPython mode.
+  `#2796 <https://github.com/pybind/pybind11/pull/2796>`_
+
+* CMake: Respect the setting for ``CMAKE_CXX_VISIBILITY_PRESET`` if defined.
+  `#2793 <https://github.com/pybind/pybind11/pull/2793>`_
+
+* CMake: Fix issue with FindPython2/FindPython3 not working with ``pybind11::embed``.
+  `#2662 <https://github.com/pybind/pybind11/pull/2662>`_
+
+* CMake: mixing local and installed pybind11's would prioritize the installed
+  one over the local one (regression in 2.6.0).
+  `#2716 <https://github.com/pybind/pybind11/pull/2716>`_
+
+
+Bug fixes:
+
+* Fixed segfault in multithreaded environments when using
+  ``scoped_ostream_redirect``.
+  `#2675 <https://github.com/pybind/pybind11/pull/2675>`_
+
+* Leave docstring unset when all docstring-related options are disabled, rather
+  than set an empty string.
+  `#2745 <https://github.com/pybind/pybind11/pull/2745>`_
+
+* The module key in builtins that pybind11 uses to store its internals changed
+  from std::string to a python str type (more natural on Python 2, no change on
+  Python 3).
+  `#2814 <https://github.com/pybind/pybind11/pull/2814>`_
+
+* Fixed assertion error related to unhandled (later overwritten) exception in
+  CPython 3.8 and 3.9 debug builds.
+  `#2685 <https://github.com/pybind/pybind11/pull/2685>`_
+
+* Fix ``py::gil_scoped_acquire`` assert with CPython 3.9 debug build.
+  `#2683 <https://github.com/pybind/pybind11/pull/2683>`_
+
+* Fix issue with a test failing on pytest 6.2.
+  `#2741 <https://github.com/pybind/pybind11/pull/2741>`_
+
+Warning fixes:
+
+* Fix warning modifying constructor parameter 'flag' that shadows a field of
+  'set_flag' ``[-Wshadow-field-in-constructor-modified]``.
+  `#2780 <https://github.com/pybind/pybind11/pull/2780>`_
+
+* Suppressed some deprecation warnings about old-style
+  ``__init__``/``__setstate__`` in the tests.
+  `#2759 <https://github.com/pybind/pybind11/pull/2759>`_
+
+Valgrind work:
+
+* Fix invalid access when calling a pybind11 ``__init__`` on a non-pybind11
+  class instance.
+  `#2755 <https://github.com/pybind/pybind11/pull/2755>`_
+
+* Fixed various minor memory leaks in pybind11's test suite.
+  `#2758 <https://github.com/pybind/pybind11/pull/2758>`_
+
+* Resolved memory leak in cpp_function initialization when exceptions occurred.
+  `#2756 <https://github.com/pybind/pybind11/pull/2756>`_
+
+* Added a Valgrind build, checking for leaks and memory-related UB, to CI.
+  `#2746 <https://github.com/pybind/pybind11/pull/2746>`_
+
+Compiler support:
+
+* Intel compiler was not activating C++14 support due to a broken define.
+  `#2679 <https://github.com/pybind/pybind11/pull/2679>`_
+
+* Support ICC and NVIDIA HPC SDK in C++17 mode.
+  `#2729 <https://github.com/pybind/pybind11/pull/2729>`_
+
+* Support Intel OneAPI compiler (ICC 20.2) and add to CI.
+  `#2573 <https://github.com/pybind/pybind11/pull/2573>`_
+
+
+
+v2.6.1 (Nov 11, 2020)
+---------------------
+
+* ``py::exec``, ``py::eval``, and ``py::eval_file`` now add the builtins module
+  as ``"__builtins__"`` to their ``globals`` argument, better matching ``exec``
+  and ``eval`` in pure Python.
+  `#2616 <https://github.com/pybind/pybind11/pull/2616>`_
+
+* ``setup_helpers`` will no longer set a minimum macOS version higher than the
+  current version.
+  `#2622 <https://github.com/pybind/pybind11/pull/2622>`_
+
+* Allow deleting static properties.
+  `#2629 <https://github.com/pybind/pybind11/pull/2629>`_
+
+* Seal a leak in ``def_buffer``, cleaning up the ``capture`` object after the
+  ``class_`` object goes out of scope.
+  `#2634 <https://github.com/pybind/pybind11/pull/2634>`_
+
+* ``pybind11_INCLUDE_DIRS`` was incorrect, potentially causing a regression if
+  it was expected to include ``PYTHON_INCLUDE_DIRS`` (please use targets
+  instead).
+  `#2636 <https://github.com/pybind/pybind11/pull/2636>`_
+
+* Added parameter names to the ``py::enum_`` constructor and methods, avoiding
+  ``arg0`` in the generated docstrings.
+  `#2637 <https://github.com/pybind/pybind11/pull/2637>`_
+
+* Added ``needs_recompile`` optional function to the ``ParallelCompiler``
+  helper, to allow a recompile to be skipped based on a user-defined function.
+  `#2643 <https://github.com/pybind/pybind11/pull/2643>`_
+
+
+v2.6.0 (Oct 21, 2020)
+---------------------
+
 See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
 
-* Provide an additional spelling of ``py::module`` - ``py::module_`` (with a
+New features:
-  trailing underscore), for C++20 compatibility. Only relevant when used
-  unqualified.
-  `#2489 <https://github.com/pybind/pybind11/pull/2489>`_
-
-* ``pybind11_add_module()`` now accepts an optional ``OPT_SIZE`` flag that
-  switches the binding target to size-based optimization regardless global
-  CMake build type (except in debug mode, where optimizations remain disabled).
-  This reduces binary size quite substantially (~25%).
-  `#2463 <https://github.com/pybind/pybind11/pull/2463>`_
 
 * Keyword-only arguments supported in Python 2 or 3 with ``py::kw_only()``.
   `#2100 <https://github.com/pybind/pybind11/pull/2100>`_
@@ -28,11 +704,17 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
 * Positional-only arguments supported in Python 2 or 3 with ``py::pos_only()``.
   `#2459 <https://github.com/pybind/pybind11/pull/2459>`_
 
+* ``py::is_final()`` class modifier to block subclassing (CPython only).
+  `#2151 <https://github.com/pybind/pybind11/pull/2151>`_
+
+* Added ``py::prepend()``, allowing a function to be placed at the beginning of
+  the overload chain.
+  `#1131 <https://github.com/pybind/pybind11/pull/1131>`_
+
 * Access to the type object now provided with ``py::type::of<T>()`` and
   ``py::type::of(h)``.
   `#2364 <https://github.com/pybind/pybind11/pull/2364>`_
 
-
 * Perfect forwarding support for methods.
   `#2048 <https://github.com/pybind/pybind11/pull/2048>`_
 
@@ -42,11 +724,48 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
 * ``py::hash`` is now public.
   `#2217 <https://github.com/pybind/pybind11/pull/2217>`_
 
-* ``py::is_final()`` class modifier to block subclassing (CPython only).
+* ``py::class_<union_type>`` is now supported. Note that writing to one data
-  `#2151 <https://github.com/pybind/pybind11/pull/2151>`_
+  member of the union and reading another (type punning) is UB in C++. Thus
+  pybind11-bound enums should never be used for such conversions.
+  `#2320 <https://github.com/pybind/pybind11/pull/2320>`_.
 
-* ``py::memoryview``  update and documentation.
+* Classes now check local scope when registering members, allowing a subclass
-  `#2223 <https://github.com/pybind/pybind11/pull/2223>`_
+  to have a member with the same name as a parent (such as an enum).
+  `#2335 <https://github.com/pybind/pybind11/pull/2335>`_
+
+Code correctness features:
+
+* Error now thrown when ``__init__`` is forgotten on subclasses.
+  `#2152 <https://github.com/pybind/pybind11/pull/2152>`_
+
+* Throw error if conversion to a pybind11 type if the Python object isn't a
+  valid instance of that type, such as ``py::bytes(o)`` when ``py::object o``
+  isn't a bytes instance.
+  `#2349 <https://github.com/pybind/pybind11/pull/2349>`_
+
+* Throw if conversion to ``str`` fails.
+  `#2477 <https://github.com/pybind/pybind11/pull/2477>`_
+
+
+API changes:
+
+* ``py::module`` was renamed ``py::module_`` to avoid issues with C++20 when
+  used unqualified, but an alias ``py::module`` is provided for backward
+  compatibility.
+  `#2489 <https://github.com/pybind/pybind11/pull/2489>`_
+
+* Public constructors for ``py::module_`` have been deprecated; please use
+  ``pybind11::module_::create_extension_module`` if you were using the public
+  constructor (fairly rare after ``PYBIND11_MODULE`` was introduced).
+  `#2552 <https://github.com/pybind/pybind11/pull/2552>`_
+
+* ``PYBIND11_OVERLOAD*`` macros and ``get_overload`` function replaced by
+  correctly-named ``PYBIND11_OVERRIDE*`` and ``get_override``, fixing
+  inconsistencies in the presence of a closing ``;`` in these macros.
+  ``get_type_overload`` is deprecated.
+  `#2325 <https://github.com/pybind/pybind11/pull/2325>`_
+
+Packaging / building improvements:
 
 * The Python package was reworked to be more powerful and useful.
   `#2433 <https://github.com/pybind/pybind11/pull/2433>`_
@@ -54,7 +773,7 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
   * :ref:`build-setuptools` is easier thanks to a new
     ``pybind11.setup_helpers`` module, which provides utilities to use
     setuptools with pybind11. It can be used via PEP 518, ``setup_requires``,
-    or by directly copying ``setup_helpers.py`` into your project.
+    or by directly importing or copying ``setup_helpers.py`` into your project.
 
   * CMake configuration files are now included in the Python package. Use
     ``pybind11.get_cmake_dir()`` or ``python -m pybind11 --cmakedir`` to get
@@ -62,17 +781,21 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
     site-packages location in your ``CMAKE_MODULE_PATH``. Or you can use the
     new ``pybind11[global]`` extra when you install ``pybind11``, which
     installs the CMake files and headers into your base environment in the
-    standard location
+    standard location.
 
   * ``pybind11-config`` is another way to write ``python -m pybind11`` if you
     have your PATH set up.
 
+  * Added external typing support to the helper module, code from
+    ``import pybind11`` can now be type checked.
+    `#2588 <https://github.com/pybind/pybind11/pull/2588>`_
+
 * Minimum CMake required increased to 3.4.
   `#2338 <https://github.com/pybind/pybind11/pull/2338>`_ and
   `#2370 <https://github.com/pybind/pybind11/pull/2370>`_
 
-  * Full integration with CMake’s C++ standard system replaces
+  * Full integration with CMake’s C++ standard system and compile features
-    ``PYBIND11_CPP_STANDARD``.
+    replaces ``PYBIND11_CPP_STANDARD``.
 
   * Generated config file is now portable to different Python/compiler/CMake
     versions.
@@ -85,27 +808,36 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
     ``CMAKE_INTERPROCEDURAL_OPTIMIZATION``, ``set(CMAKE_CXX_VISIBILITY_PRESET
     hidden)``.
 
-* Optional :ref:`find-python-mode` and :ref:`nopython-mode` with CMake.
+  * ``CUDA`` as a language is now supported.
+
+  * Helper functions ``pybind11_strip``, ``pybind11_extension``,
+    ``pybind11_find_import`` added, see :doc:`cmake/index`.
+
+  * Optional :ref:`find-python-mode` and :ref:`nopython-mode` with CMake.
     `#2370 <https://github.com/pybind/pybind11/pull/2370>`_
 
 * Uninstall target added.
   `#2265 <https://github.com/pybind/pybind11/pull/2265>`_ and
   `#2346 <https://github.com/pybind/pybind11/pull/2346>`_
 
-* ``PYBIND11_OVERLOAD*`` macros and ``get_overload`` function replaced by
+* ``pybind11_add_module()`` now accepts an optional ``OPT_SIZE`` flag that
-  correctly-named ``PYBIND11_OVERRIDE*`` and ``get_override``, fixing
+  switches the binding target to size-based optimization if the global build
-  inconsistencies in the presene of a closing ``;`` in these macros.
+  type can not always be fixed to ``MinSizeRel`` (except in debug mode, where
-  ``get_type_overload`` is deprecated.
+  optimizations remain disabled).  ``MinSizeRel`` or this flag reduces binary
-  `#2325 <https://github.com/pybind/pybind11/pull/2325>`_
+  size quite substantially (~25% on some platforms).
+  `#2463 <https://github.com/pybind/pybind11/pull/2463>`_
 
-Smaller or developer focused features:
+Smaller or developer focused features and fixes:
 
-* Moved ``mkdoc.py`` to a new repo, `pybind11-mkdoc`_.
+* Moved ``mkdoc.py`` to a new repo, `pybind11-mkdoc`_. There are no longer
+  submodules in the main repo.
 
-.. _pybind11-mkdoc: https://github.com/pybind/pybind11-mkdoc
+* ``py::memoryview`` segfault fix and update, with new
+  ``py::memoryview::from_memory`` in Python 3, and documentation.
+  `#2223 <https://github.com/pybind/pybind11/pull/2223>`_
 
-* Error now thrown when ``__init__`` is forgotten on subclasses.
+* Fix for ``buffer_info`` on Python 2.
-  `#2152 <https://github.com/pybind/pybind11/pull/2152>`_
+  `#2503 <https://github.com/pybind/pybind11/pull/2503>`_
 
 * If ``__eq__`` defined but not ``__hash__``, ``__hash__`` is now set to
   ``None``.
@@ -114,12 +846,6 @@ Smaller or developer focused features:
 * ``py::ellipsis`` now also works on Python 2.
   `#2360 <https://github.com/pybind/pybind11/pull/2360>`_
 
-* Throw if conversion to ``str`` fails.
-  `#2477 <https://github.com/pybind/pybind11/pull/2477>`_
-
-* Added missing signature for ``py::array``.
-  `#2363 <https://github.com/pybind/pybind11/pull/2363>`_
-
 * Pointer to ``std::tuple`` & ``std::pair`` supported in cast.
   `#2334 <https://github.com/pybind/pybind11/pull/2334>`_
 
@@ -127,7 +853,26 @@ Smaller or developer focused features:
   argument type.
   `#2293 <https://github.com/pybind/pybind11/pull/2293>`_
 
-* Bugfixes related to more extensive testing
+* Added missing signature for ``py::array``.
+  `#2363 <https://github.com/pybind/pybind11/pull/2363>`_
+
+* ``unchecked_mutable_reference`` has access to operator ``()`` and ``[]`` when
+  const.
+  `#2514 <https://github.com/pybind/pybind11/pull/2514>`_
+
+* ``py::vectorize`` is now supported on functions that return void.
+  `#1969 <https://github.com/pybind/pybind11/pull/1969>`_
+
+* ``py::capsule`` supports ``get_pointer`` and ``set_pointer``.
+  `#1131 <https://github.com/pybind/pybind11/pull/1131>`_
+
+* Fix crash when different instances share the same pointer of the same type.
+  `#2252 <https://github.com/pybind/pybind11/pull/2252>`_
+
+* Fix for ``py::len`` not clearing Python's error state when it fails and throws.
+  `#2575 <https://github.com/pybind/pybind11/pull/2575>`_
+
+* Bugfixes related to more extensive testing, new GitHub Actions CI.
   `#2321 <https://github.com/pybind/pybind11/pull/2321>`_
 
 * Bug in timezone issue in Eastern hemisphere midnight fixed.
@@ -141,16 +886,27 @@ Smaller or developer focused features:
   requested ordering.
   `#2484 <https://github.com/pybind/pybind11/pull/2484>`_
 
-* PyPy fixes, including support for PyPy3 and PyPy 7.
+* Avoid a segfault on some compilers when types are removed in Python.
+  `#2564 <https://github.com/pybind/pybind11/pull/2564>`_
+
+* ``py::arg::none()`` is now also respected when passing keyword arguments.
+  `#2611 <https://github.com/pybind/pybind11/pull/2611>`_
+
+* PyPy fixes, PyPy 7.3.x now supported, including PyPy3. (Known issue with
+  PyPy2 and Windows `#2596 <https://github.com/pybind/pybind11/issues/2596>`_).
   `#2146 <https://github.com/pybind/pybind11/pull/2146>`_
 
-* CPython 3.9 fixes.
+* CPython 3.9.0 workaround for undefined behavior (macOS segfault).
+  `#2576 <https://github.com/pybind/pybind11/pull/2576>`_
+
+* CPython 3.9 warning fixes.
   `#2253 <https://github.com/pybind/pybind11/pull/2253>`_
 
-* More C++20 support.
+* Improved C++20 support, now tested in CI.
   `#2489 <https://github.com/pybind/pybind11/pull/2489>`_
+  `#2599 <https://github.com/pybind/pybind11/pull/2599>`_
 
-* Debug Python interpreter support.
+* Improved but still incomplete debug Python interpreter support.
   `#2025 <https://github.com/pybind/pybind11/pull/2025>`_
 
 * NVCC (CUDA 11) now supported and tested in CI.
@@ -159,11 +915,20 @@ Smaller or developer focused features:
 * NVIDIA PGI compilers now supported and tested in CI.
   `#2475 <https://github.com/pybind/pybind11/pull/2475>`_
 
-* Extensive style checking in CI, with `pre-commit`_ support.
+* At least Intel 18 now explicitly required when compiling with Intel.
+  `#2577 <https://github.com/pybind/pybind11/pull/2577>`_
+
+* Extensive style checking in CI, with `pre-commit`_ support. Code
+  modernization, checked by clang-tidy.
+
+* Expanded docs, including new main page, new installing section, and CMake
+  helpers page, along with over a dozen new sections on existing pages.
+
+* In GitHub, new docs for contributing and new issue templates.
 
 .. _pre-commit: https://pre-commit.com
 
-
+.. _pybind11-mkdoc: https://github.com/pybind/pybind11-mkdoc
 
 v2.5.0 (Mar 31, 2020)
 -----------------------------------------------------
@@ -261,7 +1026,7 @@ v2.4.0 (Sep 19, 2019)
   `#1888 <https://github.com/pybind/pybind11/pull/1888>`_.
 
 * ``py::details::overload_cast_impl`` is available in C++11 mode, can be used
-  like ``overload_cast`` with an additional set of parantheses.
+  like ``overload_cast`` with an additional set of parentheses.
   `#1581 <https://github.com/pybind/pybind11/pull/1581>`_.
 
 * Fixed ``get_include()`` on Conda.
@@ -520,7 +1285,7 @@ v2.2.2 (February 7, 2018)
 v2.2.1 (September 14, 2017)
 -----------------------------------------------------
 
-* Added ``py::module::reload()`` member function for reloading a module.
+* Added ``py::module_::reload()`` member function for reloading a module.
   `#1040 <https://github.com/pybind/pybind11/pull/1040>`_.
 
 * Fixed a reference leak in the number converter.
@@ -583,6 +1348,7 @@ v2.2.0 (August 31, 2017)
 
       from cpp_module import CppBase1, CppBase2
 
+
       class PyDerived(CppBase1, CppBase2):
           def __init__(self):
               CppBase1.__init__(self)  # C++ bases must be initialized explicitly
@@ -795,7 +1561,7 @@ v2.2.0 (August 31, 2017)
 * Intel C++ compiler compatibility fixes.
   `#937 <https://github.com/pybind/pybind11/pull/937>`_.
 
-* Fixed implicit conversion of `py::enum_` to integer types on Python 2.7.
+* Fixed implicit conversion of ``py::enum_`` to integer types on Python 2.7.
   `#821 <https://github.com/pybind/pybind11/pull/821>`_.
 
 * Added ``py::hash`` to fetch the hash value of Python objects, and

wrap/pybind11/docs/classes.rst

@@ -44,12 +44,12 @@ interactive Python session demonstrating this example is shown below:
 
     % python
     >>> import example
-    >>> p = example.Pet('Molly')
+    >>> p = example.Pet("Molly")
     >>> print(p)
     <example.Pet object at 0x10cd98060>
     >>> p.getName()
     u'Molly'
-    >>> p.setName('Charly')
+    >>> p.setName("Charly")
     >>> p.getName()
     u'Charly'
 
@@ -122,10 +122,10 @@ This makes it possible to write
 
 .. code-block:: pycon
 
-    >>> p = example.Pet('Molly')
+    >>> p = example.Pet("Molly")
     >>> p.name
     u'Molly'
-    >>> p.name = 'Charly'
+    >>> p.name = "Charly"
     >>> p.name
     u'Charly'
 
@@ -174,10 +174,10 @@ Native Python classes can pick up new attributes dynamically:
 .. code-block:: pycon
 
     >>> class Pet:
-    ...     name = 'Molly'
+    ...     name = "Molly"
     ...
     >>> p = Pet()
-    >>> p.name = 'Charly'  # overwrite existing
+    >>> p.name = "Charly"  # overwrite existing
     >>> p.age = 2  # dynamically add a new attribute
 
 By default, classes exported from C++ do not support this and the only writable
@@ -195,7 +195,7 @@ Trying to set any other attribute results in an error:
 .. code-block:: pycon
 
     >>> p = example.Pet()
-    >>> p.name = 'Charly'  # OK, attribute defined in C++
+    >>> p.name = "Charly"  # OK, attribute defined in C++
     >>> p.age = 2  # fail
     AttributeError: 'Pet' object has no attribute 'age'
 
@@ -213,7 +213,7 @@ Now everything works as expected:
 .. code-block:: pycon
 
     >>> p = example.Pet()
-    >>> p.name = 'Charly'  # OK, overwrite value in C++
+    >>> p.name = "Charly"  # OK, overwrite value in C++
     >>> p.age = 2  # OK, dynamically add a new attribute
     >>> p.__dict__  # just like a native Python class
     {'age': 2}
@@ -280,7 +280,7 @@ expose fields and methods of both types:
 
 .. code-block:: pycon
 
-    >>> p = example.Dog('Molly')
+    >>> p = example.Dog("Molly")
     >>> p.name
     u'Molly'
     >>> p.bark()
@@ -446,8 +446,7 @@ you can use ``py::detail::overload_cast_impl`` with an additional set of parenth
 Enumerations and internal types
 ===============================
 
-Let's now suppose that the example class contains an internal enumeration type,
+Let's now suppose that the example class contains internal types like enumerations, e.g.:
-e.g.:
 
 .. code-block:: cpp
 
@@ -457,10 +456,15 @@ e.g.:
             Cat
         };
 
+        struct Attributes {
+            float age = 0;
+        };
+
         Pet(const std::string &name, Kind type) : name(name), type(type) { }
 
         std::string name;
         Kind type;
+        Attributes attr;
     };
 
 The binding code for this example looks as follows:
@@ -471,22 +475,28 @@ The binding code for this example looks as follows:
 
     pet.def(py::init<const std::string &, Pet::Kind>())
         .def_readwrite("name", &Pet::name)
-        .def_readwrite("type", &Pet::type);
+        .def_readwrite("type", &Pet::type)
+        .def_readwrite("attr", &Pet::attr);
 
     py::enum_<Pet::Kind>(pet, "Kind")
         .value("Dog", Pet::Kind::Dog)
         .value("Cat", Pet::Kind::Cat)
         .export_values();
 
-To ensure that the ``Kind`` type is created within the scope of ``Pet``, the
+    py::class_<Pet::Attributes> attributes(pet, "Attributes")
-``pet`` :class:`class_` instance must be supplied to the :class:`enum_`.
+        .def(py::init<>())
+        .def_readwrite("age", &Pet::Attributes::age);
+
+
+To ensure that the nested types ``Kind`` and ``Attributes`` are created within the scope of ``Pet``, the
+``pet`` :class:`class_` instance must be supplied to the :class:`enum_` and :class:`class_`
 constructor. The :func:`enum_::export_values` function exports the enum entries
 into the parent scope, which should be skipped for newer C++11-style strongly
 typed enums.
 
 .. code-block:: pycon
 
-    >>> p = Pet('Lucy', Pet.Cat)
+    >>> p = Pet("Lucy", Pet.Cat)
     >>> p.type
     Kind.Cat
     >>> int(p.type)
@@ -508,7 +518,7 @@ The ``name`` property returns the name of the enum value as a unicode string.
 
     .. code-block:: pycon
 
-        >>> p = Pet( "Lucy", Pet.Cat )
+        >>> p = Pet("Lucy", Pet.Cat)
         >>> pet_type = p.type
         >>> pet_type
         Pet.Cat

wrap/pybind11/docs/cmake/index.rst

@@ -0,0 +1,8 @@
+CMake helpers
+-------------
+
+Pybind11 can be used with ``add_subdirectory(extern/pybind11)``, or from an
+install with ``find_package(pybind11 CONFIG)``. The interface provided in
+either case is functionally identical.
+
+.. cmake-module:: ../../tools/pybind11Config.cmake.in

wrap/pybind11/docs/compiling.rst

@@ -31,20 +31,18 @@ An example of a ``setup.py`` using pybind11's helpers:
 
 .. code-block:: python
 
+    from glob import glob
     from setuptools import setup
     from pybind11.setup_helpers import Pybind11Extension
 
     ext_modules = [
         Pybind11Extension(
             "python_example",
-            ["src/main.cpp"],
+            sorted(glob("src/*.cpp")),  # Sort source files for reproducibility
         ),
     ]
 
-    setup(
+    setup(..., ext_modules=ext_modules)
-        ...,
-        ext_modules=ext_modules
-    )
 
 If you want to do an automatic search for the highest supported C++ standard,
 that is supported via a ``build_ext`` command override; it will only affect
@@ -52,21 +50,81 @@ that is supported via a ``build_ext`` command override; it will only affect
 
 .. code-block:: python
 
+    from glob import glob
     from setuptools import setup
     from pybind11.setup_helpers import Pybind11Extension, build_ext
 
     ext_modules = [
         Pybind11Extension(
             "python_example",
-            ["src/main.cpp"],
+            sorted(glob("src/*.cpp")),
         ),
     ]
 
-    setup(
+    setup(..., cmdclass={"build_ext": build_ext}, ext_modules=ext_modules)
-        ...,
+
-        cmdclass={"build_ext": build_ext},
+If you have single-file extension modules that are directly stored in the
-        ext_modules=ext_modules
+Python source tree (``foo.cpp`` in the same directory as where a ``foo.py``
-    )
+would be located), you can also generate ``Pybind11Extensions`` using
+``setup_helpers.intree_extensions``: ``intree_extensions(["path/to/foo.cpp",
+...])`` returns a list of ``Pybind11Extensions`` which can be passed to
+``ext_modules``, possibly after further customizing their attributes
+(``libraries``, ``include_dirs``, etc.).  By doing so, a ``foo.*.so`` extension
+module will be generated and made available upon installation.
+
+``intree_extension`` will automatically detect if you are using a ``src``-style
+layout (as long as no namespace packages are involved), but you can also
+explicitly pass ``package_dir`` to it (as in ``setuptools.setup``).
+
+Since pybind11 does not require NumPy when building, a light-weight replacement
+for NumPy's parallel compilation distutils tool is included. Use it like this:
+
+.. code-block:: python
+
+    from pybind11.setup_helpers import ParallelCompile
+
+    # Optional multithreaded build
+    ParallelCompile("NPY_NUM_BUILD_JOBS").install()
+
+    setup(...)
+
+The argument is the name of an environment variable to control the number of
+threads, such as ``NPY_NUM_BUILD_JOBS`` (as used by NumPy), though you can set
+something different if you want; ``CMAKE_BUILD_PARALLEL_LEVEL`` is another choice
+a user might expect. You can also pass ``default=N`` to set the default number
+of threads (0 will take the number of threads available) and ``max=N``, the
+maximum number of threads; if you have a large extension you may want set this
+to a memory dependent number.
+
+If you are developing rapidly and have a lot of C++ files, you may want to
+avoid rebuilding files that have not changed. For simple cases were you are
+using ``pip install -e .`` and do not have local headers, you can skip the
+rebuild if an object file is newer than its source (headers are not checked!)
+with the following:
+
+.. code-block:: python
+
+    from pybind11.setup_helpers import ParallelCompile, naive_recompile
+
+    ParallelCompile("NPY_NUM_BUILD_JOBS", needs_recompile=naive_recompile).install()
+
+
+If you have a more complex build, you can implement a smarter function and pass
+it to ``needs_recompile``, or you can use [Ccache]_ instead. ``CXX="cache g++"
+pip install -e .`` would be the way to use it with GCC, for example. Unlike the
+simple solution, this even works even when not compiling in editable mode, but
+it does require Ccache to be installed.
+
+Keep in mind that Pip will not even attempt to rebuild if it thinks it has
+already built a copy of your code, which it deduces from the version number.
+One way to avoid this is to use [setuptools_scm]_, which will generate a
+version number that includes the number of commits since your last tag and a
+hash for a dirty directory. Another way to force a rebuild is purge your cache
+or use Pip's ``--no-cache-dir`` option.
+
+.. [Ccache] https://ccache.dev
+
+.. [setuptools_scm] https://github.com/pypa/setuptools_scm
 
 .. _setup_helpers-pep518:
 
@@ -85,7 +143,7 @@ Your ``pyproject.toml`` file will likely look something like this:
 .. code-block:: toml
 
     [build-system]
-    requires = ["setuptools", "wheel", "pybind11==2.6.0"]
+    requires = ["setuptools>=42", "wheel", "pybind11~=2.6.1"]
     build-backend = "setuptools.build_meta"
 
 .. note::
@@ -96,10 +154,12 @@ Your ``pyproject.toml`` file will likely look something like this:
     in Python) using something like `cibuildwheel`_, remember that ``setup.py``
     and ``pyproject.toml`` are not even contained in the wheel, so this high
     Pip requirement is only for source builds, and will not affect users of
-    your binary wheels.
+    your binary wheels. If you are building SDists and wheels, then
+    `pypa-build`_ is the recommended official tool.
 
 .. _PEP 517: https://www.python.org/dev/peps/pep-0517/
 .. _cibuildwheel: https://cibuildwheel.readthedocs.io
+.. _pypa-build: https://pypa-build.readthedocs.io/en/latest/
 
 .. _setup_helpers-setup_requires:
 
@@ -140,6 +200,23 @@ this, you will need to import from a local file in ``setup.py`` and ensure the
 helper file is part of your MANIFEST.
 
 
+Closely related, if you include pybind11 as a subproject, you can run the
+``setup_helpers.py`` inplace. If loaded correctly, this should even pick up
+the correct include for pybind11, though you can turn it off as shown above if
+you want to input it manually.
+
+Suggested usage if you have pybind11 as a submodule in ``extern/pybind11``:
+
+.. code-block:: python
+
+    DIR = os.path.abspath(os.path.dirname(__file__))
+
+    sys.path.append(os.path.join(DIR, "extern", "pybind11"))
+    from pybind11.setup_helpers import Pybind11Extension  # noqa: E402
+
+    del sys.path[-1]
+
+
 .. versionchanged:: 2.6
 
     Added ``setup_helpers`` file.
@@ -184,6 +261,8 @@ PyPI integration, can be found in the [cmake_example]_  repository.
 .. versionchanged:: 2.6
    CMake 3.4+ is required.
 
+Further information can be found at :doc:`cmake/index`.
+
 pybind11_add_module
 -------------------
 
@@ -224,8 +303,15 @@ As stated above, LTO is enabled by default. Some newer compilers also support
 different flavors of LTO such as `ThinLTO`_. Setting ``THIN_LTO`` will cause
 the function to prefer this flavor if available. The function falls back to
 regular LTO if ``-flto=thin`` is not available. If
-``CMAKE_INTERPROCEDURAL_OPTIMIZATION`` is set (either ON or OFF), then that
+``CMAKE_INTERPROCEDURAL_OPTIMIZATION`` is set (either ``ON`` or ``OFF``), then
-will be respected instead of the built-in flag search.
+that will be respected instead of the built-in flag search.
+
+.. note::
+
+   If you want to set the property form on targets or the
+   ``CMAKE_INTERPROCEDURAL_OPTIMIZATION_<CONFIG>`` versions of this, you should
+   still use ``set(CMAKE_INTERPROCEDURAL_OPTIMIZATION OFF)`` (otherwise a
+   no-op) to disable pybind11's ipo flags.
 
 The ``OPT_SIZE`` flag enables size-based optimization equivalent to the
 standard ``/Os`` or ``-Os`` compiler flags and the ``MinSizeRel`` build type,
@@ -252,10 +338,9 @@ standard explicitly with
 
 .. code-block:: cmake
 
-    set(CMAKE_CXX_STANDARD 14)  # or 11, 14, 17, 20
+    set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ version selection")  # or 11, 14, 17, 20
     set(CMAKE_CXX_STANDARD_REQUIRED ON)  # optional, ensure standard is supported
-    set(CMAKE_CXX_EXTENSIONS OFF)  # optional, keep compiler extensionsn off
+    set(CMAKE_CXX_EXTENSIONS OFF)  # optional, keep compiler extensions off
-
 
 The variables can also be set when calling CMake from the command line using
 the ``-D<variable>=<value>`` flag. You can also manually set ``CXX_STANDARD``
@@ -325,13 +410,14 @@ can refer to the same [cmake_example]_ repository for a full sample project
 FindPython mode
 ---------------
 
-CMake 3.12+ (3.15+ recommended) added a new module called FindPython that had a
+CMake 3.12+ (3.15+ recommended, 3.18.2+ ideal) added a new module called
-highly improved search algorithm and modern targets and tools. If you use
+FindPython that had a highly improved search algorithm and modern targets
-FindPython, pybind11 will detect this and use the existing targets instead:
+and tools. If you use FindPython, pybind11 will detect this and use the
+existing targets instead:
 
 .. code-block:: cmake
 
-    cmake_minumum_required(VERSION 3.15...3.18)
+    cmake_minimum_required(VERSION 3.15...3.19)
     project(example LANGUAGES CXX)
 
     find_package(Python COMPONENTS Interpreter Development REQUIRED)
@@ -357,6 +443,14 @@ setting ``Python_ROOT_DIR`` may be the most common one (though with
 virtualenv/venv support, and Conda support, this tends to find the correct
 Python version more often than the old system did).
 
+.. warning::
+
+    When the Python libraries (i.e. ``libpythonXX.a`` and ``libpythonXX.so``
+    on Unix) are not available, as is the case on a manylinux image, the
+    ``Development`` component will not be resolved by ``FindPython``. When not
+    using the embedding functionality, CMake 3.18+ allows you to specify
+    ``Development.Module`` instead of ``Development`` to resolve this issue.
+
 .. versionadded:: 2.6
 
 Advanced: interface library targets
@@ -428,7 +522,7 @@ Instead of setting properties, you can set ``CMAKE_*`` variables to initialize t
     compiler flags are provided to ensure high quality code generation. In
     contrast to the ``pybind11_add_module()`` command, the CMake interface
     provides a *composable* set of targets to ensure that you retain flexibility.
-    It can be expecially important to provide or set these properties; the
+    It can be especially important to provide or set these properties; the
     :ref:`FAQ <faq:symhidden>` contains an explanation on why these are needed.
 
 .. versionadded:: 2.6
@@ -481,7 +575,7 @@ On Linux, you can compile an example such as the one given in
 
 .. code-block:: bash
 
-    $ c++ -O3 -Wall -shared -std=c++11 -fPIC `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+    $ c++ -O3 -Wall -shared -std=c++11 -fPIC $(python3 -m pybind11 --includes) example.cpp -o example$(python3-config --extension-suffix)
 
 The flags given here assume that you're using Python 3. For Python 2, just
 change the executable appropriately (to ``python`` or ``python2``).
@@ -493,7 +587,7 @@ using ``pip`` or ``conda``. If it hasn't, you can also manually specify
 ``python3-config --includes``.
 
 Note that Python 2.7 modules don't use a special suffix, so you should simply
-use ``example.so`` instead of ``example`python3-config --extension-suffix```.
+use ``example.so`` instead of ``example$(python3-config --extension-suffix)``.
 Besides, the ``--extension-suffix`` option may or may not be available, depending
 on the distribution; in the latter case, the module extension can be manually
 set to ``.so``.
@@ -504,7 +598,7 @@ building the module:
 
 .. code-block:: bash
 
-    $ c++ -O3 -Wall -shared -std=c++11 -undefined dynamic_lookup `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+    $ c++ -O3 -Wall -shared -std=c++11 -undefined dynamic_lookup $(python3 -m pybind11 --includes) example.cpp -o example$(python3-config --extension-suffix)
 
 In general, it is advisable to include several additional build parameters
 that can considerably reduce the size of the created binary. Refer to section
@@ -523,23 +617,11 @@ build system that works on all platforms including Windows.
     contains one (which will lead to a segfault).
 
 
-Building with vcpkg
+Building with Bazel
 ===================
-You can download and install pybind11 using the Microsoft `vcpkg
-<https://github.com/Microsoft/vcpkg/>`_ dependency manager:
 
-.. code-block:: bash
+You can build with the Bazel build system using the `pybind11_bazel
-
+<https://github.com/pybind/pybind11_bazel>`_ repository.
-    git clone https://github.com/Microsoft/vcpkg.git
-    cd vcpkg
-    ./bootstrap-vcpkg.sh
-    ./vcpkg integrate install
-    vcpkg install pybind11
-
-The pybind11 port in vcpkg is kept up to date by Microsoft team members and
-community contributors. If the version is out of date, please `create an issue
-or pull request <https://github.com/Microsoft/vcpkg/>`_ on the vcpkg
-repository.
 
 Generating binding code automatically
 =====================================

wrap/pybind11/docs/conf.py

@@ -13,57 +13,68 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
-import sys
 import os
-import shlex
+import re
 import subprocess
+import sys
+from pathlib import Path
+
+DIR = Path(__file__).parent.resolve()
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+# sys.path.insert(0, os.path.abspath('.'))
 
 # -- General configuration ------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-#needs_sphinx = '1.0'
+# needs_sphinx = '1.0'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['breathe']
+extensions = [
+    "breathe",
+    "sphinxcontrib.rsvgconverter",
+    "sphinxcontrib.moderncmakedomain",
+]
 
-breathe_projects = {'pybind11': '.build/doxygenxml/'}
+breathe_projects = {"pybind11": ".build/doxygenxml/"}
-breathe_default_project = 'pybind11'
+breathe_default_project = "pybind11"
-breathe_domain_by_extension = {'h': 'cpp'}
+breathe_domain_by_extension = {"h": "cpp"}
 
 # Add any paths that contain templates here, relative to this directory.
-templates_path = ['.templates']
+templates_path = [".templates"]
 
 # The suffix(es) of source filenames.
 # You can specify multiple suffix as a list of string:
 # source_suffix = ['.rst', '.md']
-source_suffix = '.rst'
+source_suffix = ".rst"
 
 # The encoding of source files.
-#source_encoding = 'utf-8-sig'
+# source_encoding = 'utf-8-sig'
 
 # The master toctree document.
-master_doc = 'index'
+master_doc = "index"
 
 # General information about the project.
-project = 'pybind11'
+project = "pybind11"
-copyright = '2017, Wenzel Jakob'
+copyright = "2017, Wenzel Jakob"
-author = 'Wenzel Jakob'
+author = "Wenzel Jakob"
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
 # built documents.
-#
+
-# The short X.Y version.
+# Read the listed version
-version = '2.5'
+with open("../pybind11/_version.py") as f:
+    code = compile(f.read(), "../pybind11/_version.py", "exec")
+loc = {}
+exec(code, loc)
+
 # The full version, including alpha/beta/rc tags.
-release = '2.5.dev1'
+version = loc["__version__"]
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
@@ -74,37 +85,37 @@ language = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
-#today = ''
+# today = ''
 # Else, today_fmt is used as the format for a strftime call.
-#today_fmt = '%B %d, %Y'
+# today_fmt = '%B %d, %Y'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
-exclude_patterns = ['.build', 'release.rst']
+exclude_patterns = [".build", "release.rst"]
 
 # The reST default role (used for this markup: `text`) to use for all
 # documents.
-default_role = 'any'
+default_role = "any"
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
-#add_function_parentheses = True
+# add_function_parentheses = True
 
 # If true, the current module name will be prepended to all description
 # unit titles (such as .. function::).
-#add_module_names = True
+# add_module_names = True
 
 # If true, sectionauthor and moduleauthor directives will be shown in the
 # output. They are ignored by default.
-#show_authors = False
+# show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-#pygments_style = 'monokai'
+# pygments_style = 'monokai'
 
 # A list of ignored prefixes for module index sorting.
-#modindex_common_prefix = []
+# modindex_common_prefix = []
 
 # If true, keep warnings as "system message" paragraphs in the built documents.
-#keep_warnings = False
+# keep_warnings = False
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = False
@@ -115,141 +126,150 @@ todo_include_todos = False
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+on_rtd = os.environ.get("READTHEDOCS", None) == "True"
 
 if not on_rtd:  # only import and set the theme if we're building docs locally
     import sphinx_rtd_theme
-    html_theme = 'sphinx_rtd_theme'
+
+    html_theme = "sphinx_rtd_theme"
     html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
-    html_context = {
+    html_context = {"css_files": ["_static/theme_overrides.css"]}
-        'css_files': [
-            '_static/theme_overrides.css'
-        ]
-    }
 else:
     html_context = {
-        'css_files': [
+        "css_files": [
-            '//media.readthedocs.org/css/sphinx_rtd_theme.css',
+            "//media.readthedocs.org/css/sphinx_rtd_theme.css",
-            '//media.readthedocs.org/css/readthedocs-doc-embed.css',
+            "//media.readthedocs.org/css/readthedocs-doc-embed.css",
-            '_static/theme_overrides.css'
+            "_static/theme_overrides.css",
         ]
     }
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
+# html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-#html_theme_path = []
+# html_theme_path = []
 
 # The name for this set of Sphinx documents.  If None, it defaults to
-# "<project> v<release> documentation".
+# "<project> v<version> documentation".
-#html_title = None
+# html_title = None
 
 # A shorter title for the navigation bar.  Default is the same as html_title.
-#html_short_title = None
+# html_short_title = None
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-#html_logo = None
+# html_logo = None
 
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+# html_favicon = None
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ["_static"]
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
 # directly to the root of the documentation.
-#html_extra_path = []
+# html_extra_path = []
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-#html_last_updated_fmt = '%b %d, %Y'
+# html_last_updated_fmt = '%b %d, %Y'
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.
-#html_use_smartypants = True
+# html_use_smartypants = True
 
 # Custom sidebar templates, maps document names to template names.
-#html_sidebars = {}
+# html_sidebars = {}
 
 # Additional templates that should be rendered to pages, maps page names to
 # template names.
-#html_additional_pages = {}
+# html_additional_pages = {}
 
 # If false, no module index is generated.
-#html_domain_indices = True
+# html_domain_indices = True
 
 # If false, no index is generated.
-#html_use_index = True
+# html_use_index = True
 
 # If true, the index is split into individual pages for each letter.
-#html_split_index = False
+# html_split_index = False
 
 # If true, links to the reST sources are added to the pages.
-#html_show_sourcelink = True
+# html_show_sourcelink = True
 
 # If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
-#html_show_sphinx = True
+# html_show_sphinx = True
 
 # If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
-#html_show_copyright = True
+# html_show_copyright = True
 
 # If true, an OpenSearch description file will be output, and all pages will
 # contain a <link> tag referring to it.  The value of this option must be the
 # base URL from which the finished HTML is served.
-#html_use_opensearch = ''
+# html_use_opensearch = ''
 
 # This is the file name suffix for HTML files (e.g. ".xhtml").
-#html_file_suffix = None
+# html_file_suffix = None
 
 # Language to be used for generating the HTML full-text search index.
 # Sphinx supports the following languages:
 #   'da', 'de', 'en', 'es', 'fi', 'fr', 'h', 'it', 'ja'
 #   'nl', 'no', 'pt', 'ro', 'r', 'sv', 'tr'
-#html_search_language = 'en'
+# html_search_language = 'en'
 
 # A dictionary with options for the search language support, empty by default.
 # Now only 'ja' uses this config value
-#html_search_options = {'type': 'default'}
+# html_search_options = {'type': 'default'}
 
 # The name of a javascript file (relative to the configuration directory) that
 # implements a search results scorer. If empty, the default will be used.
-#html_search_scorer = 'scorer.js'
+# html_search_scorer = 'scorer.js'
 
 # Output file base name for HTML help builder.
-htmlhelp_basename = 'pybind11doc'
+htmlhelp_basename = "pybind11doc"
 
 # -- Options for LaTeX output ---------------------------------------------
 
+latex_engine = "pdflatex"
+
 latex_elements = {
-# The paper size ('letterpaper' or 'a4paper').
+    # The paper size ('letterpaper' or 'a4paper').
-#'papersize': 'letterpaper',
+    # 'papersize': 'letterpaper',
+    #
+    # The font size ('10pt', '11pt' or '12pt').
+    # 'pointsize': '10pt',
+    #
+    # Additional stuff for the LaTeX preamble.
+    # remove blank pages (between the title page and the TOC, etc.)
+    "classoptions": ",openany,oneside",
+    "preamble": r"""
+\usepackage{fontawesome}
+\usepackage{textgreek}
+\DeclareUnicodeCharacter{00A0}{}
+\DeclareUnicodeCharacter{2194}{\faArrowsH}
+\DeclareUnicodeCharacter{1F382}{\faBirthdayCake}
+\DeclareUnicodeCharacter{1F355}{\faAdjust}
+\DeclareUnicodeCharacter{0301}{'}
+\DeclareUnicodeCharacter{03C0}{\textpi}
 
-# The font size ('10pt', '11pt' or '12pt').
+""",
-#'pointsize': '10pt',
+    # Latex figure (float) alignment
-
+    # 'figure_align': 'htbp',
-# Additional stuff for the LaTeX preamble.
-'preamble': r'\DeclareUnicodeCharacter{00A0}{}',
-
-# Latex figure (float) alignment
-#'figure_align': 'htbp',
 }
 
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
-  (master_doc, 'pybind11.tex', 'pybind11 Documentation',
+    (master_doc, "pybind11.tex", "pybind11 Documentation", "Wenzel Jakob", "manual"),
-   'Wenzel Jakob', 'manual'),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of
@@ -258,32 +278,29 @@ latex_documents = [
 
 # For "manual" documents, if this is true, then toplevel headings are parts,
 # not chapters.
-#latex_use_parts = False
+# latex_use_parts = False
 
 # If true, show page references after internal links.
-#latex_show_pagerefs = False
+# latex_show_pagerefs = False
 
 # If true, show URL addresses after external links.
-#latex_show_urls = False
+# latex_show_urls = False
 
 # Documents to append as an appendix to all manuals.
-#latex_appendices = []
+# latex_appendices = []
 
 # If false, no module index is generated.
-#latex_domain_indices = True
+# latex_domain_indices = True
 
 
 # -- Options for manual page output ---------------------------------------
 
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
-man_pages = [
+man_pages = [(master_doc, "pybind11", "pybind11 Documentation", [author], 1)]
-    (master_doc, 'pybind11', 'pybind11 Documentation',
-     [author], 1)
-]
 
 # If true, show URL addresses after external links.
-#man_show_urls = False
+# man_show_urls = False
 
 
 # -- Options for Texinfo output -------------------------------------------
@@ -292,41 +309,73 @@ man_pages = [
 # (source start file, target name, title, author,
 #  dir menu entry, description, category)
 texinfo_documents = [
-  (master_doc, 'pybind11', 'pybind11 Documentation',
+    (
-   author, 'pybind11', 'One line description of project.',
+        master_doc,
-   'Miscellaneous'),
+        "pybind11",
+        "pybind11 Documentation",
+        author,
+        "pybind11",
+        "One line description of project.",
+        "Miscellaneous",
+    ),
 ]
 
 # Documents to append as an appendix to all manuals.
-#texinfo_appendices = []
+# texinfo_appendices = []
 
 # If false, no module index is generated.
-#texinfo_domain_indices = True
+# texinfo_domain_indices = True
 
 # How to display URL addresses: 'footnote', 'no', or 'inline'.
-#texinfo_show_urls = 'footnote'
+# texinfo_show_urls = 'footnote'
 
 # If true, do not generate a @detailmenu in the "Top" node's menu.
-#texinfo_no_detailmenu = False
+# texinfo_no_detailmenu = False
 
-primary_domain = 'cpp'
+primary_domain = "cpp"
-highlight_language = 'cpp'
+highlight_language = "cpp"
 
 
 def generate_doxygen_xml(app):
-    build_dir = os.path.join(app.confdir, '.build')
+    build_dir = os.path.join(app.confdir, ".build")
     if not os.path.exists(build_dir):
         os.mkdir(build_dir)
 
     try:
-        subprocess.call(['doxygen', '--version'])
+        subprocess.call(["doxygen", "--version"])
-        retcode = subprocess.call(['doxygen'], cwd=app.confdir)
+        retcode = subprocess.call(["doxygen"], cwd=app.confdir)
         if retcode < 0:
             sys.stderr.write("doxygen error code: {}\n".format(-retcode))
     except OSError as e:
         sys.stderr.write("doxygen execution failed: {}\n".format(e))
 
 
+def prepare(app):
+    with open(DIR.parent / "README.rst") as f:
+        contents = f.read()
+
+    if app.builder.name == "latex":
+        # Remove badges and stuff from start
+        contents = contents[contents.find(r".. start") :]
+
+        # Filter out section titles for index.rst for LaTeX
+        contents = re.sub(r"^(.*)\n[-~]{3,}$", r"**\1**", contents, flags=re.MULTILINE)
+
+    with open(DIR / "readme.rst", "w") as f:
+        f.write(contents)
+
+
+def clean_up(app, exception):
+    (DIR / "readme.rst").unlink()
+
+
 def setup(app):
-    """Add hook for building doxygen xml when needed"""
+
+    # Add hook for building doxygen xml when needed
     app.connect("builder-inited", generate_doxygen_xml)
+
+    # Copy the readme in
+    app.connect("builder-inited", prepare)
+
+    # Clean up the generated readme
+    app.connect("build-finished", clean_up)

wrap/pybind11/docs/faq.rst

@@ -5,7 +5,7 @@ Frequently asked questions
 ===========================================================
 
 1. Make sure that the name specified in PYBIND11_MODULE is identical to the
-filename of the extension library (without suffixes such as .so)
+filename of the extension library (without suffixes such as ``.so``).
 
 2. If the above did not fix the issue, you are likely using an incompatible
 version of Python (for instance, the extension library was compiled against
@@ -27,18 +27,6 @@ The Python interpreter immediately crashes when importing my module
 
 See the first answer.
 
-CMake doesn't detect the right Python version
-=============================================
-
-The CMake-based build system will try to automatically detect the installed
-version of Python and link against that. When this fails, or when there are
-multiple versions of Python and it finds the wrong one, delete
-``CMakeCache.txt`` and then invoke CMake as follows:
-
-.. code-block:: bash
-
-    cmake -DPYTHON_EXECUTABLE:FILEPATH=<path-to-python-executable> .
-
 .. _faq_reference_arguments:
 
 Limitations involving reference arguments
@@ -100,8 +88,8 @@ following example:
 
 .. code-block:: cpp
 
-    void init_ex1(py::module &);
+    void init_ex1(py::module_ &);
-    void init_ex2(py::module &);
+    void init_ex2(py::module_ &);
     /* ... */
 
     PYBIND11_MODULE(example, m) {
@@ -114,7 +102,7 @@ following example:
 
 .. code-block:: cpp
 
-    void init_ex1(py::module &m) {
+    void init_ex1(py::module_ &m) {
         m.def("add", [](int a, int b) { return a + b; });
     }
 
@@ -122,7 +110,7 @@ following example:
 
 .. code-block:: cpp
 
-    void init_ex2(py::module &m) {
+    void init_ex2(py::module_ &m) {
         m.def("sub", [](int a, int b) { return a - b; });
     }
 
@@ -181,8 +169,8 @@ can be changed, but even if it isn't it is not always enough to guarantee
 complete independence of the symbols involved when not using
 ``-fvisibility=hidden``.
 
-Additionally, ``-fvisiblity=hidden`` can deliver considerably binary size
+Additionally, ``-fvisibility=hidden`` can deliver considerably binary size
-savings.  (See the following section for more details).
+savings. (See the following section for more details.)
 
 
 .. _`faq:symhidden`:
@@ -192,7 +180,7 @@ How can I create smaller binaries?
 
 To do its job, pybind11 extensively relies on a programming technique known as
 *template metaprogramming*, which is a way of performing computation at compile
-time using type information. Template metaprogamming usually instantiates code
+time using type information. Template metaprogramming usually instantiates code
 involving significant numbers of deeply nested types that are either completely
 removed or reduced to just a few instructions during the compiler's optimization
 phase. However, due to the nested nature of these types, the resulting symbol
@@ -275,17 +263,34 @@ been received, you must either explicitly interrupt execution by throwing
         });
     }
 
+CMake doesn't detect the right Python version
+=============================================
+
+The CMake-based build system will try to automatically detect the installed
+version of Python and link against that. When this fails, or when there are
+multiple versions of Python and it finds the wrong one, delete
+``CMakeCache.txt`` and then add ``-DPYTHON_EXECUTABLE=$(which python)`` to your
+CMake configure line. (Replace ``$(which python)`` with a path to python if
+your prefer.)
+
+You can alternatively try ``-DPYBIND11_FINDPYTHON=ON``, which will activate the
+new CMake FindPython support instead of pybind11's custom search. Requires
+CMake 3.12+, and 3.15+ or 3.18.2+ are even better. You can set this in your
+``CMakeLists.txt`` before adding or finding pybind11, as well.
+
 Inconsistent detection of Python version in CMake and pybind11
 ==============================================================
 
-The functions ``find_package(PythonInterp)`` and ``find_package(PythonLibs)`` provided by CMake
+The functions ``find_package(PythonInterp)`` and ``find_package(PythonLibs)``
-for Python version detection are not used by pybind11 due to unreliability and limitations that make
+provided by CMake for Python version detection are modified by pybind11 due to
-them unsuitable for pybind11's needs. Instead pybind provides its own, more reliable Python detection
+unreliability and limitations that make them unsuitable for pybind11's needs.
-CMake code. Conflicts can arise, however, when using pybind11 in a project that *also* uses the CMake
+Instead pybind11 provides its own, more reliable Python detection CMake code.
-Python detection in a system with several Python versions installed.
+Conflicts can arise, however, when using pybind11 in a project that *also* uses
+the CMake Python detection in a system with several Python versions installed.
 
-This difference may cause inconsistencies and errors if *both* mechanisms are used in the same project. Consider the following
+This difference may cause inconsistencies and errors if *both* mechanisms are
-CMake code executed in a system with Python 2.7 and 3.x installed:
+used in the same project. Consider the following CMake code executed in a
+system with Python 2.7 and 3.x installed:
 
 .. code-block:: cmake
 
@@ -303,10 +308,24 @@ In contrast this code:
     find_package(PythonInterp)
     find_package(PythonLibs)
 
-will detect Python 3.x for pybind11 and may crash on ``find_package(PythonLibs)`` afterwards.
+will detect Python 3.x for pybind11 and may crash on
+``find_package(PythonLibs)`` afterwards.
 
-It is advised to avoid using ``find_package(PythonInterp)`` and ``find_package(PythonLibs)`` from CMake and rely
+There are three possible solutions:
-on pybind11 in detecting Python version. If this is not possible CMake machinery should be called *before* including pybind11.
+
+1. Avoid using ``find_package(PythonInterp)`` and ``find_package(PythonLibs)``
+   from CMake and rely on pybind11 in detecting Python version. If this is not
+   possible, the CMake machinery should be called *before* including pybind11.
+2. Set ``PYBIND11_FINDPYTHON`` to ``True`` or use ``find_package(Python
+   COMPONENTS Interpreter Development)`` on modern CMake (3.12+, 3.15+ better,
+   3.18.2+ best). Pybind11 in these cases uses the new CMake FindPython instead
+   of the old, deprecated search tools, and these modules are much better at
+   finding the correct Python.
+3. Set ``PYBIND11_NOPYTHON`` to ``TRUE``. Pybind11 will not search for Python.
+   However, you will have to use the target-based system, and do more setup
+   yourself, because it does not know about or include things that depend on
+   Python, like ``pybind11_add_module``. This might be ideal for integrating
+   into an existing system, like scikit-build's Python helpers.
 
 How to cite this project?
 =========================

wrap/pybind11/docs/index.rst

@@ -1,18 +1,17 @@
-.. only: not latex
+.. only:: latex
 
-    .. image:: pybind11-logo.png
+   Intro
+   =====
 
-pybind11 --- Seamless operability between C++11 and Python
+.. include:: readme.rst
-==========================================================
 
-.. only: not latex
+.. only:: not latex
 
     Contents:
 
 .. toctree::
    :maxdepth: 1
 
-   intro
    changelog
    upgrade
 
@@ -20,6 +19,7 @@ pybind11 --- Seamless operability between C++11 and Python
    :caption: The Basics
    :maxdepth: 2
 
+   installing
    basics
    classes
    compiling
@@ -45,3 +45,4 @@ pybind11 --- Seamless operability between C++11 and Python
    benchmark
    limitations
    reference
+   cmake/index

wrap/pybind11/docs/intro.rst

@@ -1,93 +0,0 @@
-.. image:: pybind11-logo.png
-
-About this project
-==================
-**pybind11** is a lightweight header-only library that exposes C++ types in Python
-and vice versa, mainly to create Python bindings of existing C++ code. Its
-goals and syntax are similar to the excellent `Boost.Python`_ library by David
-Abrahams: to minimize boilerplate code in traditional extension modules by
-inferring type information using compile-time introspection.
-
-.. _Boost.Python: http://www.boost.org/doc/libs/release/libs/python/doc/index.html
-
-The main issue with Boost.Python—and the reason for creating such a similar
-project—is Boost. Boost is an enormously large and complex suite of utility
-libraries that works with almost every C++ compiler in existence. This
-compatibility has its cost: arcane template tricks and workarounds are
-necessary to support the oldest and buggiest of compiler specimens. Now that
-C++11-compatible compilers are widely available, this heavy machinery has
-become an excessively large and unnecessary dependency.
-Think of this library as a tiny self-contained version of Boost.Python with
-everything stripped away that isn't relevant for binding generation. Without
-comments, the core header files only require ~4K lines of code and depend on
-Python (2.7 or 3.x, or PyPy2.7 >= 5.7) and the C++ standard library. This
-compact implementation was possible thanks to some of the new C++11 language
-features (specifically: tuples, lambda functions and variadic templates). Since
-its creation, this library has grown beyond Boost.Python in many ways, leading
-to dramatically simpler binding code in many common situations.
-
-Core features
-*************
-The following core C++ features can be mapped to Python
-
-- Functions accepting and returning custom data structures per value, reference, or pointer
-- Instance methods and static methods
-- Overloaded functions
-- Instance attributes and static attributes
-- Arbitrary exception types
-- Enumerations
-- Callbacks
-- Iterators and ranges
-- Custom operators
-- Single and multiple inheritance
-- STL data structures
-- Smart pointers with reference counting like ``std::shared_ptr``
-- Internal references with correct reference counting
-- C++ classes with virtual (and pure virtual) methods can be extended in Python
-
-Goodies
-*******
-In addition to the core functionality, pybind11 provides some extra goodies:
-
-- Python 2.7, 3.x, and PyPy (PyPy2.7 >= 5.7) are supported with an
-  implementation-agnostic interface.
-
-- It is possible to bind C++11 lambda functions with captured variables. The
-  lambda capture data is stored inside the resulting Python function object.
-
-- pybind11 uses C++11 move constructors and move assignment operators whenever
-  possible to efficiently transfer custom data types.
-
-- It's easy to expose the internal storage of custom data types through
-  Pythons' buffer protocols. This is handy e.g. for fast conversion between
-  C++ matrix classes like Eigen and NumPy without expensive copy operations.
-
-- pybind11 can automatically vectorize functions so that they are transparently
-  applied to all entries of one or more NumPy array arguments.
-
-- Python's slice-based access and assignment operations can be supported with
-  just a few lines of code.
-
-- Everything is contained in just a few header files; there is no need to link
-  against any additional libraries.
-
-- Binaries are generally smaller by a factor of at least 2 compared to
-  equivalent bindings generated by Boost.Python. A recent pybind11 conversion
-  of `PyRosetta`_, an enormous Boost.Python binding project, reported a binary
-  size reduction of **5.4x** and compile time reduction by **5.8x**.
-
-- Function signatures are precomputed at compile time (using ``constexpr``),
-  leading to smaller binaries.
-
-- With little extra effort, C++ types can be pickled and unpickled similar to
-  regular Python objects.
-
-.. _PyRosetta: http://graylab.jhu.edu/RosettaCon2016/PyRosetta-4.pdf
-
-Supported compilers
-*******************
-
-1. Clang/LLVM (any non-ancient version with C++11 support)
-2. GCC 4.8 or newer
-3. Microsoft Visual Studio 2015 or newer
-4. Intel C++ compiler v17 or newer (v16 with pybind11 v2.0 and v15 with pybind11 v2.0 and a `workaround <https://github.com/pybind/pybind11/issues/276>`_ )

wrap/pybind11/docs/limitations.rst

@@ -1,6 +1,9 @@
 Limitations
 ###########
 
+Design choices
+^^^^^^^^^^^^^^
+
 pybind11 strives to be a general solution to binding generation, but it also has
 certain limitations:
 
@@ -11,9 +14,59 @@ certain limitations:
 
 - The NumPy interface ``pybind11::array`` greatly simplifies accessing
   numerical data from C++ (and vice versa), but it's not a full-blown array
-  class like ``Eigen::Array`` or ``boost.multi_array``.
+  class like ``Eigen::Array`` or ``boost.multi_array``. ``Eigen`` objects are
+  directly supported, however, with ``pybind11/eigen.h``.
 
-These features could be implemented but would lead to a significant increase in
+Large but useful features could be implemented in pybind11 but would lead to a
-complexity. I've decided to draw the line here to keep this project simple and
+significant increase in complexity. Pybind11 strives to be simple and compact.
-compact. Users who absolutely require these features are encouraged to fork
+Users who require large new features are encouraged to write an extension to
-pybind11.
+pybind11; see `pybind11_json <https://github.com/pybind/pybind11_json>`_ for an
+example.
+
+
+Known bugs
+^^^^^^^^^^
+
+These are issues that hopefully will one day be fixed, but currently are
+unsolved. If you know how to help with one of these issues, contributions
+are welcome!
+
+- Intel 20.2 is currently having an issue with the test suite.
+  `#2573 <https://github.com/pybind/pybind11/pull/2573>`_
+
+- Debug mode Python does not support 1-5 tests in the test suite currently.
+  `#2422 <https://github.com/pybind/pybind11/pull/2422>`_
+
+- PyPy3 7.3.1 and 7.3.2 have issues with several tests on 32-bit Windows.
+
+Known limitations
+^^^^^^^^^^^^^^^^^
+
+These are issues that are probably solvable, but have not been fixed yet. A
+clean, well written patch would likely be accepted to solve them.
+
+- Type casters are not kept alive recursively.
+  `#2527 <https://github.com/pybind/pybind11/issues/2527>`_
+  One consequence is that containers of ``char *`` are currently not supported.
+  `#2245 <https://github.com/pybind/pybind11/issues/2245>`_
+
+- The ``cpptest`` does not run on Windows with Python 3.8 or newer, due to DLL
+  loader changes. User code that is correctly installed should not be affected.
+  `#2560 <https://github.com/pybind/pybind11/issue/2560>`_
+
+Python 3.9.0 warning
+^^^^^^^^^^^^^^^^^^^^
+
+Combining older versions of pybind11 (< 2.6.0) with Python on exactly 3.9.0
+will trigger undefined behavior that typically manifests as crashes during
+interpreter shutdown (but could also destroy your data. **You have been
+warned**).
+
+This issue was `fixed in Python <https://github.com/python/cpython/pull/22670>`_.
+As a mitigation for this bug, pybind11 2.6.0 or newer includes a workaround
+specifically when Python 3.9.0 is detected at runtime, leaking about 50 bytes
+of memory when a callback function is garbage collected.  For reference, the
+pybind11 test suite has about 2,000 such callbacks, but only 49 are garbage
+collected before the end-of-process. Wheels (even if built with Python 3.9.0)
+will correctly avoid the leak when run in Python 3.9.1, and this does not
+affect other 3.X versions.

wrap/pybind11/docs/reference.rst

@@ -52,6 +52,20 @@ Convenience classes for specific Python types
 .. doxygengroup:: pytypes
     :members:
 
+Convenience functions converting to Python types
+================================================
+
+.. doxygenfunction:: make_tuple(Args&&...)
+
+.. doxygenfunction:: make_iterator(Iterator, Sentinel, Extra &&...)
+.. doxygenfunction:: make_iterator(Type &, Extra&&...)
+
+.. doxygenfunction:: make_key_iterator(Iterator, Sentinel, Extra &&...)
+.. doxygenfunction:: make_key_iterator(Type &, Extra&&...)
+
+.. doxygenfunction:: make_value_iterator(Iterator, Sentinel, Extra &&...)
+.. doxygenfunction:: make_value_iterator(Type &, Extra&&...)
+
 .. _extras:
 
 Passing extra arguments to ``def`` or ``class_``
@@ -110,7 +124,6 @@ Exceptions
 .. doxygenclass:: builtin_exception
     :members:
 
-
 Literals
 ========
 

wrap/pybind11/docs/release.rst

@@ -1,21 +1,97 @@
-To release a new version of pybind11:
+On version numbers
+^^^^^^^^^^^^^^^^^^
 
-- Update the version number and push to pypi
+The two version numbers (C++ and Python) must match when combined (checked when
-    - Update ``pybind11/_version.py`` (set release version, remove 'dev').
+you build the PyPI package), and must be a valid `PEP 440
-    - Update ``PYBIND11_VERSION_MAJOR`` etc. in ``include/pybind11/detail/common.h``.
+<https://www.python.org/dev/peps/pep-0440>`_ version when combined.
-    - Ensure that all the information in ``setup.py`` is up-to-date.
+
-    - Update version in ``docs/conf.py``.
+For example:
-    - Tag release date in ``docs/changelog.rst``.
+
-    - ``git add`` and ``git commit``.
+.. code-block:: C++
-    - if new minor version: ``git checkout -b vX.Y``, ``git push -u origin vX.Y``
+
+    #define PYBIND11_VERSION_MAJOR X
+    #define PYBIND11_VERSION_MINOR Y
+    #define PYBIND11_VERSION_PATCH Z.dev1
+
+For beta, ``PYBIND11_VERSION_PATCH`` should be ``Z.b1``. RC's can be ``Z.rc1``.
+Always include the dot (even though PEP 440 allows it to be dropped). For a
+final release, this must be a simple integer. There is also a HEX version of
+the version just below.
+
+
+To release a new version of pybind11:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you don't have nox, you should either use ``pipx run nox`` instead, or use
+``pipx install nox`` or ``brew install nox`` (Unix).
+
+- Update the version number
+    - Update ``PYBIND11_VERSION_MAJOR`` etc. in
+      ``include/pybind11/detail/common.h``. PATCH should be a simple integer.
+    - Update the version HEX just below, as well.
+    - Update ``pybind11/_version.py`` (match above)
+    - Run ``nox -s tests_packaging`` to ensure this was done correctly.
+    - Ensure that all the information in ``setup.cfg`` is up-to-date, like
+      supported Python versions.
+    - Add release date in ``docs/changelog.rst``.
+          - Check to make sure
+            `needs-changelog <https://github.com/pybind/pybind11/pulls?q=is%3Apr+is%3Aclosed+label%3A%22needs+changelog%22>`_
+            issues are entered in the changelog (clear the label when done).
+    - ``git add`` and ``git commit``, ``git push``. **Ensure CI passes**. (If it
+      fails due to a known flake issue, either ignore or restart CI.)
+- Add a release branch if this is a new minor version, or update the existing release branch if it is a patch version
+    - New branch: ``git checkout -b vX.Y``, ``git push -u origin vX.Y``
+    - Update branch: ``git checkout vX.Y``, ``git merge <release branch>``, ``git push``
+- Update tags (optional; if you skip this, the GitHub release makes a
+    non-annotated tag for you)
     - ``git tag -a vX.Y.Z -m 'vX.Y.Z release'``.
-    - ``git push``
     - ``git push --tags``.
-    - ``python setup.py sdist upload``.
+- Update stable
-    - ``python setup.py bdist_wheel upload``.
+    - ``git checkout stable``
+    - ``git merge master``
+    - ``git push``
+- Make a GitHub release (this shows up in the UI, sends new release
+  notifications to users watching releases, and also uploads PyPI packages).
+  (Note: if you do not use an existing tag, this creates a new lightweight tag
+  for you, so you could skip the above step.)
+    - GUI method: Under `releases <https://github.com/pybind/pybind11/releases>`_
+      click "Draft a new release" on the far right, fill in the tag name
+      (if you didn't tag above, it will be made here), fill in a release name
+      like "Version X.Y.Z", and copy-and-paste the markdown-formatted (!) changelog
+      into the description (usually ``cat docs/changelog.rst | pandoc -f rst -t gfm``).
+      Check "pre-release" if this is a beta/RC.
+    - CLI method: with ``gh`` installed, run ``gh release create vX.Y.Z -t "Version X.Y.Z"``
+      If this is a pre-release, add ``-p``.
+
 - Get back to work
-    - Update ``_version.py`` (add 'dev' and increment minor).
+    - Make sure you are on master, not somewhere else: ``git checkout master``
-    - Update version in ``docs/conf.py``
+    - Update version macros in ``include/pybind11/detail/common.h`` (set PATCH to
-    - Update version macros in ``include/pybind11/common.h``
+      ``0.dev1`` and increment MINOR).
-    - ``git add`` and ``git commit``.
+    - Update ``_version.py`` to match
-      ``git push``
+    - Run ``nox -s tests_packaging`` to ensure this was done correctly.
+    - Add a spot for in-development updates in ``docs/changelog.rst``.
+    - ``git add``, ``git commit``, ``git push``
+
+If a version branch is updated, remember to set PATCH to ``1.dev1``.
+
+If you'd like to bump homebrew, run:
+
+.. code-block:: console
+
+    brew bump-formula-pr --url https://github.com/pybind/pybind11/archive/vX.Y.Z.tar.gz
+
+Conda-forge should automatically make a PR in a few hours, and automatically
+merge it if there are no issues.
+
+
+Manual packaging
+^^^^^^^^^^^^^^^^
+
+If you need to manually upload releases, you can download the releases from the job artifacts and upload them with twine. You can also make the files locally (not recommended in general, as your local directory is more likely to be "dirty" and SDists love picking up random unrelated/hidden files); this is the procedure:
+
+.. code-block:: bash
+
+    nox -s build
+    twine upload dist/*
+
+This makes SDists and wheels, and the final line uploads them.

wrap/pybind11/docs/requirements.txt

@@ -1,5 +1,5 @@
-breathe==4.20.0
+breathe==4.31.0
-commonmark==0.9.1
+sphinx==3.5.4
-recommonmark==0.6.0
+sphinx_rtd_theme==1.0.0
-sphinx==3.2.1
+sphinxcontrib-moderncmakedomain==3.19
-sphinx_rtd_theme==0.5.0
+sphinxcontrib-svg2pdfconverter==1.1.1

wrap/pybind11/docs/upgrade.rst

@@ -8,31 +8,90 @@ to a new version. But it goes into more detail. This includes things like
 deprecated APIs and their replacements, build system changes, general code
 modernization and other useful information.
 
+.. _upgrade-guide-2.9:
+
+v2.9
+====
+
+* Any usage of the recently added ``py::make_simple_namespace`` should be
+  converted to using ``py::module_::import("types").attr("SimpleNamespace")``
+  instead.
+
+* The use of ``_`` in custom type casters can now be replaced with the more
+  readable ``const_name`` instead. The old ``_`` shortcut has been retained
+  unless it is being used as a macro (like for gettext).
+
+
+.. _upgrade-guide-2.7:
+
+v2.7
+====
+
+*Before* v2.7, ``py::str`` can hold ``PyUnicodeObject`` or ``PyBytesObject``,
+and ``py::isinstance<str>()`` is ``true`` for both ``py::str`` and
+``py::bytes``. Starting with v2.7, ``py::str`` exclusively holds
+``PyUnicodeObject`` (`#2409 <https://github.com/pybind/pybind11/pull/2409>`_),
+and ``py::isinstance<str>()`` is ``true`` only for ``py::str``. To help in
+the transition of user code, the ``PYBIND11_STR_LEGACY_PERMISSIVE`` macro
+is provided as an escape hatch to go back to the legacy behavior. This macro
+will be removed in future releases. Two types of required fixes are expected
+to be common:
+
+* Accidental use of ``py::str`` instead of ``py::bytes``, masked by the legacy
+  behavior. These are probably very easy to fix, by changing from
+  ``py::str`` to ``py::bytes``.
+
+* Reliance on py::isinstance<str>(obj) being ``true`` for
+  ``py::bytes``. This is likely to be easy to fix in most cases by adding
+  ``|| py::isinstance<bytes>(obj)``, but a fix may be more involved, e.g. if
+  ``py::isinstance<T>`` appears in a template. Such situations will require
+  careful review and custom fixes.
+
+
 .. _upgrade-guide-2.6:
 
 v2.6
 ====
 
-The ``tools/clang`` submodule and ``tools/mkdoc.py`` have been moved to a
+Usage of the ``PYBIND11_OVERLOAD*`` macros and ``get_overload`` function should
-standalone package, `pybind11-mkdoc`_. If you were using those tools, please
+be replaced by ``PYBIND11_OVERRIDE*`` and ``get_override``. In the future, the
-use them via a pip install from the new location.
+old macros may be deprecated and removed.
 
-.. _pybind11-mkdoc: https://github.com/pybind/pybind11-mkdoc
+``py::module`` has been renamed ``py::module_``, but a backward compatible
+typedef has been included. This change was to avoid a language change in C++20
+that requires unqualified ``module`` not be placed at the start of a logical
+line. Qualified usage is unaffected and the typedef will remain unless the
+C++ language rules change again.
+
+The public constructors of ``py::module_`` have been deprecated. Use
+``PYBIND11_MODULE`` or ``module_::create_extension_module`` instead.
 
 An error is now thrown when ``__init__`` is forgotten on subclasses. This was
 incorrect before, but was not checked. Add a call to ``__init__`` if it is
 missing.
 
+A ``py::type_error`` is now thrown when casting to a subclass (like
+``py::bytes`` from ``py::object``) if the conversion is not valid. Make a valid
+conversion instead.
+
 The undocumented ``h.get_type()`` method has been deprecated and replaced by
 ``py::type::of(h)``.
 
+Enums now have a ``__str__`` method pre-defined; if you want to override it,
+the simplest fix is to add the new ``py::prepend()`` tag when defining
+``"__str__"``.
+
 If ``__eq__`` defined but not ``__hash__``, ``__hash__`` is now set to
 ``None``, as in normal CPython. You should add ``__hash__`` if you intended the
 class to be hashable, possibly using the new ``py::hash`` shortcut.
 
-Usage of the ``PYBIND11_OVERLOAD*`` macros and ``get_overload`` function should
+The constructors for ``py::array`` now always take signed integers for size,
-be replaced by ``PYBIND11_OVERRIDE*`` and ``get_override``. In the future, the
+for consistency. This may lead to compiler warnings on some systems. Cast to
-old macros may be deprecated and removed.
+``py::ssize_t`` instead of ``std::size_t``.
+
+The ``tools/clang`` submodule and ``tools/mkdoc.py`` have been moved to a
+standalone package, `pybind11-mkdoc`_. If you were using those tools, please
+use them via a pip install from the new location.
 
 The ``pybind11`` package on PyPI no longer fills the wheel "headers" slot - if
 you were using the headers from this slot, they are available by requesting the
@@ -41,6 +100,8 @@ be unaffected, as the ``pybind11/include`` location is reported by ``python -m
 pybind11 --includes`` and ``pybind11.get_include()`` is still correct and has
 not changed since 2.5).
 
+.. _pybind11-mkdoc: https://github.com/pybind/pybind11-mkdoc
+
 CMake support:
 --------------
 
@@ -54,7 +115,7 @@ something. The changes are:
 
 * If you do not request a standard, pybind11 targets will compile with the
   compiler default, but not less than C++11, instead of forcing C++14 always.
-  If you depend on the old behavior, please use ``set(CMAKE_CXX_STANDARD 14)``
+  If you depend on the old behavior, please use ``set(CMAKE_CXX_STANDARD 14 CACHE STRING "")``
   instead.
 
 * Direct ``pybind11::module`` usage should always be accompanied by at least
@@ -80,7 +141,8 @@ In addition, the following changes may be of interest:
 * Using ``find_package(Python COMPONENTS Interpreter Development)`` before
   pybind11 will cause pybind11 to use the new Python mechanisms instead of its
   own custom search, based on a patched version of classic ``FindPythonInterp``
-  / ``FindPythonLibs``. In the future, this may become the default.
+  / ``FindPythonLibs``. In the future, this may become the default. A recent
+  (3.15+ or 3.18.2+) version of CMake is recommended.
 
 
 
@@ -170,7 +232,7 @@ way to get and set object state. See :ref:`pickling` for details.
         ...
         .def(py::pickle(
             [](const Foo &self) { // __getstate__
-                return py::make_tuple(f.value1(), f.value2(), ...); // unchanged
+                return py::make_tuple(self.value1(), self.value2(), ...); // unchanged
             },
             [](py::tuple t) { // __setstate__, note: no `self` argument
                 return new Foo(t[0].cast<std::string>(), ...);
@@ -234,7 +296,7 @@ Within pybind11's CMake build system, ``pybind11_add_module`` has always been
 setting the ``-fvisibility=hidden`` flag in release mode. From now on, it's
 being applied unconditionally, even in debug mode and it can no longer be opted
 out of with the ``NO_EXTRAS`` option. The ``pybind11::module`` target now also
-adds this flag to it's interface. The ``pybind11::embed`` target is unchanged.
+adds this flag to its interface. The ``pybind11::embed`` target is unchanged.
 
 The most significant change here is for the ``pybind11::module`` target. If you
 were previously relying on default visibility, i.e. if your Python module was

wrap/pybind11/include/pybind11/attr.h

@@ -12,13 +12,17 @@
 
 #include "cast.h"
 
+#include <functional>
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 /// \addtogroup annotations
 /// @{
 
 /// Annotation for methods
-struct is_method { handle class_; is_method(const handle &c) : class_(c) { } };
+struct is_method { handle class_;
+    explicit is_method(const handle &c) : class_(c) {}
+};
 
 /// Annotation for operators
 struct is_operator { };
@@ -27,16 +31,24 @@ struct is_operator { };
 struct is_final { };
 
 /// Annotation for parent scope
-struct scope { handle value; scope(const handle &s) : value(s) { } };
+struct scope { handle value;
+    explicit scope(const handle &s) : value(s) {}
+};
 
 /// Annotation for documentation
-struct doc { const char *value; doc(const char *value) : value(value) { } };
+struct doc { const char *value;
+    explicit doc(const char *value) : value(value) {}
+};
 
 /// Annotation for function names
-struct name { const char *value; name(const char *value) : value(value) { } };
+struct name { const char *value;
+    explicit name(const char *value) : value(value) {}
+};
 
 /// Annotation indicating that a function is an overload associated with a given "sibling"
-struct sibling { handle value; sibling(const handle &value) : value(value.ptr()) { } };
+struct sibling { handle value;
+    explicit sibling(const handle &value) : value(value.ptr()) {}
+};
 
 /// Annotation indicating that a class derives from another given type
 template <typename T> struct base {
@@ -62,18 +74,41 @@ struct metaclass {
     handle value;
 
     PYBIND11_DEPRECATED("py::metaclass() is no longer required. It's turned on by default now.")
-    metaclass() { } // NOLINT(modernize-use-equals-default): breaks MSVC 2015 when adding an attribute
+    // NOLINTNEXTLINE(modernize-use-equals-default): breaks MSVC 2015 when adding an attribute
+    metaclass() {}
 
     /// Override pybind11's default metaclass
     explicit metaclass(handle value) : value(value) { }
 };
 
+/// Specifies a custom callback with signature `void (PyHeapTypeObject*)` that
+/// may be used to customize the Python type.
+///
+/// The callback is invoked immediately before `PyType_Ready`.
+///
+/// Note: This is an advanced interface, and uses of it may require changes to
+/// work with later versions of pybind11.  You may wish to consult the
+/// implementation of `make_new_python_type` in `detail/classes.h` to understand
+/// the context in which the callback will be run.
+struct custom_type_setup {
+    using callback = std::function<void(PyHeapTypeObject *heap_type)>;
+
+    explicit custom_type_setup(callback value) : value(std::move(value)) {}
+
+    callback value;
+};
+
 /// Annotation that marks a class as local to the module:
-struct module_local { const bool value; constexpr module_local(bool v = true) : value(v) { } };
+struct module_local { const bool value;
+    constexpr explicit module_local(bool v = true) : value(v) {}
+};
 
 /// Annotation to mark enums as an arithmetic type
 struct arithmetic { };
 
+/// Mark a function for addition at the beginning of the existing overload chain instead of the end
+struct prepend { };
+
 /** \rst
     A call policy which places one or more guard variables (``Ts...``) around the function call.
 
@@ -120,7 +155,7 @@ enum op_id : int;
 enum op_type : int;
 struct undefined_t;
 template <op_id id, op_type ot, typename L = undefined_t, typename R = undefined_t> struct op_;
-inline void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
+void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
 
 /// Internal data structure which holds metadata about a keyword argument
 struct argument_record {
@@ -138,8 +173,8 @@ struct argument_record {
 struct function_record {
     function_record()
         : is_constructor(false), is_new_style_constructor(false), is_stateless(false),
-          is_operator(false), is_method(false),
+          is_operator(false), is_method(false), has_args(false),
-          has_args(false), has_kwargs(false), has_kw_only_args(false) { }
+          has_kwargs(false), prepend(false) { }
 
     /// Function name
     char *name = nullptr; /* why no C++ strings? They generate heavier code.. */
@@ -186,14 +221,15 @@ struct function_record {
     /// True if the function has a '**kwargs' argument
     bool has_kwargs : 1;
 
-    /// True once a 'py::kw_only' is encountered (any following args are keyword-only)
+    /// True if this function is to be inserted at the beginning of the overload resolution chain
-    bool has_kw_only_args : 1;
+    bool prepend : 1;
 
     /// Number of arguments (including py::args and/or py::kwargs, if present)
     std::uint16_t nargs;
 
-    /// Number of trailing arguments (counted in `nargs`) that are keyword-only
+    /// Number of leading positional arguments, which are terminated by a py::args or py::kwargs
-    std::uint16_t nargs_kw_only = 0;
+    /// argument or by a py::kw_only annotation.
+    std::uint16_t nargs_pos = 0;
 
     /// Number of leading arguments (counted in `nargs`) that are positional-only
     std::uint16_t nargs_pos_only = 0;
@@ -253,6 +289,9 @@ struct type_record {
     /// Custom metaclass (optional)
     handle metaclass;
 
+    /// Custom type setup.
+    custom_type_setup::callback custom_type_setup_callback;
+
     /// Multiple inheritance marker
     bool multiple_inheritance : 1;
 
@@ -370,20 +409,23 @@ template <> struct process_attribute<is_new_style_constructor> : process_attribu
     static void init(const is_new_style_constructor &, function_record *r) { r->is_new_style_constructor = true; }
 };
 
-inline void process_kw_only_arg(const arg &a, function_record *r) {
+inline void check_kw_only_arg(const arg &a, function_record *r) {
-    if (!a.name || strlen(a.name) == 0)
+    if (r->args.size() > r->nargs_pos && (!a.name || a.name[0] == '\0'))
-        pybind11_fail("arg(): cannot specify an unnamed argument after an kw_only() annotation");
+        pybind11_fail("arg(): cannot specify an unnamed argument after a kw_only() annotation or args() argument");
-    ++r->nargs_kw_only;
+}
+
+inline void append_self_arg_if_needed(function_record *r) {
+    if (r->is_method && r->args.empty())
+        r->args.emplace_back("self", nullptr, handle(), /*convert=*/ true, /*none=*/ false);
 }
 
 /// Process a keyword argument attribute (*without* a default value)
 template <> struct process_attribute<arg> : process_attribute_default<arg> {
     static void init(const arg &a, function_record *r) {
-        if (r->is_method && r->args.empty())
+        append_self_arg_if_needed(r);
-            r->args.emplace_back("self", nullptr, handle(), true /*convert*/, false /*none not allowed*/);
         r->args.emplace_back(a.name, nullptr, handle(), !a.flag_noconvert, a.flag_none);
 
-        if (r->has_kw_only_args) process_kw_only_arg(a, r);
+        check_kw_only_arg(a, r);
     }
 };
 
@@ -391,7 +433,7 @@ template <> struct process_attribute<arg> : process_attribute_default<arg> {
 template <> struct process_attribute<arg_v> : process_attribute_default<arg_v> {
     static void init(const arg_v &a, function_record *r) {
         if (r->is_method && r->args.empty())
-            r->args.emplace_back("self", nullptr /*descr*/, handle() /*parent*/, true /*convert*/, false /*none not allowed*/);
+            r->args.emplace_back("self", /*descr=*/ nullptr, /*parent=*/ handle(), /*convert=*/ true, /*none=*/ false);
 
         if (!a.value) {
 #if !defined(NDEBUG)
@@ -416,21 +458,28 @@ template <> struct process_attribute<arg_v> : process_attribute_default<arg_v> {
         }
         r->args.emplace_back(a.name, a.descr, a.value.inc_ref(), !a.flag_noconvert, a.flag_none);
 
-        if (r->has_kw_only_args) process_kw_only_arg(a, r);
+        check_kw_only_arg(a, r);
     }
 };
 
 /// Process a keyword-only-arguments-follow pseudo argument
 template <> struct process_attribute<kw_only> : process_attribute_default<kw_only> {
     static void init(const kw_only &, function_record *r) {
-        r->has_kw_only_args = true;
+        append_self_arg_if_needed(r);
+        if (r->has_args && r->nargs_pos != static_cast<std::uint16_t>(r->args.size()))
+            pybind11_fail("Mismatched args() and kw_only(): they must occur at the same relative argument location (or omit kw_only() entirely)");
+        r->nargs_pos = static_cast<std::uint16_t>(r->args.size());
     }
 };
 
 /// Process a positional-only-argument maker
 template <> struct process_attribute<pos_only> : process_attribute_default<pos_only> {
     static void init(const pos_only &, function_record *r) {
+        append_self_arg_if_needed(r);
         r->nargs_pos_only = static_cast<std::uint16_t>(r->args.size());
+        if (r->nargs_pos_only > r->nargs_pos)
+            pybind11_fail("pos_only(): cannot follow a py::args() argument");
+            // It also can't follow a kw_only, but a static_assert in pybind11.h checks that
     }
 };
 
@@ -457,6 +506,13 @@ struct process_attribute<dynamic_attr> : process_attribute_default<dynamic_attr>
     static void init(const dynamic_attr &, type_record *r) { r->dynamic_attr = true; }
 };
 
+template <>
+struct process_attribute<custom_type_setup> {
+    static void init(const custom_type_setup &value, type_record *r) {
+        r->custom_type_setup_callback = value.value;
+    }
+};
+
 template <>
 struct process_attribute<is_final> : process_attribute_default<is_final> {
     static void init(const is_final &, type_record *r) { r->is_final = true; }
@@ -477,6 +533,12 @@ struct process_attribute<module_local> : process_attribute_default<module_local>
     static void init(const module_local &l, type_record *r) { r->module_local = l.value; }
 };
 
+/// Process a 'prepend' attribute, putting this at the beginning of the overload chain
+template <>
+struct process_attribute<prepend> : process_attribute_default<prepend> {
+    static void init(const prepend &, function_record *r) { r->prepend = true; }
+};
+
 /// Process an 'arithmetic' attribute for enums (does nothing here)
 template <>
 struct process_attribute<arithmetic> : process_attribute_default<arithmetic> {};
@@ -503,20 +565,31 @@ template <size_t Nurse, size_t Patient> struct process_attribute<keep_alive<Nurs
 /// Recursively iterate over variadic template arguments
 template <typename... Args> struct process_attributes {
     static void init(const Args&... args, function_record *r) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(r);
+        using expander = int[];
+        (void) expander{
+            0, ((void) process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...};
     }
     static void init(const Args&... args, type_record *r) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(r);
+        using expander = int[];
+        (void) expander{0,
+                        (process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...};
     }
     static void precall(function_call &call) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::precall(call), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call);
-        ignore_unused(unused);
+        using expander = int[];
+        (void) expander{0,
+                        (process_attribute<typename std::decay<Args>::type>::precall(call), 0)...};
     }
     static void postcall(function_call &call, handle fn_ret) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call, fn_ret);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(fn_ret);
+        using expander = int[];
+        (void) expander{
+            0, (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0)...};
     }
 };
 
@@ -532,7 +605,8 @@ template <typename... Extra,
           size_t named = constexpr_sum(std::is_base_of<arg, Extra>::value...),
           size_t self  = constexpr_sum(std::is_same<is_method, Extra>::value...)>
 constexpr bool expected_num_args(size_t nargs, bool has_args, bool has_kwargs) {
-    return named == 0 || (self + named + has_args + has_kwargs) == nargs;
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(nargs, has_args, has_kwargs);
+    return named == 0 || (self + named + size_t(has_args) + size_t(has_kwargs)) == nargs;
 }
 
 PYBIND11_NAMESPACE_END(detail)

wrap/pybind11/include/pybind11/buffer_info.h

@@ -13,6 +13,29 @@
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+// Default, C-style strides
+inline std::vector<ssize_t> c_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
+    auto ndim = shape.size();
+    std::vector<ssize_t> strides(ndim, itemsize);
+    if (ndim > 0)
+        for (size_t i = ndim - 1; i > 0; --i)
+            strides[i - 1] = strides[i] * shape[i];
+    return strides;
+}
+
+// F-style strides; default when constructing an array_t with `ExtraFlags & f_style`
+inline std::vector<ssize_t> f_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
+    auto ndim = shape.size();
+    std::vector<ssize_t> strides(ndim, itemsize);
+    for (size_t i = 1; i < ndim; ++i)
+        strides[i] = strides[i - 1] * shape[i - 1];
+    return strides;
+}
+
+PYBIND11_NAMESPACE_END(detail)
+
 /// Information record describing a Python buffer object
 struct buffer_info {
     void *ptr = nullptr;          // Pointer to the underlying storage
@@ -53,7 +76,14 @@ struct buffer_info {
 
     explicit buffer_info(Py_buffer *view, bool ownview = true)
     : buffer_info(view->buf, view->itemsize, view->format, view->ndim,
-            {view->shape, view->shape + view->ndim}, {view->strides, view->strides + view->ndim}, view->readonly) {
+            {view->shape, view->shape + view->ndim},
+            /* Though buffer::request() requests PyBUF_STRIDES, ctypes objects
+             * ignore this flag and return a view with NULL strides.
+             * When strides are NULL, build them manually.  */
+            view->strides
+            ? std::vector<ssize_t>(view->strides, view->strides + view->ndim)
+            : detail::c_strides({view->shape, view->shape + view->ndim}, view->itemsize),
+            (view->readonly != 0)) {
         this->m_view = view;
         this->ownview = ownview;
     }
@@ -61,11 +91,9 @@ struct buffer_info {
     buffer_info(const buffer_info &) = delete;
     buffer_info& operator=(const buffer_info &) = delete;
 
-    buffer_info(buffer_info &&other) {
+    buffer_info(buffer_info &&other) noexcept { (*this) = std::move(other); }
-        (*this) = std::move(other);
-    }
 
-    buffer_info& operator=(buffer_info &&rhs) {
+    buffer_info &operator=(buffer_info &&rhs) noexcept {
         ptr = rhs.ptr;
         itemsize = rhs.itemsize;
         size = rhs.size;

wrap/pybind11/include/pybind11/chrono.h

@@ -11,9 +11,12 @@
 #pragma once
 
 #include "pybind11.h"
+
+#include <chrono>
 #include <cmath>
 #include <ctime>
-#include <chrono>
+#include <mutex>
+
 #include <datetime.h>
 
 // Backport the PyDateTime_DELTA functions from Python3.3 if required
@@ -32,10 +35,10 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <typename type> class duration_caster {
 public:
-    typedef typename type::rep rep;
+    using rep = typename type::rep;
     using period = typename type::period;
 
-    using days = std::chrono::duration<uint_fast32_t, std::ratio<86400>>;
+    using days = std::chrono::duration<int_least32_t, std::ratio<86400>>; // signed 25 bits required by the standard.
 
     bool load(handle src, bool) {
         using namespace std::chrono;
@@ -53,11 +56,11 @@ public:
             return true;
         }
         // If invoked with a float we assume it is seconds and convert
-        else if (PyFloat_Check(src.ptr())) {
+        if (PyFloat_Check(src.ptr())) {
             value = type(duration_cast<duration<rep, period>>(duration<double>(PyFloat_AsDouble(src.ptr()))));
             return true;
         }
-        else return false;
+        return false;
     }
 
     // If this is a duration just return it back
@@ -92,9 +95,25 @@ public:
         return PyDelta_FromDSU(dd.count(), ss.count(), us.count());
     }
 
-    PYBIND11_TYPE_CASTER(type, _("datetime.timedelta"));
+    PYBIND11_TYPE_CASTER(type, const_name("datetime.timedelta"));
 };
 
+inline std::tm *localtime_thread_safe(const std::time_t *time, std::tm *buf) {
+#if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || defined(_MSC_VER)
+    if (localtime_s(buf, time))
+        return nullptr;
+    return buf;
+#else
+    static std::mutex mtx;
+    std::lock_guard<std::mutex> lock(mtx);
+    std::tm *tm_ptr = std::localtime(time);
+    if (tm_ptr != nullptr) {
+        *buf = *tm_ptr;
+    }
+    return tm_ptr;
+#endif
+}
+
 // This is for casting times on the system clock into datetime.datetime instances
 template <typename Duration> class type_caster<std::chrono::time_point<std::chrono::system_clock, Duration>> {
 public:
@@ -161,10 +180,11 @@ public:
         // > If std::time_t has lower precision, it is implementation-defined whether the value is rounded or truncated.
         // (https://en.cppreference.com/w/cpp/chrono/system_clock/to_time_t)
         std::time_t tt = system_clock::to_time_t(time_point_cast<system_clock::duration>(src - us));
-        // this function uses static memory so it's best to copy it out asap just in case
-        // otherwise other code that is using localtime may break this (not just python code)
-        std::tm localtime = *std::localtime(&tt);
 
+        std::tm localtime;
+        std::tm *localtime_ptr = localtime_thread_safe(&tt, &localtime);
+        if (!localtime_ptr)
+            throw cast_error("Unable to represent system_clock in local time");
         return PyDateTime_FromDateAndTime(localtime.tm_year + 1900,
                                           localtime.tm_mon + 1,
                                           localtime.tm_mday,
@@ -173,7 +193,7 @@ public:
                                           localtime.tm_sec,
                                           us.count());
     }
-    PYBIND11_TYPE_CASTER(type, _("datetime.datetime"));
+    PYBIND11_TYPE_CASTER(type, const_name("datetime.datetime"));
 };
 
 // Other clocks that are not the system clock are not measured as datetime.datetime objects

wrap/pybind11/include/pybind11/complex.h

@@ -59,7 +59,7 @@ public:
         return PyComplex_FromDoubles((double) src.real(), (double) src.imag());
     }
 
-    PYBIND11_TYPE_CASTER(std::complex<T>, _("complex"));
+    PYBIND11_TYPE_CASTER(std::complex<T>, const_name("complex"));
 };
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/detail/class.h

@@ -24,6 +24,18 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 #  define PYBIND11_SET_OLDPY_QUALNAME(obj, nameobj) setattr((PyObject *) obj, "__qualname__", nameobj)
 #endif
 
+inline std::string get_fully_qualified_tp_name(PyTypeObject *type) {
+#if !defined(PYPY_VERSION)
+    return type->tp_name;
+#else
+    auto module_name = handle((PyObject *) type).attr("__module__").cast<std::string>();
+    if (module_name == PYBIND11_BUILTINS_MODULE)
+        return type->tp_name;
+    else
+        return std::move(module_name) + "." + type->tp_name;
+#endif
+}
+
 inline PyTypeObject *type_incref(PyTypeObject *type) {
     Py_INCREF(type);
     return type;
@@ -117,8 +129,9 @@ extern "C" inline int pybind11_meta_setattro(PyObject* obj, PyObject* name, PyOb
     //   2. `Type.static_prop = other_static_prop` --> setattro:  replace existing `static_prop`
     //   3. `Type.regular_attribute = value`       --> setattro:  regular attribute assignment
     const auto static_prop = (PyObject *) get_internals().static_property_type;
-    const auto call_descr_set = descr && PyObject_IsInstance(descr, static_prop)
+    const auto call_descr_set = (descr != nullptr) && (value != nullptr)
-                                && !PyObject_IsInstance(value, static_prop);
+                                && (PyObject_IsInstance(descr, static_prop) != 0)
+                                && (PyObject_IsInstance(value, static_prop) == 0);
     if (call_descr_set) {
         // Call `static_property.__set__()` instead of replacing the `static_property`.
 #if !defined(PYPY_VERSION)
@@ -150,9 +163,7 @@ extern "C" inline PyObject *pybind11_meta_getattro(PyObject *obj, PyObject *name
         Py_INCREF(descr);
         return descr;
     }
-    else {
     return PyType_Type.tp_getattro(obj, name);
-    }
 }
 #endif
 
@@ -172,7 +183,7 @@ extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, P
     for (const auto &vh : values_and_holders(instance)) {
         if (!vh.holder_constructed()) {
             PyErr_Format(PyExc_TypeError, "%.200s.__init__() must be called when overriding __init__",
-                         vh.type->type->tp_name);
+                         get_fully_qualified_tp_name(vh.type->type).c_str());
             Py_DECREF(self);
             return nullptr;
         }
@@ -181,6 +192,44 @@ extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, P
     return self;
 }
 
+/// Cleanup the type-info for a pybind11-registered type.
+extern "C" inline void pybind11_meta_dealloc(PyObject *obj) {
+    auto *type = (PyTypeObject *) obj;
+    auto &internals = get_internals();
+
+    // A pybind11-registered type will:
+    // 1) be found in internals.registered_types_py
+    // 2) have exactly one associated `detail::type_info`
+    auto found_type = internals.registered_types_py.find(type);
+    if (found_type != internals.registered_types_py.end() &&
+        found_type->second.size() == 1 &&
+        found_type->second[0]->type == type) {
+
+        auto *tinfo = found_type->second[0];
+        auto tindex = std::type_index(*tinfo->cpptype);
+        internals.direct_conversions.erase(tindex);
+
+        if (tinfo->module_local)
+            get_local_internals().registered_types_cpp.erase(tindex);
+        else
+            internals.registered_types_cpp.erase(tindex);
+        internals.registered_types_py.erase(tinfo->type);
+
+        // Actually just `std::erase_if`, but that's only available in C++20
+        auto &cache = internals.inactive_override_cache;
+        for (auto it = cache.begin(), last = cache.end(); it != last; ) {
+            if (it->first == (PyObject *) tinfo->type)
+                it = cache.erase(it);
+            else
+                ++it;
+        }
+
+        delete tinfo;
+    }
+
+    PyType_Type.tp_dealloc(obj);
+}
+
 /** This metaclass is assigned by default to all pybind11 types and is required in order
     for static properties to function correctly. Users may override this using `py::metaclass`.
     Return value: New reference. */
@@ -213,6 +262,8 @@ inline PyTypeObject* make_default_metaclass() {
     type->tp_getattro = pybind11_meta_getattro;
 #endif
 
+    type->tp_dealloc = pybind11_meta_dealloc;
+
     if (PyType_Ready(type) < 0)
         pybind11_fail("make_default_metaclass(): failure in PyType_Ready()!");
 
@@ -250,7 +301,7 @@ inline bool deregister_instance_impl(void *ptr, instance *self) {
     auto &registered_instances = get_internals().registered_instances;
     auto range = registered_instances.equal_range(ptr);
     for (auto it = range.first; it != range.second; ++it) {
-        if (Py_TYPE(self) == Py_TYPE(it->second)) {
+        if (self == it->second) {
             registered_instances.erase(it);
             return true;
         }
@@ -277,7 +328,7 @@ inline bool deregister_instance(instance *self, void *valptr, const type_info *t
 inline PyObject *make_new_instance(PyTypeObject *type) {
 #if defined(PYPY_VERSION)
     // PyPy gets tp_basicsize wrong (issue 2482) under multiple inheritance when the first inherited
-    // object is a a plain Python type (i.e. not derived from an extension type).  Fix it.
+    // object is a plain Python type (i.e. not derived from an extension type).  Fix it.
     ssize_t instance_size = static_cast<ssize_t>(sizeof(instance));
     if (type->tp_basicsize < instance_size) {
         type->tp_basicsize = instance_size;
@@ -288,8 +339,6 @@ inline PyObject *make_new_instance(PyTypeObject *type) {
     // Allocate the value/holder internals:
     inst->allocate_layout();
 
-    inst->owned = true;
-
     return self;
 }
 
@@ -304,12 +353,7 @@ extern "C" inline PyObject *pybind11_object_new(PyTypeObject *type, PyObject *,
 /// following default function will be used which simply throws an exception.
 extern "C" inline int pybind11_object_init(PyObject *self, PyObject *, PyObject *) {
     PyTypeObject *type = Py_TYPE(self);
-    std::string msg;
+    std::string msg = get_fully_qualified_tp_name(type) + ": No constructor defined!";
-#if defined(PYPY_VERSION)
-    msg += handle((PyObject *) type).attr("__module__").cast<std::string>() + ".";
-#endif
-    msg += type->tp_name;
-    msg += ": No constructor defined!";
     PyErr_SetString(PyExc_TypeError, msg.c_str());
     return -1;
 }
@@ -448,7 +492,7 @@ extern "C" inline PyObject *pybind11_get_dict(PyObject *self, void *) {
 extern "C" inline int pybind11_set_dict(PyObject *self, PyObject *new_dict, void *) {
     if (!PyDict_Check(new_dict)) {
         PyErr_Format(PyExc_TypeError, "__dict__ must be set to a dictionary, not a '%.200s'",
-                     Py_TYPE(new_dict)->tp_name);
+                     get_fully_qualified_tp_name(Py_TYPE(new_dict)).c_str());
         return -1;
     }
     PyObject *&dict = *_PyObject_GetDictPtr(self);
@@ -475,11 +519,6 @@ extern "C" inline int pybind11_clear(PyObject *self) {
 /// Give instances of this type a `__dict__` and opt into garbage collection.
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     auto type = &heap_type->ht_type;
-#if defined(PYPY_VERSION) && (PYPY_VERSION_NUM < 0x06000000)
-    pybind11_fail(std::string(type->tp_name) + ": dynamic attributes are "
-                                               "currently not supported in "
-                                               "conjunction with PyPy!");
-#endif
     type->tp_flags |= Py_TPFLAGS_HAVE_GC;
     type->tp_dictoffset = type->tp_basicsize; // place dict at the end
     type->tp_basicsize += (ssize_t)sizeof(PyObject *); // and allocate enough space for it
@@ -510,6 +549,12 @@ extern "C" inline int pybind11_getbuffer(PyObject *obj, Py_buffer *view, int fla
     }
     std::memset(view, 0, sizeof(Py_buffer));
     buffer_info *info = tinfo->get_buffer(obj, tinfo->get_buffer_data);
+    if ((flags & PyBUF_WRITABLE) == PyBUF_WRITABLE && info->readonly) {
+        delete info;
+        // view->obj = nullptr;  // Was just memset to 0, so not necessary
+        PyErr_SetString(PyExc_BufferError, "Writable buffer requested for readonly storage");
+        return -1;
+    }
     view->obj = obj;
     view->ndim = 1;
     view->internal = info;
@@ -518,13 +563,7 @@ extern "C" inline int pybind11_getbuffer(PyObject *obj, Py_buffer *view, int fla
     view->len = view->itemsize;
     for (auto s : info->shape)
         view->len *= s;
-    view->readonly = info->readonly;
+    view->readonly = static_cast<int>(info->readonly);
-    if ((flags & PyBUF_WRITABLE) == PyBUF_WRITABLE && info->readonly) {
-        if (view)
-            view->obj = nullptr;
-        PyErr_SetString(PyExc_BufferError, "Writable buffer requested for readonly storage");
-        return -1;
-    }
     if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT)
         view->format = const_cast<char *>(info->format.c_str());
     if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {
@@ -567,17 +606,17 @@ inline PyObject* make_new_python_type(const type_record &rec) {
 #endif
     }
 
-    object module;
+    object module_;
     if (rec.scope) {
         if (hasattr(rec.scope, "__module__"))
-            module = rec.scope.attr("__module__");
+            module_ = rec.scope.attr("__module__");
         else if (hasattr(rec.scope, "__name__"))
-            module = rec.scope.attr("__name__");
+            module_ = rec.scope.attr("__name__");
     }
 
     auto full_name = c_str(
 #if !defined(PYPY_VERSION)
-        module ? str(module).cast<std::string>() + "." + rec.name :
+        module_ ? str(module_).cast<std::string>() + "." + rec.name :
 #endif
         rec.name);
 
@@ -585,9 +624,9 @@ inline PyObject* make_new_python_type(const type_record &rec) {
     if (rec.doc && options::show_user_defined_docstrings()) {
         /* Allocate memory for docstring (using PyObject_MALLOC, since
            Python will free this later on) */
-        size_t size = strlen(rec.doc) + 1;
+        size_t size = std::strlen(rec.doc) + 1;
         tp_doc = (char *) PyObject_MALLOC(size);
-        memcpy((void *) tp_doc, rec.doc, size);
+        std::memcpy((void *) tp_doc, rec.doc, size);
     }
 
     auto &internals = get_internals();
@@ -644,11 +683,13 @@ inline PyObject* make_new_python_type(const type_record &rec) {
     if (rec.buffer_protocol)
         enable_buffer_protocol(heap_type);
 
+    if (rec.custom_type_setup_callback)
+        rec.custom_type_setup_callback(heap_type);
+
     if (PyType_Ready(type) < 0)
         pybind11_fail(std::string(rec.name) + ": PyType_Ready failed (" + error_string() + ")!");
 
-    assert(rec.dynamic_attr ? PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC)
+    assert(!rec.dynamic_attr || PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
-                            : !PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
 
     /* Register type with the parent scope */
     if (rec.scope)
@@ -656,8 +697,8 @@ inline PyObject* make_new_python_type(const type_record &rec) {
     else
         Py_INCREF(type); // Keep it alive forever (reference leak)
 
-    if (module) // Needed by pydoc
+    if (module_) // Needed by pydoc
-        setattr((PyObject *) type, "__module__", module);
+        setattr((PyObject *) type, "__module__", module_);
 
     PYBIND11_SET_OLDPY_QUALNAME(type, qualname);
 

wrap/pybind11/include/pybind11/detail/common.h

@@ -10,8 +10,12 @@
 #pragma once
 
 #define PYBIND11_VERSION_MAJOR 2
-#define PYBIND11_VERSION_MINOR 6
+#define PYBIND11_VERSION_MINOR 9
-#define PYBIND11_VERSION_PATCH 0.dev1
+#define PYBIND11_VERSION_PATCH 1
+
+// Similar to Python's convention: https://docs.python.org/3/c-api/apiabiversion.html
+// Additional convention: 0xD = dev
+#define PYBIND11_VERSION_HEX 0x02090100
 
 #define PYBIND11_NAMESPACE_BEGIN(name) namespace name {
 #define PYBIND11_NAMESPACE_END(name) }
@@ -27,11 +31,14 @@
 #  endif
 #endif
 
-#if !(defined(_MSC_VER) && __cplusplus == 199711L) && !defined(__INTEL_COMPILER)
+#if !(defined(_MSC_VER) && __cplusplus == 199711L)
 #  if __cplusplus >= 201402L
 #    define PYBIND11_CPP14
 #    if __cplusplus >= 201703L
 #      define PYBIND11_CPP17
+#      if __cplusplus >= 202002L
+#        define PYBIND11_CPP20
+#      endif
 #    endif
 #  endif
 #elif defined(_MSC_VER) && __cplusplus == 199711L
@@ -41,15 +48,23 @@
 #    define PYBIND11_CPP14
 #    if _MSVC_LANG > 201402L && _MSC_VER >= 1910
 #      define PYBIND11_CPP17
+#      if _MSVC_LANG >= 202002L
+#        define PYBIND11_CPP20
+#      endif
 #    endif
 #  endif
 #endif
 
 // Compiler version assertions
 #if defined(__INTEL_COMPILER)
-#  if __INTEL_COMPILER < 1700
+#  if __INTEL_COMPILER < 1800
-#    error pybind11 requires Intel C++ compiler v17 or newer
+#    error pybind11 requires Intel C++ compiler v18 or newer
+#  elif __INTEL_COMPILER < 1900 && defined(PYBIND11_CPP14)
+#    error pybind11 supports only C++11 with Intel C++ compiler v18. Use v19 or newer for C++14.
 #  endif
+/* The following pragma cannot be pop'ed:
+   https://community.intel.com/t5/Intel-C-Compiler/Inline-and-no-inline-warning/td-p/1216764 */
+#  pragma warning disable 2196 // warning #2196: routine is both "inline" and "noinline"
 #elif defined(__clang__) && !defined(__apple_build_version__)
 #  if __clang_major__ < 3 || (__clang_major__ == 3 && __clang_minor__ < 3)
 #    error pybind11 requires clang 3.3 or newer
@@ -80,13 +95,43 @@
 #  endif
 #endif
 
-#if defined(_MSC_VER)
+#if !defined(PYBIND11_EXPORT_EXCEPTION)
-#  define PYBIND11_NOINLINE __declspec(noinline)
+#  ifdef __MINGW32__
-#else
+// workaround for:
-#  define PYBIND11_NOINLINE __attribute__ ((noinline))
+// error: 'dllexport' implies default visibility, but xxx has already been declared with a different visibility
+#    define PYBIND11_EXPORT_EXCEPTION
+#  else
+#    define PYBIND11_EXPORT_EXCEPTION PYBIND11_EXPORT
+#  endif
 #endif
 
-#if defined(PYBIND11_CPP14)
+// For CUDA, GCC7, GCC8:
+// PYBIND11_NOINLINE_FORCED is incompatible with `-Wattributes -Werror`.
+// When defining PYBIND11_NOINLINE_FORCED, it is best to also use `-Wno-attributes`.
+// However, the measured shared-library size saving when using noinline are only
+// 1.7% for CUDA, -0.2% for GCC7, and 0.0% for GCC8 (using -DCMAKE_BUILD_TYPE=MinSizeRel,
+// the default under pybind11/tests).
+#if !defined(PYBIND11_NOINLINE_FORCED) && \
+    (defined(__CUDACC__) || (defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8)))
+#  define PYBIND11_NOINLINE_DISABLED
+#endif
+
+// The PYBIND11_NOINLINE macro is for function DEFINITIONS.
+// In contrast, FORWARD DECLARATIONS should never use this macro:
+// https://stackoverflow.com/questions/9317473/forward-declaration-of-inline-functions
+#if defined(PYBIND11_NOINLINE_DISABLED) // Option for maximum portability and experimentation.
+#  define PYBIND11_NOINLINE inline
+#elif defined(_MSC_VER)
+#  define PYBIND11_NOINLINE __declspec(noinline) inline
+#else
+#  define PYBIND11_NOINLINE __attribute__ ((noinline)) inline
+#endif
+
+#if defined(__MINGW32__)
+// For unknown reasons all PYBIND11_DEPRECATED member trigger a warning when declared
+// whether it is used or not
+#  define PYBIND11_DEPRECATED(reason)
+#elif defined(PYBIND11_CPP14)
 #  define PYBIND11_DEPRECATED(reason) [[deprecated(reason)]]
 #else
 #  define PYBIND11_DEPRECATED(reason) __attribute__((deprecated(reason)))
@@ -112,13 +157,61 @@
 #    define HAVE_ROUND 1
 #  endif
 #  pragma warning(push)
-#  pragma warning(disable: 4510 4610 4512 4005)
+// C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
+#  pragma warning(disable: 4505)
 #  if defined(_DEBUG) && !defined(Py_DEBUG)
+// Workaround for a VS 2022 issue.
+// NOTE: This workaround knowingly violates the Python.h include order requirement:
+// https://docs.python.org/3/c-api/intro.html#include-files
+// See https://github.com/pybind/pybind11/pull/3497 for full context.
+#    include <yvals.h>
+#    if _MSVC_STL_VERSION >= 143
+#      include <crtdefs.h>
+#    endif
 #    define PYBIND11_DEBUG_MARKER
 #    undef _DEBUG
 #  endif
 #endif
 
+// https://en.cppreference.com/w/c/chrono/localtime
+#if defined(__STDC_LIB_EXT1__) && !defined(__STDC_WANT_LIB_EXT1__)
+#  define __STDC_WANT_LIB_EXT1__
+#endif
+
+#ifdef __has_include
+// std::optional (but including it in c++14 mode isn't allowed)
+#  if defined(PYBIND11_CPP17) && __has_include(<optional>)
+#    define PYBIND11_HAS_OPTIONAL 1
+#  endif
+// std::experimental::optional (but not allowed in c++11 mode)
+#  if defined(PYBIND11_CPP14) && (__has_include(<experimental/optional>) && \
+                                 !__has_include(<optional>))
+#    define PYBIND11_HAS_EXP_OPTIONAL 1
+#  endif
+// std::variant
+#  if defined(PYBIND11_CPP17) && __has_include(<variant>)
+#    define PYBIND11_HAS_VARIANT 1
+#  endif
+#elif defined(_MSC_VER) && defined(PYBIND11_CPP17)
+#  define PYBIND11_HAS_OPTIONAL 1
+#  define PYBIND11_HAS_VARIANT 1
+#endif
+
+#if defined(PYBIND11_CPP17)
+#  if defined(__has_include)
+#    if __has_include(<string_view>)
+#      define PYBIND11_HAS_STRING_VIEW
+#    endif
+#  elif defined(_MSC_VER)
+#    define PYBIND11_HAS_STRING_VIEW
+#  endif
+#endif
+
+#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
+#  define PYBIND11_HAS_U8STRING
+#endif
+
+
 #include <Python.h>
 #include <frameobject.h>
 #include <pythread.h>
@@ -160,6 +253,24 @@
 #include <memory>
 #include <typeindex>
 #include <type_traits>
+#if defined(__has_include)
+#  if __has_include(<version>)
+#    include <version>
+#  endif
+#endif
+
+// #define PYBIND11_STR_LEGACY_PERMISSIVE
+// If DEFINED, pybind11::str can hold PyUnicodeObject or PyBytesObject
+//             (probably surprising and never documented, but this was the
+//             legacy behavior until and including v2.6.x). As a side-effect,
+//             pybind11::isinstance<str>() is true for both pybind11::str and
+//             pybind11::bytes.
+// If UNDEFINED, pybind11::str can only hold PyUnicodeObject, and
+//               pybind11::isinstance<str>() is true only for pybind11::str.
+//               However, for Python 2 only (!), the pybind11::str caster
+//               implicitly decodes bytes to PyUnicodeObject. This is to ease
+//               the transition from the legacy behavior to the non-permissive
+//               behavior.
 
 #if PY_MAJOR_VERSION >= 3 /// Compatibility macros for various Python versions
 #define PYBIND11_INSTANCE_METHOD_NEW(ptr, class_) PyInstanceMethod_New(ptr)
@@ -173,8 +284,8 @@
 #define PYBIND11_BYTES_SIZE PyBytes_Size
 #define PYBIND11_LONG_CHECK(o) PyLong_Check(o)
 #define PYBIND11_LONG_AS_LONGLONG(o) PyLong_AsLongLong(o)
-#define PYBIND11_LONG_FROM_SIGNED(o) PyLong_FromSsize_t((ssize_t) o)
+#define PYBIND11_LONG_FROM_SIGNED(o) PyLong_FromSsize_t((ssize_t) (o))
-#define PYBIND11_LONG_FROM_UNSIGNED(o) PyLong_FromSize_t((size_t) o)
+#define PYBIND11_LONG_FROM_UNSIGNED(o) PyLong_FromSize_t((size_t) (o))
 #define PYBIND11_BYTES_NAME "bytes"
 #define PYBIND11_STRING_NAME "str"
 #define PYBIND11_SLICE_OBJECT PyObject
@@ -182,6 +293,7 @@
 #define PYBIND11_STR_TYPE ::pybind11::str
 #define PYBIND11_BOOL_ATTR "__bool__"
 #define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_bool)
+#define PYBIND11_BUILTINS_MODULE "builtins"
 // Providing a separate declaration to make Clang's -Wmissing-prototypes happy.
 // See comment for PYBIND11_MODULE below for why this is marked "maybe unused".
 #define PYBIND11_PLUGIN_IMPL(name) \
@@ -209,6 +321,7 @@
 #define PYBIND11_STR_TYPE ::pybind11::bytes
 #define PYBIND11_BOOL_ATTR "__nonzero__"
 #define PYBIND11_NB_BOOL(ptr) ((ptr)->nb_nonzero)
+#define PYBIND11_BUILTINS_MODULE "__builtin__"
 // Providing a separate PyInit decl to make Clang's -Wmissing-prototypes happy.
 // See comment for PYBIND11_MODULE below for why this is marked "maybe unused".
 #define PYBIND11_PLUGIN_IMPL(name) \
@@ -250,6 +363,19 @@ extern "C" {
         }                                                                      \
     }
 
+#if PY_VERSION_HEX >= 0x03030000
+
+#define PYBIND11_CATCH_INIT_EXCEPTIONS \
+        catch (pybind11::error_already_set &e) {                                 \
+            pybind11::raise_from(e, PyExc_ImportError, "initialization failed"); \
+            return nullptr;                                                      \
+        } catch (const std::exception &e) {                                      \
+            PyErr_SetString(PyExc_ImportError, e.what());                        \
+            return nullptr;                                                      \
+        }                                                                        \
+
+#else
+
 #define PYBIND11_CATCH_INIT_EXCEPTIONS \
         catch (pybind11::error_already_set &e) {                               \
             PyErr_SetString(PyExc_ImportError, e.what());                      \
@@ -259,17 +385,19 @@ extern "C" {
             return nullptr;                                                    \
         }                                                                      \
 
+#endif
+
 /** \rst
     ***Deprecated in favor of PYBIND11_MODULE***
 
     This macro creates the entry point that will be invoked when the Python interpreter
-    imports a plugin library. Please create a `module` in the function body and return
+    imports a plugin library. Please create a `module_` in the function body and return
     the pointer to its underlying Python object at the end.
 
     .. code-block:: cpp
 
         PYBIND11_PLUGIN(example) {
-            pybind11::module m("example", "pybind11 example plugin");
+            pybind11::module_ m("example", "pybind11 example plugin");
             /// Set up bindings here
             return m.ptr();
         }
@@ -290,7 +418,7 @@ extern "C" {
     This macro creates the entry point that will be invoked when the Python interpreter
     imports an extension module. The module name is given as the fist argument and it
     should not be in quotes. The second macro argument defines a variable of type
-    `py::module` which can be used to initialize the module.
+    `py::module_` which can be used to initialize the module.
 
     The entry point is marked as "maybe unused" to aid dead-code detection analysis:
     since the entry point is typically only looked up at runtime and not referenced
@@ -308,25 +436,34 @@ extern "C" {
         }
 \endrst */
 #define PYBIND11_MODULE(name, variable)                                                           \
+    static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name)            \
+        PYBIND11_MAYBE_UNUSED;                                                                    \
     PYBIND11_MAYBE_UNUSED                                                                         \
-    static void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &);     \
+    static void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ &);                     \
     PYBIND11_PLUGIN_IMPL(name) {                                                                  \
         PYBIND11_CHECK_PYTHON_VERSION                                                             \
         PYBIND11_ENSURE_INTERNALS_READY                                                           \
-        auto m = pybind11::module(PYBIND11_TOSTRING(name));                    \
+        auto m = ::pybind11::module_::create_extension_module(                                    \
+            PYBIND11_TOSTRING(name), nullptr, &PYBIND11_CONCAT(pybind11_module_def_, name));      \
         try {                                                                                     \
             PYBIND11_CONCAT(pybind11_init_, name)(m);                                             \
             return m.ptr();                                                                       \
-        } PYBIND11_CATCH_INIT_EXCEPTIONS                                       \
         }                                                                                         \
-    void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &variable)
+        PYBIND11_CATCH_INIT_EXCEPTIONS                                                            \
-
+    }                                                                                             \
+    void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ & (variable))
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 using ssize_t = Py_ssize_t;
 using size_t  = std::size_t;
 
+template <typename IntType>
+inline ssize_t ssize_t_cast(const IntType &val) {
+    static_assert(sizeof(IntType) <= sizeof(ssize_t), "Implicit narrowing is not permitted.");
+    return static_cast<ssize_t>(val);
+}
+
 /// Approach used to cast a previously unknown C++ instance into a Python object
 enum class return_value_policy : uint8_t {
     /** This is the default return value policy, which falls back to the policy
@@ -481,6 +618,18 @@ template <typename T> using remove_cv_t = typename std::remove_cv<T>::type;
 template <typename T> using remove_reference_t = typename std::remove_reference<T>::type;
 #endif
 
+#if defined(PYBIND11_CPP20)
+using std::remove_cvref;
+using std::remove_cvref_t;
+#else
+template <class T>
+struct remove_cvref {
+    using type = remove_cv_t<remove_reference_t<T>>;
+};
+template <class T>
+using remove_cvref_t = typename remove_cvref<T>::type;
+#endif
+
 /// Index sequences
 #if defined(PYBIND11_CPP14)
 using std::index_sequence;
@@ -488,7 +637,7 @@ using std::make_index_sequence;
 #else
 template<size_t ...> struct index_sequence  { };
 template<size_t N, size_t ...S> struct make_index_sequence_impl : make_index_sequence_impl <N - 1, N - 1, S...> { };
-template<size_t ...S> struct make_index_sequence_impl <0, S...> { typedef index_sequence<S...> type; };
+template<size_t ...S> struct make_index_sequence_impl <0, S...> { using type = index_sequence<S...>; };
 template<size_t N> using make_index_sequence = typename make_index_sequence_impl<N>::type;
 #endif
 
@@ -502,10 +651,10 @@ template <bool... Bs> using select_indices = typename select_indices_impl<index_
 template <bool B> using bool_constant = std::integral_constant<bool, B>;
 template <typename T> struct negation : bool_constant<!T::value> { };
 
-// PGI cannot detect operator delete with the "compatible" void_t impl, so
+// PGI/Intel cannot detect operator delete with the "compatible" void_t impl, so
 // using the new one (C++14 defect, so generally works on newer compilers, even
 // if not in C++17 mode)
-#if defined(__PGIC__)
+#if defined(__PGIC__) || defined(__INTEL_COMPILER)
 template<typename... > using void_t = void;
 #else
 template <typename...> struct void_t_impl { using type = void; };
@@ -618,8 +767,9 @@ template <typename Base, typename Derived> using is_strict_base_of = bool_consta
 
 /// Like is_base_of, but also requires that the base type is accessible (i.e. that a Derived pointer
 /// can be converted to a Base pointer)
+/// For unions, `is_base_of<T, T>::value` is False, so we need to check `is_same` as well.
 template <typename Base, typename Derived> using is_accessible_base_of = bool_constant<
-    std::is_base_of<Base, Derived>::value && std::is_convertible<Derived *, Base *>::value>;
+    (std::is_same<Base, Derived>::value || std::is_base_of<Base, Derived>::value) && std::is_convertible<Derived *, Base *>::value>;
 
 template <template<typename...> class Base>
 struct is_template_base_of_impl {
@@ -656,6 +806,10 @@ template <typename T> using is_function_pointer = bool_constant<
     std::is_pointer<T>::value && std::is_function<typename std::remove_pointer<T>::type>::value>;
 
 template <typename F> struct strip_function_object {
+    // If you are encountering an
+    // 'error: name followed by "::" must be a class or namespace name'
+    // with the Intel compiler and a noexcept function here,
+    // try to use noexcept(true) instead of plain noexcept.
     using type = typename remove_class<decltype(&F::operator())>::type;
 };
 
@@ -677,11 +831,10 @@ using function_signature_t = conditional_t<
 template <typename T> using is_lambda = satisfies_none_of<remove_reference_t<T>,
         std::is_function, std::is_pointer, std::is_member_pointer>;
 
-/// Ignore that a variable is unused in compiler warnings
+// [workaround(intel)] Internal error on fold expression
-inline void ignore_unused(const int *) { }
-
 /// Apply a function over each element of a parameter pack
-#ifdef __cpp_fold_expressions
+#if defined(__cpp_fold_expressions) && !defined(__INTEL_COMPILER)
+// Intel compiler produces an internal error on this fold expression (tested with ICC 19.0.2)
 #define PYBIND11_EXPAND_SIDE_EFFECTS(PATTERN) (((PATTERN), void()), ...)
 #else
 using expand_side_effects = bool[];
@@ -690,16 +843,23 @@ using expand_side_effects = bool[];
 
 PYBIND11_NAMESPACE_END(detail)
 
+#if defined(_MSC_VER)
+#  pragma warning(push)
+#  pragma warning(disable: 4275) // warning C4275: An exported class was derived from a class that wasn't exported. Can be ignored when derived from a STL class.
+#endif
 /// C++ bindings of builtin Python exceptions
-class builtin_exception : public std::runtime_error {
+class PYBIND11_EXPORT_EXCEPTION builtin_exception : public std::runtime_error {
 public:
     using std::runtime_error::runtime_error;
     /// Set the error using the Python C API
     virtual void set_error() const = 0;
 };
+#if defined(_MSC_VER)
+#  pragma warning(pop)
+#endif
 
 #define PYBIND11_RUNTIME_EXCEPTION(name, type) \
-    class name : public builtin_exception { public: \
+    class PYBIND11_EXPORT_EXCEPTION name : public builtin_exception { public: \
         using builtin_exception::builtin_exception; \
         name() : name("") { } \
         void set_error() const override { PyErr_SetString(type, what()); } \
@@ -712,11 +872,12 @@ PYBIND11_RUNTIME_EXCEPTION(value_error, PyExc_ValueError)
 PYBIND11_RUNTIME_EXCEPTION(type_error, PyExc_TypeError)
 PYBIND11_RUNTIME_EXCEPTION(buffer_error, PyExc_BufferError)
 PYBIND11_RUNTIME_EXCEPTION(import_error, PyExc_ImportError)
+PYBIND11_RUNTIME_EXCEPTION(attribute_error, PyExc_AttributeError)
 PYBIND11_RUNTIME_EXCEPTION(cast_error, PyExc_RuntimeError) /// Thrown when pybind11::cast or handle::call fail due to a type casting error
 PYBIND11_RUNTIME_EXCEPTION(reference_cast_error, PyExc_RuntimeError) /// Used internally
 
-[[noreturn]] PYBIND11_NOINLINE inline void pybind11_fail(const char *reason) { throw std::runtime_error(reason); }
+[[noreturn]] PYBIND11_NOINLINE void pybind11_fail(const char *reason) { throw std::runtime_error(reason); }
-[[noreturn]] PYBIND11_NOINLINE inline void pybind11_fail(const std::string &reason) { throw std::runtime_error(reason); }
+[[noreturn]] PYBIND11_NOINLINE void pybind11_fail(const std::string &reason) { throw std::runtime_error(reason); }
 
 template <typename T, typename SFINAE = void> struct format_descriptor { };
 
@@ -761,7 +922,8 @@ struct nodelete { template <typename T> void operator()(T*) { } };
 PYBIND11_NAMESPACE_BEGIN(detail)
 template <typename... Args>
 struct overload_cast_impl {
-    constexpr overload_cast_impl() {}; // NOLINT(modernize-use-equals-default):  MSVC 2015 needs this
+    // NOLINTNEXTLINE(modernize-use-equals-default):  MSVC 2015 needs this
+    constexpr overload_cast_impl() {}
 
     template <typename Return>
     constexpr auto operator()(Return (*pf)(Args...)) const noexcept
@@ -817,6 +979,7 @@ public:
 
     // Implicit conversion constructor from any arbitrary container type with values convertible to T
     template <typename Container, typename = enable_if_t<std::is_convertible<decltype(*std::begin(std::declval<const Container &>())), T>::value>>
+    // NOLINTNEXTLINE(google-explicit-constructor)
     any_container(const Container &c) : any_container(std::begin(c), std::end(c)) { }
 
     // initializer_list's aren't deducible, so don't get matched by the above template; we need this
@@ -825,9 +988,11 @@ public:
     any_container(const std::initializer_list<TIn> &c) : any_container(c.begin(), c.end()) { }
 
     // Avoid copying if given an rvalue vector of the correct type.
+    // NOLINTNEXTLINE(google-explicit-constructor)
     any_container(std::vector<T> &&v) : v(std::move(v)) { }
 
     // Moves the vector out of an rvalue any_container
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator std::vector<T> &&() && { return std::move(v); }
 
     // Dereferencing obtains a reference to the underlying vector
@@ -839,8 +1004,60 @@ public:
     const std::vector<T> *operator->() const { return &v; }
 };
 
+// Forward-declaration; see detail/class.h
+std::string get_fully_qualified_tp_name(PyTypeObject*);
+
+template <typename T>
+inline static std::shared_ptr<T> try_get_shared_from_this(std::enable_shared_from_this<T> *holder_value_ptr) {
+// Pre C++17, this code path exploits undefined behavior, but is known to work on many platforms.
+// Use at your own risk!
+// See also https://en.cppreference.com/w/cpp/memory/enable_shared_from_this, and in particular
+// the `std::shared_ptr<Good> gp1 = not_so_good.getptr();` and `try`-`catch` parts of the example.
+#if defined(__cpp_lib_enable_shared_from_this) && (!defined(_MSC_VER) || _MSC_VER >= 1912)
+    return holder_value_ptr->weak_from_this().lock();
+#else
+    try {
+        return holder_value_ptr->shared_from_this();
+    }
+    catch (const std::bad_weak_ptr &) {
+        return nullptr;
+    }
+#endif
+}
+
+// For silencing "unused" compiler warnings in special situations.
+template <typename... Args>
+#if defined(_MSC_VER) && _MSC_VER >= 1910 && _MSC_VER < 1920 // MSVC 2017
+constexpr
+#endif
+inline void silence_unused_warnings(Args &&...) {}
+
+// MSVC warning C4100: Unreferenced formal parameter
+#if defined(_MSC_VER) && _MSC_VER <= 1916
+#    define PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(...)                                         \
+        detail::silence_unused_warnings(__VA_ARGS__)
+#else
+#    define PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(...)
+#endif
+
+// GCC -Wunused-but-set-parameter  All GCC versions (as of July 2021).
+#if defined(__GNUG__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
+#    define PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(...)                   \
+        detail::silence_unused_warnings(__VA_ARGS__)
+#else
+#    define PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(...)
+#endif
+
+#if defined(_MSC_VER) // All versions (as of July 2021).
+
+// warning C4127: Conditional expression is constant
+constexpr inline bool silence_msvc_c4127(bool cond) { return cond; }
+
+#    define PYBIND11_SILENCE_MSVC_C4127(...) ::pybind11::detail::silence_msvc_c4127(__VA_ARGS__)
+
+#else
+#    define PYBIND11_SILENCE_MSVC_C4127(...) __VA_ARGS__
+#endif
+
 PYBIND11_NAMESPACE_END(detail)
-
-
-
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/detail/descr.h

@@ -23,15 +23,17 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 /* Concatenate type signatures at compile time */
 template <size_t N, typename... Ts>
 struct descr {
-    char text[N + 1];
+    char text[N + 1]{'\0'};
 
-    constexpr descr() : text{'\0'} { }
+    constexpr descr() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor)
     constexpr descr(char const (&s)[N+1]) : descr(s, make_index_sequence<N>()) { }
 
     template <size_t... Is>
     constexpr descr(char const (&s)[N+1], index_sequence<Is...>) : text{s[Is]..., '\0'} { }
 
     template <typename... Chars>
+    // NOLINTNEXTLINE(google-explicit-constructor)
     constexpr descr(char c, Chars... cs) : text{c, static_cast<char>(cs)..., '\0'} { }
 
     static constexpr std::array<const std::type_info *, sizeof...(Ts) + 1> types() {
@@ -42,6 +44,7 @@ struct descr {
 template <size_t N1, size_t N2, typename... Ts1, typename... Ts2, size_t... Is1, size_t... Is2>
 constexpr descr<N1 + N2, Ts1..., Ts2...> plus_impl(const descr<N1, Ts1...> &a, const descr<N2, Ts2...> &b,
                                                    index_sequence<Is1...>, index_sequence<Is2...>) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(b);
     return {a.text[Is1]..., b.text[Is2]...};
 }
 
@@ -51,34 +54,64 @@ constexpr descr<N1 + N2, Ts1..., Ts2...> operator+(const descr<N1, Ts1...> &a, c
 }
 
 template <size_t N>
-constexpr descr<N - 1> _(char const(&text)[N]) { return descr<N - 1>(text); }
+constexpr descr<N - 1> const_name(char const(&text)[N]) { return descr<N - 1>(text); }
-constexpr descr<0> _(char const(&)[1]) { return {}; }
+constexpr descr<0> const_name(char const(&)[1]) { return {}; }
 
 template <size_t Rem, size_t... Digits> struct int_to_str : int_to_str<Rem/10, Rem%10, Digits...> { };
 template <size_t...Digits> struct int_to_str<0, Digits...> {
+    // WARNING: This only works with C++17 or higher.
     static constexpr auto digits = descr<sizeof...(Digits)>(('0' + Digits)...);
 };
 
 // Ternary description (like std::conditional)
 template <bool B, size_t N1, size_t N2>
-constexpr enable_if_t<B, descr<N1 - 1>> _(char const(&text1)[N1], char const(&)[N2]) {
+constexpr enable_if_t<B, descr<N1 - 1>> const_name(char const(&text1)[N1], char const(&)[N2]) {
-    return _(text1);
+    return const_name(text1);
 }
 template <bool B, size_t N1, size_t N2>
-constexpr enable_if_t<!B, descr<N2 - 1>> _(char const(&)[N1], char const(&text2)[N2]) {
+constexpr enable_if_t<!B, descr<N2 - 1>> const_name(char const(&)[N1], char const(&text2)[N2]) {
-    return _(text2);
+    return const_name(text2);
 }
 
 template <bool B, typename T1, typename T2>
-constexpr enable_if_t<B, T1> _(const T1 &d, const T2 &) { return d; }
+constexpr enable_if_t<B, T1> const_name(const T1 &d, const T2 &) { return d; }
 template <bool B, typename T1, typename T2>
-constexpr enable_if_t<!B, T2> _(const T1 &, const T2 &d) { return d; }
+constexpr enable_if_t<!B, T2> const_name(const T1 &, const T2 &d) { return d; }
 
-template <size_t Size> auto constexpr _() -> decltype(int_to_str<Size / 10, Size % 10>::digits) {
+template <size_t Size>
+auto constexpr const_name() -> remove_cv_t<decltype(int_to_str<Size / 10, Size % 10>::digits)> {
     return int_to_str<Size / 10, Size % 10>::digits;
 }
 
-template <typename Type> constexpr descr<1, Type> _() { return {'%'}; }
+template <typename Type> constexpr descr<1, Type> const_name() { return {'%'}; }
+
+// If "_" is defined as a macro, py::detail::_ cannot be provided.
+// It is therefore best to use py::detail::const_name universally.
+// This block is for backward compatibility only.
+// (The const_name code is repeated to avoid introducing a "_" #define ourselves.)
+#ifndef _
+#define PYBIND11_DETAIL_UNDERSCORE_BACKWARD_COMPATIBILITY
+template <size_t N>
+constexpr descr<N-1> _(char const(&text)[N]) { return const_name<N>(text); }
+template <bool B, size_t N1, size_t N2>
+constexpr enable_if_t<B, descr<N1 - 1>> _(char const(&text1)[N1], char const(&text2)[N2]) {
+    return const_name<B,N1,N2>(text1, text2);
+}
+template <bool B, size_t N1, size_t N2>
+constexpr enable_if_t<!B, descr<N2 - 1>> _(char const(&text1)[N1], char const(&text2)[N2]) {
+    return const_name<B,N1,N2>(text1, text2);
+}
+template <bool B, typename T1, typename T2>
+constexpr enable_if_t<B, T1> _(const T1 &d1, const T2 &d2) { return const_name<B,T1,T2>(d1, d2); }
+template <bool B, typename T1, typename T2>
+constexpr enable_if_t<!B, T2> _(const T1 &d1, const T2 &d2) { return const_name<B,T1,T2>(d1, d2); }
+
+template <size_t Size>
+auto constexpr _() -> remove_cv_t<decltype(int_to_str<Size / 10, Size % 10>::digits)> {
+    return const_name<Size>();
+}
+template <typename Type> constexpr descr<1, Type> _() { return const_name<Type>(); }
+#endif  // #ifndef _
 
 constexpr descr<0> concat() { return {}; }
 
@@ -88,12 +121,12 @@ constexpr descr<N, Ts...> concat(const descr<N, Ts...> &descr) { return descr; }
 template <size_t N, typename... Ts, typename... Args>
 constexpr auto concat(const descr<N, Ts...> &d, const Args &...args)
     -> decltype(std::declval<descr<N + 2, Ts...>>() + concat(args...)) {
-    return d + _(", ") + concat(args...);
+    return d + const_name(", ") + concat(args...);
 }
 
 template <size_t N, typename... Ts>
 constexpr descr<N + 2, Ts...> type_descr(const descr<N, Ts...> &descr) {
-    return _("{") + descr + _("}");
+    return const_name("{") + descr + const_name("}");
 }
 
 PYBIND11_NAMESPACE_END(detail)

wrap/pybind11/include/pybind11/detail/init.h

@@ -23,8 +23,8 @@ public:
     }
 
     template <typename> using cast_op_type = value_and_holder &;
-    operator value_and_holder &() { return *value; }
+    explicit operator value_and_holder &() { return *value; }
-    static constexpr auto name = _<value_and_holder>();
+    static constexpr auto name = const_name<value_and_holder>();
 
 private:
     value_and_holder *value = nullptr;
@@ -94,8 +94,9 @@ void construct(...) {
 // construct an Alias from the returned base instance.
 template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     no_nullptr(ptr);
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
         // We're going to try to construct an alias by moving the cpp type.  Whether or not
         // that succeeds, we still need to destroy the original cpp pointer (either the
         // moved away leftover, if the alias construction works, or the value itself if we
@@ -131,10 +132,11 @@ void construct(value_and_holder &v_h, Alias<Class> *alias_ptr, bool) {
 // derived type (through those holder's implicit conversion from derived class holder constructors).
 template <typename Class>
 void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     auto *ptr = holder_helper<Holder<Class>>::get(holder);
     no_nullptr(ptr);
     // If we need an alias, check that the held pointer is actually an alias instance
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr))
         throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
                          "is not an alias instance");
 
@@ -148,9 +150,10 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
 // need it, we simply move-construct the cpp value into a new instance.
 template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     static_assert(std::is_move_constructible<Cpp<Class>>::value,
         "pybind11::init() return-by-value factory function requires a movable class");
-    if (Class::has_alias && need_alias)
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias)
         construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
     else
         v_h.value_ptr() = new Cpp<Class>(std::move(result));
@@ -219,7 +222,8 @@ template <typename Func, typename Return, typename... Args>
 struct factory<Func, void_type (*)(), Return(Args...)> {
     remove_reference_t<Func> class_factory;
 
-    factory(Func &&f) : class_factory(std::forward<Func>(f)) { }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    factory(Func &&f) : class_factory(std::forward<Func>(f)) {}
 
     // The given class either has no alias or has no separate alias factory;
     // this always constructs the class itself.  If the class is registered with an alias
@@ -293,7 +297,13 @@ template <typename Class, typename T, typename O,
           enable_if_t<std::is_convertible<O, handle>::value, int> = 0>
 void setstate(value_and_holder &v_h, std::pair<T, O> &&result, bool need_alias) {
     construct<Class>(v_h, std::move(result.first), need_alias);
-    setattr((PyObject *) v_h.inst, "__dict__", result.second);
+    auto d = handle(result.second);
+    if (PyDict_Check(d.ptr()) && PyDict_Size(d.ptr()) == 0) {
+        // Skipping setattr below, to not force use of py::dynamic_attr() for Class unnecessarily.
+        // See PR #2972 for details.
+        return;
+    }
+    setattr((PyObject *) v_h.inst, "__dict__", d);
 }
 
 /// Implementation for py::pickle(GetState, SetState)

wrap/pybind11/include/pybind11/detail/internals.h

@@ -10,9 +10,32 @@
 #pragma once
 
 #include "../pytypes.h"
+#include <exception>
+
+/// Tracks the `internals` and `type_info` ABI version independent of the main library version.
+///
+/// Some portions of the code use an ABI that is conditional depending on this
+/// version number.  That allows ABI-breaking changes to be "pre-implemented".
+/// Once the default version number is incremented, the conditional logic that
+/// no longer applies can be removed.  Additionally, users that need not
+/// maintain ABI compatibility can increase the version number in order to take
+/// advantage of any functionality/efficiency improvements that depend on the
+/// newer ABI.
+///
+/// WARNING: If you choose to manually increase the ABI version, note that
+/// pybind11 may not be tested as thoroughly with a non-default ABI version, and
+/// further ABI-incompatible changes may be made before the ABI is officially
+/// changed to the new version.
+#ifndef PYBIND11_INTERNALS_VERSION
+#    define PYBIND11_INTERNALS_VERSION 4
+#endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+using ExceptionTranslator = void (*)(std::exception_ptr);
+
 PYBIND11_NAMESPACE_BEGIN(detail)
+
 // Forward declarations
 inline PyTypeObject *make_static_property_type();
 inline PyTypeObject *make_default_metaclass();
@@ -21,30 +44,59 @@ inline PyObject *make_object_base_type(PyTypeObject *metaclass);
 // The old Python Thread Local Storage (TLS) API is deprecated in Python 3.7 in favor of the new
 // Thread Specific Storage (TSS) API.
 #if PY_VERSION_HEX >= 0x03070000
-#    define PYBIND11_TLS_KEY_INIT(var) Py_tss_t *var = nullptr
+// Avoid unnecessary allocation of `Py_tss_t`, since we cannot use
+// `Py_LIMITED_API` anyway.
+#    if PYBIND11_INTERNALS_VERSION > 4
+#        define PYBIND11_TLS_KEY_REF Py_tss_t &
+#        ifdef __GNUC__
+// Clang on macOS warns due to `Py_tss_NEEDS_INIT` not specifying an initializer
+// for every field.
+#            define PYBIND11_TLS_KEY_INIT(var)                                                    \
+                _Pragma("GCC diagnostic push")                                         /**/       \
+                    _Pragma("GCC diagnostic ignored \"-Wmissing-field-initializers\"") /**/       \
+                    Py_tss_t var                                                                  \
+                    = Py_tss_NEEDS_INIT;                                                          \
+                _Pragma("GCC diagnostic pop")
+#        else
+#            define PYBIND11_TLS_KEY_INIT(var) Py_tss_t var = Py_tss_NEEDS_INIT;
+#        endif
+#        define PYBIND11_TLS_KEY_CREATE(var) (PyThread_tss_create(&(var)) == 0)
+#        define PYBIND11_TLS_GET_VALUE(key) PyThread_tss_get(&(key))
+#        define PYBIND11_TLS_REPLACE_VALUE(key, value) PyThread_tss_set(&(key), (value))
+#        define PYBIND11_TLS_DELETE_VALUE(key) PyThread_tss_set(&(key), nullptr)
+#        define PYBIND11_TLS_FREE(key) PyThread_tss_delete(&(key))
+#    else
+#        define PYBIND11_TLS_KEY_REF Py_tss_t *
+#        define PYBIND11_TLS_KEY_INIT(var) Py_tss_t *var = nullptr;
+#        define PYBIND11_TLS_KEY_CREATE(var)                                                      \
+            (((var) = PyThread_tss_alloc()) != nullptr && (PyThread_tss_create((var)) == 0))
 #        define PYBIND11_TLS_GET_VALUE(key) PyThread_tss_get((key))
 #        define PYBIND11_TLS_REPLACE_VALUE(key, value) PyThread_tss_set((key), (value))
 #        define PYBIND11_TLS_DELETE_VALUE(key) PyThread_tss_set((key), nullptr)
 #        define PYBIND11_TLS_FREE(key) PyThread_tss_free(key)
-#else
-    // Usually an int but a long on Cygwin64 with Python 3.x
-#    define PYBIND11_TLS_KEY_INIT(var) decltype(PyThread_create_key()) var = 0
-#    define PYBIND11_TLS_GET_VALUE(key) PyThread_get_key_value((key))
-#    if PY_MAJOR_VERSION < 3
-#        define PYBIND11_TLS_DELETE_VALUE(key)                               \
-             PyThread_delete_key_value(key)
-#        define PYBIND11_TLS_REPLACE_VALUE(key, value)                       \
-             do {                                                            \
-                 PyThread_delete_key_value((key));                           \
-                 PyThread_set_key_value((key), (value));                     \
-             } while (false)
-#    else
-#        define PYBIND11_TLS_DELETE_VALUE(key)                               \
-             PyThread_set_key_value((key), nullptr)
-#        define PYBIND11_TLS_REPLACE_VALUE(key, value)                       \
-             PyThread_set_key_value((key), (value))
 #    endif
-#    define PYBIND11_TLS_FREE(key) (void)key
+#else
+// Usually an int but a long on Cygwin64 with Python 3.x
+#    define PYBIND11_TLS_KEY_REF decltype(PyThread_create_key())
+#    define PYBIND11_TLS_KEY_INIT(var) PYBIND11_TLS_KEY_REF var = 0;
+#    define PYBIND11_TLS_KEY_CREATE(var) (((var) = PyThread_create_key()) != -1)
+#    define PYBIND11_TLS_GET_VALUE(key) PyThread_get_key_value((key))
+#    if PY_MAJOR_VERSION < 3 || defined(PYPY_VERSION)
+// On CPython < 3.4 and on PyPy, `PyThread_set_key_value` strangely does not set
+// the value if it has already been set.  Instead, it must first be deleted and
+// then set again.
+inline void tls_replace_value(PYBIND11_TLS_KEY_REF key, void *value) {
+    PyThread_delete_key_value(key);
+    PyThread_set_key_value(key, value);
+}
+#        define PYBIND11_TLS_DELETE_VALUE(key) PyThread_delete_key_value(key)
+#        define PYBIND11_TLS_REPLACE_VALUE(key, value)                                            \
+            ::pybind11::detail::tls_replace_value((key), (value))
+#    else
+#        define PYBIND11_TLS_DELETE_VALUE(key) PyThread_set_key_value((key), nullptr)
+#        define PYBIND11_TLS_REPLACE_VALUE(key, value) PyThread_set_key_value((key), (value))
+#    endif
+#    define PYBIND11_TLS_FREE(key) (void) key
 #endif
 
 // Python loads modules by default with dlopen with the RTLD_LOCAL flag; under libc++ and possibly
@@ -100,24 +152,33 @@ struct internals {
     std::unordered_set<std::pair<const PyObject *, const char *>, override_hash> inactive_override_cache;
     type_map<std::vector<bool (*)(PyObject *, void *&)>> direct_conversions;
     std::unordered_map<const PyObject *, std::vector<PyObject *>> patients;
-    std::forward_list<void (*) (std::exception_ptr)> registered_exception_translators;
+    std::forward_list<ExceptionTranslator> registered_exception_translators;
     std::unordered_map<std::string, void *> shared_data; // Custom data to be shared across extensions
-    std::vector<PyObject *> loader_patient_stack; // Used by `loader_life_support`
+#if PYBIND11_INTERNALS_VERSION == 4
+    std::vector<PyObject *> unused_loader_patient_stack_remove_at_v5;
+#endif
     std::forward_list<std::string> static_strings; // Stores the std::strings backing detail::c_str()
     PyTypeObject *static_property_type;
     PyTypeObject *default_metaclass;
     PyObject *instance_base;
 #if defined(WITH_THREAD)
-    PYBIND11_TLS_KEY_INIT(tstate);
+    PYBIND11_TLS_KEY_INIT(tstate)
+#    if PYBIND11_INTERNALS_VERSION > 4
+    PYBIND11_TLS_KEY_INIT(loader_life_support_tls_key)
+#    endif // PYBIND11_INTERNALS_VERSION > 4
     PyInterpreterState *istate = nullptr;
     ~internals() {
+#    if PYBIND11_INTERNALS_VERSION > 4
+        PYBIND11_TLS_FREE(loader_life_support_tls_key);
+#    endif // PYBIND11_INTERNALS_VERSION > 4
+
         // This destructor is called *after* Py_Finalize() in finalize_interpreter().
-        // That *SHOULD BE* fine. The following details what happens whe PyThread_tss_free is called.
+        // That *SHOULD BE* fine. The following details what happens when PyThread_tss_free is
-        // PYBIND11_TLS_FREE is PyThread_tss_free on python 3.7+. On older python, it does nothing.
+        // called. PYBIND11_TLS_FREE is PyThread_tss_free on python 3.7+. On older python, it does
-        // PyThread_tss_free calls PyThread_tss_delete and PyMem_RawFree.
+        // nothing. PyThread_tss_free calls PyThread_tss_delete and PyMem_RawFree.
-        // PyThread_tss_delete just calls TlsFree (on Windows) or pthread_key_delete (on *NIX). Neither
+        // PyThread_tss_delete just calls TlsFree (on Windows) or pthread_key_delete (on *NIX).
-        // of those have anything to do with CPython internals.
+        // Neither of those have anything to do with CPython internals. PyMem_RawFree *requires*
-        // PyMem_RawFree *requires* that the `tstate` be allocated with the CPython allocator.
+        // that the `tstate` be allocated with the CPython allocator.
         PYBIND11_TLS_FREE(tstate);
     }
 #endif
@@ -139,7 +200,9 @@ struct type_info {
     void *get_buffer_data = nullptr;
     void *(*module_local_load)(PyObject *, const type_info *) = nullptr;
     /* A simple type never occurs as a (direct or indirect) parent
-     * of a class that makes use of multiple inheritance */
+     * of a class that makes use of multiple inheritance.
+     * A type can be simple even if it has non-simple ancestors as long as it has no descendants.
+     */
     bool simple_type : 1;
     /* True if there is no multiple inheritance in this type's inheritance tree */
     bool simple_ancestors : 1;
@@ -149,9 +212,6 @@ struct type_info {
     bool module_local : 1;
 };
 
-/// Tracks the `internals` and `type_info` ABI version independent of the main library version
-#define PYBIND11_INTERNALS_VERSION 4
-
 /// On MSVC, debug and release builds are not ABI-compatible!
 #if defined(_MSC_VER) && defined(_DEBUG)
 #  define PYBIND11_BUILD_TYPE "_debug"
@@ -160,43 +220,54 @@ struct type_info {
 #endif
 
 /// Let's assume that different compilers are ABI-incompatible.
-#if defined(_MSC_VER)
+/// A user can manually set this string if they know their
+/// compiler is compatible.
+#ifndef PYBIND11_COMPILER_TYPE
+#  if defined(_MSC_VER)
 #    define PYBIND11_COMPILER_TYPE "_msvc"
-#elif defined(__INTEL_COMPILER)
+#  elif defined(__INTEL_COMPILER)
 #    define PYBIND11_COMPILER_TYPE "_icc"
-#elif defined(__clang__)
+#  elif defined(__clang__)
 #    define PYBIND11_COMPILER_TYPE "_clang"
-#elif defined(__PGI)
+#  elif defined(__PGI)
 #    define PYBIND11_COMPILER_TYPE "_pgi"
-#elif defined(__MINGW32__)
+#  elif defined(__MINGW32__)
 #    define PYBIND11_COMPILER_TYPE "_mingw"
-#elif defined(__CYGWIN__)
+#  elif defined(__CYGWIN__)
 #    define PYBIND11_COMPILER_TYPE "_gcc_cygwin"
-#elif defined(__GNUC__)
+#  elif defined(__GNUC__)
 #    define PYBIND11_COMPILER_TYPE "_gcc"
-#else
+#  else
 #    define PYBIND11_COMPILER_TYPE "_unknown"
+#  endif
 #endif
 
-#if defined(_LIBCPP_VERSION)
+/// Also standard libs
+#ifndef PYBIND11_STDLIB
+#  if defined(_LIBCPP_VERSION)
 #    define PYBIND11_STDLIB "_libcpp"
-#elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
+#  elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
 #    define PYBIND11_STDLIB "_libstdcpp"
-#else
+#  else
 #    define PYBIND11_STDLIB ""
+#  endif
 #endif
 
 /// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
-#if defined(__GXX_ABI_VERSION)
+#ifndef PYBIND11_BUILD_ABI
+#  if defined(__GXX_ABI_VERSION)
 #    define PYBIND11_BUILD_ABI "_cxxabi" PYBIND11_TOSTRING(__GXX_ABI_VERSION)
-#else
+#  else
 #    define PYBIND11_BUILD_ABI ""
+#  endif
 #endif
 
-#if defined(WITH_THREAD)
+#ifndef PYBIND11_INTERNALS_KIND
+#  if defined(WITH_THREAD)
 #    define PYBIND11_INTERNALS_KIND ""
-#else
+#  else
 #    define PYBIND11_INTERNALS_KIND "_without_thread"
+#  endif
 #endif
 
 #define PYBIND11_INTERNALS_ID "__pybind11_internals_v" \
@@ -212,21 +283,104 @@ inline internals **&get_internals_pp() {
     return internals_pp;
 }
 
+#if PY_VERSION_HEX >= 0x03030000
+// forward decl
+inline void translate_exception(std::exception_ptr);
+
+template <class T,
+          enable_if_t<std::is_same<std::nested_exception, remove_cvref_t<T>>::value, int> = 0>
+bool handle_nested_exception(const T &exc, const std::exception_ptr &p) {
+    std::exception_ptr nested = exc.nested_ptr();
+    if (nested != nullptr && nested != p) {
+        translate_exception(nested);
+        return true;
+    }
+    return false;
+}
+
+template <class T,
+          enable_if_t<!std::is_same<std::nested_exception, remove_cvref_t<T>>::value, int> = 0>
+bool handle_nested_exception(const T &exc, const std::exception_ptr &p) {
+    if (auto *nep = dynamic_cast<const std::nested_exception *>(std::addressof(exc))) {
+        return handle_nested_exception(*nep, p);
+    }
+    return false;
+}
+
+#else
+
+template <class T>
+bool handle_nested_exception(const T &, std::exception_ptr &) {
+    return false;
+}
+#endif
+
+inline bool raise_err(PyObject *exc_type, const char *msg) {
+#if PY_VERSION_HEX >= 0x03030000
+    if (PyErr_Occurred()) {
+        raise_from(exc_type, msg);
+        return true;
+    }
+#endif
+    PyErr_SetString(exc_type, msg);
+    return false;
+}
+
 inline void translate_exception(std::exception_ptr p) {
+    if (!p) {
+        return;
+    }
     try {
-        if (p) std::rethrow_exception(p);
+        std::rethrow_exception(p);
-    } catch (error_already_set &e)           { e.restore();                                    return;
+    } catch (error_already_set &e) {
-    } catch (const builtin_exception &e)     { e.set_error();                                  return;
+        handle_nested_exception(e, p);
-    } catch (const std::bad_alloc &e)        { PyErr_SetString(PyExc_MemoryError,   e.what()); return;
+        e.restore();
-    } catch (const std::domain_error &e)     { PyErr_SetString(PyExc_ValueError,    e.what()); return;
+        return;
-    } catch (const std::invalid_argument &e) { PyErr_SetString(PyExc_ValueError,    e.what()); return;
+    } catch (const builtin_exception &e) {
-    } catch (const std::length_error &e)     { PyErr_SetString(PyExc_ValueError,    e.what()); return;
+        // Could not use template since it's an abstract class.
-    } catch (const std::out_of_range &e)     { PyErr_SetString(PyExc_IndexError,    e.what()); return;
+        if (auto *nep = dynamic_cast<const std::nested_exception *>(std::addressof(e))) {
-    } catch (const std::range_error &e)      { PyErr_SetString(PyExc_ValueError,    e.what()); return;
+            handle_nested_exception(*nep, p);
-    } catch (const std::overflow_error &e)   { PyErr_SetString(PyExc_OverflowError, e.what()); return;
+        }
-    } catch (const std::exception &e)        { PyErr_SetString(PyExc_RuntimeError,  e.what()); return;
+        e.set_error();
+        return;
+    } catch (const std::bad_alloc &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_MemoryError, e.what());
+        return;
+    } catch (const std::domain_error &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_ValueError, e.what());
+        return;
+    } catch (const std::invalid_argument &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_ValueError, e.what());
+        return;
+    } catch (const std::length_error &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_ValueError, e.what());
+        return;
+    } catch (const std::out_of_range &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_IndexError, e.what());
+        return;
+    } catch (const std::range_error &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_ValueError, e.what());
+        return;
+    } catch (const std::overflow_error &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_OverflowError, e.what());
+        return;
+    } catch (const std::exception &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_RuntimeError, e.what());
+        return;
+    } catch (const std::nested_exception &e) {
+        handle_nested_exception(e, p);
+        raise_err(PyExc_RuntimeError, "Caught an unknown nested exception!");
+        return;
     } catch (...) {
-        PyErr_SetString(PyExc_RuntimeError, "Caught an unknown exception!");
+        raise_err(PyExc_RuntimeError, "Caught an unknown exception!");
         return;
     }
 }
@@ -242,7 +396,7 @@ inline void translate_local_exception(std::exception_ptr p) {
 #endif
 
 /// Return a reference to the current `internals` data
-PYBIND11_NOINLINE inline internals &get_internals() {
+PYBIND11_NOINLINE internals &get_internals() {
     auto **&internals_pp = get_internals_pp();
     if (internals_pp && *internals_pp)
         return **internals_pp;
@@ -255,7 +409,7 @@ PYBIND11_NOINLINE inline internals &get_internals() {
         const PyGILState_STATE state;
     } gil;
 
-    constexpr auto *id = PYBIND11_INTERNALS_ID;
+    PYBIND11_STR_TYPE id(PYBIND11_INTERNALS_ID);
     auto builtins = handle(PyEval_GetBuiltins());
     if (builtins.contains(id) && isinstance<capsule>(builtins[id])) {
         internals_pp = static_cast<internals **>(capsule(builtins[id]));
@@ -265,6 +419,8 @@ PYBIND11_NOINLINE inline internals &get_internals() {
         // initial exception translator, below, so add another for our local exception classes.
         //
         // libstdc++ doesn't require this (types there are identified only by name)
+        // libc++ with CPython doesn't require this (types are explicitly exported)
+        // libc++ with PyPy still need it, awaiting further investigation
 #if !defined(__GLIBCXX__)
         (*internals_pp)->registered_exception_translators.push_front(&translate_local_exception);
 #endif
@@ -274,21 +430,21 @@ PYBIND11_NOINLINE inline internals &get_internals() {
         internals_ptr = new internals();
 #if defined(WITH_THREAD)
 
-        #if PY_VERSION_HEX < 0x03090000
+#    if PY_VERSION_HEX < 0x03090000
         PyEval_InitThreads();
-        #endif
+#    endif
         PyThreadState *tstate = PyThreadState_Get();
-        #if PY_VERSION_HEX >= 0x03070000
+        if (!PYBIND11_TLS_KEY_CREATE(internals_ptr->tstate)) {
-            internals_ptr->tstate = PyThread_tss_alloc();
+            pybind11_fail("get_internals: could not successfully initialize the tstate TSS key!");
-            if (!internals_ptr->tstate || PyThread_tss_create(internals_ptr->tstate))
+        }
-                pybind11_fail("get_internals: could not successfully initialize the TSS key!");
+        PYBIND11_TLS_REPLACE_VALUE(internals_ptr->tstate, tstate);
-            PyThread_tss_set(internals_ptr->tstate, tstate);
+
-        #else
+#    if PYBIND11_INTERNALS_VERSION > 4
-            internals_ptr->tstate = PyThread_create_key();
+        if (!PYBIND11_TLS_KEY_CREATE(internals_ptr->loader_life_support_tls_key)) {
-            if (internals_ptr->tstate == -1)
+            pybind11_fail("get_internals: could not successfully initialize the "
-                pybind11_fail("get_internals: could not successfully initialize the TLS key!");
+                          "loader_life_support TSS key!");
-            PyThread_set_key_value(internals_ptr->tstate, tstate);
+        }
-        #endif
+#    endif
         internals_ptr->istate = tstate->interp;
 #endif
         builtins[id] = capsule(internals_pp);
@@ -300,12 +456,57 @@ PYBIND11_NOINLINE inline internals &get_internals() {
     return **internals_pp;
 }
 
-/// Works like `internals.registered_types_cpp`, but for module-local registered types:
+// the internals struct (above) is shared between all the modules. local_internals are only
-inline type_map<type_info *> &registered_local_types_cpp() {
+// for a single module. Any changes made to internals may require an update to
-    static type_map<type_info *> locals{};
+// PYBIND11_INTERNALS_VERSION, breaking backwards compatibility. local_internals is, by design,
+// restricted to a single module. Whether a module has local internals or not should not
+// impact any other modules, because the only things accessing the local internals is the
+// module that contains them.
+struct local_internals {
+    type_map<type_info *> registered_types_cpp;
+    std::forward_list<ExceptionTranslator> registered_exception_translators;
+#if defined(WITH_THREAD) && PYBIND11_INTERNALS_VERSION == 4
+
+    // For ABI compatibility, we can't store the loader_life_support TLS key in
+    // the `internals` struct directly.  Instead, we store it in `shared_data` and
+    // cache a copy in `local_internals`.  If we allocated a separate TLS key for
+    // each instance of `local_internals`, we could end up allocating hundreds of
+    // TLS keys if hundreds of different pybind11 modules are loaded (which is a
+    // plausible number).
+    PYBIND11_TLS_KEY_INIT(loader_life_support_tls_key)
+
+    // Holds the shared TLS key for the loader_life_support stack.
+    struct shared_loader_life_support_data {
+        PYBIND11_TLS_KEY_INIT(loader_life_support_tls_key)
+        shared_loader_life_support_data() {
+            if (!PYBIND11_TLS_KEY_CREATE(loader_life_support_tls_key)) {
+                pybind11_fail("local_internals: could not successfully initialize the "
+                              "loader_life_support TLS key!");
+            }
+        }
+        // We can't help but leak the TLS key, because Python never unloads extension modules.
+    };
+
+    local_internals() {
+        auto &internals = get_internals();
+        // Get or create the `loader_life_support_stack_key`.
+        auto &ptr = internals.shared_data["_life_support"];
+        if (!ptr) {
+            ptr = new shared_loader_life_support_data;
+        }
+        loader_life_support_tls_key
+            = static_cast<shared_loader_life_support_data *>(ptr)->loader_life_support_tls_key;
+    }
+#endif //  defined(WITH_THREAD) && PYBIND11_INTERNALS_VERSION == 4
+};
+
+/// Works like `get_internals`, but for things which are locally registered.
+inline local_internals &get_local_internals() {
+  static local_internals locals;
   return locals;
 }
 
+
 /// Constructs a std::string with the given arguments, stores it in `internals`, and returns its
 /// `c_str()`.  Such strings objects have a long storage duration -- the internal strings are only
 /// cleared when the program exits or after interpreter shutdown (when embedding), and so are
@@ -322,14 +523,14 @@ PYBIND11_NAMESPACE_END(detail)
 /// Returns a named pointer that is shared among all extension modules (using the same
 /// pybind11 version) running in the current interpreter. Names starting with underscores
 /// are reserved for internal usage. Returns `nullptr` if no matching entry was found.
-inline PYBIND11_NOINLINE void *get_shared_data(const std::string &name) {
+PYBIND11_NOINLINE void *get_shared_data(const std::string &name) {
     auto &internals = detail::get_internals();
     auto it = internals.shared_data.find(name);
     return it != internals.shared_data.end() ? it->second : nullptr;
 }
 
 /// Set the shared data that can be later recovered by `get_shared_data()`.
-inline PYBIND11_NOINLINE void *set_shared_data(const std::string &name, void *data) {
+PYBIND11_NOINLINE void *set_shared_data(const std::string &name, void *data) {
     detail::get_internals().shared_data[name] = data;
     return data;
 }

wrap/pybind11/include/pybind11/detail/type_caster_base.h

@@ -0,0 +1,985 @@
+/*
+    pybind11/detail/type_caster_base.h (originally first part of pybind11/cast.h)
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "../pytypes.h"
+#include "common.h"
+#include "descr.h"
+#include "internals.h"
+#include "typeid.h"
+#include <cstdint>
+#include <iterator>
+#include <new>
+#include <string>
+#include <type_traits>
+#include <typeindex>
+#include <typeinfo>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+/// A life support system for temporary objects created by `type_caster::load()`.
+/// Adding a patient will keep it alive up until the enclosing function returns.
+class loader_life_support {
+private:
+    loader_life_support* parent = nullptr;
+    std::unordered_set<PyObject *> keep_alive;
+
+#if defined(WITH_THREAD)
+    // Store stack pointer in thread-local storage.
+    static PYBIND11_TLS_KEY_REF get_stack_tls_key() {
+#    if PYBIND11_INTERNALS_VERSION == 4
+        return get_local_internals().loader_life_support_tls_key;
+#    else
+        return get_internals().loader_life_support_tls_key;
+#    endif
+    }
+    static loader_life_support *get_stack_top() {
+        return static_cast<loader_life_support *>(PYBIND11_TLS_GET_VALUE(get_stack_tls_key()));
+    }
+    static void set_stack_top(loader_life_support *value) {
+        PYBIND11_TLS_REPLACE_VALUE(get_stack_tls_key(), value);
+    }
+#else
+    // Use single global variable for stack.
+    static loader_life_support **get_stack_pp() {
+        static loader_life_support *global_stack = nullptr;
+        return global_stack;
+    }
+    static loader_life_support *get_stack_top() { return *get_stack_pp(); }
+    static void set_stack_top(loader_life_support *value) { *get_stack_pp() = value; }
+#endif
+
+public:
+    /// A new patient frame is created when a function is entered
+    loader_life_support() {
+        parent = get_stack_top();
+        set_stack_top(this);
+    }
+
+    /// ... and destroyed after it returns
+    ~loader_life_support() {
+        if (get_stack_top() != this)
+            pybind11_fail("loader_life_support: internal error");
+        set_stack_top(parent);
+        for (auto* item : keep_alive)
+            Py_DECREF(item);
+    }
+
+    /// This can only be used inside a pybind11-bound function, either by `argument_loader`
+    /// at argument preparation time or by `py::cast()` at execution time.
+    PYBIND11_NOINLINE static void add_patient(handle h) {
+        loader_life_support *frame = get_stack_top();
+        if (!frame) {
+            // NOTE: It would be nice to include the stack frames here, as this indicates
+            // use of pybind11::cast<> outside the normal call framework, finding such
+            // a location is challenging. Developers could consider printing out
+            // stack frame addresses here using something like __builtin_frame_address(0)
+            throw cast_error("When called outside a bound function, py::cast() cannot "
+                             "do Python -> C++ conversions which require the creation "
+                             "of temporary values");
+        }
+
+        if (frame->keep_alive.insert(h.ptr()).second)
+            Py_INCREF(h.ptr());
+    }
+};
+
+// Gets the cache entry for the given type, creating it if necessary.  The return value is the pair
+// returned by emplace, i.e. an iterator for the entry and a bool set to `true` if the entry was
+// just created.
+inline std::pair<decltype(internals::registered_types_py)::iterator, bool> all_type_info_get_cache(PyTypeObject *type);
+
+// Populates a just-created cache entry.
+PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_info *> &bases) {
+    std::vector<PyTypeObject *> check;
+    for (handle parent : reinterpret_borrow<tuple>(t->tp_bases))
+        check.push_back((PyTypeObject *) parent.ptr());
+
+    auto const &type_dict = get_internals().registered_types_py;
+    for (size_t i = 0; i < check.size(); i++) {
+        auto type = check[i];
+        // Ignore Python2 old-style class super type:
+        if (!PyType_Check((PyObject *) type)) continue;
+
+        // Check `type` in the current set of registered python types:
+        auto it = type_dict.find(type);
+        if (it != type_dict.end()) {
+            // We found a cache entry for it, so it's either pybind-registered or has pre-computed
+            // pybind bases, but we have to make sure we haven't already seen the type(s) before: we
+            // want to follow Python/virtual C++ rules that there should only be one instance of a
+            // common base.
+            for (auto *tinfo : it->second) {
+                // NB: Could use a second set here, rather than doing a linear search, but since
+                // having a large number of immediate pybind11-registered types seems fairly
+                // unlikely, that probably isn't worthwhile.
+                bool found = false;
+                for (auto *known : bases) {
+                    if (known == tinfo) { found = true; break; }
+                }
+                if (!found) bases.push_back(tinfo);
+            }
+        }
+        else if (type->tp_bases) {
+            // It's some python type, so keep follow its bases classes to look for one or more
+            // registered types
+            if (i + 1 == check.size()) {
+                // When we're at the end, we can pop off the current element to avoid growing
+                // `check` when adding just one base (which is typical--i.e. when there is no
+                // multiple inheritance)
+                check.pop_back();
+                i--;
+            }
+            for (handle parent : reinterpret_borrow<tuple>(type->tp_bases))
+                check.push_back((PyTypeObject *) parent.ptr());
+        }
+    }
+}
+
+/**
+ * Extracts vector of type_info pointers of pybind-registered roots of the given Python type.  Will
+ * be just 1 pybind type for the Python type of a pybind-registered class, or for any Python-side
+ * derived class that uses single inheritance.  Will contain as many types as required for a Python
+ * class that uses multiple inheritance to inherit (directly or indirectly) from multiple
+ * pybind-registered classes.  Will be empty if neither the type nor any base classes are
+ * pybind-registered.
+ *
+ * The value is cached for the lifetime of the Python type.
+ */
+inline const std::vector<detail::type_info *> &all_type_info(PyTypeObject *type) {
+    auto ins = all_type_info_get_cache(type);
+    if (ins.second)
+        // New cache entry: populate it
+        all_type_info_populate(type, ins.first->second);
+
+    return ins.first->second;
+}
+
+/**
+ * Gets a single pybind11 type info for a python type.  Returns nullptr if neither the type nor any
+ * ancestors are pybind11-registered.  Throws an exception if there are multiple bases--use
+ * `all_type_info` instead if you want to support multiple bases.
+ */
+PYBIND11_NOINLINE detail::type_info* get_type_info(PyTypeObject *type) {
+    auto &bases = all_type_info(type);
+    if (bases.empty())
+        return nullptr;
+    if (bases.size() > 1)
+        pybind11_fail("pybind11::detail::get_type_info: type has multiple pybind11-registered bases");
+    return bases.front();
+}
+
+inline detail::type_info *get_local_type_info(const std::type_index &tp) {
+    auto &locals = get_local_internals().registered_types_cpp;
+    auto it = locals.find(tp);
+    if (it != locals.end())
+        return it->second;
+    return nullptr;
+}
+
+inline detail::type_info *get_global_type_info(const std::type_index &tp) {
+    auto &types = get_internals().registered_types_cpp;
+    auto it = types.find(tp);
+    if (it != types.end())
+        return it->second;
+    return nullptr;
+}
+
+/// Return the type info for a given C++ type; on lookup failure can either throw or return nullptr.
+PYBIND11_NOINLINE detail::type_info *get_type_info(const std::type_index &tp,
+                                                          bool throw_if_missing = false) {
+    if (auto ltype = get_local_type_info(tp))
+        return ltype;
+    if (auto gtype = get_global_type_info(tp))
+        return gtype;
+
+    if (throw_if_missing) {
+        std::string tname = tp.name();
+        detail::clean_type_id(tname);
+        pybind11_fail("pybind11::detail::get_type_info: unable to find type info for \"" + tname + "\"");
+    }
+    return nullptr;
+}
+
+PYBIND11_NOINLINE handle get_type_handle(const std::type_info &tp, bool throw_if_missing) {
+    detail::type_info *type_info = get_type_info(tp, throw_if_missing);
+    return handle(type_info ? ((PyObject *) type_info->type) : nullptr);
+}
+
+// Searches the inheritance graph for a registered Python instance, using all_type_info().
+PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
+                                                                const detail::type_info *tinfo) {
+    auto it_instances = get_internals().registered_instances.equal_range(src);
+    for (auto it_i = it_instances.first; it_i != it_instances.second; ++it_i) {
+        for (auto instance_type : detail::all_type_info(Py_TYPE(it_i->second))) {
+            if (instance_type && same_type(*instance_type->cpptype, *tinfo->cpptype))
+                return handle((PyObject *) it_i->second).inc_ref();
+        }
+    }
+    return handle();
+}
+
+struct value_and_holder {
+    instance *inst = nullptr;
+    size_t index = 0u;
+    const detail::type_info *type = nullptr;
+    void **vh = nullptr;
+
+    // Main constructor for a found value/holder:
+    value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index) :
+        inst{i}, index{index}, type{type},
+        vh{inst->simple_layout ? inst->simple_value_holder : &inst->nonsimple.values_and_holders[vpos]}
+    {}
+
+    // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
+    value_and_holder() = default;
+
+    // Used for past-the-end iterator
+    explicit value_and_holder(size_t index) : index{index} {}
+
+    template <typename V = void> V *&value_ptr() const {
+        return reinterpret_cast<V *&>(vh[0]);
+    }
+    // True if this `value_and_holder` has a non-null value pointer
+    explicit operator bool() const { return value_ptr() != nullptr; }
+
+    template <typename H> H &holder() const {
+        return reinterpret_cast<H &>(vh[1]);
+    }
+    bool holder_constructed() const {
+        return inst->simple_layout
+                   ? inst->simple_holder_constructed
+                   : (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_holder_constructed(bool v = true) {
+        if (inst->simple_layout)
+            inst->simple_holder_constructed = v;
+        else if (v)
+            inst->nonsimple.status[index] |= instance::status_holder_constructed;
+        else
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
+    }
+    bool instance_registered() const {
+        return inst->simple_layout
+            ? inst->simple_instance_registered
+            : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_instance_registered(bool v = true) {
+        if (inst->simple_layout)
+            inst->simple_instance_registered = v;
+        else if (v)
+            inst->nonsimple.status[index] |= instance::status_instance_registered;
+        else
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
+    }
+};
+
+// Container for accessing and iterating over an instance's values/holders
+struct values_and_holders {
+private:
+    instance *inst;
+    using type_vec = std::vector<detail::type_info *>;
+    const type_vec &tinfo;
+
+public:
+    explicit values_and_holders(instance *inst)
+        : inst{inst}, tinfo(all_type_info(Py_TYPE(inst))) {}
+
+    struct iterator {
+    private:
+        instance *inst = nullptr;
+        const type_vec *types = nullptr;
+        value_and_holder curr;
+        friend struct values_and_holders;
+        iterator(instance *inst, const type_vec *tinfo)
+            : inst{inst}, types{tinfo},
+            curr(inst /* instance */,
+                 types->empty() ? nullptr : (*types)[0] /* type info */,
+                 0, /* vpos: (non-simple types only): the first vptr comes first */
+                 0 /* index */)
+        {}
+        // Past-the-end iterator:
+        explicit iterator(size_t end) : curr(end) {}
+
+    public:
+        bool operator==(const iterator &other) const { return curr.index == other.curr.index; }
+        bool operator!=(const iterator &other) const { return curr.index != other.curr.index; }
+        iterator &operator++() {
+            if (!inst->simple_layout)
+                curr.vh += 1 + (*types)[curr.index]->holder_size_in_ptrs;
+            ++curr.index;
+            curr.type = curr.index < types->size() ? (*types)[curr.index] : nullptr;
+            return *this;
+        }
+        value_and_holder &operator*() { return curr; }
+        value_and_holder *operator->() { return &curr; }
+    };
+
+    iterator begin() { return iterator(inst, &tinfo); }
+    iterator end() { return iterator(tinfo.size()); }
+
+    iterator find(const type_info *find_type) {
+        auto it = begin(), endit = end();
+        while (it != endit && it->type != find_type) ++it;
+        return it;
+    }
+
+    size_t size() { return tinfo.size(); }
+};
+
+/**
+ * Extracts C++ value and holder pointer references from an instance (which may contain multiple
+ * values/holders for python-side multiple inheritance) that match the given type.  Throws an error
+ * if the given type (or ValueType, if omitted) is not a pybind11 base of the given instance.  If
+ * `find_type` is omitted (or explicitly specified as nullptr) the first value/holder are returned,
+ * regardless of type (and the resulting .type will be nullptr).
+ *
+ * The returned object should be short-lived: in particular, it must not outlive the called-upon
+ * instance.
+ */
+PYBIND11_NOINLINE value_and_holder instance::get_value_and_holder(const type_info *find_type /*= nullptr default in common.h*/, bool throw_if_missing /*= true in common.h*/) {
+    // Optimize common case:
+    if (!find_type || Py_TYPE(this) == find_type->type)
+        return value_and_holder(this, find_type, 0, 0);
+
+    detail::values_and_holders vhs(this);
+    auto it = vhs.find(find_type);
+    if (it != vhs.end())
+        return *it;
+
+    if (!throw_if_missing)
+        return value_and_holder();
+
+#if defined(NDEBUG)
+    pybind11_fail("pybind11::detail::instance::get_value_and_holder: "
+            "type is not a pybind11 base of the given instance "
+            "(compile in debug mode for type details)");
+#else
+    pybind11_fail("pybind11::detail::instance::get_value_and_holder: `" +
+            get_fully_qualified_tp_name(find_type->type) + "' is not a pybind11 base of the given `" +
+            get_fully_qualified_tp_name(Py_TYPE(this)) + "' instance");
+#endif
+}
+
+PYBIND11_NOINLINE void instance::allocate_layout() {
+    auto &tinfo = all_type_info(Py_TYPE(this));
+
+    const size_t n_types = tinfo.size();
+
+    if (n_types == 0)
+        pybind11_fail("instance allocation failed: new instance has no pybind11-registered base types");
+
+    simple_layout =
+        n_types == 1 && tinfo.front()->holder_size_in_ptrs <= instance_simple_holder_in_ptrs();
+
+    // Simple path: no python-side multiple inheritance, and a small-enough holder
+    if (simple_layout) {
+        simple_value_holder[0] = nullptr;
+        simple_holder_constructed = false;
+        simple_instance_registered = false;
+    }
+    else { // multiple base types or a too-large holder
+        // Allocate space to hold: [v1*][h1][v2*][h2]...[bb...] where [vN*] is a value pointer,
+        // [hN] is the (uninitialized) holder instance for value N, and [bb...] is a set of bool
+        // values that tracks whether each associated holder has been initialized.  Each [block] is
+        // padded, if necessary, to an integer multiple of sizeof(void *).
+        size_t space = 0;
+        for (auto t : tinfo) {
+            space += 1; // value pointer
+            space += t->holder_size_in_ptrs; // holder instance
+        }
+        size_t flags_at = space;
+        space += size_in_ptrs(n_types); // status bytes (holder_constructed and instance_registered)
+
+        // Allocate space for flags, values, and holders, and initialize it to 0 (flags and values,
+        // in particular, need to be 0).  Use Python's memory allocation functions: in Python 3.6
+        // they default to using pymalloc, which is designed to be efficient for small allocations
+        // like the one we're doing here; in earlier versions (and for larger allocations) they are
+        // just wrappers around malloc.
+#if PY_VERSION_HEX >= 0x03050000
+        nonsimple.values_and_holders = (void **) PyMem_Calloc(space, sizeof(void *));
+        if (!nonsimple.values_and_holders) throw std::bad_alloc();
+#else
+        nonsimple.values_and_holders = (void **) PyMem_New(void *, space);
+        if (!nonsimple.values_and_holders) throw std::bad_alloc();
+        std::memset(nonsimple.values_and_holders, 0, space * sizeof(void *));
+#endif
+        nonsimple.status = reinterpret_cast<std::uint8_t *>(&nonsimple.values_and_holders[flags_at]);
+    }
+    owned = true;
+}
+
+// NOLINTNEXTLINE(readability-make-member-function-const)
+PYBIND11_NOINLINE void instance::deallocate_layout() {
+    if (!simple_layout)
+        PyMem_Free(nonsimple.values_and_holders);
+}
+
+PYBIND11_NOINLINE bool isinstance_generic(handle obj, const std::type_info &tp) {
+    handle type = detail::get_type_handle(tp, false);
+    if (!type)
+        return false;
+    return isinstance(obj, type);
+}
+
+PYBIND11_NOINLINE std::string error_string() {
+    if (!PyErr_Occurred()) {
+        PyErr_SetString(PyExc_RuntimeError, "Unknown internal error occurred");
+        return "Unknown internal error occurred";
+    }
+
+    error_scope scope; // Preserve error state
+
+    std::string errorString;
+    if (scope.type) {
+        errorString += handle(scope.type).attr("__name__").cast<std::string>();
+        errorString += ": ";
+    }
+    if (scope.value)
+        errorString += (std::string) str(scope.value);
+
+    PyErr_NormalizeException(&scope.type, &scope.value, &scope.trace);
+
+#if PY_MAJOR_VERSION >= 3
+    if (scope.trace != nullptr)
+        PyException_SetTraceback(scope.value, scope.trace);
+#endif
+
+#if !defined(PYPY_VERSION)
+    if (scope.trace) {
+        auto *trace = (PyTracebackObject *) scope.trace;
+
+        /* Get the deepest trace possible */
+        while (trace->tb_next)
+            trace = trace->tb_next;
+
+        PyFrameObject *frame = trace->tb_frame;
+        errorString += "\n\nAt:\n";
+        while (frame) {
+#if PY_VERSION_HEX >= 0x03090000
+            PyCodeObject *f_code = PyFrame_GetCode(frame);
+#else
+            PyCodeObject *f_code = frame->f_code;
+            Py_INCREF(f_code);
+#endif
+            int lineno = PyFrame_GetLineNumber(frame);
+            errorString +=
+                "  " + handle(f_code->co_filename).cast<std::string>() +
+                "(" + std::to_string(lineno) + "): " +
+                handle(f_code->co_name).cast<std::string>() + "\n";
+            frame = frame->f_back;
+            Py_DECREF(f_code);
+        }
+    }
+#endif
+
+    return errorString;
+}
+
+PYBIND11_NOINLINE handle get_object_handle(const void *ptr, const detail::type_info *type ) {
+    auto &instances = get_internals().registered_instances;
+    auto range = instances.equal_range(ptr);
+    for (auto it = range.first; it != range.second; ++it) {
+        for (const auto &vh : values_and_holders(it->second)) {
+            if (vh.type == type)
+                return handle((PyObject *) it->second);
+        }
+    }
+    return handle();
+}
+
+inline PyThreadState *get_thread_state_unchecked() {
+#if defined(PYPY_VERSION)
+    return PyThreadState_GET();
+#elif PY_VERSION_HEX < 0x03000000
+    return _PyThreadState_Current;
+#elif PY_VERSION_HEX < 0x03050000
+    return (PyThreadState*) _Py_atomic_load_relaxed(&_PyThreadState_Current);
+#elif PY_VERSION_HEX < 0x03050200
+    return (PyThreadState*) _PyThreadState_Current.value;
+#else
+    return _PyThreadState_UncheckedGet();
+#endif
+}
+
+// Forward declarations
+void keep_alive_impl(handle nurse, handle patient);
+inline PyObject *make_new_instance(PyTypeObject *type);
+
+class type_caster_generic {
+public:
+    PYBIND11_NOINLINE explicit type_caster_generic(const std::type_info &type_info)
+        : typeinfo(get_type_info(type_info)), cpptype(&type_info) {}
+
+    explicit type_caster_generic(const type_info *typeinfo)
+        : typeinfo(typeinfo), cpptype(typeinfo ? typeinfo->cpptype : nullptr) {}
+
+    bool load(handle src, bool convert) {
+        return load_impl<type_caster_generic>(src, convert);
+    }
+
+    PYBIND11_NOINLINE static handle cast(const void *_src, return_value_policy policy, handle parent,
+                                         const detail::type_info *tinfo,
+                                         void *(*copy_constructor)(const void *),
+                                         void *(*move_constructor)(const void *),
+                                         const void *existing_holder = nullptr) {
+        if (!tinfo) // no type info: error will be set already
+            return handle();
+
+        void *src = const_cast<void *>(_src);
+        if (src == nullptr)
+            return none().release();
+
+        if (handle registered_inst = find_registered_python_instance(src, tinfo))
+            return registered_inst;
+
+        auto inst = reinterpret_steal<object>(make_new_instance(tinfo->type));
+        auto wrapper = reinterpret_cast<instance *>(inst.ptr());
+        wrapper->owned = false;
+        void *&valueptr = values_and_holders(wrapper).begin()->value_ptr();
+
+        switch (policy) {
+            case return_value_policy::automatic:
+            case return_value_policy::take_ownership:
+                valueptr = src;
+                wrapper->owned = true;
+                break;
+
+            case return_value_policy::automatic_reference:
+            case return_value_policy::reference:
+                valueptr = src;
+                wrapper->owned = false;
+                break;
+
+            case return_value_policy::copy:
+                if (copy_constructor)
+                    valueptr = copy_constructor(src);
+                else {
+#if defined(NDEBUG)
+                    throw cast_error("return_value_policy = copy, but type is "
+                                     "non-copyable! (compile in debug mode for details)");
+#else
+                    std::string type_name(tinfo->cpptype->name());
+                    detail::clean_type_id(type_name);
+                    throw cast_error("return_value_policy = copy, but type " +
+                                     type_name + " is non-copyable!");
+#endif
+                }
+                wrapper->owned = true;
+                break;
+
+            case return_value_policy::move:
+                if (move_constructor)
+                    valueptr = move_constructor(src);
+                else if (copy_constructor)
+                    valueptr = copy_constructor(src);
+                else {
+#if defined(NDEBUG)
+                    throw cast_error("return_value_policy = move, but type is neither "
+                                     "movable nor copyable! "
+                                     "(compile in debug mode for details)");
+#else
+                    std::string type_name(tinfo->cpptype->name());
+                    detail::clean_type_id(type_name);
+                    throw cast_error("return_value_policy = move, but type " +
+                                     type_name + " is neither movable nor copyable!");
+#endif
+                }
+                wrapper->owned = true;
+                break;
+
+            case return_value_policy::reference_internal:
+                valueptr = src;
+                wrapper->owned = false;
+                keep_alive_impl(inst, parent);
+                break;
+
+            default:
+                throw cast_error("unhandled return_value_policy: should not happen!");
+        }
+
+        tinfo->init_instance(wrapper, existing_holder);
+
+        return inst.release();
+    }
+
+    // Base methods for generic caster; there are overridden in copyable_holder_caster
+    void load_value(value_and_holder &&v_h) {
+        auto *&vptr = v_h.value_ptr();
+        // Lazy allocation for unallocated values:
+        if (vptr == nullptr) {
+            auto *type = v_h.type ? v_h.type : typeinfo;
+            if (type->operator_new) {
+                vptr = type->operator_new(type->type_size);
+            } else {
+                #if defined(__cpp_aligned_new) && (!defined(_MSC_VER) || _MSC_VER >= 1912)
+                    if (type->type_align > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+                        vptr = ::operator new(type->type_size,
+                                              std::align_val_t(type->type_align));
+                    else
+                #endif
+                vptr = ::operator new(type->type_size);
+            }
+        }
+        value = vptr;
+    }
+    bool try_implicit_casts(handle src, bool convert) {
+        for (auto &cast : typeinfo->implicit_casts) {
+            type_caster_generic sub_caster(*cast.first);
+            if (sub_caster.load(src, convert)) {
+                value = cast.second(sub_caster.value);
+                return true;
+            }
+        }
+        return false;
+    }
+    bool try_direct_conversions(handle src) {
+        for (auto &converter : *typeinfo->direct_conversions) {
+            if (converter(src.ptr(), value))
+                return true;
+        }
+        return false;
+    }
+    void check_holder_compat() {}
+
+    PYBIND11_NOINLINE static void *local_load(PyObject *src, const type_info *ti) {
+        auto caster = type_caster_generic(ti);
+        if (caster.load(src, false))
+            return caster.value;
+        return nullptr;
+    }
+
+    /// Try to load with foreign typeinfo, if available. Used when there is no
+    /// native typeinfo, or when the native one wasn't able to produce a value.
+    PYBIND11_NOINLINE bool try_load_foreign_module_local(handle src) {
+        constexpr auto *local_key = PYBIND11_MODULE_LOCAL_ID;
+        const auto pytype = type::handle_of(src);
+        if (!hasattr(pytype, local_key))
+            return false;
+
+        type_info *foreign_typeinfo = reinterpret_borrow<capsule>(getattr(pytype, local_key));
+        // Only consider this foreign loader if actually foreign and is a loader of the correct cpp type
+        if (foreign_typeinfo->module_local_load == &local_load
+            || (cpptype && !same_type(*cpptype, *foreign_typeinfo->cpptype)))
+            return false;
+
+        if (auto result = foreign_typeinfo->module_local_load(src.ptr(), foreign_typeinfo)) {
+            value = result;
+            return true;
+        }
+        return false;
+    }
+
+    // Implementation of `load`; this takes the type of `this` so that it can dispatch the relevant
+    // bits of code between here and copyable_holder_caster where the two classes need different
+    // logic (without having to resort to virtual inheritance).
+    template <typename ThisT>
+    PYBIND11_NOINLINE bool load_impl(handle src, bool convert) {
+        if (!src) return false;
+        if (!typeinfo) return try_load_foreign_module_local(src);
+
+        auto &this_ = static_cast<ThisT &>(*this);
+        this_.check_holder_compat();
+
+        PyTypeObject *srctype = Py_TYPE(src.ptr());
+
+        // Case 1: If src is an exact type match for the target type then we can reinterpret_cast
+        // the instance's value pointer to the target type:
+        if (srctype == typeinfo->type) {
+            this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder());
+            return true;
+        }
+        // Case 2: We have a derived class
+        if (PyType_IsSubtype(srctype, typeinfo->type)) {
+            auto &bases = all_type_info(srctype);
+            bool no_cpp_mi = typeinfo->simple_type;
+
+            // Case 2a: the python type is a Python-inherited derived class that inherits from just
+            // one simple (no MI) pybind11 class, or is an exact match, so the C++ instance is of
+            // the right type and we can use reinterpret_cast.
+            // (This is essentially the same as case 2b, but because not using multiple inheritance
+            // is extremely common, we handle it specially to avoid the loop iterator and type
+            // pointer lookup overhead)
+            if (bases.size() == 1 && (no_cpp_mi || bases.front()->type == typeinfo->type)) {
+                this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder());
+                return true;
+            }
+            // Case 2b: the python type inherits from multiple C++ bases.  Check the bases to see if
+            // we can find an exact match (or, for a simple C++ type, an inherited match); if so, we
+            // can safely reinterpret_cast to the relevant pointer.
+            if (bases.size() > 1) {
+                for (auto base : bases) {
+                    if (no_cpp_mi ? PyType_IsSubtype(base->type, typeinfo->type) : base->type == typeinfo->type) {
+                        this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder(base));
+                        return true;
+                    }
+                }
+            }
+
+            // Case 2c: C++ multiple inheritance is involved and we couldn't find an exact type match
+            // in the registered bases, above, so try implicit casting (needed for proper C++ casting
+            // when MI is involved).
+            if (this_.try_implicit_casts(src, convert))
+                return true;
+        }
+
+        // Perform an implicit conversion
+        if (convert) {
+            for (auto &converter : typeinfo->implicit_conversions) {
+                auto temp = reinterpret_steal<object>(converter(src.ptr(), typeinfo->type));
+                if (load_impl<ThisT>(temp, false)) {
+                    loader_life_support::add_patient(temp);
+                    return true;
+                }
+            }
+            if (this_.try_direct_conversions(src))
+                return true;
+        }
+
+        // Failed to match local typeinfo. Try again with global.
+        if (typeinfo->module_local) {
+            if (auto gtype = get_global_type_info(*typeinfo->cpptype)) {
+                typeinfo = gtype;
+                return load(src, false);
+            }
+        }
+
+        // Global typeinfo has precedence over foreign module_local
+        if (try_load_foreign_module_local(src)) {
+           return true;
+        }
+
+        // Custom converters didn't take None, now we convert None to nullptr.
+        if (src.is_none()) {
+           // Defer accepting None to other overloads (if we aren't in convert mode):
+           if (!convert) return false;
+           value = nullptr;
+           return true;
+        }
+
+        return false;
+    }
+
+
+    // Called to do type lookup and wrap the pointer and type in a pair when a dynamic_cast
+    // isn't needed or can't be used.  If the type is unknown, sets the error and returns a pair
+    // with .second = nullptr.  (p.first = nullptr is not an error: it becomes None).
+    PYBIND11_NOINLINE static std::pair<const void *, const type_info *> src_and_type(
+            const void *src, const std::type_info &cast_type, const std::type_info *rtti_type = nullptr) {
+        if (auto *tpi = get_type_info(cast_type))
+            return {src, const_cast<const type_info *>(tpi)};
+
+        // Not found, set error:
+        std::string tname = rtti_type ? rtti_type->name() : cast_type.name();
+        detail::clean_type_id(tname);
+        std::string msg = "Unregistered type : " + tname;
+        PyErr_SetString(PyExc_TypeError, msg.c_str());
+        return {nullptr, nullptr};
+    }
+
+    const type_info *typeinfo = nullptr;
+    const std::type_info *cpptype = nullptr;
+    void *value = nullptr;
+};
+
+/**
+ * Determine suitable casting operator for pointer-or-lvalue-casting type casters.  The type caster
+ * needs to provide `operator T*()` and `operator T&()` operators.
+ *
+ * If the type supports moving the value away via an `operator T&&() &&` method, it should use
+ * `movable_cast_op_type` instead.
+ */
+template <typename T>
+using cast_op_type =
+    conditional_t<std::is_pointer<remove_reference_t<T>>::value,
+        typename std::add_pointer<intrinsic_t<T>>::type,
+        typename std::add_lvalue_reference<intrinsic_t<T>>::type>;
+
+/**
+ * Determine suitable casting operator for a type caster with a movable value.  Such a type caster
+ * needs to provide `operator T*()`, `operator T&()`, and `operator T&&() &&`.  The latter will be
+ * called in appropriate contexts where the value can be moved rather than copied.
+ *
+ * These operator are automatically provided when using the PYBIND11_TYPE_CASTER macro.
+ */
+template <typename T>
+using movable_cast_op_type =
+    conditional_t<std::is_pointer<typename std::remove_reference<T>::type>::value,
+        typename std::add_pointer<intrinsic_t<T>>::type,
+    conditional_t<std::is_rvalue_reference<T>::value,
+        typename std::add_rvalue_reference<intrinsic_t<T>>::type,
+        typename std::add_lvalue_reference<intrinsic_t<T>>::type>>;
+
+// std::is_copy_constructible isn't quite enough: it lets std::vector<T> (and similar) through when
+// T is non-copyable, but code containing such a copy constructor fails to actually compile.
+template <typename T, typename SFINAE = void> struct is_copy_constructible : std::is_copy_constructible<T> {};
+
+// Specialization for types that appear to be copy constructible but also look like stl containers
+// (we specifically check for: has `value_type` and `reference` with `reference = value_type&`): if
+// so, copy constructability depends on whether the value_type is copy constructible.
+template <typename Container> struct is_copy_constructible<Container, enable_if_t<all_of<
+        std::is_copy_constructible<Container>,
+        std::is_same<typename Container::value_type &, typename Container::reference>,
+        // Avoid infinite recursion
+        negation<std::is_same<Container, typename Container::value_type>>
+    >::value>> : is_copy_constructible<typename Container::value_type> {};
+
+// Likewise for std::pair
+// (after C++17 it is mandatory that the copy constructor not exist when the two types aren't themselves
+// copy constructible, but this can not be relied upon when T1 or T2 are themselves containers).
+template <typename T1, typename T2> struct is_copy_constructible<std::pair<T1, T2>>
+    : all_of<is_copy_constructible<T1>, is_copy_constructible<T2>> {};
+
+// The same problems arise with std::is_copy_assignable, so we use the same workaround.
+template <typename T, typename SFINAE = void> struct is_copy_assignable : std::is_copy_assignable<T> {};
+template <typename Container> struct is_copy_assignable<Container, enable_if_t<all_of<
+        std::is_copy_assignable<Container>,
+        std::is_same<typename Container::value_type &, typename Container::reference>
+    >::value>> : is_copy_assignable<typename Container::value_type> {};
+template <typename T1, typename T2> struct is_copy_assignable<std::pair<T1, T2>>
+    : all_of<is_copy_assignable<T1>, is_copy_assignable<T2>> {};
+
+PYBIND11_NAMESPACE_END(detail)
+
+// polymorphic_type_hook<itype>::get(src, tinfo) determines whether the object pointed
+// to by `src` actually is an instance of some class derived from `itype`.
+// If so, it sets `tinfo` to point to the std::type_info representing that derived
+// type, and returns a pointer to the start of the most-derived object of that type
+// (in which `src` is a subobject; this will be the same address as `src` in most
+// single inheritance cases). If not, or if `src` is nullptr, it simply returns `src`
+// and leaves `tinfo` at its default value of nullptr.
+//
+// The default polymorphic_type_hook just returns src. A specialization for polymorphic
+// types determines the runtime type of the passed object and adjusts the this-pointer
+// appropriately via dynamic_cast<void*>. This is what enables a C++ Animal* to appear
+// to Python as a Dog (if Dog inherits from Animal, Animal is polymorphic, Dog is
+// registered with pybind11, and this Animal is in fact a Dog).
+//
+// You may specialize polymorphic_type_hook yourself for types that want to appear
+// polymorphic to Python but do not use C++ RTTI. (This is a not uncommon pattern
+// in performance-sensitive applications, used most notably in LLVM.)
+//
+// polymorphic_type_hook_base allows users to specialize polymorphic_type_hook with
+// std::enable_if. User provided specializations will always have higher priority than
+// the default implementation and specialization provided in polymorphic_type_hook_base.
+template <typename itype, typename SFINAE = void>
+struct polymorphic_type_hook_base
+{
+    static const void *get(const itype *src, const std::type_info*&) { return src; }
+};
+template <typename itype>
+struct polymorphic_type_hook_base<itype, detail::enable_if_t<std::is_polymorphic<itype>::value>>
+{
+    static const void *get(const itype *src, const std::type_info*& type) {
+        type = src ? &typeid(*src) : nullptr;
+        return dynamic_cast<const void*>(src);
+    }
+};
+template <typename itype, typename SFINAE = void>
+struct polymorphic_type_hook : public polymorphic_type_hook_base<itype> {};
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+/// Generic type caster for objects stored on the heap
+template <typename type> class type_caster_base : public type_caster_generic {
+    using itype = intrinsic_t<type>;
+
+public:
+    static constexpr auto name = const_name<type>();
+
+    type_caster_base() : type_caster_base(typeid(type)) { }
+    explicit type_caster_base(const std::type_info &info) : type_caster_generic(info) { }
+
+    static handle cast(const itype &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic || policy == return_value_policy::automatic_reference)
+            policy = return_value_policy::copy;
+        return cast(&src, policy, parent);
+    }
+
+    static handle cast(itype &&src, return_value_policy, handle parent) {
+        return cast(&src, return_value_policy::move, parent);
+    }
+
+    // Returns a (pointer, type_info) pair taking care of necessary type lookup for a
+    // polymorphic type (using RTTI by default, but can be overridden by specializing
+    // polymorphic_type_hook). If the instance isn't derived, returns the base version.
+    static std::pair<const void *, const type_info *> src_and_type(const itype *src) {
+        auto &cast_type = typeid(itype);
+        const std::type_info *instance_type = nullptr;
+        const void *vsrc = polymorphic_type_hook<itype>::get(src, instance_type);
+        if (instance_type && !same_type(cast_type, *instance_type)) {
+            // This is a base pointer to a derived type. If the derived type is registered
+            // with pybind11, we want to make the full derived object available.
+            // In the typical case where itype is polymorphic, we get the correct
+            // derived pointer (which may be != base pointer) by a dynamic_cast to
+            // most derived type. If itype is not polymorphic, we won't get here
+            // except via a user-provided specialization of polymorphic_type_hook,
+            // and the user has promised that no this-pointer adjustment is
+            // required in that case, so it's OK to use static_cast.
+            if (const auto *tpi = get_type_info(*instance_type))
+                return {vsrc, tpi};
+        }
+        // Otherwise we have either a nullptr, an `itype` pointer, or an unknown derived pointer, so
+        // don't do a cast
+        return type_caster_generic::src_and_type(src, cast_type, instance_type);
+    }
+
+    static handle cast(const itype *src, return_value_policy policy, handle parent) {
+        auto st = src_and_type(src);
+        return type_caster_generic::cast(
+            st.first, policy, parent, st.second,
+            make_copy_constructor(src), make_move_constructor(src));
+    }
+
+    static handle cast_holder(const itype *src, const void *holder) {
+        auto st = src_and_type(src);
+        return type_caster_generic::cast(
+            st.first, return_value_policy::take_ownership, {}, st.second,
+            nullptr, nullptr, holder);
+    }
+
+    template <typename T> using cast_op_type = detail::cast_op_type<T>;
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator itype*() { return (type *) value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator itype&() { if (!value) throw reference_cast_error(); return *((itype *) value); }
+
+protected:
+    using Constructor = void *(*)(const void *);
+
+    /* Only enabled when the types are {copy,move}-constructible *and* when the type
+       does not have a private operator new implementation. A comma operator is used in the decltype
+       argument to apply SFINAE to the public copy/move constructors.*/
+    template <typename T, typename = enable_if_t<is_copy_constructible<T>::value>>
+    static auto make_copy_constructor(const T *) -> decltype(new T(std::declval<const T>()), Constructor{}) {
+        return [](const void *arg) -> void * {
+            return new T(*reinterpret_cast<const T *>(arg));
+        };
+    }
+
+    template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
+    static auto make_move_constructor(const T *) -> decltype(new T(std::declval<T&&>()), Constructor{}) {
+        return [](const void *arg) -> void * {
+            return new T(std::move(*const_cast<T *>(reinterpret_cast<const T *>(arg))));
+        };
+    }
+
+    static Constructor make_copy_constructor(...) { return nullptr; }
+    static Constructor make_move_constructor(...) { return nullptr; }
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/detail/typeid.h

@@ -29,7 +29,7 @@ inline void erase_all(std::string &string, const std::string &search) {
     }
 }
 
-PYBIND11_NOINLINE inline void clean_type_id(std::string &name) {
+PYBIND11_NOINLINE void clean_type_id(std::string &name) {
 #if defined(__GNUG__)
     int status = 0;
     std::unique_ptr<char, void (*)(void *)> res {

wrap/pybind11/include/pybind11/eigen.h

@@ -9,33 +9,31 @@
 
 #pragma once
 
+/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
+   See also:
+       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
+       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
+*/
+
 #include "numpy.h"
 
-#if defined(__INTEL_COMPILER)
+// The C4127 suppression was introduced for Eigen 3.4.0. In theory we could
-#  pragma warning(disable: 1682) // implicit conversion of a 64-bit integral type to a smaller integral type (potential portability problem)
+// make it version specific, or even remove it later, but considering that
-#elif defined(__GNUG__) || defined(__clang__)
+// 1. C4127 is generally far more distracting than useful for modern template code, and
-#  pragma GCC diagnostic push
+// 2. we definitely want to ignore any MSVC warnings originating from Eigen code,
-#  pragma GCC diagnostic ignored "-Wconversion"
+// it is probably best to keep this around indefinitely.
-#  pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#  ifdef __clang__
-//   Eigen generates a bunch of implicit-copy-constructor-is-deprecated warnings with -Wdeprecated
-//   under Clang, so disable that warning here:
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#  endif
-#  if __GNUC__ >= 7
-#    pragma GCC diagnostic ignored "-Wint-in-bool-context"
-#  endif
-#endif
-
 #if defined(_MSC_VER)
 #  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
+#  pragma warning(disable: 4127) // C4127: conditional expression is constant
-#  pragma warning(disable: 4996) // warning C4996: std::unary_negate is deprecated in C++17
 #endif
 
 #include <Eigen/Core>
 #include <Eigen/SparseCore>
 
+#if defined(_MSC_VER)
+#  pragma warning(pop)
+#endif
+
 // Eigen prior to 3.2.7 doesn't have proper move constructors--but worse, some classes get implicit
 // move constructors that break things.  We could detect this an explicitly copy, but an extra copy
 // of matrices seems highly undesirable.
@@ -52,8 +50,12 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 
 #if EIGEN_VERSION_AT_LEAST(3,3,0)
 using EigenIndex = Eigen::Index;
+template<typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::Map<Eigen::SparseMatrix<Scalar, Flags, StorageIndex>>;
 #else
 using EigenIndex = EIGEN_DEFAULT_DENSE_INDEX_TYPE;
+template<typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::MappedSparseMatrix<Scalar, Flags, StorageIndex>;
 #endif
 
 // Matches Eigen::Map, Eigen::Ref, blocks, etc:
@@ -77,18 +79,17 @@ template <bool EigenRowMajor> struct EigenConformable {
     EigenDStride stride{0, 0};      // Only valid if negativestrides is false!
     bool negativestrides = false;   // If true, do not use stride!
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     EigenConformable(bool fits = false) : conformable{fits} {}
     // Matrix type:
     EigenConformable(EigenIndex r, EigenIndex c,
             EigenIndex rstride, EigenIndex cstride) :
-        conformable{true}, rows{r}, cols{c} {
+        conformable{true}, rows{r}, cols{c},
-        // TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity. http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
+        //TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity. http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
-        if (rstride < 0 || cstride < 0) {
+        stride{EigenRowMajor ? (rstride > 0 ? rstride : 0) : (cstride > 0 ? cstride : 0) /* outer stride */,
-            negativestrides = true;
+               EigenRowMajor ? (cstride > 0 ? cstride : 0) : (rstride > 0 ? rstride : 0) /* inner stride */ },
-        } else {
+        negativestrides{rstride < 0 || cstride < 0} {
-            stride = {EigenRowMajor ? rstride : cstride /* outer stride */,
+
-                      EigenRowMajor ? cstride : rstride /* inner stride */ };
-        }
     }
     // Vector type:
     EigenConformable(EigenIndex r, EigenIndex c, EigenIndex stride)
@@ -104,6 +105,7 @@ template <bool EigenRowMajor> struct EigenConformable {
             (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer() ||
                 (EigenRowMajor ? rows : cols) == 1);
     }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator bool() const { return conformable; }
 };
 
@@ -153,7 +155,8 @@ template <typename Type_> struct EigenProps {
                 np_cols = a.shape(1),
                 np_rstride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar)),
                 np_cstride = a.strides(1) / static_cast<ssize_t>(sizeof(Scalar));
-            if ((fixed_rows && np_rows != rows) || (fixed_cols && np_cols != cols))
+            if ((PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && np_rows != rows) ||
+                (PYBIND11_SILENCE_MSVC_C4127(fixed_cols) && np_cols != cols))
                 return false;
 
             return {np_rows, np_cols, np_rstride, np_cstride};
@@ -165,26 +168,23 @@ template <typename Type_> struct EigenProps {
               stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
 
         if (vector) { // Eigen type is a compile-time vector
-            if (fixed && size != n)
+            if (PYBIND11_SILENCE_MSVC_C4127(fixed) && size != n)
                 return false; // Vector size mismatch
             return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
         }
-        else if (fixed) {
+        if (fixed) {
             // The type has a fixed size, but is not a vector: abort
             return false;
         }
-        else if (fixed_cols) {
+        if (fixed_cols) {
             // Since this isn't a vector, cols must be != 1.  We allow this only if it exactly
             // equals the number of elements (rows is Dynamic, and so 1 row is allowed).
             if (cols != n) return false;
             return {1, n, stride};
-        }
+        } // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
-        else {
+            if (PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && rows != n) return false;
-            // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
-            if (fixed_rows && rows != n) return false;
             return {n, 1, stride};
     }
-    }
 
     static constexpr bool show_writeable = is_eigen_dense_map<Type>::value && is_eigen_mutable_map<Type>::value;
     static constexpr bool show_order = is_eigen_dense_map<Type>::value;
@@ -192,20 +192,20 @@ template <typename Type_> struct EigenProps {
     static constexpr bool show_f_contiguous = !show_c_contiguous && show_order && requires_col_major;
 
     static constexpr auto descriptor =
-        _("numpy.ndarray[") + npy_format_descriptor<Scalar>::name +
+        const_name("numpy.ndarray[") + npy_format_descriptor<Scalar>::name +
-        _("[")  + _<fixed_rows>(_<(size_t) rows>(), _("m")) +
+        const_name("[")  + const_name<fixed_rows>(const_name<(size_t) rows>(), const_name("m")) +
-        _(", ") + _<fixed_cols>(_<(size_t) cols>(), _("n")) +
+        const_name(", ") + const_name<fixed_cols>(const_name<(size_t) cols>(), const_name("n")) +
-        _("]") +
+        const_name("]") +
         // For a reference type (e.g. Ref<MatrixXd>) we have other constraints that might need to be
         // satisfied: writeable=True (for a mutable reference), and, depending on the map's stride
         // options, possibly f_contiguous or c_contiguous.  We include them in the descriptor output
         // to provide some hint as to why a TypeError is occurring (otherwise it can be confusing to
         // see that a function accepts a 'numpy.ndarray[float64[3,2]]' and an error message that you
         // *gave* a numpy.ndarray of the right type and dimensions.
-        _<show_writeable>(", flags.writeable", "") +
+        const_name<show_writeable>(", flags.writeable", "") +
-        _<show_c_contiguous>(", flags.c_contiguous", "") +
+        const_name<show_c_contiguous>(", flags.c_contiguous", "") +
-        _<show_f_contiguous>(", flags.f_contiguous", "") +
+        const_name<show_f_contiguous>(", flags.f_contiguous", "") +
-        _("]");
+        const_name("]");
 };
 
 // Casts an Eigen type to numpy array.  If given a base, the numpy array references the src data,
@@ -344,8 +344,11 @@ public:
 
     static constexpr auto name = props::descriptor;
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator Type*() { return &value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator Type&() { return value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator Type&&() && { return std::move(value); }
     template <typename T> using cast_op_type = movable_cast_op_type<T>;
 
@@ -432,7 +435,7 @@ public:
         if (!need_copy) {
             // We don't need a converting copy, but we also need to check whether the strides are
             // compatible with the Ref's stride requirements
-            Array aref = reinterpret_borrow<Array>(src);
+            auto aref = reinterpret_borrow<Array>(src);
 
             if (aref && (!need_writeable || aref.writeable())) {
                 fits = props::conformable(aref);
@@ -469,7 +472,9 @@ public:
         return true;
     }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator Type*() { return ref.get(); }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator Type&() { return *ref; }
     template <typename _T> using cast_op_type = pybind11::detail::cast_op_type<_T>;
 
@@ -539,9 +544,9 @@ public:
 
 template<typename Type>
 struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
-    typedef typename Type::Scalar Scalar;
+    using Scalar = typename Type::Scalar;
-    typedef remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())> StorageIndex;
+    using StorageIndex = remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())>;
-    typedef typename Type::Index Index;
+    using Index = typename Type::Index;
     static constexpr bool rowMajor = Type::IsRowMajor;
 
     bool load(handle src, bool) {
@@ -549,7 +554,7 @@ struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
             return false;
 
         auto obj = reinterpret_borrow<object>(src);
-        object sparse_module = module::import("scipy.sparse");
+        object sparse_module = module_::import("scipy.sparse");
         object matrix_type = sparse_module.attr(
             rowMajor ? "csr_matrix" : "csc_matrix");
 
@@ -570,7 +575,9 @@ struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
         if (!values || !innerIndices || !outerIndices)
             return false;
 
-        value = Eigen::MappedSparseMatrix<Scalar, Type::Flags, StorageIndex>(
+        value = EigenMapSparseMatrix<Scalar,
+                                     Type::Flags & (Eigen::RowMajor | Eigen::ColMajor),
+                                     StorageIndex>(
             shape[0].cast<Index>(), shape[1].cast<Index>(), nnz,
             outerIndices.mutable_data(), innerIndices.mutable_data(), values.mutable_data());
 
@@ -580,7 +587,7 @@ struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
     static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
         const_cast<Type&>(src).makeCompressed();
 
-        object matrix_type = module::import("scipy.sparse").attr(
+        object matrix_type = module_::import("scipy.sparse").attr(
             rowMajor ? "csr_matrix" : "csc_matrix");
 
         array data(src.nonZeros(), src.valuePtr());
@@ -593,15 +600,9 @@ struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
         ).release();
     }
 
-    PYBIND11_TYPE_CASTER(Type, _<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[", "scipy.sparse.csc_matrix[")
+    PYBIND11_TYPE_CASTER(Type, const_name<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[", "scipy.sparse.csc_matrix[")
-            + npy_format_descriptor<Scalar>::name + _("]"));
+            + npy_format_descriptor<Scalar>::name + const_name("]"));
 };
 
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(__GNUG__) || defined(__clang__)
-#  pragma GCC diagnostic pop
-#elif defined(_MSC_VER)
-#  pragma warning(pop)
-#endif

wrap/pybind11/include/pybind11/embed.h

@@ -12,6 +12,9 @@
 #include "pybind11.h"
 #include "eval.h"
 
+#include <memory>
+#include <vector>
+
 #if defined(PYPY_VERSION)
 #  error Embedding the interpreter is not supported with PyPy
 #endif
@@ -46,26 +49,22 @@
         }
  \endrst */
 #define PYBIND11_EMBEDDED_MODULE(name, variable)                                                  \
-    static void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &);    \
+    static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name);           \
+    static void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ &);                     \
     static PyObject PYBIND11_CONCAT(*pybind11_init_wrapper_, name)() {                            \
-        auto m = pybind11::module(PYBIND11_TOSTRING(name));                   \
+        auto m = ::pybind11::module_::create_extension_module(                                    \
+            PYBIND11_TOSTRING(name), nullptr, &PYBIND11_CONCAT(pybind11_module_def_, name));      \
         try {                                                                                     \
             PYBIND11_CONCAT(pybind11_init_, name)(m);                                             \
             return m.ptr();                                                                       \
-        } catch (pybind11::error_already_set &e) {                            \
-            PyErr_SetString(PyExc_ImportError, e.what());                     \
-            return nullptr;                                                   \
-        } catch (const std::exception &e) {                                   \
-            PyErr_SetString(PyExc_ImportError, e.what());                     \
-            return nullptr;                                                   \
         }                                                                                         \
+        PYBIND11_CATCH_INIT_EXCEPTIONS                                                            \
     }                                                                                             \
     PYBIND11_EMBEDDED_MODULE_IMPL(name)                                                           \
-    pybind11::detail::embedded_module PYBIND11_CONCAT(pybind11_module_, name) \
+    ::pybind11::detail::embedded_module PYBIND11_CONCAT(pybind11_module_, name)(                  \
-                              (PYBIND11_TOSTRING(name),             \
+        PYBIND11_TOSTRING(name), PYBIND11_CONCAT(pybind11_init_impl_, name));                     \
-                               PYBIND11_CONCAT(pybind11_init_impl_, name));   \
+    void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_                                \
-    void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &variable)
+                                               & variable) // NOLINT(bugprone-macro-parentheses)
-
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -78,7 +77,7 @@ struct embedded_module {
     using init_t = void (*)();
 #endif
     embedded_module(const char *name, init_t init) {
-        if (Py_IsInitialized())
+        if (Py_IsInitialized() != 0)
             pybind11_fail("Can't add new modules after the interpreter has been initialized");
 
         auto result = PyImport_AppendInittab(name, init);
@@ -87,29 +86,118 @@ struct embedded_module {
     }
 };
 
+struct wide_char_arg_deleter {
+    void operator()(wchar_t *ptr) const {
+#if PY_VERSION_HEX >= 0x030500f0
+        // API docs: https://docs.python.org/3/c-api/sys.html#c.Py_DecodeLocale
+        PyMem_RawFree(ptr);
+#else
+        delete[] ptr;
+#endif
+    }
+};
+
+inline wchar_t *widen_chars(const char *safe_arg) {
+#if PY_VERSION_HEX >= 0x030500f0
+    wchar_t *widened_arg = Py_DecodeLocale(safe_arg, nullptr);
+#else
+    wchar_t *widened_arg = nullptr;
+
+// warning C4996: 'mbstowcs': This function or variable may be unsafe.
+#if defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable:4996)
+#endif
+
+#    if defined(HAVE_BROKEN_MBSTOWCS) && HAVE_BROKEN_MBSTOWCS
+    size_t count = std::strlen(safe_arg);
+#    else
+    size_t count = std::mbstowcs(nullptr, safe_arg, 0);
+#    endif
+    if (count != static_cast<size_t>(-1)) {
+        widened_arg = new wchar_t[count + 1];
+        std::mbstowcs(widened_arg, safe_arg, count + 1);
+    }
+
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+
+#endif
+    return widened_arg;
+}
+
+/// Python 2.x/3.x-compatible version of `PySys_SetArgv`
+inline void set_interpreter_argv(int argc, const char *const *argv, bool add_program_dir_to_path) {
+    // Before it was special-cased in python 3.8, passing an empty or null argv
+    // caused a segfault, so we have to reimplement the special case ourselves.
+    bool special_case = (argv == nullptr || argc <= 0);
+
+    const char *const empty_argv[]{"\0"};
+    const char *const *safe_argv = special_case ? empty_argv : argv;
+    if (special_case)
+        argc = 1;
+
+    auto argv_size = static_cast<size_t>(argc);
+#if PY_MAJOR_VERSION >= 3
+    // SetArgv* on python 3 takes wchar_t, so we have to convert.
+    std::unique_ptr<wchar_t *[]> widened_argv(new wchar_t *[argv_size]);
+    std::vector<std::unique_ptr<wchar_t[], wide_char_arg_deleter>> widened_argv_entries;
+    widened_argv_entries.reserve(argv_size);
+    for (size_t ii = 0; ii < argv_size; ++ii) {
+        widened_argv_entries.emplace_back(widen_chars(safe_argv[ii]));
+        if (!widened_argv_entries.back()) {
+            // A null here indicates a character-encoding failure or the python
+            // interpreter out of memory. Give up.
+            return;
+        }
+        widened_argv[ii] = widened_argv_entries.back().get();
+    }
+
+    auto pysys_argv = widened_argv.get();
+#else
+    // python 2.x
+    std::vector<std::string> strings{safe_argv, safe_argv + argv_size};
+    std::vector<char *> char_strings{argv_size};
+    for (std::size_t i = 0; i < argv_size; ++i)
+        char_strings[i] = &strings[i][0];
+    char **pysys_argv = char_strings.data();
+#endif
+
+    PySys_SetArgvEx(argc, pysys_argv, static_cast<int>(add_program_dir_to_path));
+}
+
 PYBIND11_NAMESPACE_END(detail)
 
 /** \rst
     Initialize the Python interpreter. No other pybind11 or CPython API functions can be
     called before this is done; with the exception of `PYBIND11_EMBEDDED_MODULE`. The
-    optional parameter can be used to skip the registration of signal handlers (see the
+    optional `init_signal_handlers` parameter can be used to skip the registration of
-    `Python documentation`_ for details). Calling this function again after the interpreter
+    signal handlers (see the `Python documentation`_ for details). Calling this function
-    has already been initialized is a fatal error.
+    again after the interpreter has already been initialized is a fatal error.
 
     If initializing the Python interpreter fails, then the program is terminated.  (This
     is controlled by the CPython runtime and is an exception to pybind11's normal behavior
     of throwing exceptions on errors.)
 
+    The remaining optional parameters, `argc`, `argv`, and `add_program_dir_to_path` are
+    used to populate ``sys.argv`` and ``sys.path``.
+    See the |PySys_SetArgvEx documentation|_ for details.
+
     .. _Python documentation: https://docs.python.org/3/c-api/init.html#c.Py_InitializeEx
+    .. |PySys_SetArgvEx documentation| replace:: ``PySys_SetArgvEx`` documentation
+    .. _PySys_SetArgvEx documentation: https://docs.python.org/3/c-api/init.html#c.PySys_SetArgvEx
  \endrst */
-inline void initialize_interpreter(bool init_signal_handlers = true) {
+inline void initialize_interpreter(bool init_signal_handlers = true,
-    if (Py_IsInitialized())
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
+    if (Py_IsInitialized() != 0)
         pybind11_fail("The interpreter is already running");
 
     Py_InitializeEx(init_signal_handlers ? 1 : 0);
 
-    // Make .py files in the working directory available by default
+    detail::set_interpreter_argv(argc, argv, add_program_dir_to_path);
-    module::import("sys").attr("path").cast<list>().append(".");
 }
 
 /** \rst
@@ -171,6 +259,8 @@ inline void finalize_interpreter() {
     Scope guard version of `initialize_interpreter` and `finalize_interpreter`.
     This a move-only guard and only a single instance can exist.
 
+    See `initialize_interpreter` for a discussion of its constructor arguments.
+
     .. code-block:: cpp
 
         #include <pybind11/embed.h>
@@ -182,8 +272,11 @@ inline void finalize_interpreter() {
  \endrst */
 class scoped_interpreter {
 public:
-    scoped_interpreter(bool init_signal_handlers = true) {
+    explicit scoped_interpreter(bool init_signal_handlers = true,
-        initialize_interpreter(init_signal_handlers);
+                                int argc = 0,
+                                const char *const *argv = nullptr,
+                                bool add_program_dir_to_path = true) {
+        initialize_interpreter(init_signal_handlers, argc, argv, add_program_dir_to_path);
     }
 
     scoped_interpreter(const scoped_interpreter &) = delete;

wrap/pybind11/include/pybind11/eval.h

@@ -1,5 +1,5 @@
 /*
-    pybind11/exec.h: Support for evaluating Python expressions and statements
+    pybind11/eval.h: Support for evaluating Python expressions and statements
     from strings and files
 
     Copyright (c) 2016 Klemens Morgenstern <klemens.morgenstern@ed-chemnitz.de> and
@@ -11,9 +11,27 @@
 
 #pragma once
 
+#include <utility>
+
 #include "pybind11.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+inline void ensure_builtins_in_globals(object &global) {
+    #if defined(PYPY_VERSION) || PY_VERSION_HEX < 0x03080000
+        // Running exec and eval on Python 2 and 3 adds `builtins` module under
+        // `__builtins__` key to globals if not yet present.
+        // Python 3.8 made PyRun_String behave similarly. Let's also do that for
+        // older versions, for consistency. This was missing from PyPy3.8 7.3.7.
+        if (!global.contains("__builtins__"))
+            global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
+    #else
+        (void) global;
+    #endif
+}
+
+PYBIND11_NAMESPACE_END(detail)
 
 enum eval_mode {
     /// Evaluate a string containing an isolated expression
@@ -27,15 +45,17 @@ enum eval_mode {
 };
 
 template <eval_mode mode = eval_expr>
-object eval(str expr, object global = globals(), object local = object()) {
+object eval(const str &expr, object global = globals(), object local = object()) {
     if (!local)
         local = global;
 
+    detail::ensure_builtins_in_globals(global);
+
     /* PyRun_String does not accept a PyObject / encoding specifier,
        this seems to be the only alternative */
     std::string buffer = "# -*- coding: utf-8 -*-\n" + (std::string) expr;
 
-    int start;
+    int start = 0;
     switch (mode) {
         case eval_expr:             start = Py_eval_input;   break;
         case eval_single_statement: start = Py_single_input; break;
@@ -52,13 +72,13 @@ object eval(str expr, object global = globals(), object local = object()) {
 template <eval_mode mode = eval_expr, size_t N>
 object eval(const char (&s)[N], object global = globals(), object local = object()) {
     /* Support raw string literals by removing common leading whitespace */
-    auto expr = (s[0] == '\n') ? str(module::import("textwrap").attr("dedent")(s))
+    auto expr = (s[0] == '\n') ? str(module_::import("textwrap").attr("dedent")(s))
                                : str(s);
     return eval<mode>(expr, global, local);
 }
 
-inline void exec(str expr, object global = globals(), object local = object()) {
+inline void exec(const str &expr, object global = globals(), object local = object()) {
-    eval<eval_statements>(expr, global, local);
+    eval<eval_statements>(expr, std::move(global), std::move(local));
 }
 
 template <size_t N>
@@ -66,7 +86,7 @@ void exec(const char (&s)[N], object global = globals(), object local = object()
     eval<eval_statements>(s, global, local);
 }
 
-#if defined(PYPY_VERSION) && PY_VERSION_HEX >= 0x3000000
+#if defined(PYPY_VERSION) && PY_VERSION_HEX >= 0x03000000
 template <eval_mode mode = eval_statements>
 object eval_file(str, object, object) {
     pybind11_fail("eval_file not supported in PyPy3. Use eval");
@@ -85,7 +105,9 @@ object eval_file(str fname, object global = globals(), object local = object())
     if (!local)
         local = global;
 
-    int start;
+    detail::ensure_builtins_in_globals(global);
+
+    int start = 0;
     switch (mode) {
         case eval_expr:             start = Py_eval_input;   break;
         case eval_single_statement: start = Py_single_input; break;
@@ -114,6 +136,15 @@ object eval_file(str fname, object global = globals(), object local = object())
         pybind11_fail("File \"" + fname_str + "\" could not be opened!");
     }
 
+    // In Python2, this should be encoded by getfilesystemencoding.
+    // We don't boher setting it since Python2 is past EOL anyway.
+    // See PR#3233
+#if PY_VERSION_HEX >= 0x03000000
+    if (!global.contains("__file__")) {
+        global["__file__"] = std::move(fname);
+    }
+#endif
+
 #if PY_VERSION_HEX < 0x03000000 && defined(PYPY_VERSION)
     PyObject *result = PyRun_File(f, fname_str.c_str(), start, global.ptr(),
                                   local.ptr());

wrap/pybind11/include/pybind11/functional.h

@@ -43,22 +43,43 @@ public:
            captured variables), in which case the roundtrip can be avoided.
          */
         if (auto cfunc = func.cpp_function()) {
-            auto c = reinterpret_borrow<capsule>(PyCFunction_GET_SELF(cfunc.ptr()));
+            auto cfunc_self = PyCFunction_GET_SELF(cfunc.ptr());
+            if (isinstance<capsule>(cfunc_self)) {
+                auto c = reinterpret_borrow<capsule>(cfunc_self);
                 auto rec = (function_record *) c;
 
-            if (rec && rec->is_stateless &&
+                while (rec != nullptr) {
-                    same_type(typeid(function_type), *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
+                    if (rec->is_stateless
-                struct capture { function_type f; };
+                        && same_type(typeid(function_type),
+                                     *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
+                        struct capture {
+                            function_type f;
+                        };
                         value = ((capture *) &rec->data)->f;
                         return true;
                     }
+                    rec = rec->next;
+                }
+            }
+            // PYPY segfaults here when passing builtin function like sum.
+            // Raising an fail exception here works to prevent the segfault, but only on gcc.
+            // See PR #1413 for full details
         }
 
         // ensure GIL is held during functor destruction
         struct func_handle {
             function f;
-            func_handle(function&& f_) : f(std::move(f_)) {}
+#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
-            func_handle(const func_handle&) = default;
+            // This triggers a syntax error under very special conditions (very weird indeed).
+            explicit
+#endif
+            func_handle(function &&f_) noexcept : f(std::move(f_)) {}
+            func_handle(const func_handle &f_) { operator=(f_); }
+            func_handle &operator=(const func_handle &f_) {
+                gil_scoped_acquire acq;
+                f = f_.f;
+                return *this;
+            }
             ~func_handle() {
                 gil_scoped_acquire acq;
                 function kill_f(std::move(f));
@@ -68,7 +89,7 @@ public:
         // to emulate 'move initialization capture' in C++11
         struct func_wrapper {
             func_handle hfunc;
-            func_wrapper(func_handle&& hf): hfunc(std::move(hf)) {}
+            explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
             Return operator()(Args... args) const {
                 gil_scoped_acquire acq;
                 object retval(hfunc.f(std::forward<Args>(args)...));
@@ -89,12 +110,11 @@ public:
         auto result = f_.template target<function_type>();
         if (result)
             return cpp_function(*result, policy).release();
-        else
         return cpp_function(std::forward<Func>(f_), policy).release();
     }
 
-    PYBIND11_TYPE_CASTER(type, _("Callable[[") + concat(make_caster<Args>::name...) + _("], ")
+    PYBIND11_TYPE_CASTER(type, const_name("Callable[[") + concat(make_caster<Args>::name...) + const_name("], ")
-                               + make_caster<retval_type>::name + _("]"));
+                               + make_caster<retval_type>::name + const_name("]"));
 };
 
 PYBIND11_NAMESPACE_END(detail)

wrap/pybind11/include/pybind11/gil.h

@@ -0,0 +1,193 @@
+/*
+    pybind11/gil.h: RAII helpers for managing the GIL
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "detail/common.h"
+#include "detail/internals.h"
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+// forward declarations
+PyThreadState *get_thread_state_unchecked();
+
+PYBIND11_NAMESPACE_END(detail)
+
+
+#if defined(WITH_THREAD) && !defined(PYPY_VERSION)
+
+/* The functions below essentially reproduce the PyGILState_* API using a RAII
+ * pattern, but there are a few important differences:
+ *
+ * 1. When acquiring the GIL from an non-main thread during the finalization
+ *    phase, the GILState API blindly terminates the calling thread, which
+ *    is often not what is wanted. This API does not do this.
+ *
+ * 2. The gil_scoped_release function can optionally cut the relationship
+ *    of a PyThreadState and its associated thread, which allows moving it to
+ *    another thread (this is a fairly rare/advanced use case).
+ *
+ * 3. The reference count of an acquired thread state can be controlled. This
+ *    can be handy to prevent cases where callbacks issued from an external
+ *    thread would otherwise constantly construct and destroy thread state data
+ *    structures.
+ *
+ * See the Python bindings of NanoGUI (http://github.com/wjakob/nanogui) for an
+ * example which uses features 2 and 3 to migrate the Python thread of
+ * execution to another thread (to run the event loop on the original thread,
+ * in this case).
+ */
+
+class gil_scoped_acquire {
+public:
+    PYBIND11_NOINLINE gil_scoped_acquire() {
+        auto &internals = detail::get_internals();
+        tstate = (PyThreadState *) PYBIND11_TLS_GET_VALUE(internals.tstate);
+
+        if (!tstate) {
+            /* Check if the GIL was acquired using the PyGILState_* API instead (e.g. if
+               calling from a Python thread). Since we use a different key, this ensures
+               we don't create a new thread state and deadlock in PyEval_AcquireThread
+               below. Note we don't save this state with internals.tstate, since we don't
+               create it we would fail to clear it (its reference count should be > 0). */
+            tstate = PyGILState_GetThisThreadState();
+        }
+
+        if (!tstate) {
+            tstate = PyThreadState_New(internals.istate);
+            #if !defined(NDEBUG)
+                if (!tstate)
+                    pybind11_fail("scoped_acquire: could not create thread state!");
+            #endif
+            tstate->gilstate_counter = 0;
+            PYBIND11_TLS_REPLACE_VALUE(internals.tstate, tstate);
+        } else {
+            release = detail::get_thread_state_unchecked() != tstate;
+        }
+
+        if (release) {
+            PyEval_AcquireThread(tstate);
+        }
+
+        inc_ref();
+    }
+
+    void inc_ref() {
+        ++tstate->gilstate_counter;
+    }
+
+    PYBIND11_NOINLINE void dec_ref() {
+        --tstate->gilstate_counter;
+        #if !defined(NDEBUG)
+            if (detail::get_thread_state_unchecked() != tstate)
+                pybind11_fail("scoped_acquire::dec_ref(): thread state must be current!");
+            if (tstate->gilstate_counter < 0)
+                pybind11_fail("scoped_acquire::dec_ref(): reference count underflow!");
+        #endif
+        if (tstate->gilstate_counter == 0) {
+            #if !defined(NDEBUG)
+                if (!release)
+                    pybind11_fail("scoped_acquire::dec_ref(): internal error!");
+            #endif
+            PyThreadState_Clear(tstate);
+            if (active)
+                PyThreadState_DeleteCurrent();
+            PYBIND11_TLS_DELETE_VALUE(detail::get_internals().tstate);
+            release = false;
+        }
+    }
+
+    /// This method will disable the PyThreadState_DeleteCurrent call and the
+    /// GIL won't be acquired. This method should be used if the interpreter
+    /// could be shutting down when this is called, as thread deletion is not
+    /// allowed during shutdown. Check _Py_IsFinalizing() on Python 3.7+, and
+    /// protect subsequent code.
+    PYBIND11_NOINLINE void disarm() {
+        active = false;
+    }
+
+    PYBIND11_NOINLINE ~gil_scoped_acquire() {
+        dec_ref();
+        if (release)
+           PyEval_SaveThread();
+    }
+private:
+    PyThreadState *tstate = nullptr;
+    bool release = true;
+    bool active = true;
+};
+
+class gil_scoped_release {
+public:
+    explicit gil_scoped_release(bool disassoc = false) : disassoc(disassoc) {
+        // `get_internals()` must be called here unconditionally in order to initialize
+        // `internals.tstate` for subsequent `gil_scoped_acquire` calls. Otherwise, an
+        // initialization race could occur as multiple threads try `gil_scoped_acquire`.
+        auto &internals = detail::get_internals();
+        tstate = PyEval_SaveThread();
+        if (disassoc) {
+            auto key = internals.tstate;
+            PYBIND11_TLS_DELETE_VALUE(key);
+        }
+    }
+
+    /// This method will disable the PyThreadState_DeleteCurrent call and the
+    /// GIL won't be acquired. This method should be used if the interpreter
+    /// could be shutting down when this is called, as thread deletion is not
+    /// allowed during shutdown. Check _Py_IsFinalizing() on Python 3.7+, and
+    /// protect subsequent code.
+    PYBIND11_NOINLINE void disarm() {
+        active = false;
+    }
+
+    ~gil_scoped_release() {
+        if (!tstate)
+            return;
+        // `PyEval_RestoreThread()` should not be called if runtime is finalizing
+        if (active)
+            PyEval_RestoreThread(tstate);
+        if (disassoc) {
+            auto key = detail::get_internals().tstate;
+            PYBIND11_TLS_REPLACE_VALUE(key, tstate);
+        }
+    }
+private:
+    PyThreadState *tstate;
+    bool disassoc;
+    bool active = true;
+};
+#elif defined(PYPY_VERSION)
+class gil_scoped_acquire {
+    PyGILState_STATE state;
+public:
+    gil_scoped_acquire() { state = PyGILState_Ensure(); }
+    ~gil_scoped_acquire() { PyGILState_Release(state); }
+    void disarm() {}
+};
+
+class gil_scoped_release {
+    PyThreadState *state;
+public:
+    gil_scoped_release() { state = PyEval_SaveThread(); }
+    ~gil_scoped_release() { PyEval_RestoreThread(state); }
+    void disarm() {}
+};
+#else
+class gil_scoped_acquire {
+    void disarm() {}
+};
+class gil_scoped_release {
+    void disarm() {}
+};
+#endif
+
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/iostream.h

@@ -5,17 +5,31 @@
 
     All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file.
+
+    WARNING: The implementation in this file is NOT thread safe. Multiple
+    threads writing to a redirected ostream concurrently cause data races
+    and potentially buffer overflows. Therefore it is currently a requirement
+    that all (possibly) concurrent redirected ostream writes are protected by
+    a mutex.
+    #HelpAppreciated: Work on iostream.h thread safety.
+    For more background see the discussions under
+    https://github.com/pybind/pybind11/pull/2982 and
+    https://github.com/pybind/pybind11/pull/2995.
 */
 
 #pragma once
 
 #include "pybind11.h"
 
-#include <streambuf>
+#include <algorithm>
-#include <ostream>
+#include <cstring>
-#include <string>
-#include <memory>
 #include <iostream>
+#include <iterator>
+#include <memory>
+#include <ostream>
+#include <streambuf>
+#include <string>
+#include <utility>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -38,21 +52,68 @@ private:
         return sync() == 0 ? traits_type::not_eof(c) : traits_type::eof();
     }
 
-    // This function must be non-virtual to be called in a destructor. If the
+    // Computes how many bytes at the end of the buffer are part of an
-    // rare MSVC test failure shows up with this version, then this should be
+    // incomplete sequence of UTF-8 bytes.
-    // simplified to a fully qualified call.
+    // Precondition: pbase() < pptr()
-    int _sync() {
+    size_t utf8_remainder() const {
-        if (pbase() != pptr()) {
+        const auto rbase = std::reverse_iterator<char *>(pbase());
-            // This subtraction cannot be negative, so dropping the sign
+        const auto rpptr = std::reverse_iterator<char *>(pptr());
-            str line(pbase(), static_cast<size_t>(pptr() - pbase()));
+        auto is_ascii = [](char c) {
+            return (static_cast<unsigned char>(c) & 0x80) == 0x00;
+        };
+        auto is_leading = [](char c) {
+            return (static_cast<unsigned char>(c) & 0xC0) == 0xC0;
+        };
+        auto is_leading_2b = [](char c) {
+            return static_cast<unsigned char>(c) <= 0xDF;
+        };
+        auto is_leading_3b = [](char c) {
+            return static_cast<unsigned char>(c) <= 0xEF;
+        };
+        // If the last character is ASCII, there are no incomplete code points
+        if (is_ascii(*rpptr))
+            return 0;
+        // Otherwise, work back from the end of the buffer and find the first
+        // UTF-8 leading byte
+        const auto rpend   = rbase - rpptr >= 3 ? rpptr + 3 : rbase;
+        const auto leading = std::find_if(rpptr, rpend, is_leading);
+        if (leading == rbase)
+            return 0;
+        const auto dist    = static_cast<size_t>(leading - rpptr);
+        size_t remainder   = 0;
 
-            {
+        if (dist == 0)
+            remainder = 1; // 1-byte code point is impossible
+        else if (dist == 1)
+            remainder = is_leading_2b(*leading) ? 0 : dist + 1;
+        else if (dist == 2)
+            remainder = is_leading_3b(*leading) ? 0 : dist + 1;
+        // else if (dist >= 3), at least 4 bytes before encountering an UTF-8
+        // leading byte, either no remainder or invalid UTF-8.
+        // Invalid UTF-8 will cause an exception later when converting
+        // to a Python string, so that's not handled here.
+        return remainder;
+    }
+
+    // This function must be non-virtual to be called in a destructor.
+    int _sync() {
+        if (pbase() != pptr()) { // If buffer is not empty
             gil_scoped_acquire tmp;
+            // This subtraction cannot be negative, so dropping the sign.
+            auto size        = static_cast<size_t>(pptr() - pbase());
+            size_t remainder = utf8_remainder();
+
+            if (size > remainder) {
+                str line(pbase(), size - remainder);
                 pywrite(line);
                 pyflush();
             }
 
+            // Copy the remainder at the end of the buffer to the beginning:
+            if (remainder > 0)
+                std::memmove(pbase(), pptr() - remainder, remainder);
             setp(pbase(), epptr());
+            pbump(static_cast<int>(remainder));
         }
         return 0;
     }
@@ -62,11 +123,8 @@ private:
     }
 
 public:
-
+    explicit pythonbuf(const object &pyostream, size_t buffer_size = 1024)
-    pythonbuf(object pyostream, size_t buffer_size = 1024)
+        : buf_size(buffer_size), d_buffer(new char[buf_size]), pywrite(pyostream.attr("write")),
-        : buf_size(buffer_size),
-          d_buffer(new char[buf_size]),
-          pywrite(pyostream.attr("write")),
           pyflush(pyostream.attr("flush")) {
         setp(d_buffer.get(), d_buffer.get() + buf_size - 1);
     }
@@ -103,7 +161,7 @@ PYBIND11_NAMESPACE_END(detail)
 
         {
             py::scoped_ostream_redirect output{std::cerr, py::module::import("sys").attr("stderr")};
-            std::cerr << "Hello, World!";
+            std::cout << "Hello, World!";
         }
  \endrst */
 class scoped_ostream_redirect {
@@ -113,9 +171,9 @@ protected:
     detail::pythonbuf buffer;
 
 public:
-    scoped_ostream_redirect(
+    explicit scoped_ostream_redirect(std::ostream &costream = std::cout,
-            std::ostream &costream = std::cout,
+                                     const object &pyostream
-            object pyostream = module::import("sys").attr("stdout"))
+                                     = module_::import("sys").attr("stdout"))
         : costream(costream), buffer(pyostream) {
         old = costream.rdbuf(&buffer);
     }
@@ -144,10 +202,10 @@ public:
 \endrst */
 class scoped_estream_redirect : public scoped_ostream_redirect {
 public:
-    scoped_estream_redirect(
+    explicit scoped_estream_redirect(std::ostream &costream = std::cerr,
-            std::ostream &costream = std::cerr,
+                                     const object &pyostream
-            object pyostream = module::import("sys").attr("stderr"))
+                                     = module_::import("sys").attr("stderr"))
-        : scoped_ostream_redirect(costream,pyostream) {}
+        : scoped_ostream_redirect(costream, pyostream) {}
 };
 
 
@@ -161,7 +219,7 @@ class OstreamRedirect {
     std::unique_ptr<scoped_estream_redirect> redirect_stderr;
 
 public:
-    OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
+    explicit OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
         : do_stdout_(do_stdout), do_stderr_(do_stderr) {}
 
     void enter() {
@@ -206,11 +264,12 @@ PYBIND11_NAMESPACE_END(detail)
             m.noisy_function_with_error_printing()
 
  \endrst */
-inline class_<detail::OstreamRedirect> add_ostream_redirect(module m, std::string name = "ostream_redirect") {
+inline class_<detail::OstreamRedirect>
-    return class_<detail::OstreamRedirect>(m, name.c_str(), module_local())
+add_ostream_redirect(module_ m, const std::string &name = "ostream_redirect") {
-        .def(init<bool,bool>(), arg("stdout")=true, arg("stderr")=true)
+    return class_<detail::OstreamRedirect>(std::move(m), name.c_str(), module_local())
+        .def(init<bool, bool>(), arg("stdout") = true, arg("stderr") = true)
         .def("__enter__", &detail::OstreamRedirect::enter)
-        .def("__exit__", [](detail::OstreamRedirect &self_, args) { self_.exit(); });
+        .def("__exit__", [](detail::OstreamRedirect &self_, const args &) { self_.exit(); });
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/numpy.h

@@ -20,20 +20,18 @@
 #include <sstream>
 #include <string>
 #include <functional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 #include <typeindex>
 
-#if defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 /* This will be true on all flat address space platforms and allows us to reduce the
    whole npy_intp / ssize_t / Py_intptr_t business down to just ssize_t for all size
    and dimension types (e.g. shape, strides, indexing), instead of inflicting this
    upon the library user. */
-static_assert(sizeof(ssize_t) == sizeof(Py_intptr_t), "ssize_t != Py_intptr_t");
+static_assert(sizeof(::pybind11::ssize_t) == sizeof(Py_intptr_t), "ssize_t != Py_intptr_t");
+static_assert(std::is_signed<Py_intptr_t>::value, "Py_intptr_t must be signed");
+// We now can reinterpret_cast between py::ssize_t and Py_intptr_t (MSVC + PyPy cares)
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -41,7 +39,7 @@ class array; // Forward declaration
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
-template <> struct handle_type_name<array> { static constexpr auto name = _("numpy.ndarray"); };
+template <> struct handle_type_name<array> { static constexpr auto name = const_name("numpy.ndarray"); };
 
 template <typename type, typename SFINAE = void> struct npy_format_descriptor;
 
@@ -101,7 +99,7 @@ struct numpy_internals {
     }
 };
 
-inline PYBIND11_NOINLINE void load_numpy_internals(numpy_internals* &ptr) {
+PYBIND11_NOINLINE void load_numpy_internals(numpy_internals* &ptr) {
     ptr = &get_or_create_shared_data<numpy_internals>("_numpy_internals");
 }
 
@@ -161,10 +159,10 @@ struct npy_api {
             NPY_ULONG_, NPY_ULONGLONG_, NPY_UINT_),
     };
 
-    typedef struct {
+    struct PyArray_Dims {
         Py_intptr_t *ptr;
         int len;
-    } PyArray_Dims;
+    };
 
     static npy_api& get() {
         static npy_api api = lookup();
@@ -172,10 +170,10 @@ struct npy_api {
     }
 
     bool PyArray_Check_(PyObject *obj) const {
-        return (bool) PyObject_TypeCheck(obj, PyArray_Type_);
+        return PyObject_TypeCheck(obj, PyArray_Type_) != 0;
     }
     bool PyArrayDescr_Check_(PyObject *obj) const {
-        return (bool) PyObject_TypeCheck(obj, PyArrayDescr_Type_);
+        return PyObject_TypeCheck(obj, PyArrayDescr_Type_) != 0;
     }
 
     unsigned int (*PyArray_GetNDArrayCFeatureVersion_)();
@@ -200,6 +198,9 @@ struct npy_api {
     // Unused. Not removed because that affects ABI of the class.
     int (*PyArray_SetBaseObject_)(PyObject *, PyObject *);
     PyObject* (*PyArray_Resize_)(PyObject*, PyArray_Dims*, int, int);
+    PyObject* (*PyArray_Newshape_)(PyObject*, PyArray_Dims*, int);
+    PyObject* (*PyArray_View_)(PyObject*, PyObject*, PyObject*);
+
 private:
     enum functions {
         API_PyArray_GetNDArrayCFeatureVersion = 211,
@@ -214,15 +215,17 @@ private:
         API_PyArray_NewCopy = 85,
         API_PyArray_NewFromDescr = 94,
         API_PyArray_DescrNewFromType = 96,
+        API_PyArray_Newshape = 135,
+        API_PyArray_Squeeze = 136,
+        API_PyArray_View = 137,
         API_PyArray_DescrConverter = 174,
         API_PyArray_EquivTypes = 182,
         API_PyArray_GetArrayParamsFromObject = 278,
-        API_PyArray_Squeeze = 136,
         API_PyArray_SetBaseObject = 282
     };
 
     static npy_api lookup() {
-        module_ m = module::import("numpy.core.multiarray");
+        module_ m = module_::import("numpy.core.multiarray");
         auto c = m.attr("_ARRAY_API");
 #if PY_MAJOR_VERSION >= 3
         void **api_ptr = (void **) PyCapsule_GetPointer(c.ptr(), NULL);
@@ -245,11 +248,14 @@ private:
         DECL_NPY_API(PyArray_NewCopy);
         DECL_NPY_API(PyArray_NewFromDescr);
         DECL_NPY_API(PyArray_DescrNewFromType);
+        DECL_NPY_API(PyArray_Newshape);
+        DECL_NPY_API(PyArray_Squeeze);
+        DECL_NPY_API(PyArray_View);
         DECL_NPY_API(PyArray_DescrConverter);
         DECL_NPY_API(PyArray_EquivTypes);
         DECL_NPY_API(PyArray_GetArrayParamsFromObject);
-        DECL_NPY_API(PyArray_Squeeze);
         DECL_NPY_API(PyArray_SetBaseObject);
+
 #undef DECL_NPY_API
         return api;
     }
@@ -284,7 +290,7 @@ template <typename T> struct array_info_scalar {
     using type = T;
     static constexpr bool is_array = false;
     static constexpr bool is_empty = false;
-    static constexpr auto extents = _("");
+    static constexpr auto extents = const_name("");
     static void append_extents(list& /* shape */) { }
 };
 // Computes underlying type and a comma-separated list of extents for array
@@ -303,8 +309,8 @@ template <typename T, size_t N> struct array_info<std::array<T, N>> {
         array_info<T>::append_extents(shape);
     }
 
-    static constexpr auto extents = _<array_info<T>::is_array>(
+    static constexpr auto extents = const_name<array_info<T>::is_array>(
-        concat(_<N>(), array_info<T>::extents), _<N>()
+        concat(const_name<N>(), array_info<T>::extents), const_name<N>()
     );
 };
 // For numpy we have special handling for arrays of characters, so we don't include
@@ -316,18 +322,23 @@ template <typename T> using remove_all_extents_t = typename array_info<T>::type;
 
 template <typename T> using is_pod_struct = all_of<
     std::is_standard_layout<T>,     // since we're accessing directly in memory we need a standard layout type
-#if !defined(__GNUG__) || defined(_LIBCPP_VERSION) || defined(_GLIBCXX_USE_CXX11_ABI)
+#if defined(__GLIBCXX__) && (__GLIBCXX__ < 20150422 || __GLIBCXX__ == 20150426 || __GLIBCXX__ == 20150623 || __GLIBCXX__ == 20150626 || __GLIBCXX__ == 20160803)
-    // _GLIBCXX_USE_CXX11_ABI indicates that we're using libstdc++ from GCC 5 or newer, independent
+    // libstdc++ < 5 (including versions 4.8.5, 4.9.3 and 4.9.4 which were released after 5)
-    // of the actual compiler (Clang can also use libstdc++, but it always defines __GNUC__ == 4).
+    // don't implement is_trivially_copyable, so approximate it
-    std::is_trivially_copyable<T>,
-#else
-    // GCC 4 doesn't implement is_trivially_copyable, so approximate it
     std::is_trivially_destructible<T>,
     satisfies_any_of<T, std::has_trivial_copy_constructor, std::has_trivial_copy_assign>,
+#else
+    std::is_trivially_copyable<T>,
 #endif
     satisfies_none_of<T, std::is_reference, std::is_array, is_std_array, std::is_arithmetic, is_complex, std::is_enum>
 >;
 
+// Replacement for std::is_pod (deprecated in C++20)
+template <typename T> using is_pod = all_of<
+    std::is_standard_layout<T>,
+    std::is_trivial<T>
+>;
+
 template <ssize_t Dim = 0, typename Strides> ssize_t byte_offset_unsafe(const Strides &) { return 0; }
 template <ssize_t Dim = 0, typename Strides, typename... Ix>
 ssize_t byte_offset_unsafe(const Strides &strides, ssize_t i, Ix... index) {
@@ -419,6 +430,10 @@ class unchecked_mutable_reference : public unchecked_reference<T, Dims> {
     using ConstBase::ConstBase;
     using ConstBase::Dynamic;
 public:
+    // Bring in const-qualified versions from base class
+    using ConstBase::operator();
+    using ConstBase::operator[];
+
     /// Mutable, unchecked access to data at the given indices.
     template <typename... Ix> T& operator()(Ix... index) {
         static_assert(ssize_t{sizeof...(Ix)} == Dims || Dynamic,
@@ -453,28 +468,30 @@ public:
     explicit dtype(const buffer_info &info) {
         dtype descr(_dtype_from_pep3118()(PYBIND11_STR_TYPE(info.format)));
         // If info.itemsize == 0, use the value calculated from the format string
-        m_ptr = descr.strip_padding(info.itemsize ? info.itemsize : descr.itemsize()).release().ptr();
+        m_ptr = descr.strip_padding(info.itemsize != 0 ? info.itemsize : descr.itemsize())
+                    .release()
+                    .ptr();
     }
 
     explicit dtype(const std::string &format) {
         m_ptr = from_args(pybind11::str(format)).release().ptr();
     }
 
-    dtype(const char *format) : dtype(std::string(format)) { }
+    explicit dtype(const char *format) : dtype(std::string(format)) {}
 
     dtype(list names, list formats, list offsets, ssize_t itemsize) {
         dict args;
-        args["names"] = names;
+        args["names"] = std::move(names);
-        args["formats"] = formats;
+        args["formats"] = std::move(formats);
-        args["offsets"] = offsets;
+        args["offsets"] = std::move(offsets);
         args["itemsize"] = pybind11::int_(itemsize);
-        m_ptr = from_args(args).release().ptr();
+        m_ptr = from_args(std::move(args)).release().ptr();
     }
 
     /// This is essentially the same as calling numpy.dtype(args) in Python.
     static dtype from_args(object args) {
         PyObject *ptr = nullptr;
-        if (!detail::npy_api::get().PyArray_DescrConverter_(args.ptr(), &ptr) || !ptr)
+        if ((detail::npy_api::get().PyArray_DescrConverter_(args.ptr(), &ptr) == 0) || !ptr)
             throw error_already_set();
         return reinterpret_steal<dtype>(ptr);
     }
@@ -494,14 +511,24 @@ public:
         return detail::array_descriptor_proxy(m_ptr)->names != nullptr;
     }
 
-    /// Single-character type code.
+    /// Single-character code for dtype's kind.
+    /// For example, floating point types are 'f' and integral types are 'i'.
     char kind() const {
         return detail::array_descriptor_proxy(m_ptr)->kind;
     }
 
+    /// Single-character for dtype's type.
+    /// For example, ``float`` is 'f', ``double`` 'd', ``int`` 'i', and ``long`` 'l'.
+    char char_() const {
+        // Note: The signature, `dtype::char_` follows the naming of NumPy's
+        // public Python API (i.e., ``dtype.char``), rather than its internal
+        // C API (``PyArray_Descr::type``).
+        return detail::array_descriptor_proxy(m_ptr)->type;
+    }
+
 private:
     static object _dtype_from_pep3118() {
-        static PyObject *obj = module::import("numpy.core._internal")
+        static PyObject *obj = module_::import("numpy.core._internal")
             .attr("_dtype_from_pep3118").cast<object>().release().ptr();
         return reinterpret_borrow<object>(obj);
     }
@@ -520,7 +547,7 @@ private:
             auto name = spec[0].cast<pybind11::str>();
             auto format = spec[1].cast<tuple>()[0].cast<dtype>();
             auto offset = spec[1].cast<tuple>()[1].cast<pybind11::int_>();
-            if (!len(name) && format.kind() == 'V')
+            if ((len(name) == 0u) && format.kind() == 'V')
                 continue;
             field_descriptors.push_back({(PYBIND11_STR_TYPE) name, format.strip_padding(format.itemsize()), offset});
         }
@@ -536,7 +563,7 @@ private:
             formats.append(descr.format);
             offsets.append(descr.offset);
         }
-        return dtype(names, formats, offsets, itemsize);
+        return dtype(std::move(names), std::move(formats), std::move(offsets), itemsize);
     }
 };
 
@@ -560,7 +587,7 @@ public:
           const void *ptr = nullptr, handle base = handle()) {
 
         if (strides->empty())
-            *strides = c_strides(*shape, dt.itemsize());
+            *strides = detail::c_strides(*shape, dt.itemsize());
 
         auto ndim = shape->size();
         if (ndim != strides->size())
@@ -579,7 +606,10 @@ public:
 
         auto &api = detail::npy_api::get();
         auto tmp = reinterpret_steal<object>(api.PyArray_NewFromDescr_(
-            api.PyArray_Type_, descr.release().ptr(), (int) ndim, shape->data(), strides->data(),
+            api.PyArray_Type_, descr.release().ptr(), (int) ndim,
+            // Use reinterpret_cast for PyPy on Windows (remove if fixed, checked on 7.3.1)
+            reinterpret_cast<Py_intptr_t*>(shape->data()),
+            reinterpret_cast<Py_intptr_t*>(strides->data()),
             const_cast<void *>(ptr), flags, nullptr));
         if (!tmp)
             throw error_already_set();
@@ -720,7 +750,7 @@ public:
      * and the caller must take care not to access invalid dimensions or dimension indices.
      */
     template <typename T, ssize_t Dims = -1> detail::unchecked_mutable_reference<T, Dims> mutable_unchecked() & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
             throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                     "; expected " + std::to_string(Dims));
         return detail::unchecked_mutable_reference<T, Dims>(mutable_data(), shape(), strides(), ndim());
@@ -734,7 +764,7 @@ public:
      * invalid dimensions or dimension indices.
      */
     template <typename T, ssize_t Dims = -1> detail::unchecked_reference<T, Dims> unchecked() const & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
             throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                     "; expected " + std::to_string(Dims));
         return detail::unchecked_reference<T, Dims>(data(), shape(), strides(), ndim());
@@ -751,16 +781,45 @@ public:
     /// then resize will succeed only if it makes a reshape, i.e. original size doesn't change
     void resize(ShapeContainer new_shape, bool refcheck = true) {
         detail::npy_api::PyArray_Dims d = {
-            new_shape->data(), int(new_shape->size())
+            // Use reinterpret_cast for PyPy on Windows (remove if fixed, checked on 7.3.1)
+            reinterpret_cast<Py_intptr_t*>(new_shape->data()),
+            int(new_shape->size())
         };
         // try to resize, set ordering param to -1 cause it's not used anyway
-        object new_array = reinterpret_steal<object>(
+        auto new_array = reinterpret_steal<object>(
             detail::npy_api::get().PyArray_Resize_(m_ptr, &d, int(refcheck), -1)
         );
         if (!new_array) throw error_already_set();
         if (isinstance<array>(new_array)) { *this = std::move(new_array); }
     }
 
+    /// Optional `order` parameter omitted, to be added as needed.
+    array reshape(ShapeContainer new_shape) {
+        detail::npy_api::PyArray_Dims d
+            = {reinterpret_cast<Py_intptr_t *>(new_shape->data()), int(new_shape->size())};
+        auto new_array
+            = reinterpret_steal<array>(detail::npy_api::get().PyArray_Newshape_(m_ptr, &d, 0));
+        if (!new_array) {
+            throw error_already_set();
+        }
+        return new_array;
+    }
+
+    /// Create a view of an array in a different data type.
+    /// This function may fundamentally reinterpret the data in the array.
+    /// It is the responsibility of the caller to ensure that this is safe.
+    /// Only supports the `dtype` argument, the `type` argument is omitted,
+    /// to be added as needed.
+    array view(const std::string &dtype) {
+        auto &api = detail::npy_api::get();
+        auto new_view = reinterpret_steal<array>(api.PyArray_View_(
+            m_ptr, dtype::from_args(pybind11::str(dtype)).release().ptr(), nullptr));
+        if (!new_view) {
+            throw error_already_set();
+        }
+        return new_view;
+    }
+
     /// Ensure that the argument is a NumPy array
     /// In case of an error, nullptr is returned and the Python error is cleared.
     static array ensure(handle h, int ExtraFlags = 0) {
@@ -788,25 +847,6 @@ protected:
             throw std::domain_error("array is not writeable");
     }
 
-    // Default, C-style strides
-    static std::vector<ssize_t> c_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
-        auto ndim = shape.size();
-        std::vector<ssize_t> strides(ndim, itemsize);
-        if (ndim > 0)
-            for (size_t i = ndim - 1; i > 0; --i)
-                strides[i - 1] = strides[i] * shape[i];
-        return strides;
-    }
-
-    // F-style strides; default when constructing an array_t with `ExtraFlags & f_style`
-    static std::vector<ssize_t> f_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
-        auto ndim = shape.size();
-        std::vector<ssize_t> strides(ndim, itemsize);
-        for (size_t i = 1; i < ndim; ++i)
-            strides[i] = strides[i - 1] * shape[i - 1];
-        return strides;
-    }
-
     template<typename... Ix> void check_dimensions(Ix... index) const {
         check_dimensions_impl(ssize_t(0), shape(), ssize_t(index)...);
     }
@@ -854,6 +894,7 @@ public:
         if (!is_borrowed) Py_XDECREF(h.ptr());
     }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     array_t(const object &o) : array(raw_array_t(o.ptr()), stolen_t{}) {
         if (!m_ptr) throw error_already_set();
     }
@@ -864,9 +905,12 @@ public:
         : array(std::move(shape), std::move(strides), ptr, base) { }
 
     explicit array_t(ShapeContainer shape, const T *ptr = nullptr, handle base = handle())
-        : array_t(private_ctor{}, std::move(shape),
+        : array_t(private_ctor{},
-                ExtraFlags & f_style ? f_strides(*shape, itemsize()) : c_strides(*shape, itemsize()),
+                  std::move(shape),
-                ptr, base) { }
+                  (ExtraFlags & f_style) != 0 ? detail::f_strides(*shape, itemsize())
+                                              : detail::c_strides(*shape, itemsize()),
+                  ptr,
+                  base) {}
 
     explicit array_t(ssize_t count, const T *ptr = nullptr, handle base = handle())
         : array({count}, {}, ptr, base) { }
@@ -977,7 +1021,7 @@ template <typename T>
 struct format_descriptor<T, detail::enable_if_t<detail::array_info<T>::is_array>> {
     static std::string format() {
         using namespace detail;
-        static constexpr auto extents = _("(") + array_info<T>::extents + _(")");
+        static constexpr auto extents = const_name("(") + array_info<T>::extents + const_name(")");
         return extents.text + format_descriptor<remove_all_extents_t<T>>::format();
     }
 };
@@ -1012,23 +1056,28 @@ struct npy_format_descriptor_name;
 
 template <typename T>
 struct npy_format_descriptor_name<T, enable_if_t<std::is_integral<T>::value>> {
-    static constexpr auto name = _<std::is_same<T, bool>::value>(
+    static constexpr auto name = const_name<std::is_same<T, bool>::value>(
-        _("bool"), _<std::is_signed<T>::value>("numpy.int", "numpy.uint") + _<sizeof(T)*8>()
+        const_name("bool"), const_name<std::is_signed<T>::value>("numpy.int", "numpy.uint") + const_name<sizeof(T)*8>()
     );
 };
 
 template <typename T>
 struct npy_format_descriptor_name<T, enable_if_t<std::is_floating_point<T>::value>> {
-    static constexpr auto name = _<std::is_same<T, float>::value || std::is_same<T, double>::value>(
+    static constexpr auto name = const_name<std::is_same<T, float>::value
-        _("numpy.float") + _<sizeof(T)*8>(), _("numpy.longdouble")
+                                   || std::is_same<T, const float>::value
+                                   || std::is_same<T, double>::value
+                                   || std::is_same<T, const double>::value>(
+        const_name("numpy.float") + const_name<sizeof(T)*8>(), const_name("numpy.longdouble")
     );
 };
 
 template <typename T>
 struct npy_format_descriptor_name<T, enable_if_t<is_complex<T>::value>> {
-    static constexpr auto name = _<std::is_same<typename T::value_type, float>::value
+    static constexpr auto name = const_name<std::is_same<typename T::value_type, float>::value
-                                   || std::is_same<typename T::value_type, double>::value>(
+                                   || std::is_same<typename T::value_type, const float>::value
-        _("numpy.complex") + _<sizeof(typename T::value_type)*16>(), _("numpy.longcomplex")
+                                   || std::is_same<typename T::value_type, double>::value
+                                   || std::is_same<typename T::value_type, const double>::value>(
+        const_name("numpy.complex") + const_name<sizeof(typename T::value_type)*16>(), const_name("numpy.longcomplex")
     );
 };
 
@@ -1056,7 +1105,7 @@ public:
 };
 
 #define PYBIND11_DECL_CHAR_FMT \
-    static constexpr auto name = _("S") + _<N>(); \
+    static constexpr auto name = const_name("S") + const_name<N>(); \
     static pybind11::dtype dtype() { return pybind11::dtype(std::string("S") + std::to_string(N)); }
 template <size_t N> struct npy_format_descriptor<char[N]> { PYBIND11_DECL_CHAR_FMT };
 template <size_t N> struct npy_format_descriptor<std::array<char, N>> { PYBIND11_DECL_CHAR_FMT };
@@ -1068,7 +1117,7 @@ private:
 public:
     static_assert(!array_info<T>::is_empty, "Zero-sized arrays are not supported");
 
-    static constexpr auto name = _("(") + array_info<T>::extents + _(")") + base_descr::name;
+    static constexpr auto name = const_name("(") + array_info<T>::extents + const_name(")") + base_descr::name;
     static pybind11::dtype dtype() {
         list shape;
         array_info<T>::append_extents(shape);
@@ -1092,7 +1141,7 @@ struct field_descriptor {
     dtype descr;
 };
 
-inline PYBIND11_NOINLINE void register_structured_dtype(
+PYBIND11_NOINLINE void register_structured_dtype(
     any_container<field_descriptor> fields,
     const std::type_info& tinfo, ssize_t itemsize,
     bool (*direct_converter)(PyObject *, void *&)) {
@@ -1116,7 +1165,10 @@ inline PYBIND11_NOINLINE void register_structured_dtype(
         formats.append(field.descr);
         offsets.append(pybind11::int_(field.offset));
     }
-    auto dtype_ptr = pybind11::dtype(names, formats, offsets, itemsize).release().ptr();
+    auto dtype_ptr
+        = pybind11::dtype(std::move(names), std::move(formats), std::move(offsets), itemsize)
+              .release()
+              .ptr();
 
     // There is an existing bug in NumPy (as of v1.11): trailing bytes are
     // not encoded explicitly into the format string. This will supposedly
@@ -1270,26 +1322,13 @@ private:
 
 #endif // __CLION_IDE__
 
-template  <class T>
-using array_iterator = typename std::add_pointer<T>::type;
-
-template <class T>
-array_iterator<T> array_begin(const buffer_info& buffer) {
-    return array_iterator<T>(reinterpret_cast<T*>(buffer.ptr));
-}
-
-template <class T>
-array_iterator<T> array_end(const buffer_info& buffer) {
-    return array_iterator<T>(reinterpret_cast<T*>(buffer.ptr) + buffer.size);
-}
-
 class common_iterator {
 public:
     using container_type = std::vector<ssize_t>;
     using value_type = container_type::value_type;
     using size_type = container_type::size_type;
 
-    common_iterator() : p_ptr(0), m_strides() {}
+    common_iterator() : m_strides() {}
 
     common_iterator(void* ptr, const container_type& strides, const container_type& shape)
         : p_ptr(reinterpret_cast<char*>(ptr)), m_strides(strides.size()) {
@@ -1310,7 +1349,7 @@ public:
     }
 
 private:
-    char* p_ptr;
+    char *p_ptr{0};
     container_type m_strides;
 };
 
@@ -1338,9 +1377,8 @@ public:
             if (++m_index[i] != m_shape[i]) {
                 increment_common_iterator(i);
                 break;
-            } else {
-                m_index[i] = 0;
             }
+            m_index[i] = 0;
         }
         return *this;
     }
@@ -1474,7 +1512,7 @@ struct vectorize_arg {
     using call_type = remove_reference_t<T>;
     // Is this a vectorized argument?
     static constexpr bool vectorize =
-        satisfies_any_of<call_type, std::is_arithmetic, is_complex, std::is_pod>::value &&
+        satisfies_any_of<call_type, std::is_arithmetic, is_complex, is_pod>::value &&
         satisfies_none_of<call_type, std::is_pointer, std::is_array, is_std_array, std::is_enum>::value &&
         (!std::is_reference<T>::value ||
          (std::is_lvalue_reference<T>::value && std::is_const<call_type>::value));
@@ -1482,6 +1520,55 @@ struct vectorize_arg {
     using type = conditional_t<vectorize, array_t<remove_cv_t<call_type>, array::forcecast>, T>;
 };
 
+
+// py::vectorize when a return type is present
+template <typename Func, typename Return, typename... Args>
+struct vectorize_returned_array {
+    using Type = array_t<Return>;
+
+    static Type create(broadcast_trivial trivial, const std::vector<ssize_t> &shape) {
+        if (trivial == broadcast_trivial::f_trivial)
+            return array_t<Return, array::f_style>(shape);
+        return array_t<Return>(shape);
+    }
+
+    static Return *mutable_data(Type &array) {
+        return array.mutable_data();
+    }
+
+    static Return call(Func &f, Args &... args) {
+        return f(args...);
+    }
+
+    static void call(Return *out, size_t i, Func &f, Args &... args) {
+        out[i] = f(args...);
+    }
+};
+
+// py::vectorize when a return type is not present
+template <typename Func, typename... Args>
+struct vectorize_returned_array<Func, void, Args...> {
+    using Type = none;
+
+    static Type create(broadcast_trivial, const std::vector<ssize_t> &) {
+        return none();
+    }
+
+    static void *mutable_data(Type &) {
+        return nullptr;
+    }
+
+    static detail::void_type call(Func &f, Args &... args) {
+        f(args...);
+        return {};
+    }
+
+    static void call(void *, size_t, Func &f, Args &... args) {
+        f(args...);
+    }
+};
+
+
 template <typename Func, typename Return, typename... Args>
 struct vectorize_helper {
 
@@ -1498,8 +1585,11 @@ private:
             "pybind11::vectorize(...) requires a function with at least one vectorizable argument");
 
 public:
-    template <typename T>
+    template <typename T,
-    explicit vectorize_helper(T &&f) : f(std::forward<T>(f)) { }
+              // SFINAE to prevent shadowing the copy constructor.
+              typename = detail::enable_if_t<
+                  !std::is_same<vectorize_helper, typename std::decay<T>::type>::value>>
+    explicit vectorize_helper(T &&f) : f(std::forward<T>(f)) {}
 
     object operator()(typename vectorize_arg<Args>::type... args) {
         return run(args...,
@@ -1516,6 +1606,8 @@ private:
     using arg_call_types = std::tuple<typename vectorize_arg<Args>::call_type...>;
     template <size_t Index> using param_n_t = typename std::tuple_element<Index, arg_call_types>::type;
 
+    using returned_array = vectorize_returned_array<Func, Return, Args...>;
+
     // Runs a vectorized function given arguments tuple and three index sequences:
     //     - Index is the full set of 0 ... (N-1) argument indices;
     //     - VIndex is the subset of argument indices with vectorized parameters, letting us access
@@ -1547,20 +1639,19 @@ private:
         // not wrapped in an array).
         if (size == 1 && ndim == 0) {
             PYBIND11_EXPAND_SIDE_EFFECTS(params[VIndex] = buffers[BIndex].ptr);
-            return cast(f(*reinterpret_cast<param_n_t<Index> *>(params[Index])...));
+            return cast(returned_array::call(f, *reinterpret_cast<param_n_t<Index> *>(params[Index])...));
         }
 
-        array_t<Return> result;
+        auto result = returned_array::create(trivial, shape);
-        if (trivial == broadcast_trivial::f_trivial) result = array_t<Return, array::f_style>(shape);
-        else result = array_t<Return>(shape);
 
         if (size == 0) return std::move(result);
 
         /* Call the function */
+        auto mutable_data = returned_array::mutable_data(result);
         if (trivial == broadcast_trivial::non_trivial)
-            apply_broadcast(buffers, params, result, i_seq, vi_seq, bi_seq);
+            apply_broadcast(buffers, params, mutable_data, size, shape, i_seq, vi_seq, bi_seq);
         else
-            apply_trivial(buffers, params, result.mutable_data(), size, i_seq, vi_seq, bi_seq);
+            apply_trivial(buffers, params, mutable_data, size, i_seq, vi_seq, bi_seq);
 
         return std::move(result);
     }
@@ -1583,7 +1674,7 @@ private:
         }};
 
         for (size_t i = 0; i < size; ++i) {
-            out[i] = f(*reinterpret_cast<param_n_t<Index> *>(params[Index])...);
+            returned_array::call(out, i, f, *reinterpret_cast<param_n_t<Index> *>(params[Index])...);
             for (auto &x : vecparams) x.first += x.second;
         }
     }
@@ -1591,19 +1682,18 @@ private:
     template <size_t... Index, size_t... VIndex, size_t... BIndex>
     void apply_broadcast(std::array<buffer_info, NVectorized> &buffers,
                          std::array<void *, N> &params,
-                         array_t<Return> &output_array,
+                         Return *out,
+                         size_t size,
+                         const std::vector<ssize_t> &output_shape,
                          index_sequence<Index...>, index_sequence<VIndex...>, index_sequence<BIndex...>) {
 
-        buffer_info output = output_array.request();
+        multi_array_iterator<NVectorized> input_iter(buffers, output_shape);
-        multi_array_iterator<NVectorized> input_iter(buffers, output.shape);
 
-        for (array_iterator<Return> iter = array_begin<Return>(output), end = array_end<Return>(output);
+        for (size_t i = 0; i < size; ++i, ++input_iter) {
-             iter != end;
-             ++iter, ++input_iter) {
             PYBIND11_EXPAND_SIDE_EFFECTS((
                 params[VIndex] = input_iter.template data<BIndex>()
             ));
-            *iter = f(*reinterpret_cast<param_n_t<Index> *>(std::get<Index>(params))...);
+            returned_array::call(out, i, f, *reinterpret_cast<param_n_t<Index> *>(std::get<Index>(params))...);
         }
     }
 };
@@ -1615,7 +1705,7 @@ vectorize_extractor(const Func &f, Return (*) (Args ...)) {
 }
 
 template <typename T, int Flags> struct handle_type_name<array_t<T, Flags>> {
-    static constexpr auto name = _("numpy.ndarray[") + npy_format_descriptor<T>::name + _("]");
+    static constexpr auto name = const_name("numpy.ndarray[") + npy_format_descriptor<T>::name + const_name("]");
 };
 
 PYBIND11_NAMESPACE_END(detail)
@@ -1649,7 +1739,3 @@ Helper vectorize(Return (Class::*f)(Args...) const) {
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif

wrap/pybind11/include/pybind11/operators.h

@@ -11,13 +11,6 @@
 
 #include "pybind11.h"
 
-#if defined(__clang__) && !defined(__INTEL_COMPILER)
-#  pragma clang diagnostic ignored "-Wunsequenced" // multiple unsequenced modifications to 'self' (when using def(py::self OP Type()))
-#elif defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
@@ -58,7 +51,8 @@ template <op_id id, op_type ot, typename L, typename R> struct op_ {
         using op = op_impl<id, ot, Base, L_type, R_type>;
         cl.def(op::name(), &op::execute, is_operator(), extra...);
         #if PY_MAJOR_VERSION < 3
-        if (id == op_truediv || id == op_itruediv)
+        if (PYBIND11_SILENCE_MSVC_C4127(id == op_truediv) ||
+            PYBIND11_SILENCE_MSVC_C4127(id == op_itruediv))
             cl.def(id == op_itruediv ? "__idiv__" : ot == op_l ? "__div__" : "__rdiv__",
                     &op::execute, is_operator(), extra...);
         #endif
@@ -167,7 +161,3 @@ using detail::self;
 using detail::hash;
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#  pragma warning(pop)
-#endif

wrap/pybind11/include/pybind11/pytypes.h

@@ -14,6 +14,14 @@
 #include <utility>
 #include <type_traits>
 
+#if defined(PYBIND11_HAS_OPTIONAL)
+#  include <optional>
+#endif
+
+#ifdef PYBIND11_HAS_STRING_VIEW
+#  include <string_view>
+#endif
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 /* A few forward declarations */
@@ -24,7 +32,7 @@ struct arg; struct arg_v;
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 class args_proxy;
-inline bool isinstance_generic(handle obj, const std::type_info &tp);
+bool isinstance_generic(handle obj, const std::type_info &tp);
 
 // Accessor forward declarations
 template <typename Policy> class accessor;
@@ -153,7 +161,7 @@ public:
     /// Return the object's current reference count
     int ref_count() const { return static_cast<int>(Py_REFCNT(derived().ptr())); }
 
-    PYBIND11_DEPRECATED("Call py::type::handle_of(h) or py::type::of(h) instead of h.get_type()")
+    // TODO PYBIND11_DEPRECATED("Call py::type::handle_of(h) or py::type::of(h) instead of h.get_type()")
     handle get_type() const;
 
 private:
@@ -178,6 +186,7 @@ public:
     /// The default constructor creates a handle with a ``nullptr``-valued pointer
     handle() = default;
     /// Creates a ``handle`` from the given raw Python object pointer
+    // NOLINTNEXTLINE(google-explicit-constructor)
     handle(PyObject *ptr) : m_ptr(ptr) { } // Allow implicit conversion from PyObject*
 
     /// Return the underlying ``PyObject *`` pointer
@@ -254,8 +263,11 @@ public:
 
     object& operator=(const object &other) {
         other.inc_ref();
-        dec_ref();
+        // Use temporary variable to ensure `*this` remains valid while
+        // `Py_XDECREF` executes, in case `*this` is accessible from Python.
+        handle temp(m_ptr);
         m_ptr = other.m_ptr;
+        temp.dec_ref();
         return *this;
     }
 
@@ -279,8 +291,10 @@ protected:
     struct borrowed_t { };
     struct stolen_t { };
 
+    /// @cond BROKEN
     template <typename T> friend T reinterpret_borrow(handle);
     template <typename T> friend T reinterpret_steal(handle);
+    /// @endcond
 
 public:
     // Only accessible from derived classes and the reinterpret_* functions
@@ -314,14 +328,18 @@ template <typename T> T reinterpret_borrow(handle h) { return {h, object::borrow
 template <typename T> T reinterpret_steal(handle h) { return {h, object::stolen_t{}}; }
 
 PYBIND11_NAMESPACE_BEGIN(detail)
-inline std::string error_string();
+std::string error_string();
 PYBIND11_NAMESPACE_END(detail)
 
+#if defined(_MSC_VER)
+#  pragma warning(push)
+#  pragma warning(disable: 4275 4251) // warning C4275: An exported class was derived from a class that wasn't exported. Can be ignored when derived from a STL class.
+#endif
 /// Fetch and hold an error which was already set in Python.  An instance of this is typically
 /// thrown to propagate python-side errors back through C++ which can either be caught manually or
 /// else falls back to the function dispatcher (which then raises the captured error back to
 /// python).
-class error_already_set : public std::runtime_error {
+class PYBIND11_EXPORT_EXCEPTION error_already_set : public std::runtime_error {
 public:
     /// Constructs a new exception from the current Python error indicator, if any.  The current
     /// Python error indicator will be cleared.
@@ -339,16 +357,17 @@ public:
     /// error variables (but the `.what()` string is still available).
     void restore() { PyErr_Restore(m_type.release().ptr(), m_value.release().ptr(), m_trace.release().ptr()); }
 
-    /// If it is impossible to raise the currently-held error, such as in destructor, we can write
+    /// If it is impossible to raise the currently-held error, such as in a destructor, we can write
-    /// it out using Python's unraisable hook (sys.unraisablehook). The error context should be
+    /// it out using Python's unraisable hook (`sys.unraisablehook`). The error context should be
-    /// some object whose repr() helps identify the location of the error. Python already knows the
+    /// some object whose `repr()` helps identify the location of the error. Python already knows the
-    /// type and value of the error, so there is no need to repeat that. For example, __func__ could
+    /// type and value of the error, so there is no need to repeat that. After this call, the current
-    /// be helpful. After this call, the current object no longer stores the error variables,
+    /// object no longer stores the error variables, and neither does Python.
-    /// and neither does Python.
     void discard_as_unraisable(object err_context) {
         restore();
         PyErr_WriteUnraisable(err_context.ptr());
     }
+    /// An alternate version of `discard_as_unraisable()`, where a string provides information on the
+    /// location of the error. For example, `__func__` could be helpful.
     void discard_as_unraisable(const char *err_context) {
         discard_as_unraisable(reinterpret_steal<object>(PYBIND11_FROM_STRING(err_context)));
     }
@@ -360,7 +379,9 @@ public:
     /// Check if the currently trapped error type matches the given Python exception class (or a
     /// subclass thereof).  May also be passed a tuple to search for any exception class matches in
     /// the given tuple.
-    bool matches(handle exc) const { return PyErr_GivenExceptionMatches(m_type.ptr(), exc.ptr()); }
+    bool matches(handle exc) const {
+        return (PyErr_GivenExceptionMatches(m_type.ptr(), exc.ptr()) != 0);
+    }
 
     const object& type() const { return m_type; }
     const object& value() const { return m_value; }
@@ -369,8 +390,52 @@ public:
 private:
     object m_type, m_value, m_trace;
 };
+#if defined(_MSC_VER)
+#  pragma warning(pop)
+#endif
 
-/** \defgroup python_builtins _
+#if PY_VERSION_HEX >= 0x03030000
+
+/// Replaces the current Python error indicator with the chosen error, performing a
+/// 'raise from' to indicate that the chosen error was caused by the original error.
+inline void raise_from(PyObject *type, const char *message) {
+    // Based on _PyErr_FormatVFromCause:
+    // https://github.com/python/cpython/blob/467ab194fc6189d9f7310c89937c51abeac56839/Python/errors.c#L405
+    // See https://github.com/pybind/pybind11/pull/2112 for details.
+    PyObject *exc = nullptr, *val = nullptr, *val2 = nullptr, *tb = nullptr;
+
+    assert(PyErr_Occurred());
+    PyErr_Fetch(&exc, &val, &tb);
+    PyErr_NormalizeException(&exc, &val, &tb);
+    if (tb != nullptr) {
+        PyException_SetTraceback(val, tb);
+        Py_DECREF(tb);
+    }
+    Py_DECREF(exc);
+    assert(!PyErr_Occurred());
+
+    PyErr_SetString(type, message);
+
+    PyErr_Fetch(&exc, &val2, &tb);
+    PyErr_NormalizeException(&exc, &val2, &tb);
+    Py_INCREF(val);
+    PyException_SetCause(val2, val);
+    PyException_SetContext(val2, val);
+    PyErr_Restore(exc, val2, tb);
+}
+
+/// Sets the current Python error indicator with the chosen error, performing a 'raise from'
+/// from the error contained in error_already_set to indicate that the chosen error was
+/// caused by the original error. After this function is called error_already_set will
+/// no longer contain an error.
+inline void raise_from(error_already_set& err, PyObject *type, const char *message) {
+    err.restore();
+    raise_from(type, message);
+}
+
+#endif
+
+/** \defgroup python_builtins const_name
     Unless stated otherwise, the following C++ functions behave the same
     as their Python counterparts.
  */
@@ -431,19 +496,17 @@ inline object getattr(handle obj, const char *name) {
 inline object getattr(handle obj, handle name, handle default_) {
     if (PyObject *result = PyObject_GetAttr(obj.ptr(), name.ptr())) {
         return reinterpret_steal<object>(result);
-    } else {
+    }
     PyErr_Clear();
     return reinterpret_borrow<object>(default_);
-    }
 }
 
 inline object getattr(handle obj, const char *name, handle default_) {
     if (PyObject *result = PyObject_GetAttrString(obj.ptr(), name)) {
         return reinterpret_steal<object>(result);
-    } else {
+    }
     PyErr_Clear();
     return reinterpret_borrow<object>(default_);
-    }
 }
 
 inline void setattr(handle obj, handle name, handle value) {
@@ -476,6 +539,43 @@ inline handle get_function(handle value) {
     return value;
 }
 
+// Reimplementation of python's dict helper functions to ensure that exceptions
+// aren't swallowed (see #2862)
+
+// copied from cpython _PyDict_GetItemStringWithError
+inline PyObject * dict_getitemstring(PyObject *v, const char *key)
+{
+#if PY_MAJOR_VERSION >= 3
+    PyObject *kv = nullptr, *rv = nullptr;
+    kv = PyUnicode_FromString(key);
+    if (kv == NULL) {
+        throw error_already_set();
+    }
+
+    rv = PyDict_GetItemWithError(v, kv);
+    Py_DECREF(kv);
+    if (rv == NULL && PyErr_Occurred()) {
+        throw error_already_set();
+    }
+    return rv;
+#else
+    return PyDict_GetItemString(v, key);
+#endif
+}
+
+inline PyObject * dict_getitem(PyObject *v, PyObject *key)
+{
+#if PY_MAJOR_VERSION >= 3
+    PyObject *rv = PyDict_GetItemWithError(v, key);
+    if (rv == NULL && PyErr_Occurred()) {
+        throw error_already_set();
+    }
+    return rv;
+#else
+    return PyDict_GetItem(v, key);
+#endif
+}
+
 // Helper aliases/functions to support implicit casting of values given to python accessors/methods.
 // When given a pyobject, this simply returns the pyobject as-is; for other C++ type, the value goes
 // through pybind11::cast(obj) to convert it to an `object`.
@@ -487,6 +587,10 @@ object object_or_cast(T &&o);
 // Match a PyObject*, which we want to convert directly to handle via its converting constructor
 inline handle object_or_cast(PyObject *ptr) { return ptr; }
 
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#  pragma warning(push)
+#  pragma warning(disable: 4522) // warning C4522: multiple assignment operators specified
+#endif
 template <typename Policy>
 class accessor : public object_api<accessor<Policy>> {
     using key_type = typename Policy::key_type;
@@ -494,7 +598,7 @@ class accessor : public object_api<accessor<Policy>> {
 public:
     accessor(handle obj, key_type key) : obj(obj), key(std::move(key)) { }
     accessor(const accessor &) = default;
-    accessor(accessor &&) = default;
+    accessor(accessor &&) noexcept = default;
 
     // accessor overload required to override default assignment operator (templates are not allowed
     // to replace default compiler-generated assignments).
@@ -520,6 +624,7 @@ public:
         return obj.contains(key);
     }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator object() const { return get_cache(); }
     PyObject *ptr() const { return get_cache().ptr(); }
     template <typename T> T cast() const { return get_cache().template cast<T>(); }
@@ -535,6 +640,9 @@ private:
     key_type key;
     mutable object cache;
 };
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#  pragma warning(pop)
+#endif
 
 PYBIND11_NAMESPACE_BEGIN(accessor_policies)
 struct obj_attr {
@@ -566,15 +674,17 @@ struct generic_item {
 struct sequence_item {
     using key_type = size_t;
 
-    static object get(handle obj, size_t index) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
-        PyObject *result = PySequence_GetItem(obj.ptr(), static_cast<ssize_t>(index));
+    static object get(handle obj, const IdxType &index) {
+        PyObject *result = PySequence_GetItem(obj.ptr(), ssize_t_cast(index));
         if (!result) { throw error_already_set(); }
         return reinterpret_steal<object>(result);
     }
 
-    static void set(handle obj, size_t index, handle val) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
+    static void set(handle obj, const IdxType &index, handle val) {
         // PySequence_SetItem does not steal a reference to 'val'
-        if (PySequence_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.ptr()) != 0) {
+        if (PySequence_SetItem(obj.ptr(), ssize_t_cast(index), val.ptr()) != 0) {
             throw error_already_set();
         }
     }
@@ -583,15 +693,17 @@ struct sequence_item {
 struct list_item {
     using key_type = size_t;
 
-    static object get(handle obj, size_t index) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
-        PyObject *result = PyList_GetItem(obj.ptr(), static_cast<ssize_t>(index));
+    static object get(handle obj, const IdxType &index) {
+        PyObject *result = PyList_GetItem(obj.ptr(), ssize_t_cast(index));
         if (!result) { throw error_already_set(); }
         return reinterpret_borrow<object>(result);
     }
 
-    static void set(handle obj, size_t index, handle val) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
+    static void set(handle obj, const IdxType &index, handle val) {
         // PyList_SetItem steals a reference to 'val'
-        if (PyList_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
+        if (PyList_SetItem(obj.ptr(), ssize_t_cast(index), val.inc_ref().ptr()) != 0) {
             throw error_already_set();
         }
     }
@@ -600,15 +712,17 @@ struct list_item {
 struct tuple_item {
     using key_type = size_t;
 
-    static object get(handle obj, size_t index) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
-        PyObject *result = PyTuple_GetItem(obj.ptr(), static_cast<ssize_t>(index));
+    static object get(handle obj, const IdxType &index) {
+        PyObject *result = PyTuple_GetItem(obj.ptr(), ssize_t_cast(index));
         if (!result) { throw error_already_set(); }
         return reinterpret_borrow<object>(result);
     }
 
-    static void set(handle obj, size_t index, handle val) {
+    template <typename IdxType, detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
+    static void set(handle obj, const IdxType &index, handle val) {
         // PyTuple_SetItem steals a reference to 'val'
-        if (PyTuple_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
+        if (PyTuple_SetItem(obj.ptr(), ssize_t_cast(index), val.inc_ref().ptr()) != 0) {
             throw error_already_set();
         }
     }
@@ -630,7 +744,9 @@ public:
     generic_iterator() = default;
     generic_iterator(handle seq, ssize_t index) : Policy(seq, index) { }
 
+    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference operator*() const { return Policy::dereference(); }
+    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference operator[](difference_type n) const { return *(*this + n); }
     pointer operator->() const { return **this; }
 
@@ -660,7 +776,8 @@ template <typename T>
 struct arrow_proxy {
     T value;
 
-    arrow_proxy(T &&value) : value(std::move(value)) { }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    arrow_proxy(T &&value) noexcept : value(std::move(value)) { }
     T *operator->() const { return &value; }
 };
 
@@ -669,11 +786,12 @@ class sequence_fast_readonly {
 protected:
     using iterator_category = std::random_access_iterator_tag;
     using value_type = handle;
-    using reference = const handle;
+    using reference = const handle; // PR #3263
     using pointer = arrow_proxy<const handle>;
 
     sequence_fast_readonly(handle obj, ssize_t n) : ptr(PySequence_Fast_ITEMS(obj.ptr()) + n) { }
 
+    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference dereference() const { return *ptr; }
     void increment() { ++ptr; }
     void decrement() { --ptr; }
@@ -712,14 +830,19 @@ class dict_readonly {
 protected:
     using iterator_category = std::forward_iterator_tag;
     using value_type = std::pair<handle, handle>;
-    using reference = const value_type;
+    using reference = const value_type; // PR #3263
     using pointer = arrow_proxy<const value_type>;
 
     dict_readonly() = default;
     dict_readonly(handle obj, ssize_t pos) : obj(obj), pos(pos) { increment(); }
 
+    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference dereference() const { return {key, value}; }
-    void increment() { if (!PyDict_Next(obj.ptr(), &pos, &key, &value)) { pos = -1; } }
+    void increment() {
+        if (PyDict_Next(obj.ptr(), &pos, &key, &value) == 0) {
+            pos = -1;
+        }
+    }
     bool equal(const dict_readonly &b) const { return pos == b.pos; }
 
 private:
@@ -745,16 +868,20 @@ inline bool PyIterable_Check(PyObject *obj) {
     if (iter) {
         Py_DECREF(iter);
         return true;
-    } else {
+    }
     PyErr_Clear();
     return false;
-    }
 }
 
 inline bool PyNone_Check(PyObject *o) { return o == Py_None; }
 inline bool PyEllipsis_Check(PyObject *o) { return o == Py_Ellipsis; }
 
+#ifdef PYBIND11_STR_LEGACY_PERMISSIVE
 inline bool PyUnicode_Check_Permissive(PyObject *o) { return PyUnicode_Check(o) || PYBIND11_BYTES_CHECK(o); }
+#define PYBIND11_STR_CHECK_FUN detail::PyUnicode_Check_Permissive
+#else
+#define PYBIND11_STR_CHECK_FUN PyUnicode_Check
+#endif
 
 inline bool PyStaticMethod_Check(PyObject *o) { return o->ob_type == &PyStaticMethod_Type; }
 
@@ -797,26 +924,42 @@ PYBIND11_NAMESPACE_END(detail)
         Name(handle h, borrowed_t) : Parent(h, borrowed_t{}) { } \
         Name(handle h, stolen_t) : Parent(h, stolen_t{}) { } \
         PYBIND11_DEPRECATED("Use py::isinstance<py::python_type>(obj) instead") \
-        bool check() const { return m_ptr != nullptr && (bool) CheckFun(m_ptr); } \
+        bool check() const { return m_ptr != nullptr && (CheckFun(m_ptr) != 0); } \
         static bool check_(handle h) { return h.ptr() != nullptr && CheckFun(h.ptr()); } \
         template <typename Policy_> \
+        /* NOLINTNEXTLINE(google-explicit-constructor) */ \
         Name(const ::pybind11::detail::accessor<Policy_> &a) : Name(object(a)) { }
 
 #define PYBIND11_OBJECT_CVT(Name, Parent, CheckFun, ConvertFun) \
     PYBIND11_OBJECT_COMMON(Name, Parent, CheckFun) \
     /* This is deliberately not 'explicit' to allow implicit conversion from object: */ \
+    /* NOLINTNEXTLINE(google-explicit-constructor) */ \
     Name(const object &o) \
     : Parent(check_(o) ? o.inc_ref().ptr() : ConvertFun(o.ptr()), stolen_t{}) \
     { if (!m_ptr) throw error_already_set(); } \
+    /* NOLINTNEXTLINE(google-explicit-constructor) */ \
     Name(object &&o) \
     : Parent(check_(o) ? o.release().ptr() : ConvertFun(o.ptr()), stolen_t{}) \
     { if (!m_ptr) throw error_already_set(); }
 
+#define PYBIND11_OBJECT_CVT_DEFAULT(Name, Parent, CheckFun, ConvertFun) \
+    PYBIND11_OBJECT_CVT(Name, Parent, CheckFun, ConvertFun) \
+    Name() : Parent() { }
+
+#define PYBIND11_OBJECT_CHECK_FAILED(Name, o_ptr) \
+    ::pybind11::type_error("Object of type '" + \
+                           ::pybind11::detail::get_fully_qualified_tp_name(Py_TYPE(o_ptr)) + \
+                           "' is not an instance of '" #Name "'")
+
 #define PYBIND11_OBJECT(Name, Parent, CheckFun) \
     PYBIND11_OBJECT_COMMON(Name, Parent, CheckFun) \
     /* This is deliberately not 'explicit' to allow implicit conversion from object: */ \
-    Name(const object &o) : Parent(o) { } \
+    /* NOLINTNEXTLINE(google-explicit-constructor) */ \
-    Name(object &&o) : Parent(std::move(o)) { }
+    Name(const object &o) : Parent(o) \
+    { if (m_ptr && !check_(m_ptr)) throw PYBIND11_OBJECT_CHECK_FAILED(Name, m_ptr); } \
+    /* NOLINTNEXTLINE(google-explicit-constructor) */ \
+    Name(object &&o) : Parent(std::move(o)) \
+    { if (m_ptr && !check_(m_ptr)) throw PYBIND11_OBJECT_CHECK_FAILED(Name, m_ptr); }
 
 #define PYBIND11_OBJECT_DEFAULT(Name, Parent, CheckFun) \
     PYBIND11_OBJECT(Name, Parent, CheckFun) \
@@ -838,7 +981,7 @@ public:
     using iterator_category = std::input_iterator_tag;
     using difference_type = ssize_t;
     using value_type = handle;
-    using reference = const handle;
+    using reference = const handle; // PR #3263
     using pointer = const handle *;
 
     PYBIND11_OBJECT_DEFAULT(iterator, object, PyIter_Check)
@@ -854,6 +997,7 @@ public:
         return rv;
     }
 
+    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference operator*() const {
         if (m_ptr && !value.ptr()) {
             auto& self = const_cast<iterator &>(*this);
@@ -927,21 +1071,38 @@ class bytes;
 
 class str : public object {
 public:
-    PYBIND11_OBJECT_CVT(str, object, detail::PyUnicode_Check_Permissive, raw_str)
+    PYBIND11_OBJECT_CVT(str, object, PYBIND11_STR_CHECK_FUN, raw_str)
 
-    str(const char *c, size_t n)
+    template <typename SzType, detail::enable_if_t<std::is_integral<SzType>::value, int> = 0>
-        : object(PyUnicode_FromStringAndSize(c, (ssize_t) n), stolen_t{}) {
+    str(const char *c, const SzType &n)
+        : object(PyUnicode_FromStringAndSize(c, ssize_t_cast(n)), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate string object!");
     }
 
     // 'explicit' is explicitly omitted from the following constructors to allow implicit conversion to py::str from C++ string-like objects
+    // NOLINTNEXTLINE(google-explicit-constructor)
     str(const char *c = "")
         : object(PyUnicode_FromString(c), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate string object!");
     }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     str(const std::string &s) : str(s.data(), s.size()) { }
 
+#ifdef PYBIND11_HAS_STRING_VIEW
+    // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
+    template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    str(T s) : str(s.data(), s.size()) { }
+
+# ifdef PYBIND11_HAS_U8STRING
+    // reinterpret_cast here is safe (C++20 guarantees char8_t has the same size/alignment as char)
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    str(std::u8string_view s) : str(reinterpret_cast<const char*>(s.data()), s.size()) { }
+# endif
+
+#endif
+
     explicit str(const bytes &b);
 
     /** \rst
@@ -950,15 +1111,16 @@ public:
     \endrst */
     explicit str(handle h) : object(raw_str(h.ptr()), stolen_t{}) { if (!m_ptr) throw error_already_set(); }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator std::string() const {
         object temp = *this;
         if (PyUnicode_Check(m_ptr)) {
             temp = reinterpret_steal<object>(PyUnicode_AsUTF8String(m_ptr));
             if (!temp)
-                pybind11_fail("Unable to extract string contents! (encoding issue)");
+                throw error_already_set();
         }
-        char *buffer;
+        char *buffer = nullptr;
-        ssize_t length;
+        ssize_t length = 0;
         if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
             pybind11_fail("Unable to extract string contents! (invalid type)");
         return std::string(buffer, (size_t) length);
@@ -997,28 +1159,52 @@ public:
     PYBIND11_OBJECT(bytes, object, PYBIND11_BYTES_CHECK)
 
     // Allow implicit conversion:
+    // NOLINTNEXTLINE(google-explicit-constructor)
     bytes(const char *c = "")
         : object(PYBIND11_BYTES_FROM_STRING(c), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate bytes object!");
     }
 
-    bytes(const char *c, size_t n)
+    template <typename SzType, detail::enable_if_t<std::is_integral<SzType>::value, int> = 0>
-        : object(PYBIND11_BYTES_FROM_STRING_AND_SIZE(c, (ssize_t) n), stolen_t{}) {
+    bytes(const char *c, const SzType &n)
+        : object(PYBIND11_BYTES_FROM_STRING_AND_SIZE(c, ssize_t_cast(n)), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate bytes object!");
     }
 
     // Allow implicit conversion:
+    // NOLINTNEXTLINE(google-explicit-constructor)
     bytes(const std::string &s) : bytes(s.data(), s.size()) { }
 
     explicit bytes(const pybind11::str &s);
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator std::string() const {
-        char *buffer;
+        char *buffer = nullptr;
-        ssize_t length;
+        ssize_t length = 0;
         if (PYBIND11_BYTES_AS_STRING_AND_SIZE(m_ptr, &buffer, &length))
             pybind11_fail("Unable to extract bytes contents!");
         return std::string(buffer, (size_t) length);
     }
+
+#ifdef PYBIND11_HAS_STRING_VIEW
+    // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
+    template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    bytes(T s) : bytes(s.data(), s.size()) { }
+
+    // Obtain a string view that views the current `bytes` buffer value.  Note that this is only
+    // valid so long as the `bytes` instance remains alive and so generally should not outlive the
+    // lifetime of the `bytes` instance.
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator std::string_view() const {
+        char *buffer = nullptr;
+        ssize_t length = 0;
+        if (PYBIND11_BYTES_AS_STRING_AND_SIZE(m_ptr, &buffer, &length))
+            pybind11_fail("Unable to extract bytes contents!");
+        return {buffer, static_cast<size_t>(length)};
+    }
+#endif
+
 };
 // Note: breathe >= 4.17.0 will fail to build docs if the below two constructors
 // are included in the doxygen group; close here and reopen after as a workaround
@@ -1031,8 +1217,8 @@ inline bytes::bytes(const pybind11::str &s) {
         if (!temp)
             pybind11_fail("Unable to extract string contents! (encoding issue)");
     }
-    char *buffer;
+    char *buffer = nullptr;
-    ssize_t length;
+    ssize_t length = 0;
     if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
         pybind11_fail("Unable to extract string contents! (invalid type)");
     auto obj = reinterpret_steal<object>(PYBIND11_BYTES_FROM_STRING_AND_SIZE(buffer, length));
@@ -1042,16 +1228,45 @@ inline bytes::bytes(const pybind11::str &s) {
 }
 
 inline str::str(const bytes& b) {
-    char *buffer;
+    char *buffer = nullptr;
-    ssize_t length;
+    ssize_t length = 0;
     if (PYBIND11_BYTES_AS_STRING_AND_SIZE(b.ptr(), &buffer, &length))
         pybind11_fail("Unable to extract bytes contents!");
-    auto obj = reinterpret_steal<object>(PyUnicode_FromStringAndSize(buffer, (ssize_t) length));
+    auto obj = reinterpret_steal<object>(PyUnicode_FromStringAndSize(buffer, length));
     if (!obj)
         pybind11_fail("Could not allocate string object!");
     m_ptr = obj.release().ptr();
 }
 
+/// \addtogroup pytypes
+/// @{
+class bytearray : public object {
+public:
+    PYBIND11_OBJECT_CVT(bytearray, object, PyByteArray_Check, PyByteArray_FromObject)
+
+    template <typename SzType, detail::enable_if_t<std::is_integral<SzType>::value, int> = 0>
+    bytearray(const char *c, const SzType &n)
+        : object(PyByteArray_FromStringAndSize(c, ssize_t_cast(n)), stolen_t{}) {
+        if (!m_ptr) pybind11_fail("Could not allocate bytearray object!");
+    }
+
+    bytearray()
+        : bytearray("", 0) {}
+
+    explicit bytearray(const std::string &s) : bytearray(s.data(), s.size()) { }
+
+    size_t size() const { return static_cast<size_t>(PyByteArray_Size(m_ptr)); }
+
+    explicit operator std::string() const {
+        char *buffer = PyByteArray_AS_STRING(m_ptr);
+        ssize_t size = PyByteArray_GET_SIZE(m_ptr);
+        return std::string(buffer, static_cast<size_t>(size));
+    }
+};
+// Note: breathe >= 4.17.0 will fail to build docs if the below two constructors
+// are included in the doxygen group; close here and reopen after as a workaround
+/// @} pytypes
+
 /// \addtogroup pytypes
 /// @{
 class none : public object {
@@ -1071,15 +1286,17 @@ public:
     PYBIND11_OBJECT_CVT(bool_, object, PyBool_Check, raw_bool)
     bool_() : object(Py_False, borrowed_t{}) { }
     // Allow implicit conversion from and to `bool`:
+    // NOLINTNEXTLINE(google-explicit-constructor)
     bool_(bool value) : object(value ? Py_True : Py_False, borrowed_t{}) { }
-    operator bool() const { return m_ptr && PyLong_AsLong(m_ptr) != 0; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator bool() const { return (m_ptr != nullptr) && PyLong_AsLong(m_ptr) != 0; }
 
 private:
     /// Return the truth value of an object -- always returns a new reference
     static PyObject *raw_bool(PyObject *op) {
         const auto value = PyObject_IsTrue(op);
         if (value == -1) return nullptr;
-        return handle(value ? Py_True : Py_False).inc_ref().ptr();
+        return handle(value != 0 ? Py_True : Py_False).inc_ref().ptr();
     }
 };
 
@@ -1090,7 +1307,7 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 // unsigned type: (A)-1 != (B)-1 when A and B are unsigned types of different sizes).
 template <typename Unsigned>
 Unsigned as_unsigned(PyObject *o) {
-    if (sizeof(Unsigned) <= sizeof(unsigned long)
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(Unsigned) <= sizeof(unsigned long))
 #if PY_VERSION_HEX < 0x03000000
         || PyInt_Check(o)
 #endif
@@ -1098,10 +1315,8 @@ Unsigned as_unsigned(PyObject *o) {
         unsigned long v = PyLong_AsUnsignedLong(o);
         return v == (unsigned long) -1 && PyErr_Occurred() ? (Unsigned) -1 : (Unsigned) v;
     }
-    else {
     unsigned long long v = PyLong_AsUnsignedLongLong(o);
     return v == (unsigned long long) -1 && PyErr_Occurred() ? (Unsigned) -1 : (Unsigned) v;
-    }
 }
 PYBIND11_NAMESPACE_END(detail)
 
@@ -1112,8 +1327,9 @@ public:
     // Allow implicit conversion from C++ integral types:
     template <typename T,
               detail::enable_if_t<std::is_integral<T>::value, int> = 0>
+    // NOLINTNEXTLINE(google-explicit-constructor)
     int_(T value) {
-        if (sizeof(T) <= sizeof(long)) {
+        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(T) <= sizeof(long))) {
             if (std::is_signed<T>::value)
                 m_ptr = PyLong_FromLong((long) value);
             else
@@ -1129,6 +1345,7 @@ public:
 
     template <typename T,
               detail::enable_if_t<std::is_integral<T>::value, int> = 0>
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator T() const {
         return std::is_unsigned<T>::value
             ? detail::as_unsigned<T>(m_ptr)
@@ -1142,33 +1359,51 @@ class float_ : public object {
 public:
     PYBIND11_OBJECT_CVT(float_, object, PyFloat_Check, PyNumber_Float)
     // Allow implicit conversion from float/double:
+    // NOLINTNEXTLINE(google-explicit-constructor)
     float_(float value) : object(PyFloat_FromDouble((double) value), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate float object!");
     }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     float_(double value = .0) : object(PyFloat_FromDouble((double) value), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate float object!");
     }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator float() const { return (float) PyFloat_AsDouble(m_ptr); }
+    // NOLINTNEXTLINE(google-explicit-constructor)
     operator double() const { return (double) PyFloat_AsDouble(m_ptr); }
 };
 
 class weakref : public object {
 public:
-    PYBIND11_OBJECT_DEFAULT(weakref, object, PyWeakref_Check)
+    PYBIND11_OBJECT_CVT_DEFAULT(weakref, object, PyWeakref_Check, raw_weakref)
     explicit weakref(handle obj, handle callback = {})
         : object(PyWeakref_NewRef(obj.ptr(), callback.ptr()), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate weak reference!");
     }
+
+private:
+    static PyObject *raw_weakref(PyObject *o) {
+        return PyWeakref_NewRef(o, nullptr);
+    }
 };
 
 class slice : public object {
 public:
     PYBIND11_OBJECT_DEFAULT(slice, object, PySlice_Check)
-    slice(ssize_t start_, ssize_t stop_, ssize_t step_) {
+    slice(handle start, handle stop, handle step) {
-        int_ start(start_), stop(stop_), step(step_);
         m_ptr = PySlice_New(start.ptr(), stop.ptr(), step.ptr());
-        if (!m_ptr) pybind11_fail("Could not allocate slice object!");
+        if (!m_ptr)
+            pybind11_fail("Could not allocate slice object!");
     }
+
+#ifdef PYBIND11_HAS_OPTIONAL
+    slice(std::optional<ssize_t> start, std::optional<ssize_t> stop, std::optional<ssize_t> step)
+        : slice(index_to_object(start), index_to_object(stop), index_to_object(step)) {}
+#else
+    slice(ssize_t start_, ssize_t stop_, ssize_t step_)
+        : slice(int_(start_), int_(stop_), int_(step_)) {}
+#endif
+
     bool compute(size_t length, size_t *start, size_t *stop, size_t *step,
                  size_t *slicelength) const {
         return PySlice_GetIndicesEx((PYBIND11_SLICE_OBJECT *) m_ptr,
@@ -1183,6 +1418,12 @@ public:
           stop, step,
           slicelength) == 0;
     }
+
+private:
+    template <typename T>
+    static object index_to_object(T index) {
+        return index ? object(int_(*index)) : object(none());
+    }
 };
 
 class capsule : public object {
@@ -1218,7 +1459,7 @@ public:
             pybind11_fail("Could not set capsule context!");
     }
 
-    capsule(void (*destructor)()) {
+    explicit capsule(void (*destructor)()) {
         m_ptr = PyCapsule_New(reinterpret_cast<void *>(destructor), nullptr, [](PyObject *o) {
             auto destructor = reinterpret_cast<void (*)()>(PyCapsule_GetPointer(o, nullptr));
             destructor();
@@ -1228,20 +1469,41 @@ public:
             pybind11_fail("Could not allocate capsule object!");
     }
 
+    // NOLINTNEXTLINE(google-explicit-constructor)
     template <typename T> operator T *() const {
+        return get_pointer<T>();
+    }
+
+    /// Get the pointer the capsule holds.
+    template<typename T = void>
+    T* get_pointer() const {
         auto name = this->name();
-        T * result = static_cast<T *>(PyCapsule_GetPointer(m_ptr, name));
+        T *result = static_cast<T *>(PyCapsule_GetPointer(m_ptr, name));
-        if (!result) pybind11_fail("Unable to extract capsule contents!");
+        if (!result) {
+            PyErr_Clear();
+            pybind11_fail("Unable to extract capsule contents!");
+        }
         return result;
     }
 
+    /// Replaces a capsule's pointer *without* calling the destructor on the existing one.
+    void set_pointer(const void *value) {
+        if (PyCapsule_SetPointer(m_ptr, const_cast<void *>(value)) != 0) {
+            PyErr_Clear();
+            pybind11_fail("Could not set capsule pointer");
+        }
+    }
+
     const char *name() const { return PyCapsule_GetName(m_ptr); }
 };
 
 class tuple : public object {
 public:
     PYBIND11_OBJECT_CVT(tuple, object, PyTuple_Check, PySequence_Tuple)
-    explicit tuple(size_t size = 0) : object(PyTuple_New((ssize_t) size), stolen_t{}) {
+    template <typename SzType = ssize_t,
+              detail::enable_if_t<std::is_integral<SzType>::value, int> = 0>
+    // Some compilers generate link errors when using `const SzType &` here:
+    explicit tuple(SzType size = 0) : object(PyTuple_New(ssize_t_cast(size)), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate tuple object!");
     }
     size_t size() const { return (size_t) PyTuple_Size(m_ptr); }
@@ -1252,6 +1514,15 @@ public:
     detail::tuple_iterator end() const { return {*this, PyTuple_GET_SIZE(m_ptr)}; }
 };
 
+// We need to put this into a separate function because the Intel compiler
+// fails to compile enable_if_t<all_of<is_keyword_or_ds<Args>...>::value> part below
+// (tested with ICC 2021.1 Beta 20200827).
+template <typename... Args>
+constexpr bool args_are_all_keyword_or_ds()
+{
+  return detail::all_of<detail::is_keyword_or_ds<Args>...>::value;
+}
+
 class dict : public object {
 public:
     PYBIND11_OBJECT_CVT(dict, object, PyDict_Check, raw_dict)
@@ -1259,7 +1530,7 @@ public:
         if (!m_ptr) pybind11_fail("Could not allocate dict object!");
     }
     template <typename... Args,
-              typename = detail::enable_if_t<detail::all_of<detail::is_keyword_or_ds<Args>...>::value>,
+              typename = detail::enable_if_t<args_are_all_keyword_or_ds<Args...>()>,
               // MSVC workaround: it can't compile an out-of-line definition, so defer the collector
               typename collector = detail::deferred_t<detail::unpacking_collector<>, Args...>>
     explicit dict(Args &&...args) : dict(collector(std::forward<Args>(args)...).kwargs()) { }
@@ -1268,7 +1539,7 @@ public:
     bool empty() const { return size() == 0; }
     detail::dict_iterator begin() const { return {*this, 0}; }
     detail::dict_iterator end() const { return {}; }
-    void clear() const { PyDict_Clear(ptr()); }
+    void clear() /* py-non-const */ { PyDict_Clear(ptr()); }
     template <typename T> bool contains(T &&key) const {
         return PyDict_Contains(m_ptr, detail::object_or_cast(std::forward<T>(key)).ptr()) == 1;
     }
@@ -1301,7 +1572,10 @@ public:
 class list : public object {
 public:
     PYBIND11_OBJECT_CVT(list, object, PyList_Check, PySequence_List)
-    explicit list(size_t size = 0) : object(PyList_New((ssize_t) size), stolen_t{}) {
+    template <typename SzType = ssize_t,
+              detail::enable_if_t<std::is_integral<SzType>::value, int> = 0>
+    // Some compilers generate link errors when using `const SzType &` here:
+    explicit list(SzType size = 0) : object(PyList_New(ssize_t_cast(size)), stolen_t{}) {
         if (!m_ptr) pybind11_fail("Could not allocate list object!");
     }
     size_t size() const { return (size_t) PyList_Size(m_ptr); }
@@ -1310,12 +1584,15 @@ public:
     detail::item_accessor operator[](handle h) const { return object::operator[](h); }
     detail::list_iterator begin() const { return {*this, 0}; }
     detail::list_iterator end() const { return {*this, PyList_GET_SIZE(m_ptr)}; }
-    template <typename T> void append(T &&val) const {
+    template <typename T> void append(T &&val) /* py-non-const */ {
         PyList_Append(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr());
     }
-    template <typename T> void insert(size_t index, T &&val) const {
+    template <typename IdxType,
-        PyList_Insert(m_ptr, static_cast<ssize_t>(index),
+              typename ValType,
-            detail::object_or_cast(std::forward<T>(val)).ptr());
+              detail::enable_if_t<std::is_integral<IdxType>::value, int> = 0>
+    void insert(const IdxType &index, ValType &&val) /* py-non-const */ {
+        PyList_Insert(
+            m_ptr, ssize_t_cast(index), detail::object_or_cast(std::forward<ValType>(val)).ptr());
     }
 };
 
@@ -1330,10 +1607,10 @@ public:
     }
     size_t size() const { return (size_t) PySet_Size(m_ptr); }
     bool empty() const { return size() == 0; }
-    template <typename T> bool add(T &&val) const {
+    template <typename T> bool add(T &&val) /* py-non-const */ {
         return PySet_Add(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr()) == 0;
     }
-    void clear() const { PySet_Clear(m_ptr); }
+    void clear() /* py-non-const */ { PySet_Clear(m_ptr); }
     template <typename T> bool contains(T &&val) const {
         return PySet_Contains(m_ptr, detail::object_or_cast(std::forward<T>(val)).ptr()) == 1;
     }
@@ -1429,7 +1706,7 @@ public:
         detail::any_container<ssize_t> shape,
         detail::any_container<ssize_t> strides) {
         return memoryview::from_buffer(
-            const_cast<void*>(ptr), itemsize, format, shape, strides, true);
+            const_cast<void *>(ptr), itemsize, format, std::move(shape), std::move(strides), true);
     }
 
     template<typename T>
@@ -1475,10 +1752,17 @@ public:
     static memoryview from_memory(const void *mem, ssize_t size) {
         return memoryview::from_memory(const_cast<void*>(mem), size, true);
     }
+
+#ifdef PYBIND11_HAS_STRING_VIEW
+    static memoryview from_memory(std::string_view mem) {
+        return from_memory(const_cast<char*>(mem.data()), static_cast<ssize_t>(mem.size()), true);
+    }
+#endif
+
 #endif
 };
 
-#ifndef DOXYGEN_SHOULD_SKIP_THIS
+/// @cond DUPLICATE
 inline memoryview memoryview::from_buffer(
     void *ptr, ssize_t itemsize, const char* format,
     detail::any_container<ssize_t> shape,
@@ -1486,7 +1770,7 @@ inline memoryview memoryview::from_buffer(
     size_t ndim = shape->size();
     if (ndim != strides->size())
         pybind11_fail("memoryview: shape length doesn't match strides length");
-    ssize_t size = ndim ? 1 : 0;
+    ssize_t size = ndim != 0u ? 1 : 0;
     for (size_t i = 0; i < ndim; ++i)
         size *= (*shape)[i];
     Py_buffer view;
@@ -1506,18 +1790,22 @@ inline memoryview memoryview::from_buffer(
         throw error_already_set();
     return memoryview(object(obj, stolen_t{}));
 }
-#endif  // DOXYGEN_SHOULD_SKIP_THIS
+/// @endcond
 /// @} pytypes
 
 /// \addtogroup python_builtins
 /// @{
+
+/// Get the length of a Python object.
 inline size_t len(handle h) {
     ssize_t result = PyObject_Length(h.ptr());
     if (result < 0)
-        pybind11_fail("Unable to compute length of object");
+        throw error_already_set();
     return (size_t) result;
 }
 
+/// Get the length hint of a Python object.
+/// Returns 0 when this cannot be determined.
 inline size_t len_hint(handle h) {
 #if PY_VERSION_HEX >= 0x03040000
     ssize_t result = PyObject_LengthHint(h.ptr(), 0);
@@ -1580,8 +1868,7 @@ template <typename D>
 str_attr_accessor object_api<D>::doc() const { return attr("__doc__"); }
 
 template <typename D>
-PYBIND11_DEPRECATED("Use py::type::of(h) instead of h.get_type()")
+handle object_api<D>::get_type() const { return type::handle_of(derived()); }
-handle object_api<D>::get_type() const { return type::handle_of(*this); }
 
 template <typename D>
 bool object_api<D>::rich_compare(object_api const &other, int value) const {

wrap/pybind11/include/pybind11/stl.h

@@ -9,6 +9,7 @@
 
 #pragma once
 
+#include "detail/common.h"
 #include "pybind11.h"
 #include <set>
 #include <unordered_set>
@@ -19,33 +20,15 @@
 #include <deque>
 #include <valarray>
 
-#if defined(_MSC_VER)
+// See `detail/common.h` for implementation of these guards.
-#pragma warning(push)
+#if defined(PYBIND11_HAS_OPTIONAL)
-#pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
+#  include <optional>
+#elif defined(PYBIND11_HAS_EXP_OPTIONAL)
+#  include <experimental/optional>
 #endif
 
-#ifdef __has_include
+#if defined(PYBIND11_HAS_VARIANT)
-// std::optional (but including it in c++14 mode isn't allowed)
-#  if defined(PYBIND11_CPP17) && __has_include(<optional>)
-#    include <optional>
-#    define PYBIND11_HAS_OPTIONAL 1
-#  endif
-// std::experimental::optional (but not allowed in c++11 mode)
-#  if defined(PYBIND11_CPP14) && (__has_include(<experimental/optional>) && \
-                                 !__has_include(<optional>))
-#    include <experimental/optional>
-#    define PYBIND11_HAS_EXP_OPTIONAL 1
-#  endif
-// std::variant
-#  if defined(PYBIND11_CPP17) && __has_include(<variant>)
 #  include <variant>
-#    define PYBIND11_HAS_VARIANT 1
-#  endif
-#elif defined(_MSC_VER) && defined(PYBIND11_CPP17)
-#  include <optional>
-#  include <variant>
-#  define PYBIND11_HAS_OPTIONAL 1
-#  define PYBIND11_HAS_VARIANT 1
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
@@ -95,7 +78,7 @@ template <typename Type, typename Key> struct set_caster {
         return s.release();
     }
 
-    PYBIND11_TYPE_CASTER(type, _("Set[") + key_conv::name + _("]"));
+    PYBIND11_TYPE_CASTER(type, const_name("Set[") + key_conv::name + const_name("]"));
 };
 
 template <typename Type, typename Key, typename Value> struct map_caster {
@@ -137,14 +120,14 @@ template <typename Type, typename Key, typename Value> struct map_caster {
         return d.release();
     }
 
-    PYBIND11_TYPE_CASTER(Type, _("Dict[") + key_conv::name + _(", ") + value_conv::name + _("]"));
+    PYBIND11_TYPE_CASTER(Type, const_name("Dict[") + key_conv::name + const_name(", ") + value_conv::name + const_name("]"));
 };
 
 template <typename Type, typename Value> struct list_caster {
     using value_conv = make_caster<Value>;
 
     bool load(handle src, bool convert) {
-        if (!isinstance<sequence>(src) || isinstance<str>(src))
+        if (!isinstance<sequence>(src) || isinstance<bytes>(src) || isinstance<str>(src))
             return false;
         auto s = reinterpret_borrow<sequence>(src);
         value.clear();
@@ -159,10 +142,13 @@ template <typename Type, typename Value> struct list_caster {
     }
 
 private:
-    template <typename T = Type,
+    template <
+        typename T                                                                          = Type,
         enable_if_t<std::is_same<decltype(std::declval<T>().reserve(0)), void>::value, int> = 0>
-    void reserve_maybe(sequence s, Type *) { value.reserve(s.size()); }
+    void reserve_maybe(const sequence &s, Type *) {
-    void reserve_maybe(sequence, void *) { }
+        value.reserve(s.size());
+    }
+    void reserve_maybe(const sequence &, void *) {}
 
 public:
     template <typename T>
@@ -170,17 +156,17 @@ public:
         if (!std::is_lvalue_reference<T>::value)
             policy = return_value_policy_override<Value>::policy(policy);
         list l(src.size());
-        size_t index = 0;
+        ssize_t index = 0;
         for (auto &&value : src) {
             auto value_ = reinterpret_steal<object>(value_conv::cast(forward_like<T>(value), policy, parent));
             if (!value_)
                 return handle();
-            PyList_SET_ITEM(l.ptr(), (ssize_t) index++, value_.release().ptr()); // steals a reference
+            PyList_SET_ITEM(l.ptr(), index++, value_.release().ptr()); // steals a reference
         }
         return l.release();
     }
 
-    PYBIND11_TYPE_CASTER(Type, _("List[") + value_conv::name + _("]"));
+    PYBIND11_TYPE_CASTER(Type, const_name("List[") + value_conv::name + const_name("]"));
 };
 
 template <typename Type, typename Alloc> struct type_caster<std::vector<Type, Alloc>>
@@ -227,17 +213,17 @@ public:
     template <typename T>
     static handle cast(T &&src, return_value_policy policy, handle parent) {
         list l(src.size());
-        size_t index = 0;
+        ssize_t index = 0;
         for (auto &&value : src) {
             auto value_ = reinterpret_steal<object>(value_conv::cast(forward_like<T>(value), policy, parent));
             if (!value_)
                 return handle();
-            PyList_SET_ITEM(l.ptr(), (ssize_t) index++, value_.release().ptr()); // steals a reference
+            PyList_SET_ITEM(l.ptr(), index++, value_.release().ptr()); // steals a reference
         }
         return l.release();
     }
 
-    PYBIND11_TYPE_CASTER(ArrayType, _("List[") + value_conv::name + _<Resizable>(_(""), _("[") + _<Size>() + _("]")) + _("]"));
+    PYBIND11_TYPE_CASTER(ArrayType, const_name("List[") + value_conv::name + const_name<Resizable>(const_name(""), const_name("[") + const_name<Size>() + const_name("]")) + const_name("]"));
 };
 
 template <typename Type, size_t Size> struct type_caster<std::array<Type, Size>>
@@ -259,34 +245,35 @@ template <typename Key, typename Value, typename Hash, typename Equal, typename
   : map_caster<std::unordered_map<Key, Value, Hash, Equal, Alloc>, Key, Value> { };
 
 // This type caster is intended to be used for std::optional and std::experimental::optional
-template<typename T> struct optional_caster {
+template<typename Type, typename Value = typename Type::value_type> struct optional_caster {
-    using value_conv = make_caster<typename T::value_type>;
+    using value_conv = make_caster<Value>;
 
-    template <typename T_>
+    template <typename T>
-    static handle cast(T_ &&src, return_value_policy policy, handle parent) {
+    static handle cast(T &&src, return_value_policy policy, handle parent) {
         if (!src)
             return none().inc_ref();
         if (!std::is_lvalue_reference<T>::value) {
-            policy = return_value_policy_override<T>::policy(policy);
+            policy = return_value_policy_override<Value>::policy(policy);
         }
-        return value_conv::cast(*std::forward<T_>(src), policy, parent);
+        return value_conv::cast(*std::forward<T>(src), policy, parent);
     }
 
     bool load(handle src, bool convert) {
         if (!src) {
             return false;
-        } else if (src.is_none()) {
+        }
+        if (src.is_none()) {
             return true;  // default-constructed value is already empty
         }
         value_conv inner_caster;
         if (!inner_caster.load(src, convert))
             return false;
 
-        value.emplace(cast_op<typename T::value_type &&>(std::move(inner_caster)));
+        value.emplace(cast_op<Value &&>(std::move(inner_caster)));
         return true;
     }
 
-    PYBIND11_TYPE_CASTER(T, _("Optional[") + value_conv::name + _("]"));
+    PYBIND11_TYPE_CASTER(Type, const_name("Optional[") + value_conv::name + const_name("]"));
 };
 
 #if defined(PYBIND11_HAS_OPTIONAL)
@@ -366,7 +353,7 @@ struct variant_caster<V<Ts...>> {
     }
 
     using Type = V<Ts...>;
-    PYBIND11_TYPE_CASTER(Type, _("Union[") + detail::concat(make_caster<Ts>::name...) + _("]"));
+    PYBIND11_TYPE_CASTER(Type, const_name("Union[") + detail::concat(make_caster<Ts>::name...) + const_name("]"));
 };
 
 #if defined(PYBIND11_HAS_VARIANT)
@@ -377,12 +364,12 @@ struct type_caster<std::variant<Ts...>> : variant_caster<std::variant<Ts...>> {
 PYBIND11_NAMESPACE_END(detail)
 
 inline std::ostream &operator<<(std::ostream &os, const handle &obj) {
+#ifdef PYBIND11_HAS_STRING_VIEW
+    os << str(obj).cast<std::string_view>();
+#else
     os << (std::string) str(obj);
+#endif
     return os;
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif

wrap/pybind11/include/pybind11/stl/filesystem.h

@@ -0,0 +1,103 @@
+// Copyright (c) 2021 The Pybind Development Team.
+// All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#pragma once
+
+#include "../cast.h"
+#include "../pybind11.h"
+#include "../pytypes.h"
+
+#include "../detail/common.h"
+#include "../detail/descr.h"
+
+#include <string>
+
+#ifdef __has_include
+#  if defined(PYBIND11_CPP17) && __has_include(<filesystem>) && \
+      PY_VERSION_HEX >= 0x03060000
+#    include <filesystem>
+#    define PYBIND11_HAS_FILESYSTEM 1
+#  endif
+#endif
+
+#if !defined(PYBIND11_HAS_FILESYSTEM) && !defined(PYBIND11_HAS_FILESYSTEM_IS_OPTIONAL)
+#    error                                                                                        \
+        "#include <filesystem> is not available. (Use -DPYBIND11_HAS_FILESYSTEM_IS_OPTIONAL to ignore.)"
+#endif
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+#if defined(PYBIND11_HAS_FILESYSTEM)
+template<typename T> struct path_caster {
+
+private:
+    static PyObject* unicode_from_fs_native(const std::string& w) {
+#if !defined(PYPY_VERSION)
+        return PyUnicode_DecodeFSDefaultAndSize(w.c_str(), ssize_t(w.size()));
+#else
+        // PyPy mistakenly declares the first parameter as non-const.
+        return PyUnicode_DecodeFSDefaultAndSize(
+            const_cast<char*>(w.c_str()), ssize_t(w.size()));
+#endif
+    }
+
+    static PyObject* unicode_from_fs_native(const std::wstring& w) {
+        return PyUnicode_FromWideChar(w.c_str(), ssize_t(w.size()));
+    }
+
+public:
+    static handle cast(const T& path, return_value_policy, handle) {
+        if (auto py_str = unicode_from_fs_native(path.native())) {
+            return module_::import("pathlib").attr("Path")(reinterpret_steal<object>(py_str))
+                   .release();
+        }
+        return nullptr;
+    }
+
+    bool load(handle handle, bool) {
+        // PyUnicode_FSConverter and PyUnicode_FSDecoder normally take care of
+        // calling PyOS_FSPath themselves, but that's broken on PyPy (PyPy
+        // issue #3168) so we do it ourselves instead.
+        PyObject* buf = PyOS_FSPath(handle.ptr());
+        if (!buf) {
+            PyErr_Clear();
+            return false;
+        }
+        PyObject* native = nullptr;
+        if constexpr (std::is_same_v<typename T::value_type, char>) {
+            if (PyUnicode_FSConverter(buf, &native) != 0) {
+                if (auto c_str = PyBytes_AsString(native)) {
+                    // AsString returns a pointer to the internal buffer, which
+                    // must not be free'd.
+                    value = c_str;
+                }
+            }
+        } else if constexpr (std::is_same_v<typename T::value_type, wchar_t>) {
+            if (PyUnicode_FSDecoder(buf, &native) != 0) {
+                if (auto c_str = PyUnicode_AsWideCharString(native, nullptr)) {
+                    // AsWideCharString returns a new string that must be free'd.
+                    value = c_str;  // Copies the string.
+                    PyMem_Free(c_str);
+                }
+            }
+        }
+        Py_XDECREF(native);
+        Py_DECREF(buf);
+        if (PyErr_Occurred()) {
+            PyErr_Clear();
+            return false;
+        }
+        return true;
+    }
+
+    PYBIND11_TYPE_CASTER(T, const_name("os.PathLike"));
+};
+
+template<> struct type_caster<std::filesystem::path>
+    : public path_caster<std::filesystem::path> {};
+#endif // PYBIND11_HAS_FILESYSTEM
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

wrap/pybind11/include/pybind11/stl_bind.h

@@ -128,7 +128,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
            arg("x"),
            "Add an item to the end of the list");
 
-    cl.def(init([](iterable it) {
+    cl.def(init([](const iterable &it) {
         auto v = std::unique_ptr<Vector>(new Vector());
         v->reserve(len_hint(it));
         for (handle h : it)
@@ -151,8 +151,9 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
        "Extend the list by appending all the items in the given list"
     );
 
-    cl.def("extend",
+    cl.def(
-       [](Vector &v, iterable it) {
+        "extend",
+        [](Vector &v, const iterable &it) {
             const size_t old_size = v.size();
             v.reserve(old_size + len_hint(it));
             try {
@@ -160,7 +161,8 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
                     v.push_back(h.cast<T>());
                 }
             } catch (const cast_error &) {
-               v.erase(v.begin() + static_cast<typename Vector::difference_type>(old_size), v.end());
+                v.erase(v.begin() + static_cast<typename Vector::difference_type>(old_size),
+                        v.end());
                 try {
                     v.shrink_to_fit();
                 } catch (const std::exception &) {
@@ -170,8 +172,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
             }
         },
         arg("L"),
-       "Extend the list by appending all the items in the given list"
+        "Extend the list by appending all the items in the given list");
-    );
 
     cl.def("insert",
         [](Vector &v, DiffType i, const T &x) {
@@ -190,7 +191,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
         [](Vector &v) {
             if (v.empty())
                 throw index_error();
-            T t = v.back();
+            T t = std::move(v.back());
             v.pop_back();
             return t;
         },
@@ -200,8 +201,8 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
     cl.def("pop",
         [wrap_i](Vector &v, DiffType i) {
             i = wrap_i(i, v.size());
-            T t = v[(SizeType) i];
+            T t = std::move(v[(SizeType) i]);
-            v.erase(v.begin() + i);
+            v.erase(std::next(v.begin(), i));
             return t;
         },
         arg("i"),
@@ -216,9 +217,10 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
     );
 
     /// Slicing protocol
-    cl.def("__getitem__",
+    cl.def(
+        "__getitem__",
         [](const Vector &v, slice slice) -> Vector * {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
 
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
@@ -233,12 +235,12 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
             return seq;
         },
         arg("s"),
-        "Retrieve list elements using a slice object"
+        "Retrieve list elements using a slice object");
-    );
 
-    cl.def("__setitem__",
+    cl.def(
+        "__setitem__",
         [](Vector &v, slice slice, const Vector &value) {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
 
@@ -250,8 +252,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
                 start += step;
             }
         },
-        "Assign list elements using a slice object"
+        "Assign list elements using a slice object");
-    );
 
     cl.def("__delitem__",
         [wrap_i](Vector &v, DiffType i) {
@@ -261,9 +262,10 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
         "Delete the list elements at index ``i``"
     );
 
-    cl.def("__delitem__",
+    cl.def(
+        "__delitem__",
         [](Vector &v, slice slice) {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
 
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
@@ -277,9 +279,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
                 }
             }
         },
-        "Delete list elements using a slice object"
+        "Delete list elements using a slice object");
-    );
-
 }
 
 // If the type has an operator[] that doesn't return a reference (most notably std::vector<bool>),
@@ -375,10 +375,20 @@ struct vector_has_data_and_format : std::false_type {};
 template <typename Vector>
 struct vector_has_data_and_format<Vector, enable_if_t<std::is_same<decltype(format_descriptor<typename Vector::value_type>::format(), std::declval<Vector>().data()), typename Vector::value_type*>::value>> : std::true_type {};
 
+// [workaround(intel)] Separate function required here
+// Workaround as the Intel compiler does not compile the enable_if_t part below
+// (tested with icc (ICC) 2021.1 Beta 20200827)
+template <typename... Args>
+constexpr bool args_any_are_buffer() {
+    return detail::any_of<std::is_same<Args, buffer_protocol>...>::value;
+}
+
+// [workaround(intel)] Separate function required here
+// [workaround(msvc)] Can't use constexpr bool in return type
+
 // Add the buffer interface to a vector
 template <typename Vector, typename Class_, typename... Args>
-enable_if_t<detail::any_of<std::is_same<Args, buffer_protocol>...>::value>
+void vector_buffer_impl(Class_& cl, std::true_type) {
-vector_buffer(Class_& cl) {
     using T = typename Vector::value_type;
 
     static_assert(vector_has_data_and_format<Vector>::value, "There is not an appropriate format descriptor for this vector");
@@ -390,7 +400,7 @@ vector_buffer(Class_& cl) {
         return buffer_info(v.data(), static_cast<ssize_t>(sizeof(T)), format_descriptor<T>::format(), 1, {v.size()}, {sizeof(T)});
     });
 
-    cl.def(init([](buffer buf) {
+    cl.def(init([](const buffer &buf) {
         auto info = buf.request();
         if (info.ndim != 1 || info.strides[0] % static_cast<ssize_t>(sizeof(T)))
             throw type_error("Only valid 1D buffers can be copied to a vector");
@@ -403,20 +413,24 @@ vector_buffer(Class_& cl) {
         if (step == 1) {
             return Vector(p, end);
         }
-        else {
         Vector vec;
         vec.reserve((size_t) info.shape[0]);
         for (; p != end; p += step)
             vec.push_back(*p);
         return vec;
-        }
+
     }));
 
     return;
 }
 
 template <typename Vector, typename Class_, typename... Args>
-enable_if_t<!detail::any_of<std::is_same<Args, buffer_protocol>...>::value> vector_buffer(Class_&) {}
+void vector_buffer_impl(Class_&, std::false_type) {}
+
+template <typename Vector, typename Class_, typename... Args>
+void vector_buffer(Class_& cl) {
+    vector_buffer_impl<Vector, Class_, Args...>(cl, detail::any_of<std::is_same<Args, buffer_protocol>...>{});
+}
 
 PYBIND11_NAMESPACE_END(detail)
 
@@ -581,6 +595,23 @@ template <typename Map, typename Class_> auto map_if_insertion_operator(Class_ &
     );
 }
 
+template<typename Map>
+struct keys_view
+{
+    Map &map;
+};
+
+template<typename Map>
+struct values_view
+{
+    Map &map;
+};
+
+template<typename Map>
+struct items_view
+{
+    Map &map;
+};
 
 PYBIND11_NAMESPACE_END(detail)
 
@@ -588,6 +619,9 @@ template <typename Map, typename holder_type = std::unique_ptr<Map>, typename...
 class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&... args) {
     using KeyType = typename Map::key_type;
     using MappedType = typename Map::mapped_type;
+    using KeysView = detail::keys_view<Map>;
+    using ValuesView = detail::values_view<Map>;
+    using ItemsView = detail::items_view<Map>;
     using Class_ = class_<Map, holder_type>;
 
     // If either type is a non-module-local bound type then make the map binding non-local as well;
@@ -601,6 +635,12 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
     }
 
     Class_ cl(scope, name.c_str(), pybind11::module_local(local), std::forward<Args>(args)...);
+    class_<KeysView> keys_view(
+        scope, ("KeysView[" + name + "]").c_str(), pybind11::module_local(local));
+    class_<ValuesView> values_view(
+        scope, ("ValuesView[" + name + "]").c_str(), pybind11::module_local(local));
+    class_<ItemsView> items_view(
+        scope, ("ItemsView[" + name + "]").c_str(), pybind11::module_local(local));
 
     cl.def(init<>());
 
@@ -614,12 +654,22 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
 
     cl.def("__iter__",
            [](Map &m) { return make_key_iterator(m.begin(), m.end()); },
-           keep_alive<0, 1>() /* Essential: keep list alive while iterator exists */
+           keep_alive<0, 1>() /* Essential: keep map alive while iterator exists */
+    );
+
+    cl.def("keys",
+           [](Map &m) { return KeysView{m}; },
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
+    );
+
+    cl.def("values",
+           [](Map &m) { return ValuesView{m}; },
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def("items",
-           [](Map &m) { return make_iterator(m.begin(), m.end()); },
+           [](Map &m) { return ItemsView{m}; },
-           keep_alive<0, 1>() /* Essential: keep list alive while iterator exists */
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def("__getitem__",
@@ -640,6 +690,8 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
            return true;
         }
     );
+    // Fallback for when the object is not of the key type
+    cl.def("__contains__", [](Map &, const object &) -> bool { return false; });
 
     // Assignment provided only if the type is copyable
     detail::map_assignment<Map, Class_>(cl);
@@ -655,6 +707,40 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
 
     cl.def("__len__", &Map::size);
 
+    keys_view.def("__len__", [](KeysView &view) { return view.map.size(); });
+    keys_view.def("__iter__",
+        [](KeysView &view) {
+            return make_key_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
+    keys_view.def("__contains__",
+        [](KeysView &view, const KeyType &k) -> bool {
+            auto it = view.map.find(k);
+            if (it == view.map.end())
+                return false;
+            return true;
+        }
+    );
+    // Fallback for when the object is not of the key type
+    keys_view.def("__contains__", [](KeysView &, const object &) -> bool { return false; });
+
+    values_view.def("__len__", [](ValuesView &view) { return view.map.size(); });
+    values_view.def("__iter__",
+        [](ValuesView &view) {
+            return make_value_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
+
+    items_view.def("__len__", [](ItemsView &view) { return view.map.size(); });
+    items_view.def("__iter__",
+        [](ItemsView &view) {
+            return make_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
+
     return cl;
 }
 

wrap/pybind11/noxfile.py

@@ -0,0 +1,93 @@
+import nox
+
+nox.options.sessions = ["lint", "tests", "tests_packaging"]
+
+PYTHON_VERISONS = ["2.7", "3.5", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11"]
+
+
+@nox.session(reuse_venv=True)
+def lint(session: nox.Session) -> None:
+    """
+    Lint the codebase (except for clang-format/tidy).
+    """
+    session.install("pre-commit")
+    session.run("pre-commit", "run", "-a")
+
+
+@nox.session(python=PYTHON_VERISONS)
+def tests(session: nox.Session) -> None:
+    """
+    Run the tests (requires a compiler).
+    """
+    tmpdir = session.create_tmp()
+    session.install("cmake")
+    session.install("-r", "tests/requirements.txt")
+    session.run(
+        "cmake",
+        "-S",
+        ".",
+        "-B",
+        tmpdir,
+        "-DPYBIND11_WERROR=ON",
+        "-DDOWNLOAD_CATCH=ON",
+        "-DDOWNLOAD_EIGEN=ON",
+        *session.posargs
+    )
+    session.run("cmake", "--build", tmpdir)
+    session.run("cmake", "--build", tmpdir, "--config=Release", "--target", "check")
+
+
+@nox.session
+def tests_packaging(session: nox.Session) -> None:
+    """
+    Run the packaging tests.
+    """
+
+    session.install("-r", "tests/requirements.txt", "--prefer-binary")
+    session.run("pytest", "tests/extra_python_package")
+
+
+@nox.session(reuse_venv=True)
+def docs(session: nox.Session) -> None:
+    """
+    Build the docs. Pass "serve" to serve.
+    """
+
+    session.install("-r", "docs/requirements.txt")
+    session.chdir("docs")
+
+    if "pdf" in session.posargs:
+        session.run("sphinx-build", "-b", "latexpdf", ".", "_build")
+        return
+
+    session.run("sphinx-build", "-b", "html", ".", "_build")
+
+    if "serve" in session.posargs:
+        session.log("Launching docs at http://localhost:8000/ - use Ctrl-C to quit")
+        session.run("python", "-m", "http.server", "8000", "-d", "_build/html")
+    elif session.posargs:
+        session.error("Unsupported argument to docs")
+
+
+@nox.session(reuse_venv=True)
+def make_changelog(session: nox.Session) -> None:
+    """
+    Inspect the closed issues and make entries for a changelog.
+    """
+    session.install("ghapi", "rich")
+    session.run("python", "tools/make_changelog.py")
+
+
+@nox.session(reuse_venv=True)
+def build(session: nox.Session) -> None:
+    """
+    Build SDists and wheels.
+    """
+
+    session.install("build")
+    session.log("Building normal files")
+    session.run("python", "-m", "build", *session.posargs)
+    session.log("Building pybind11-global files (PYBIND11_GLOBAL_SDIST=1)")
+    session.run(
+        "python", "-m", "build", *session.posargs, env={"PYBIND11_GLOBAL_SDIST": "1"}
+    )

wrap/pybind11/pybind11/__init__.py

@@ -1,8 +1,7 @@
 # -*- coding: utf-8 -*-
 
-from ._version import version_info, __version__
+from ._version import __version__, version_info
-from .commands import get_include, get_cmake_dir
+from .commands import get_cmake_dir, get_include
-
 
 __all__ = (
     "version_info",

wrap/pybind11/pybind11/__main__.py

@@ -5,10 +5,11 @@ import argparse
 import sys
 import sysconfig
 
-from .commands import get_include, get_cmake_dir
+from .commands import get_cmake_dir, get_include
 
 
 def print_includes():
+    # type: () -> None
     dirs = [
         sysconfig.get_path("include"),
         sysconfig.get_path("platinclude"),
@@ -18,13 +19,15 @@ def print_includes():
     # Make unique but preserve order
     unique_dirs = []
     for d in dirs:
-        if d not in unique_dirs:
+        if d and d not in unique_dirs:
             unique_dirs.append(d)
 
     print(" ".join("-I" + d for d in unique_dirs))
 
 
 def main():
+    # type: () -> None
+
     parser = argparse.ArgumentParser()
     parser.add_argument(
         "--includes",

wrap/pybind11/pybind11/_version.py

@@ -8,5 +8,5 @@ def _to_int(s):
         return s
 
 
-__version__ = "2.6.0.dev1"
+__version__ = "2.9.1"
 version_info = tuple(_to_int(s) for s in __version__.split("."))

wrap/pybind11/pybind11/_version.pyi

@@ -0,0 +1,6 @@
+from typing import Tuple, Union
+
+def _to_int(s: str) -> Union[int, str]: ...
+
+__version__: str
+version_info: Tuple[Union[int, str], ...]

wrap/pybind11/pybind11/commands.py

@@ -1,17 +1,18 @@
 # -*- coding: utf-8 -*-
 import os
 
-
 DIR = os.path.abspath(os.path.dirname(__file__))
 
 
 def get_include(user=False):
+    # type: (bool) -> str
     installed_path = os.path.join(DIR, "include")
     source_path = os.path.join(os.path.dirname(DIR), "include")
     return installed_path if os.path.exists(installed_path) else source_path
 
 
 def get_cmake_dir():
+    # type: () -> str
     cmake_installed_path = os.path.join(DIR, "share", "cmake", "pybind11")
     if os.path.exists(cmake_installed_path):
         return cmake_installed_path

wrap/pybind11/pybind11/setup_helpers.py

@@ -33,25 +33,34 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 """
 
+# IMPORTANT: If you change this file in the pybind11 repo, also review
+# setup_helpers.pyi for matching changes.
+#
+# If you copy this file in, you don't
+# need the .pyi file; it's just an interface file for static type checkers.
+
 import contextlib
 import os
+import platform
+import shlex
 import shutil
 import sys
+import sysconfig
 import tempfile
 import threading
 import warnings
 
 try:
-    from setuptools.command.build_ext import build_ext as _build_ext
     from setuptools import Extension as _Extension
+    from setuptools.command.build_ext import build_ext as _build_ext
 except ImportError:
     from distutils.command.build_ext import build_ext as _build_ext
     from distutils.extension import Extension as _Extension
 
+import distutils.ccompiler
 import distutils.errors
 
-
+WIN = sys.platform.startswith("win32") and "mingw" not in sysconfig.get_platform()
-WIN = sys.platform.startswith("win32")
 PY2 = sys.version_info[0] < 3
 MACOS = sys.platform.startswith("darwin")
 STD_TMPL = "/std:c++{}" if WIN else "-std=c++{}"
@@ -76,7 +85,7 @@ class Pybind11Extension(_Extension):
     * ``stdlib=libc++`` on macOS
     * ``visibility=hidden`` and ``-g0`` on Unix
 
-    Finally, you can set ``cxx_std`` via constructor or afterwords to enable
+    Finally, you can set ``cxx_std`` via constructor or afterwards to enable
     flags for C++ std, and a few extra helper flags related to the C++ standard
     level. It is _highly_ recommended you either set this, or use the provided
     ``build_ext``, which will search for the highest supported extension for
@@ -91,15 +100,14 @@ class Pybind11Extension(_Extension):
     this is an ugly old-style class due to Distutils.
     """
 
-    def _add_cflags(self, *flags):
+    # flags are prepended, so that they can be further overridden, e.g. by
-        for flag in flags:
+    # ``extra_compile_args=["-g"]``.
-            if flag not in self.extra_compile_args:
-                self.extra_compile_args.append(flag)
 
-    def _add_lflags(self, *flags):
+    def _add_cflags(self, flags):
-        for flag in flags:
+        self.extra_compile_args[:0] = flags
-            if flag not in self.extra_compile_args:
+
-                self.extra_link_args.append(flag)
+    def _add_ldflags(self, flags):
+        self.extra_link_args[:0] = flags
 
     def __init__(self, *args, **kwargs):
 
@@ -131,13 +139,22 @@ class Pybind11Extension(_Extension):
         # Have to use the accessor manually to support Python 2 distutils
         Pybind11Extension.cxx_std.__set__(self, cxx_std)
 
+        cflags = []
+        ldflags = []
         if WIN:
-            self._add_cflags("/EHsc", "/bigobj")
+            cflags += ["/EHsc", "/bigobj"]
         else:
-            self._add_cflags("-fvisibility=hidden", "-g0")
+            cflags += ["-fvisibility=hidden"]
+            env_cflags = os.environ.get("CFLAGS", "")
+            env_cppflags = os.environ.get("CPPFLAGS", "")
+            c_cpp_flags = shlex.split(env_cflags) + shlex.split(env_cppflags)
+            if not any(opt.startswith("-g") for opt in c_cpp_flags):
+                cflags += ["-g0"]
             if MACOS:
-                self._add_cflags("-stdlib=libc++")
+                cflags += ["-stdlib=libc++"]
-                self._add_lflags("-stdlib=libc++")
+                ldflags += ["-stdlib=libc++"]
+        self._add_cflags(cflags)
+        self._add_ldflags(ldflags)
 
     @property
     def cxx_std(self):
@@ -156,7 +173,8 @@ class Pybind11Extension(_Extension):
         if self._cxx_level:
             warnings.warn("You cannot safely change the cxx_level after setting it!")
 
-        # MSVC 2015 Update 3 and later only have 14 (and later 17) modes
+        # MSVC 2015 Update 3 and later only have 14 (and later 17) modes, so
+        # force a valid flag here.
         if WIN and level == 11:
             level = 14
 
@@ -165,19 +183,34 @@ class Pybind11Extension(_Extension):
         if not level:
             return
 
-        self.extra_compile_args.append(STD_TMPL.format(level))
+        cflags = [STD_TMPL.format(level)]
+        ldflags = []
 
         if MACOS and "MACOSX_DEPLOYMENT_TARGET" not in os.environ:
-            # C++17 requires a higher min version of macOS
+            # C++17 requires a higher min version of macOS. An earlier version
-            macosx_min = "-mmacosx-version-min=" + ("10.9" if level < 17 else "10.14")
+            # (10.12 or 10.13) can be set manually via environment variable if
-            self.extra_compile_args.append(macosx_min)
+            # you are careful in your feature usage, but 10.14 is the safest
-            self.extra_link_args.append(macosx_min)
+            # setting for general use. However, never set higher than the
+            # current macOS version!
+            current_macos = tuple(int(x) for x in platform.mac_ver()[0].split(".")[:2])
+            desired_macos = (10, 9) if level < 17 else (10, 14)
+            macos_string = ".".join(str(x) for x in min(current_macos, desired_macos))
+            macosx_min = "-mmacosx-version-min=" + macos_string
+            cflags += [macosx_min]
+            ldflags += [macosx_min]
 
         if PY2:
-            if level >= 17:
+            if WIN:
-                self.extra_compile_args.append("/wd503" if WIN else "-Wno-register")
+                # Will be ignored on MSVC 2015, where C++17 is not supported so
-            elif not WIN and level >= 14:
+                # this flag is not valid.
-                self.extra_compile_args.append("-Wno-deprecated-register")
+                cflags += ["/wd5033"]
+            elif level >= 17:
+                cflags += ["-Wno-register"]
+            elif level >= 14:
+                cflags += ["-Wno-deprecated-register"]
+
+        self._add_cflags(cflags)
+        self._add_ldflags(ldflags)
 
 
 # Just in case someone clever tries to multithread
@@ -212,7 +245,8 @@ def has_flag(compiler, flag):
     with tmp_chdir():
         fname = "flagcheck.cpp"
         with open(fname, "w") as f:
-            f.write("int main (int argc, char **argv) { return 0; }")
+            # Don't trigger -Wunused-parameter.
+            f.write("int main (int, char **) { return 0; }")
 
         try:
             compiler.compile([fname], extra_postargs=[flag])
@@ -227,9 +261,12 @@ cpp_flag_cache = None
 
 def auto_cpp_level(compiler):
     """
-    Return the max supported C++ std level (17, 14, or 11).
+    Return the max supported C++ std level (17, 14, or 11). Returns latest on Windows.
     """
 
+    if WIN:
+        return "latest"
+
     global cpp_flag_cache
 
     # If this has been previously calculated with the same args, return that
@@ -237,7 +274,7 @@ def auto_cpp_level(compiler):
         if cpp_flag_cache:
             return cpp_flag_cache
 
-    levels = [17, 14] + ([] if WIN else [11])
+    levels = [17, 14, 11]
 
     for level in levels:
         if has_flag(compiler, STD_TMPL.format(level)):
@@ -252,7 +289,8 @@ def auto_cpp_level(compiler):
 class build_ext(_build_ext):  # noqa: N801
     """
     Customized build_ext that allows an auto-search for the highest supported
-    C++ level for Pybind11Extension.
+    C++ level for Pybind11Extension. This is only needed for the auto-search
+    for now, and is completely optional otherwise.
     """
 
     def build_extensions(self):
@@ -268,3 +306,189 @@ class build_ext(_build_ext):  # noqa: N801
         # Python 2 doesn't allow super here, since distutils uses old-style
         # classes!
         _build_ext.build_extensions(self)
+
+
+def intree_extensions(paths, package_dir=None):
+    """
+    Generate Pybind11Extensions from source files directly located in a Python
+    source tree.
+
+    ``package_dir`` behaves as in ``setuptools.setup``.  If unset, the Python
+    package root parent is determined as the first parent directory that does
+    not contain an ``__init__.py`` file.
+    """
+    exts = []
+    for path in paths:
+        if package_dir is None:
+            parent, _ = os.path.split(path)
+            while os.path.exists(os.path.join(parent, "__init__.py")):
+                parent, _ = os.path.split(parent)
+            relname, _ = os.path.splitext(os.path.relpath(path, parent))
+            qualified_name = relname.replace(os.path.sep, ".")
+            exts.append(Pybind11Extension(qualified_name, [path]))
+        else:
+            found = False
+            for prefix, parent in package_dir.items():
+                if path.startswith(parent):
+                    found = True
+                    relname, _ = os.path.splitext(os.path.relpath(path, parent))
+                    qualified_name = relname.replace(os.path.sep, ".")
+                    if prefix:
+                        qualified_name = prefix + "." + qualified_name
+                    exts.append(Pybind11Extension(qualified_name, [path]))
+            if not found:
+                raise ValueError(
+                    "path {} is not a child of any of the directories listed "
+                    "in 'package_dir' ({})".format(path, package_dir)
+                )
+    return exts
+
+
+def naive_recompile(obj, src):
+    """
+    This will recompile only if the source file changes. It does not check
+    header files, so a more advanced function or Ccache is better if you have
+    editable header files in your package.
+    """
+    return os.stat(obj).st_mtime < os.stat(src).st_mtime
+
+
+def no_recompile(obg, src):
+    """
+    This is the safest but slowest choice (and is the default) - will always
+    recompile sources.
+    """
+    return True
+
+
+# Optional parallel compile utility
+# inspired by: http://stackoverflow.com/questions/11013851/speeding-up-build-process-with-distutils
+# and: https://github.com/tbenthompson/cppimport/blob/stable/cppimport/build_module.py
+# and NumPy's parallel distutils module:
+#              https://github.com/numpy/numpy/blob/master/numpy/distutils/ccompiler.py
+class ParallelCompile(object):
+    """
+    Make a parallel compile function. Inspired by
+    numpy.distutils.ccompiler.CCompiler_compile and cppimport.
+
+    This takes several arguments that allow you to customize the compile
+    function created:
+
+    envvar:
+        Set an environment variable to control the compilation threads, like
+        NPY_NUM_BUILD_JOBS
+    default:
+        0 will automatically multithread, or 1 will only multithread if the
+        envvar is set.
+    max:
+        The limit for automatic multithreading if non-zero
+    needs_recompile:
+        A function of (obj, src) that returns True when recompile is needed.  No
+        effect in isolated mode; use ccache instead, see
+        https://github.com/matplotlib/matplotlib/issues/1507/
+
+    To use::
+
+        ParallelCompile("NPY_NUM_BUILD_JOBS").install()
+
+    or::
+
+        with ParallelCompile("NPY_NUM_BUILD_JOBS"):
+            setup(...)
+
+    By default, this assumes all files need to be recompiled. A smarter
+    function can be provided via needs_recompile.  If the output has not yet
+    been generated, the compile will always run, and this function is not
+    called.
+    """
+
+    __slots__ = ("envvar", "default", "max", "_old", "needs_recompile")
+
+    def __init__(self, envvar=None, default=0, max=0, needs_recompile=no_recompile):
+        self.envvar = envvar
+        self.default = default
+        self.max = max
+        self.needs_recompile = needs_recompile
+        self._old = []
+
+    def function(self):
+        """
+        Builds a function object usable as distutils.ccompiler.CCompiler.compile.
+        """
+
+        def compile_function(
+            compiler,
+            sources,
+            output_dir=None,
+            macros=None,
+            include_dirs=None,
+            debug=0,
+            extra_preargs=None,
+            extra_postargs=None,
+            depends=None,
+        ):
+
+            # These lines are directly from distutils.ccompiler.CCompiler
+            macros, objects, extra_postargs, pp_opts, build = compiler._setup_compile(
+                output_dir, macros, include_dirs, sources, depends, extra_postargs
+            )
+            cc_args = compiler._get_cc_args(pp_opts, debug, extra_preargs)
+
+            # The number of threads; start with default.
+            threads = self.default
+
+            # Determine the number of compilation threads, unless set by an environment variable.
+            if self.envvar is not None:
+                threads = int(os.environ.get(self.envvar, self.default))
+
+            def _single_compile(obj):
+                try:
+                    src, ext = build[obj]
+                except KeyError:
+                    return
+
+                if not os.path.exists(obj) or self.needs_recompile(obj, src):
+                    compiler._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
+
+            try:
+                # Importing .synchronize checks for platforms that have some multiprocessing
+                # capabilities but lack semaphores, such as AWS Lambda and Android Termux.
+                import multiprocessing.synchronize
+                from multiprocessing.pool import ThreadPool
+            except ImportError:
+                threads = 1
+
+            if threads == 0:
+                try:
+                    threads = multiprocessing.cpu_count()
+                    threads = self.max if self.max and self.max < threads else threads
+                except NotImplementedError:
+                    threads = 1
+
+            if threads > 1:
+                pool = ThreadPool(threads)
+                # In Python 2, ThreadPool can't be used as a context manager.
+                # Once we are no longer supporting it, this can be 'with pool:'
+                try:
+                    for _ in pool.imap_unordered(_single_compile, objects):
+                        pass
+                finally:
+                    pool.terminate()
+            else:
+                for ob in objects:
+                    _single_compile(ob)
+
+            return objects
+
+        return compile_function
+
+    def install(self):
+        distutils.ccompiler.CCompiler.compile = self.function()
+        return self
+
+    def __enter__(self):
+        self._old.append(distutils.ccompiler.CCompiler.compile)
+        return self.install()
+
+    def __exit__(self, *args):
+        distutils.ccompiler.CCompiler.compile = self._old.pop()

wrap/pybind11/pybind11/setup_helpers.pyi

@@ -0,0 +1,63 @@
+# IMPORTANT: Should stay in sync with setup_helpers.py (mostly checked by CI /
+# pre-commit).
+
+import contextlib
+import distutils.ccompiler
+from distutils.command.build_ext import build_ext as _build_ext  # type: ignore
+from distutils.extension import Extension as _Extension
+from types import TracebackType
+from typing import Any, Callable, Dict, Iterator, List, Optional, Type, TypeVar, Union
+
+WIN: bool
+PY2: bool
+MACOS: bool
+STD_TMPL: str
+
+class Pybind11Extension(_Extension):
+    def _add_cflags(self, *flags: str) -> None: ...
+    def _add_lflags(self, *flags: str) -> None: ...
+    def __init__(
+        self, *args: Any, cxx_std: int = 0, language: str = "c++", **kwargs: Any
+    ) -> None: ...
+    @property
+    def cxx_std(self) -> int: ...
+    @cxx_std.setter
+    def cxx_std(self, level: int) -> None: ...
+
+@contextlib.contextmanager
+def tmp_chdir() -> Iterator[str]: ...
+def has_flag(compiler: distutils.ccompiler.CCompiler, flag: str) -> bool: ...
+def auto_cpp_level(compiler: distutils.ccompiler.CCompiler) -> Union[int, str]: ...
+
+class build_ext(_build_ext):  # type: ignore
+    def build_extensions(self) -> None: ...
+
+def intree_extensions(
+    paths: Iterator[str], package_dir: Optional[Dict[str, str]] = None
+) -> List[Pybind11Extension]: ...
+def no_recompile(obj: str, src: str) -> bool: ...
+def naive_recompile(obj: str, src: str) -> bool: ...
+
+T = TypeVar("T", bound="ParallelCompile")
+
+class ParallelCompile:
+    envvar: Optional[str]
+    default: int
+    max: int
+    needs_recompile: Callable[[str, str], bool]
+    def __init__(
+        self,
+        envvar: Optional[str] = None,
+        default: int = 0,
+        max: int = 0,
+        needs_recompile: Callable[[str, str], bool] = no_recompile,
+    ) -> None: ...
+    def function(self) -> Any: ...
+    def install(self: T) -> T: ...
+    def __enter__(self: T) -> T: ...
+    def __exit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc_value: Optional[BaseException],
+        traceback: Optional[TracebackType],
+    ) -> None: ...

wrap/pybind11/pyproject.toml

@@ -1,3 +1,41 @@
 [build-system]
-requires = ["setuptools", "wheel", "cmake==3.18.0", "ninja"]
+requires = ["setuptools>=42", "wheel", "cmake>=3.18", "ninja"]
 build-backend = "setuptools.build_meta"
+
+[tool.check-manifest]
+ignore = [
+    "tests/**",
+    "docs/**",
+    "tools/**",
+    "include/**",
+    ".*",
+    "pybind11/include/**",
+    "pybind11/share/**",
+    "CMakeLists.txt",
+    "noxfile.py",
+]
+
+[tool.isort]
+# Needs the compiled .so modules and env.py from tests
+known_first_party = "env,pybind11_cross_module_tests,pybind11_tests,"
+# For black compatibility
+profile = "black"
+
+[tool.mypy]
+files = "pybind11"
+python_version = "2.7"
+warn_unused_configs = true
+
+disallow_any_generics = true
+disallow_subclassing_any = true
+disallow_untyped_calls = true
+disallow_untyped_defs = true
+disallow_incomplete_defs = true
+check_untyped_defs = true
+disallow_untyped_decorators = true
+no_implicit_optional = true
+warn_redundant_casts = true
+warn_unused_ignores = true
+warn_return_any = true
+no_implicit_reexport = true
+strict_equality = true

wrap/pybind11/setup.cfg

@@ -1,10 +1,10 @@
 [metadata]
-long_description = file: README.md
+long_description = file: README.rst
-long_description_content_type = text/markdown
+long_description_content_type = text/x-rst
 description = Seamless operability between C++11 and Python
 author = Wenzel Jakob
-author_email = "wenzel.jakob@epfl.ch"
+author_email = wenzel.jakob@epfl.ch
-url = "https://github.com/pybind/pybind11"
+url = https://github.com/pybind/pybind11
 license = BSD
 
 classifiers =
@@ -19,6 +19,8 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
     License :: OSI Approved :: BSD License
     Programming Language :: Python :: Implementation :: PyPy
     Programming Language :: Python :: Implementation :: CPython
@@ -29,29 +31,20 @@ keywords =
     C++11
     Python bindings
 
+project_urls =
+    Documentation = https://pybind11.readthedocs.io/
+    Bug Tracker = https://github.com/pybind/pybind11/issues
+    Discussions = https://github.com/pybind/pybind11/discussions
+    Changelog = https://pybind11.readthedocs.io/en/latest/changelog.html
+    Chat = https://gitter.im/pybind/Lobby
+
 [options]
-python_requires = >=2.7, !=3.0, !=3.1, !=3.2, !=3.3, !=3.4
+python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*
 zip_safe = False
 
 [bdist_wheel]
 universal=1
 
-[check-manifest]
-ignore =
-    tests/**
-    docs/**
-    tools/**
-    include/**
-    .appveyor.yml
-    .cmake-format.yaml
-    .gitmodules
-    .pre-commit-config.yaml
-    .readthedocs.yml
-    .clang-tidy
-    pybind11/include/**
-    pybind11/share/**
-    CMakeLists.txt
-
 
 [flake8]
 max-line-length = 99
@@ -64,3 +57,7 @@ ignore =
     N813
     # Black conflict
     W503, E203
+
+
+[tool:pytest]
+timeout = 300

wrap/pybind11/setup.py

@@ -4,6 +4,7 @@
 # Setup script for PyPI; use CMakeFile.txt to build extension modules
 
 import contextlib
+import io
 import os
 import re
 import shutil
@@ -19,6 +20,36 @@ VERSION_REGEX = re.compile(
     r"^\s*#\s*define\s+PYBIND11_VERSION_([A-Z]+)\s+(.*)$", re.MULTILINE
 )
 
+
+def build_expected_version_hex(matches):
+    patch_level_serial = matches["PATCH"]
+    serial = None
+    try:
+        major = int(matches["MAJOR"])
+        minor = int(matches["MINOR"])
+        flds = patch_level_serial.split(".")
+        if flds:
+            patch = int(flds[0])
+            level = None
+            if len(flds) == 1:
+                level = "0"
+                serial = 0
+            elif len(flds) == 2:
+                level_serial = flds[1]
+                for level in ("a", "b", "c", "dev"):
+                    if level_serial.startswith(level):
+                        serial = int(level_serial[len(level) :])
+                        break
+    except ValueError:
+        pass
+    if serial is None:
+        msg = 'Invalid PYBIND11_VERSION_PATCH: "{}"'.format(patch_level_serial)
+        raise RuntimeError(msg)
+    return "0x{:02x}{:02x}{:02x}{}{:x}".format(
+        major, minor, patch, level[:1].upper(), serial
+    )
+
+
 # PYBIND11_GLOBAL_SDIST will build a different sdist, with the python-headers
 # files, and the sys.prefix files (CMake and headers).
 
@@ -35,12 +66,12 @@ to_src = (
 # Read the listed version
 with open("pybind11/_version.py") as f:
     code = compile(f.read(), "pybind11/_version.py", "exec")
-    loc = {}
+loc = {}
-    exec(code, loc)
+exec(code, loc)
-    version = loc["__version__"]
+version = loc["__version__"]
 
 # Verify that the version matches the one in C++
-with open("include/pybind11/detail/common.h") as f:
+with io.open("include/pybind11/detail/common.h", encoding="utf8") as f:
     matches = dict(VERSION_REGEX.findall(f.read()))
 cpp_version = "{MAJOR}.{MINOR}.{PATCH}".format(**matches)
 if version != cpp_version:
@@ -49,6 +80,15 @@ if version != cpp_version:
     )
     raise RuntimeError(msg)
 
+version_hex = matches.get("HEX", "MISSING")
+expected_version_hex = build_expected_version_hex(matches)
+if version_hex != expected_version_hex:
+    msg = "PYBIND11_VERSION_HEX {} does not match expected value {}!".format(
+        version_hex,
+        expected_version_hex,
+    )
+    raise RuntimeError(msg)
+
 
 def get_and_replace(filename, binary=False, **opts):
     with open(filename, "rb" if binary else "r") as f:
@@ -106,6 +146,13 @@ with remove_output("pybind11/include", "pybind11/share"):
             "-DBUILD_TESTING=OFF",
             "-DPYBIND11_NOPYTHON=ON",
         ]
+        if "CMAKE_ARGS" in os.environ:
+            fcommand = [
+                c
+                for c in os.environ["CMAKE_ARGS"].split()
+                if "DCMAKE_INSTALL_PREFIX" not in c
+            ]
+            cmd += fcommand
         cmake_opts = dict(cwd=DIR, stdout=sys.stdout, stderr=sys.stderr)
         subprocess.check_call(cmd, **cmake_opts)
         subprocess.check_call(["cmake", "--install", tmpdir], **cmake_opts)

wrap/pybind11/tests/CMakeLists.txt

@@ -10,27 +10,34 @@ cmake_minimum_required(VERSION 3.4)
 # The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.21)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.21)
 endif()
 
 # Only needed for CMake < 3.5 support
 include(CMakeParseArguments)
 
-# Filter out items; print an optional message if any items filtered
+# Filter out items; print an optional message if any items filtered. This ignores extensions.
 #
 # Usage:
 #   pybind11_filter_tests(LISTNAME file1.cpp file2.cpp ... MESSAGE "")
 #
-macro(PYBIND11_FILTER_TESTS LISTNAME)
+macro(pybind11_filter_tests LISTNAME)
   cmake_parse_arguments(ARG "" "MESSAGE" "" ${ARGN})
   set(PYBIND11_FILTER_TESTS_FOUND OFF)
+  # Make a list of the test without any extensions, for easier filtering.
+  set(_TMP_ACTUAL_LIST "${${LISTNAME}};") # enforce ';' at the end to allow matching last item.
+  string(REGEX REPLACE "\\.[^.;]*;" ";" LIST_WITHOUT_EXTENSIONS "${_TMP_ACTUAL_LIST}")
   foreach(filename IN LISTS ARG_UNPARSED_ARGUMENTS)
-    list(FIND ${LISTNAME} ${filename} _FILE_FOUND)
+    string(REGEX REPLACE "\\.[^.]*$" "" filename_no_ext ${filename})
+    # Search in the list without extensions.
+    list(FIND LIST_WITHOUT_EXTENSIONS ${filename_no_ext} _FILE_FOUND)
     if(_FILE_FOUND GREATER -1)
-      list(REMOVE_AT ${LISTNAME} ${_FILE_FOUND})
+      list(REMOVE_AT ${LISTNAME} ${_FILE_FOUND}) # And remove from the list with extensions.
+      list(REMOVE_AT LIST_WITHOUT_EXTENSIONS ${_FILE_FOUND}
+      )# And our search list, to ensure it is in sync.
       set(PYBIND11_FILTER_TESTS_FOUND ON)
     endif()
   endforeach()
@@ -39,6 +46,26 @@ macro(PYBIND11_FILTER_TESTS LISTNAME)
   endif()
 endmacro()
 
+macro(possibly_uninitialized)
+  foreach(VARNAME ${ARGN})
+    if(NOT DEFINED "${VARNAME}")
+      set("${VARNAME}" "")
+    endif()
+  endforeach()
+endmacro()
+
+# Function to add additional targets if any of the provided tests are found.
+# Needles; Specifies the test names to look for.
+# Additions; Specifies the additional test targets to add when any of the needles are found.
+macro(tests_extra_targets needles additions)
+  # Add the index for this relation to the index extra targets map.
+  list(LENGTH PYBIND11_TEST_EXTRA_TARGETS PYBIND11_TEST_EXTRA_TARGETS_LEN)
+  list(APPEND PYBIND11_TEST_EXTRA_TARGETS ${PYBIND11_TEST_EXTRA_TARGETS_LEN})
+  # Add the test names to look for, and the associated test target additions.
+  set(PYBIND11_TEST_EXTRA_TARGETS_NEEDLES_${PYBIND11_TEST_EXTRA_TARGETS_LEN} ${needles})
+  set(PYBIND11_TEST_EXTRA_TARGETS_ADDITION_${PYBIND11_TEST_EXTRA_TARGETS_LEN} ${additions})
+endmacro()
+
 # New Python support
 if(DEFINED Python_EXECUTABLE)
   set(PYTHON_EXECUTABLE "${Python_EXECUTABLE}")
@@ -67,7 +94,7 @@ if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
   find_package(pybind11 REQUIRED CONFIG)
 endif()
 
-if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+if(NOT CMAKE_BUILD_TYPE AND NOT DEFINED CMAKE_CONFIGURATION_TYPES)
   message(STATUS "Setting tests build type to MinSizeRel as none was specified")
   set(CMAKE_BUILD_TYPE
       MinSizeRel
@@ -84,52 +111,67 @@ if(PYBIND11_CUDA_TESTS)
   set(CMAKE_CUDA_STANDARD_REQUIRED ON)
 endif()
 
-# Full set of test files (you can override these; see below)
+# Full set of test files (you can override these; see below, overrides ignore extension)
+# Any test that has no extension is both .py and .cpp, so 'foo' will add 'foo.cpp' and 'foo.py'.
+# Any test that has an extension is exclusively that and handled as such.
 set(PYBIND11_TEST_FILES
-    test_async.cpp
+    test_async
-    test_buffers.cpp
+    test_buffers
-    test_builtin_casters.cpp
+    test_builtin_casters
-    test_call_policies.cpp
+    test_call_policies
-    test_callbacks.cpp
+    test_callbacks
-    test_chrono.cpp
+    test_chrono
-    test_class.cpp
+    test_class
-    test_constants_and_functions.cpp
+    test_const_name
-    test_copy_move.cpp
+    test_constants_and_functions
-    test_custom_type_casters.cpp
+    test_copy_move
-    test_docstring_options.cpp
+    test_custom_type_casters
-    test_eigen.cpp
+    test_custom_type_setup
-    test_enum.cpp
+    test_docstring_options
-    test_eval.cpp
+    test_eigen
-    test_exceptions.cpp
+    test_enum
-    test_factory_constructors.cpp
+    test_eval
-    test_gil_scoped.cpp
+    test_exceptions
-    test_iostream.cpp
+    test_factory_constructors
-    test_kwargs_and_defaults.cpp
+    test_gil_scoped
-    test_local_bindings.cpp
+    test_iostream
-    test_methods_and_attributes.cpp
+    test_kwargs_and_defaults
-    test_modules.cpp
+    test_local_bindings
-    test_multiple_inheritance.cpp
+    test_methods_and_attributes
-    test_numpy_array.cpp
+    test_modules
-    test_numpy_dtypes.cpp
+    test_multiple_inheritance
-    test_numpy_vectorize.cpp
+    test_numpy_array
-    test_opaque_types.cpp
+    test_numpy_dtypes
-    test_operator_overloading.cpp
+    test_numpy_vectorize
-    test_pickling.cpp
+    test_opaque_types
-    test_pytypes.cpp
+    test_operator_overloading
-    test_sequences_and_iterators.cpp
+    test_pickling
-    test_smart_ptr.cpp
+    test_pytypes
-    test_stl.cpp
+    test_sequences_and_iterators
-    test_stl_binders.cpp
+    test_smart_ptr
-    test_tagbased_polymorphic.cpp
+    test_stl
-    test_union.cpp
+    test_stl_binders
-    test_virtual_functions.cpp)
+    test_tagbased_polymorphic
+    test_thread
+    test_union
+    test_virtual_functions)
 
 # Invoking cmake with something like:
 #     cmake -DPYBIND11_TEST_OVERRIDE="test_callbacks.cpp;test_pickling.cpp" ..
 # lets you override the tests that get compiled and run.  You can restore to all tests with:
 #     cmake -DPYBIND11_TEST_OVERRIDE= ..
 if(PYBIND11_TEST_OVERRIDE)
-  set(PYBIND11_TEST_FILES ${PYBIND11_TEST_OVERRIDE})
+  # Instead of doing a direct override here, we iterate over the overrides without extension and
+  # match them against entries from the PYBIND11_TEST_FILES, anything that not matches goes into the filter list.
+  string(REGEX REPLACE "\\.[^.;]*;" ";" TEST_OVERRIDE_NO_EXT "${PYBIND11_TEST_OVERRIDE};")
+  string(REGEX REPLACE "\\.[^.;]*;" ";" TEST_FILES_NO_EXT "${PYBIND11_TEST_FILES};")
+  # This allows the override to be done with extensions, preserving backwards compatibility.
+  foreach(test_name ${TEST_FILES_NO_EXT})
+    if(NOT ${test_name} IN_LIST TEST_OVERRIDE_NO_EXT
+    )# If not in the whitelist, add to be filtered out.
+      list(APPEND PYBIND11_TEST_FILTER ${test_name})
+    endif()
+  endforeach()
 endif()
 
 # You can also filter tests:
@@ -151,15 +193,46 @@ if(PYBIND11_CUDA_TESTS)
     "Skipping test_constants_and_functions due to incompatible exception specifications")
 endif()
 
-string(REPLACE ".cpp" ".py" PYBIND11_PYTEST_FILES "${PYBIND11_TEST_FILES}")
+# Now that the test filtering is complete, we need to split the list into the test for PYTEST
+# and the list for the cpp targets.
+set(PYBIND11_CPPTEST_FILES "")
+set(PYBIND11_PYTEST_FILES "")
+
+foreach(test_name ${PYBIND11_TEST_FILES})
+  if(test_name MATCHES "\\.py$") # Ends in .py, purely python test.
+    list(APPEND PYBIND11_PYTEST_FILES ${test_name})
+  elseif(test_name MATCHES "\\.cpp$") # Ends in .cpp, purely cpp test.
+    list(APPEND PYBIND11_CPPTEST_FILES ${test_name})
+  elseif(NOT test_name MATCHES "\\.") # No extension specified, assume both, add extension.
+    list(APPEND PYBIND11_PYTEST_FILES ${test_name}.py)
+    list(APPEND PYBIND11_CPPTEST_FILES ${test_name}.cpp)
+  else()
+    message(WARNING "Unhanded test extension in test: ${test_name}")
+  endif()
+endforeach()
+set(PYBIND11_TEST_FILES ${PYBIND11_CPPTEST_FILES})
+list(SORT PYBIND11_PYTEST_FILES)
 
 # Contains the set of test files that require pybind11_cross_module_tests to be
 # built; if none of these are built (i.e. because TEST_OVERRIDE is used and
 # doesn't include them) the second module doesn't get built.
-set(PYBIND11_CROSS_MODULE_TESTS test_exceptions.py test_local_bindings.py test_stl.py
+tests_extra_targets("test_exceptions.py;test_local_bindings.py;test_stl.py;test_stl_binders.py"
-                                test_stl_binders.py)
+                    "pybind11_cross_module_tests")
 
-set(PYBIND11_CROSS_MODULE_GIL_TESTS test_gil_scoped.py)
+# And add additional targets for other tests.
+tests_extra_targets("test_gil_scoped.py" "cross_module_gil_utils")
+
+set(PYBIND11_EIGEN_REPO
+    "https://gitlab.com/libeigen/eigen.git"
+    CACHE STRING "Eigen repository to use for tests")
+# Always use a hash for reconfigure speed and security reasons
+# Include the version number for pretty printing (keep in sync)
+set(PYBIND11_EIGEN_VERSION_AND_HASH
+    "3.4.0;929bc0e191d0927b1735b9a1ddc0e8b77e3a25ec"
+    CACHE STRING "Eigen version to use for tests, format: VERSION;HASH")
+
+list(GET PYBIND11_EIGEN_VERSION_AND_HASH 0 PYBIND11_EIGEN_VERSION_STRING)
+list(GET PYBIND11_EIGEN_VERSION_AND_HASH 1 PYBIND11_EIGEN_VERSION_HASH)
 
 # Check if Eigen is available; if not, remove from PYBIND11_TEST_FILES (but
 # keep it in PYBIND11_PYTEST_FILES, so that we get the "eigen is not installed"
@@ -174,22 +247,26 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
       message(FATAL_ERROR "CMake 3.11+ required when using DOWNLOAD_EIGEN")
     endif()
 
-    set(EIGEN3_VERSION_STRING "3.3.7")
-
     include(FetchContent)
     FetchContent_Declare(
       eigen
-      GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
+      GIT_REPOSITORY "${PYBIND11_EIGEN_REPO}"
-      GIT_TAG ${EIGEN3_VERSION_STRING})
+      GIT_TAG "${PYBIND11_EIGEN_VERSION_HASH}")
 
     FetchContent_GetProperties(eigen)
     if(NOT eigen_POPULATED)
-      message(STATUS "Downloading Eigen")
+      message(
+        STATUS
+          "Downloading Eigen ${PYBIND11_EIGEN_VERSION_STRING} (${PYBIND11_EIGEN_VERSION_HASH}) from ${PYBIND11_EIGEN_REPO}"
+      )
       FetchContent_Populate(eigen)
     endif()
 
     set(EIGEN3_INCLUDE_DIR ${eigen_SOURCE_DIR})
     set(EIGEN3_FOUND TRUE)
+    # When getting locally, the version is not visible from a superprojet,
+    # so just force it.
+    set(EIGEN3_VERSION "${PYBIND11_EIGEN_VERSION_STRING}")
 
   else()
     find_package(Eigen3 3.2.7 QUIET CONFIG)
@@ -217,7 +294,8 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
     message(STATUS "Building tests with Eigen v${EIGEN3_VERSION}")
   else()
     list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
-    message(STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN on CMake 3.11+ to download")
+    message(
+      STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN=ON on CMake 3.11+ to download")
   endif()
 endif()
 
@@ -226,25 +304,69 @@ find_package(Boost 1.56)
 
 if(Boost_FOUND)
   if(NOT TARGET Boost::headers)
+    add_library(Boost::headers IMPORTED INTERFACE)
     if(TARGET Boost::boost)
       # Classic FindBoost
-      add_library(Boost::headers ALIAS Boost::boost)
+      set_property(TARGET Boost::boost PROPERTY INTERFACE_LINK_LIBRARIES Boost::boost)
     else()
       # Very old FindBoost, or newer Boost than CMake in older CMakes
-      add_library(Boost::headers IMPORTED INTERFACE)
       set_property(TARGET Boost::headers PROPERTY INTERFACE_INCLUDE_DIRECTORIES
                                                   ${Boost_INCLUDE_DIRS})
     endif()
   endif()
 endif()
 
+# Check if we need to add -lstdc++fs or -lc++fs or nothing
+if(DEFINED CMAKE_CXX_STANDARD AND CMAKE_CXX_STANDARD LESS 17)
+  set(STD_FS_NO_LIB_NEEDED TRUE)
+elseif(MSVC)
+  set(STD_FS_NO_LIB_NEEDED TRUE)
+else()
+  file(
+    WRITE ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    "#include <filesystem>\nint main(int argc, char ** argv) {\n  std::filesystem::path p(argv[0]);\n  return p.string().length();\n}"
+  )
+  try_compile(
+    STD_FS_NO_LIB_NEEDED ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17)
+  try_compile(
+    STD_FS_NEEDS_STDCXXFS ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17
+    LINK_LIBRARIES stdc++fs)
+  try_compile(
+    STD_FS_NEEDS_CXXFS ${CMAKE_CURRENT_BINARY_DIR}
+    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
+    COMPILE_DEFINITIONS -std=c++17
+    LINK_LIBRARIES c++fs)
+endif()
+
+if(${STD_FS_NEEDS_STDCXXFS})
+  set(STD_FS_LIB stdc++fs)
+elseif(${STD_FS_NEEDS_CXXFS})
+  set(STD_FS_LIB c++fs)
+elseif(${STD_FS_NO_LIB_NEEDED})
+  set(STD_FS_LIB "")
+else()
+  message(WARNING "Unknown C++17 compiler - not passing -lstdc++fs")
+  set(STD_FS_LIB "")
+endif()
+
 # Compile with compiler warnings turned on
 function(pybind11_enable_warnings target_name)
   if(MSVC)
     target_compile_options(${target_name} PRIVATE /W4)
   elseif(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Intel|Clang)" AND NOT PYBIND11_CUDA_TESTS)
-    target_compile_options(${target_name} PRIVATE -Wall -Wextra -Wconversion -Wcast-qual
+    target_compile_options(
-                                                  -Wdeprecated -Wundef)
+      ${target_name}
+      PRIVATE -Wall
+              -Wextra
+              -Wconversion
+              -Wcast-qual
+              -Wdeprecated
+              -Wundef
+              -Wnon-virtual-dtor)
   endif()
 
   if(PYBIND11_WERROR)
@@ -252,12 +374,22 @@ function(pybind11_enable_warnings target_name)
       target_compile_options(${target_name} PRIVATE /WX)
     elseif(PYBIND11_CUDA_TESTS)
       target_compile_options(${target_name} PRIVATE "SHELL:-Werror all-warnings")
-    elseif(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Intel|Clang)")
+    elseif(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Clang|IntelLLVM)")
       target_compile_options(${target_name} PRIVATE -Werror)
+    elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Intel")
+      if(CMAKE_CXX_STANDARD EQUAL 17) # See PR #3570
+        target_compile_options(${target_name} PRIVATE -Wno-conversion)
+      endif()
+      target_compile_options(
+        ${target_name}
+        PRIVATE
+          -Werror-all
+          # "Inlining inhibited by limit max-size", "Inlining inhibited by limit max-total-size"
+          -diag-disable 11074,11076)
     endif()
   endif()
 
-  # Needs to be readded since the ordering requires these to be after the ones above
+  # Needs to be re-added since the ordering requires these to be after the ones above
   if(CMAKE_CXX_STANDARD
      AND CMAKE_CXX_COMPILER_ID MATCHES "Clang"
      AND PYTHON_VERSION VERSION_LESS 3.0)
@@ -271,21 +403,17 @@ endfunction()
 
 set(test_targets pybind11_tests)
 
-# Build pybind11_cross_module_tests if any test_whatever.py are being built that require it
+# Check if any tests need extra targets by iterating through the mappings registered.
-foreach(t ${PYBIND11_CROSS_MODULE_TESTS})
+foreach(i ${PYBIND11_TEST_EXTRA_TARGETS})
-  list(FIND PYBIND11_PYTEST_FILES ${t} i)
+  foreach(needle ${PYBIND11_TEST_EXTRA_TARGETS_NEEDLES_${i}})
-  if(i GREATER -1)
+    if(needle IN_LIST PYBIND11_PYTEST_FILES)
-    list(APPEND test_targets pybind11_cross_module_tests)
+      # Add all the additional targets to the test list. List join in newer cmake.
-    break()
+      foreach(extra_target ${PYBIND11_TEST_EXTRA_TARGETS_ADDITION_${i}})
-  endif()
+        list(APPEND test_targets ${extra_target})
-endforeach()
+      endforeach()
-
+      break() # Breaks out of the needle search, continues with the next mapping.
-foreach(t ${PYBIND11_CROSS_MODULE_GIL_TESTS})
-  list(FIND PYBIND11_PYTEST_FILES ${t} i)
-  if(i GREATER -1)
-    list(APPEND test_targets cross_module_gil_utils)
-    break()
     endif()
+  endforeach()
 endforeach()
 
 # Support CUDA testing by forcing the target file to compile with NVCC
@@ -334,38 +462,34 @@ foreach(target ${test_targets})
     target_compile_definitions(${target} PRIVATE -DPYBIND11_TEST_BOOST)
   endif()
 
+  target_link_libraries(${target} PRIVATE ${STD_FS_LIB})
+
   # Always write the output file directly into the 'tests' directory (even on MSVC)
   if(NOT CMAKE_LIBRARY_OUTPUT_DIRECTORY)
     set_target_properties(${target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY
                                                "${CMAKE_CURRENT_BINARY_DIR}")
+
+    if(DEFINED CMAKE_CONFIGURATION_TYPES)
       foreach(config ${CMAKE_CONFIGURATION_TYPES})
         string(TOUPPER ${config} config)
         set_target_properties(${target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY_${config}
                                                    "${CMAKE_CURRENT_BINARY_DIR}")
       endforeach()
     endif()
+  endif()
 endforeach()
 
-# Make sure pytest is found or produce a warning
+# Provide nice organisation in IDEs
-if(NOT PYBIND11_PYTEST_FOUND)
+if(NOT CMAKE_VERSION VERSION_LESS 3.8)
-  execute_process(
+  source_group(
-    COMMAND ${PYTHON_EXECUTABLE} -c "import pytest; print(pytest.__version__)"
+    TREE "${CMAKE_CURRENT_SOURCE_DIR}/../include"
-    RESULT_VARIABLE pytest_not_found
+    PREFIX "Header Files"
-    OUTPUT_VARIABLE pytest_version
+    FILES ${PYBIND11_HEADERS})
-    ERROR_QUIET)
-  if(pytest_not_found)
-    message(WARNING "Running the tests requires pytest. Please install it manually"
-                    " (try: ${PYTHON_EXECUTABLE} -m pip install pytest)")
-  elseif(pytest_version VERSION_LESS 3.1)
-    message(WARNING "Running the tests requires pytest >= 3.1. Found: ${pytest_version}"
-                    "Please update it (try: ${PYTHON_EXECUTABLE} -m pip install -U pytest)")
-  else()
-    set(PYBIND11_PYTEST_FOUND
-        TRUE
-        CACHE INTERNAL "")
-  endif()
 endif()
 
+# Make sure pytest is found or produce a warning
+pybind11_find_import(pytest VERSION 3.1)
+
 if(NOT CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR)
   # This is not used later in the build, so it's okay to regenerate each time.
   configure_file("${CMAKE_CURRENT_SOURCE_DIR}/pytest.ini" "${CMAKE_CURRENT_BINARY_DIR}/pytest.ini"
@@ -377,15 +501,20 @@ endif()
 
 # cmake 3.12 added list(transform <list> prepend
 # but we can't use it yet
-string(REPLACE "test_" "${CMAKE_CURRENT_BINARY_DIR}/test_" PYBIND11_BINARY_TEST_FILES
+string(REPLACE "test_" "${CMAKE_CURRENT_SOURCE_DIR}/test_" PYBIND11_ABS_PYTEST_FILES
                "${PYBIND11_PYTEST_FILES}")
 
+set(PYBIND11_TEST_PREFIX_COMMAND
+    ""
+    CACHE STRING "Put this before pytest, use for checkers and such")
+
 # A single command to compile and run the tests
 add_custom_target(
   pytest
-  COMMAND ${PYTHON_EXECUTABLE} -m pytest ${PYBIND11_BINARY_PYTEST_FILES}
+  COMMAND ${PYBIND11_TEST_PREFIX_COMMAND} ${PYTHON_EXECUTABLE} -m pytest
+          ${PYBIND11_ABS_PYTEST_FILES}
   DEPENDS ${test_targets}
-  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
   USES_TERMINAL)
 
 if(PYBIND11_TEST_OVERRIDE)
@@ -396,6 +525,27 @@ if(PYBIND11_TEST_OVERRIDE)
             "Note: not all tests run: -DPYBIND11_TEST_OVERRIDE is in effect")
 endif()
 
+# cmake-format: off
+add_custom_target(
+  memcheck
+  COMMAND
+    PYTHONMALLOC=malloc
+    valgrind
+    --leak-check=full
+    --show-leak-kinds=definite,indirect
+    --errors-for-leak-kinds=definite,indirect
+    --error-exitcode=1
+    --read-var-info=yes
+    --track-origins=yes
+    --suppressions="${CMAKE_CURRENT_SOURCE_DIR}/valgrind-python.supp"
+    --suppressions="${CMAKE_CURRENT_SOURCE_DIR}/valgrind-numpy-scipy.supp"
+    --gen-suppressions=all
+    ${PYTHON_EXECUTABLE} -m pytest ${PYBIND11_ABS_PYTEST_FILES}
+  DEPENDS ${test_targets}
+  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+  USES_TERMINAL)
+# cmake-format: on
+
 # Add a check target to run all the tests, starting with pytest (we add dependencies to this below)
 add_custom_target(check DEPENDS pytest)
 

wrap/pybind11/tests/conftest.py

@@ -18,9 +18,9 @@ import env
 # Early diagnostic for failed imports
 import pybind11_tests  # noqa: F401
 
-_unicode_marker = re.compile(r'u(\'[^\']*\')')
+_unicode_marker = re.compile(r"u(\'[^\']*\')")
-_long_marker = re.compile(r'([0-9])L')
+_long_marker = re.compile(r"([0-9])L")
-_hexadecimal = re.compile(r'0x[0-9a-fA-F]+')
+_hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
 
 # Avoid collecting Python3 only files
 collect_ignore = []
@@ -30,7 +30,7 @@ if env.PY2:
 
 def _strip_and_dedent(s):
     """For triple-quote strings"""
-    return textwrap.dedent(s.lstrip('\n').rstrip())
+    return textwrap.dedent(s.lstrip("\n").rstrip())
 
 
 def _split_and_sort(s):
@@ -40,11 +40,14 @@ def _split_and_sort(s):
 
 def _make_explanation(a, b):
     """Explanation for a failed assert -- the a and b arguments are List[str]"""
-    return ["--- actual / +++ expected"] + [line.strip('\n') for line in difflib.ndiff(a, b)]
+    return ["--- actual / +++ expected"] + [
+        line.strip("\n") for line in difflib.ndiff(a, b)
+    ]
 
 
 class Output(object):
     """Basic output post-processing and comparison"""
+
     def __init__(self, string):
         self.string = string
         self.explanation = []
@@ -54,7 +57,11 @@ class Output(object):
 
     def __eq__(self, other):
         # Ignore constructor/destructor output which is prefixed with "###"
-        a = [line for line in self.string.strip().splitlines() if not line.startswith("###")]
+        a = [
+            line
+            for line in self.string.strip().splitlines()
+            if not line.startswith("###")
+        ]
         b = _strip_and_dedent(other).splitlines()
         if a == b:
             return True
@@ -65,6 +72,7 @@ class Output(object):
 
 class Unordered(Output):
     """Custom comparison for output without strict line ordering"""
+
     def __eq__(self, other):
         a = _split_and_sort(self.string)
         b = _split_and_sort(other)
@@ -175,7 +183,7 @@ def msg():
 # noinspection PyUnusedLocal
 def pytest_assertrepr_compare(op, left, right):
     """Hook to insert custom failure explanation"""
-    if hasattr(left, 'explanation'):
+    if hasattr(left, "explanation"):
         return left.explanation
 
 
@@ -189,8 +197,8 @@ def suppress(exception):
 
 
 def gc_collect():
-    ''' Run the garbage collector twice (needed when running
+    """Run the garbage collector twice (needed when running
-    reference counting tests with PyPy) '''
+    reference counting tests with PyPy)"""
     gc.collect()
     gc.collect()
 

wrap/pybind11/tests/constructor_stats.h

@@ -120,7 +120,7 @@ public:
             throw py::error_already_set();
         Py_DECREF(result);
 #else
-        py::module::import("gc").attr("collect")();
+        py::module_::import("gc").attr("collect")();
 #endif
     }
 

wrap/pybind11/tests/env.py

@@ -2,6 +2,8 @@
 import platform
 import sys
 
+import pytest
+
 LINUX = sys.platform.startswith("linux")
 MACOS = sys.platform.startswith("darwin")
 WIN = sys.platform.startswith("win32") or sys.platform.startswith("cygwin")
@@ -12,3 +14,20 @@ PYPY = platform.python_implementation() == "PyPy"
 PY2 = sys.version_info.major == 2
 
 PY = sys.version_info
+
+
+def deprecated_call():
+    """
+    pytest.deprecated_call() seems broken in pytest<3.9.x; concretely, it
+    doesn't work on CPython 3.8.0 with pytest==3.3.2 on Ubuntu 18.04 (#2922).
+
+    This is a narrowed reimplementation of the following PR :(
+    https://github.com/pytest-dev/pytest/pull/4104
+    """
+    # TODO: Remove this when testing requires pytest>=3.9.
+    pieces = pytest.__version__.split(".")
+    pytest_major_minor = (int(pieces[0]), int(pieces[1]))
+    if pytest_major_minor < (3, 9):
+        return pytest.warns((DeprecationWarning, PendingDeprecationWarning))
+    else:
+        return pytest.deprecated_call()

wrap/pybind11/tests/extra_python_package/test_files.py

@@ -25,6 +25,7 @@ main_headers = {
     "include/pybind11/embed.h",
     "include/pybind11/eval.h",
     "include/pybind11/functional.h",
+    "include/pybind11/gil.h",
     "include/pybind11/iostream.h",
     "include/pybind11/numpy.h",
     "include/pybind11/operators.h",
@@ -41,9 +42,14 @@ detail_headers = {
     "include/pybind11/detail/descr.h",
     "include/pybind11/detail/init.h",
     "include/pybind11/detail/internals.h",
+    "include/pybind11/detail/type_caster_base.h",
     "include/pybind11/detail/typeid.h",
 }
 
+stl_headers = {
+    "include/pybind11/stl/filesystem.h",
+}
+
 cmake_files = {
     "share/cmake/pybind11/FindPythonLibsNew.cmake",
     "share/cmake/pybind11/pybind11Common.cmake",
@@ -58,11 +64,14 @@ py_files = {
     "__init__.py",
     "__main__.py",
     "_version.py",
+    "_version.pyi",
     "commands.py",
+    "py.typed",
     "setup_helpers.py",
+    "setup_helpers.pyi",
 }
 
-headers = main_headers | detail_headers
+headers = main_headers | detail_headers | stl_headers
 src_files = headers | cmake_files
 all_files = src_files | py_files
 
@@ -72,6 +81,7 @@ sdist_files = {
     "pybind11/include",
     "pybind11/include/pybind11",
     "pybind11/include/pybind11/detail",
+    "pybind11/include/pybind11/stl",
     "pybind11/share",
     "pybind11/share/cmake",
     "pybind11/share/cmake/pybind11",
@@ -80,7 +90,7 @@ sdist_files = {
     "setup.py",
     "LICENSE",
     "MANIFEST.in",
-    "README.md",
+    "README.rst",
     "PKG-INFO",
 }
 
@@ -116,7 +126,7 @@ def test_build_sdist(monkeypatch, tmpdir):
     with tarfile.open(str(sdist)) as tar:
         start = tar.getnames()[0] + "/"
         version = start[9:-1]
-        simpler = set(n.split("/", 1)[-1] for n in tar.getnames()[1:])
+        simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
         with contextlib.closing(
             tar.extractfile(tar.getmember(start + "setup.py"))
@@ -128,9 +138,19 @@ def test_build_sdist(monkeypatch, tmpdir):
         ) as f:
             pyproject_toml = f.read()
 
-    files = set("pybind11/{}".format(n) for n in all_files)
+        with contextlib.closing(
+            tar.extractfile(
+                tar.getmember(
+                    start + "pybind11/share/cmake/pybind11/pybind11Config.cmake"
+                )
+            )
+        ) as f:
+            contents = f.read().decode("utf8")
+        assert 'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")' in contents
+
+    files = {"pybind11/{}".format(n) for n in all_files}
     files |= sdist_files
-    files |= set("pybind11{}".format(n) for n in local_sdist_files)
+    files |= {"pybind11{}".format(n) for n in local_sdist_files}
     files.add("pybind11.egg-info/entry_points.txt")
     files.add("pybind11.egg-info/requires.txt")
     assert simpler == files
@@ -171,7 +191,7 @@ def test_build_global_dist(monkeypatch, tmpdir):
     with tarfile.open(str(sdist)) as tar:
         start = tar.getnames()[0] + "/"
         version = start[16:-1]
-        simpler = set(n.split("/", 1)[-1] for n in tar.getnames()[1:])
+        simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
         with contextlib.closing(
             tar.extractfile(tar.getmember(start + "setup.py"))
@@ -183,9 +203,9 @@ def test_build_global_dist(monkeypatch, tmpdir):
         ) as f:
             pyproject_toml = f.read()
 
-    files = set("pybind11/{}".format(n) for n in all_files)
+    files = {"pybind11/{}".format(n) for n in all_files}
     files |= sdist_files
-    files |= set("pybind11_global{}".format(n) for n in local_sdist_files)
+    files |= {"pybind11_global{}".format(n) for n in local_sdist_files}
     assert simpler == files
 
     with open(os.path.join(MAIN_DIR, "tools", "setup_global.py.in"), "rb") as f:
@@ -210,7 +230,7 @@ def tests_build_wheel(monkeypatch, tmpdir):
 
     (wheel,) = tmpdir.visit("*.whl")
 
-    files = set("pybind11/{}".format(n) for n in all_files)
+    files = {"pybind11/{}".format(n) for n in all_files}
     files |= {
         "dist-info/LICENSE",
         "dist-info/METADATA",
@@ -223,10 +243,10 @@ def tests_build_wheel(monkeypatch, tmpdir):
     with zipfile.ZipFile(str(wheel)) as z:
         names = z.namelist()
 
-    trimmed = set(n for n in names if "dist-info" not in n)
+    trimmed = {n for n in names if "dist-info" not in n}
-    trimmed |= set(
+    trimmed |= {
         "dist-info/{}".format(n.split("/", 1)[-1]) for n in names if "dist-info" in n
-    )
+    }
     assert files == trimmed
 
 
@@ -240,8 +260,8 @@ def tests_build_global_wheel(monkeypatch, tmpdir):
 
     (wheel,) = tmpdir.visit("*.whl")
 
-    files = set("data/data/{}".format(n) for n in src_files)
+    files = {"data/data/{}".format(n) for n in src_files}
-    files |= set("data/headers/{}".format(n[8:]) for n in headers)
+    files |= {"data/headers/{}".format(n[8:]) for n in headers}
     files |= {
         "dist-info/LICENSE",
         "dist-info/METADATA",
@@ -254,6 +274,6 @@ def tests_build_global_wheel(monkeypatch, tmpdir):
         names = z.namelist()
 
     beginning = names[0].split("/", 1)[0].rsplit(".", 1)[0]
-    trimmed = set(n[len(beginning) + 1 :] for n in names)
+    trimmed = {n[len(beginning) + 1 :] for n in names}
 
     assert files == trimmed

wrap/pybind11/tests/extra_setuptools/test_setuphelper.py

@@ -1,17 +1,19 @@
 # -*- coding: utf-8 -*-
 import os
-import sys
 import subprocess
+import sys
 from textwrap import dedent
 
 import pytest
 
 DIR = os.path.abspath(os.path.dirname(__file__))
 MAIN_DIR = os.path.dirname(os.path.dirname(DIR))
+WIN = sys.platform.startswith("win32") or sys.platform.startswith("cygwin")
 
 
+@pytest.mark.parametrize("parallel", [False, True])
 @pytest.mark.parametrize("std", [11, 0])
-def test_simple_setup_py(monkeypatch, tmpdir, std):
+def test_simple_setup_py(monkeypatch, tmpdir, parallel, std):
     monkeypatch.chdir(tmpdir)
     monkeypatch.syspath_prepend(MAIN_DIR)
 
@@ -39,13 +41,18 @@ def test_simple_setup_py(monkeypatch, tmpdir, std):
                 cmdclass["build_ext"] = build_ext
 
 
+            parallel = {parallel}
+            if parallel:
+                from pybind11.setup_helpers import ParallelCompile
+                ParallelCompile().install()
+
             setup(
                 name="simple_setup_package",
                 cmdclass=cmdclass,
                 ext_modules=ext_modules,
             )
             """
-        ).format(MAIN_DIR=MAIN_DIR, std=std),
+        ).format(MAIN_DIR=MAIN_DIR, std=std, parallel=parallel),
         encoding="ascii",
     )
 
@@ -65,13 +72,20 @@ def test_simple_setup_py(monkeypatch, tmpdir, std):
         encoding="ascii",
     )
 
-    subprocess.check_call(
+    out = subprocess.check_output(
         [sys.executable, "setup.py", "build_ext", "--inplace"],
-        stdout=sys.stdout,
-        stderr=sys.stderr,
     )
+    if not WIN:
+        assert b"-g0" in out
+    out = subprocess.check_output(
+        [sys.executable, "setup.py", "build_ext", "--inplace", "--force"],
+        env=dict(os.environ, CFLAGS="-g"),
+    )
+    if not WIN:
+        assert b"-g0" not in out
 
     # Debug helper printout, normally hidden
+    print(out)
     for item in tmpdir.listdir():
         print(item.basename)
 
@@ -93,3 +107,45 @@ def test_simple_setup_py(monkeypatch, tmpdir, std):
     subprocess.check_call(
         [sys.executable, "test.py"], stdout=sys.stdout, stderr=sys.stderr
     )
+
+
+def test_intree_extensions(monkeypatch, tmpdir):
+    monkeypatch.syspath_prepend(MAIN_DIR)
+
+    from pybind11.setup_helpers import intree_extensions
+
+    monkeypatch.chdir(tmpdir)
+    root = tmpdir
+    root.ensure_dir()
+    subdir = root / "dir"
+    subdir.ensure_dir()
+    src = subdir / "ext.cpp"
+    src.ensure()
+    (ext,) = intree_extensions([src.relto(tmpdir)])
+    assert ext.name == "ext"
+    subdir.ensure("__init__.py")
+    (ext,) = intree_extensions([src.relto(tmpdir)])
+    assert ext.name == "dir.ext"
+
+
+def test_intree_extensions_package_dir(monkeypatch, tmpdir):
+    monkeypatch.syspath_prepend(MAIN_DIR)
+
+    from pybind11.setup_helpers import intree_extensions
+
+    monkeypatch.chdir(tmpdir)
+    root = tmpdir / "src"
+    root.ensure_dir()
+    subdir = root / "dir"
+    subdir.ensure_dir()
+    src = subdir / "ext.cpp"
+    src.ensure()
+    (ext,) = intree_extensions([src.relto(tmpdir)], package_dir={"": "src"})
+    assert ext.name == "dir.ext"
+    (ext,) = intree_extensions([src.relto(tmpdir)], package_dir={"foo": "src"})
+    assert ext.name == "foo.dir.ext"
+    subdir.ensure("__init__.py")
+    (ext,) = intree_extensions([src.relto(tmpdir)], package_dir={"": "src"})
+    assert ext.name == "dir.ext"
+    (ext,) = intree_extensions([src.relto(tmpdir)], package_dir={"foo": "src"})
+    assert ext.name == "foo.dir.ext"

wrap/pybind11/tests/local_bindings.h

@@ -1,10 +1,12 @@
 #pragma once
+#include <utility>
+
 #include "pybind11_tests.h"
 
 /// Simple class used to test py::local:
 template <int> class LocalBase {
 public:
-    LocalBase(int i) : i(i) { }
+    explicit LocalBase(int i) : i(i) { }
     int i = -1;
 };
 
@@ -33,6 +35,25 @@ using NonLocalVec2 = std::vector<NonLocal2>;
 using NonLocalMap = std::unordered_map<std::string, NonLocalType>;
 using NonLocalMap2 = std::unordered_map<std::string, uint8_t>;
 
+
+// Exception that will be caught via the module local translator.
+class LocalException : public std::exception {
+public:
+    explicit LocalException(const char * m) : message{m} {}
+    const char * what() const noexcept override {return message.c_str();}
+private:
+    std::string message = "";
+};
+
+// Exception that will be registered with register_local_exception_translator
+class LocalSimpleException : public std::exception {
+public:
+    explicit LocalSimpleException(const char * m) : message{m} {}
+    const char * what() const noexcept override {return message.c_str();}
+private:
+    std::string message = "";
+};
+
 PYBIND11_MAKE_OPAQUE(LocalVec);
 PYBIND11_MAKE_OPAQUE(LocalVec2);
 PYBIND11_MAKE_OPAQUE(LocalMap);
@@ -54,11 +75,11 @@ py::class_<T> bind_local(Args && ...args) {
 namespace pets {
 class Pet {
 public:
-    Pet(std::string name) : name_(name) {}
+    explicit Pet(std::string name) : name_(std::move(name)) {}
     std::string name_;
-    const std::string &name() { return name_; }
+    const std::string &name() const { return name_; }
 };
 } // namespace pets
 
-struct MixGL { int i; MixGL(int i) : i{i} {} };
+struct MixGL { int i; explicit MixGL(int i) : i{i} {} };
-struct MixGL2 { int i; MixGL2(int i) : i{i} {} };
+struct MixGL2 { int i; explicit MixGL2(int i) : i{i} {} };