force checking cython version in cmake

cmake/FindCython.cmake

@@ -0,0 +1,69 @@
+# Modifed from: https://github.com/nest/nest-simulator/blob/master/cmake/FindCython.cmake
+#
+# Find the Cython compiler.
+#
+# This code sets the following variables:
+#
+#  CYTHON_EXECUTABLE
+#  CYTHON_FOUND
+#  CYTHON_VERSION
+#
+# See also UseCython.cmake
+
+#=============================================================================
+# Copyright 2011 Kitware, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#=============================================================================
+
+# Use the Cython executable that lives next to the Python executable
+# if it is a local installation.
+find_package( PythonInterp )
+if ( PYTHONINTERP_FOUND )
+  get_filename_component( _python_path ${PYTHON_EXECUTABLE} PATH )
+  find_program( CYTHON_EXECUTABLE
+      NAMES cython cython.bat cython3
+      PATHS ${_python_path}
+      NO_DEFAULT_PATH
+      )
+else ()
+  find_program( CYTHON_EXECUTABLE
+      NAMES cython cython.bat cython3
+      )
+endif ()
+
+if ( NOT CYTHON_EXECUTABLE STREQUAL "CYTHON_EXECUTABLE-NOTFOUND" )
+  execute_process(
+      COMMAND ${CYTHON_EXECUTABLE} --version
+      RESULT_VARIABLE RESULT
+      OUTPUT_VARIABLE CYTHON_VAR_OUTPUT
+      ERROR_VARIABLE CYTHON_VAR_OUTPUT
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+  if ( RESULT EQUAL 0 )
+    string( REGEX REPLACE ".* ([0-9]+\\.[0-9]+(\\.[0-9]+)?).*" "\\1"
+                          CYTHON_VERSION "${CYTHON_VAR_OUTPUT}" )
+  endif ()
+endif ()
+
+include( FindPackageHandleStandardArgs )
+find_package_handle_standard_args( Cython
+  FOUND_VAR
+    CYTHON_FOUND
+  REQUIRED_VARS
+    CYTHON_EXECUTABLE
+  VERSION_VAR
+    CYTHON_VERSION
+    )
+
+mark_as_advanced( CYTHON_EXECUTABLE )

cmake/GtsamCythonWrap.cmake

@@ -1,3 +1,10 @@
+# Check Cython version, need to be >=0.25.2
+# Unset these cached variables to avoid surprises when the python/cython
+# in the current environment are different from the cached!
+unset(PYTHON_EXECUTABLE CACHE)
+unset(CYTHON_EXECUTABLE CACHE)
+find_package(Cython 0.25.2 REQUIRED)
+
 # Set up cache options
 set(GTSAM_CYTHON_INSTALL_PATH "" CACHE PATH "Cython toolbox destination, blank defaults to CMAKE_INSTALL_PREFIX/gtsam_cython")
 if(NOT GTSAM_CYTHON_INSTALL_PATH)