[GitHub] [qpid-proton] astitcher commented on a change in pull request #294: PROTON-2217 Prefer first working Python on PATH, prefer Py3 over Py2

[GitBox <gi...@apache.org>]

astitcher commented on a change in pull request #294:
URL: https://github.com/apache/qpid-proton/pull/294#discussion_r569466506



##########
File path: CMakeLists.txt
##########
@@ -32,7 +32,27 @@ include (CheckPythonModule)
 
 find_package (OpenSSL)
 find_package (Threads)
-find_package (PythonInterp REQUIRED)
+# FindPython was added in CMake 3.12, but there it always returned
+#  newest Python on the entire PATH. We want to use the first one.
+if (CMAKE_VERSION VERSION_LESS "3.15.0")
+  find_package (PythonInterp REQUIRED)
+  # forward compatibility with FindPython
+  set(Python_EXECUTABLE "${PYTHON_EXECUTABLE}")
+  set(Python_LIBRARIES "${PYTHON_LIBRARIES}")
+  set(Python_INCLUDE_DIRS "${PYTHON_INCLUDE_PATH}")
+  set(Python_VERSION_STRING "${PYTHON_VERSION_STRING}")
+  # for completeness, these are not actually used now
+  set(Python_VERSION_MAJOR "${PYTHON_VERSION_MAJOR}")
+  set(Python_VERSION_MINOR "${PYTHON_VERSION_MINOR}")
+  set(Python_VERSION_PATCH "${PYTHON_VERSION_PATCH}")
+else ()
+  if (POLICY CMP0094)  # https://cmake.org/cmake/help/latest/policy/CMP0094.html
+    cmake_policy(SET CMP0094 NEW)  # FindPython should return the first matching Python on PATH
+  endif ()
+
+  find_package(Python REQUIRED COMPONENTS Interpreter
+          OPTIONAL_COMPONENTS Development)
+endif()

Review comment:
       **This is totally the wrong approach!**
   We already have a way to "branch" the processing so that we can use newer features. Create our own FindPython.cmake in tools/cmake/Modules which imitates the cmake 3 find_package(Python) processing so far as we use it.
   Also make sure that any installed script will work with cmake 2.8.12 as our target environment is cmake 2.8.12 (sadly).




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