fix(cmake): Add an author warning that auto-calculated PYTHON_MODULE_EXTENSION may not respect SETUPTOOLS_EXT_SUFFIX during cross-compilation

[XuehaiPan]

Description

During cross-compilation, the variable PYTHON_MODULE_EXTENSION is calculated via the host Python interpreter rather than the target Python. For example, the build host is x64 Python and the target is ARM64, the calculated PYTHON_MODULE_EXTENSION will be .cpXY-win_amd64.pxd rather than .cpXY-win_arm64.pxd. See also:

• [BUG] optree on Windows on ARM64 metaopt/optree#182 (comment)

This PR adds an author warning to prompt the developer to set PYTHON_MODULE_EXTENSION manually during cross-compilation.

Maybe related:

• [BUG]: Overwriting CMake PYTHON_MODULE_EXTENSION needs PYBIND11_PYTHON_EXECUTABLE_LAST #3640

Suggested changelog entry:

Add an author warning that auto-calculated ``PYTHON_MODULE_EXTENSION`` may not respect ``SETUPTOOLS_EXT_SUFFIX`` during cross-compilation

[mark-bchoi]

Hi, this issue would remains for other version.

I have tried to build rosbag2-py in the yocto system with cross-compile, aarch64 , by the way, it have created shared libraries with name :

   |-- _info.cpython-312-x86_64-linux-gnu.so
   |-- _reader.cpython-312-x86_64-linux-gnu.so
   |-- _reindexer.cpython-312-x86_64-linux-gnu.so
   |-- _storage.cpython-312-x86_64-linux-gnu.so
   |-- _transport.cpython-312-x86_64-linux-gnu.so
   `-- _writer.cpython-312-x86_64-linux-gnu.so

which prevent rosbag2 from binding these libraries.

I have used pybind v2.11.

I can avoid this issue by renaming them into aarch64. Can you please look into and backport it to v2.11 ?

BR,
Mark