cmake: Rework python.cmake

[Mizux]

After few discussions with conda-forge maintainer few things to improve:

• [x] 0) Fix check of __version__ in CheckPythonModule (not available for absl, mypy_protobuf etc...) (v9.2)
• [x] 1) Add flags to fail if missing python deps than trying to install them (in user space) (v9.2)
• [ ] 2) Be able to build a python lib using an already preinstalled or-tools C++
  • [ ] 2.5) need a FindORTOOLS.cmake
• [ ] 3) Migrate our setup.py to an pyproject.toml file (see PEP 621, PEP 518)
• [x] 4) #2860 (v9.2)

ps: feel free to give feedback and I will add them to this list.

DevNote

You can (re)read the thread on or-tools integration to conda forge, TLDR: it wasn't as smooth as it should have so let's fix what we can on the or-tools cmake side if possible... src: https://github.com/conda-forge/staged-recipes/pull/16147

Some preliminary PoC can be done using https://github.com/Mizux/python-native which compile in few dozen of seconds contrary to ortools...

For 0. could use:

import subprocess, sys
from email.parser import BytesHeaderParser
p = subprocess.run([sys.executable, '-m', 'pip', 'show', 'pip', '--files'], stdout=subprocess.PIPE)
h = BytesHeaderParser().parsebytes(p.stdout)
print(h['Version'])
21.3

src: https://github.com/conda-forge/staged-recipes/pull/16147#issuecomment-945934282 note: --files seems not needed.

For 1. https://github.com/google/or-tools/blob/86d4c543f717fa8716a9d66c25143660668bf825/ortools/python/setup.py.in#L49 basically replace this or adding a "is external lib" check then do nothing -> which could be done by checking property IMPORTED ? https://cmake.org/cmake/help/latest/prop_tgt/IMPORTED.html

[BastianZim]

(Conda-forge maintainer here)

For 0.

Yes it's not needed. I had seen it suggested as a way to get it formatted but it seems like it's the same. Pypa is also currently working on a --json flag. ref: https://github.com/pypa/pip/issues/5261

For 1.:

I'm currently just replacing the installation part with

message(FATAL_ERROR "Can't find python module \"${MODULE_NAME}\", please install it using your system package manager.")

Installation: https://github.com/google/or-tools/blob/86d4c543f717fa8716a9d66c25143660668bf825/cmake/python.cmake#L42-L46

As a quick fix.

For 3)

I like poetry as a build backend: https://github.com/python-poetry/poetry-core