Build in MingW fails under very specific circumstances - What to do?

[theCapypara]

Sorry for the bad title, but this is a hairy issue:
I'm trying to compile cairocffi with Python 3.11 for Msys2 Mingw. This used to work in the past, however they switched to the new packaging structure using pyproject.toml (before they used setup.py.

The build fails in distutils/_msvccompiler.py where it shouldn't even end up in afaik. (distutils.errors.DistutilsPlatformError: --plat-name must be one of ('win32', 'win-amd64', 'win-arm32', 'win-arm64')).

The issue and problem description is here, but I'll summarize my findings below:
Kozea/cairocffi#213

• It tries to build cffi, which is a legacy setup.py based package/wheel
• That tries to determine if msvc is used by calling try_compile
• try_compile in setuptools tries to get the default compiler via distutils, which uses sys.platform and somehow* ends up thinking the MSVC version of Python is used and returns that compiler
• That compiler obviously fails

Does anybody have any idea where the bug is here? I guess the way cffi tries to determine if MSVC is used is already kinda dumb, but I think there's a bug in setuptools and/or distutils here somewhere. From what I can tell by reading the code, I think it somehow must end up manipulating sys.platform or a related variable, because otherwise I don't know how this would happen. Also everything worked back when cairocffi was still using setup.py!

I sadly don't have access to a physical Windows machine, and debugging via GitHub actions isn't really possible, so if anybody got any idea, that'd be great!

*edit: Actually the platform and osname can be passed in, so it might be set somewhere else.

[webknjaz]

Use https://github.com/marketplace/actions/debugging-with-tmate for debugging.