distutils.ccompiler: Make has_function work with more C99 compilers

[fweimer-rh]

Summary of changes

C99 removed support for implicit function declarations. This means that just calling a function, without declaring the function first, can result in a compilation error. Today, has_function works with most compilers because they issue just a warning, create an object file, and attempt a link, which then detects available of the symbol at link time, as intended. With future compilers, compilation will already fail, and no link test is performed.

The has_function interface provides the caller with a way to supply a list of header files to include. However, even with today's compilers, this only works if the function does not expect any parameters. Otherwise, the function call in the C fragment created by has_function will not supply the correct argument list and fail compilation. Therefore, this change supplies and incorrect prototype without arguments. This is what autoconf does today in a very similar situation, so it is quite likely that compilers will support this construct in this context in the future.

The includes and include_dirs arguments are deprecated because of the parameter list mismatch issue.

Closes #3648.

Pull Request Checklist

• Changes have tests
• News fragment added in [changelog.d/].

[abravalheri]

Hi @fweimer-rh thank you very much for the contribution.

Since the _distutils folder comes directly from the pypa/distutils repository (unaltered) I think the best would be suggesting these changes directly to that other repository (otherwise we have problems for merging/risk of overwriting it in a future change).

Would you like to submit the PR to pypa/distutils so the distutils maintainers can have a look?

Alternatively you can try to implement the changes without touching the _distutils folder (I don't know if it is possible...)

[fweimer-rh]

Fair enough, I submitted pypa/distutils#195 and will come back once I've managed to get that merged.

[thesamesam]

pypa/distutils#195 is now merged and landed in setuptools via #3809 in release 67.2.0.

It seems a shame to not fix it in cpython itself for at least 3.10/3.11 but python/cpython#98529 makes it seem like that's not going to happen.

[jaraco]

Sounds like this work is complete. Thanks thesamesam.

By the way, you do get the fix in Python 3.7+ by way of the distutils hack. As long as you have setuptools installed and haven't set SETUPTOOLS_USE_DISTUTILS=stdlib, import distutils will pull in the distutils from Setuptools. I would avoid depending too heavily on that behavior, however, as we'd like to remove it. If you have a use-case for distutils that isn't served by the core interfaces of Setuptools (i.e. requires import distutils), please report that as a bug to the distutils project.