setuptools patching (semi-randomly) breaks setuptools-rust, resulting in nonfunctional packages

[mgorny]

If setuptools-rust and scikit-build-core are installed within the same build environment, depending on plugin load order, the latter could cause Rust extensions to be silently skipped and nonfunctional packages to be built.

The problem is that both packages define setuptools.finalize_distribution_options entry points, and both override has_ext_modules method:

• scikit-build-core/src/scikit_build_core/setuptools/build_cmake.py

  Line 185 in 9ed3539

  dist.has_ext_modules = lambda: type(dist).has_ext_modules(dist) or _has_cmake(dist) # type: ignore[method-assign]

• https://github.com/PyO3/setuptools-rust/blob/0ca3eb47bbadd7b4de32c302bf0380500187a807/setuptools_rust/setuptools_ext.py#L277-L279

If the entry point from setuptools-rust is executed first, then scikit-build-core overwrites its has_ext_modules method. As a result, the Rust extensions aren't detected, build command doesn't invoke build_rust and the package is installed without any Rust extensions.

FWICS setuptools-rust avoids the problem by storing and calling the previous value of has_ext_modules rather than the generic method from Distribution. FWICS doing the same in scikit-build-core fixes building Rust extensions (but I haven't tested whether it doesn't break something related to scikit-build-core). I tested changing the linked line to:

    orig_has_ext_modules = dist.has_ext_modules
    dist.has_ext_modules = lambda: orig_has_ext_modules() or _has_cmake(dist)

Gentoo bug report: https://bugs.gentoo.org/909035