Error when using libraries argument with Python setuptools

[radarhere]

Description / Steps to reproduce the issue

installing gcc and python-pip, I created the following Python script, along with an empty file called demo.c in the current directory

from setuptools import setup

setup(
    name='msys2demo',
    libraries=[
      ("example", {"sources": ["demo.c"]}),
    ],
    version='0.0.1'
)%                                                                              [

I then ran python3 -m pip install .

For an exact replica, I've created https://github.com/radarhere/msys2 where you can see the output in GitHub Actions.

Expected behavior A successful installation of my custom Python module. You can see the expected success if I change the situation in the following ways

• If I don't use the libraries argument in the Python script, it works.
• If I run the same Python script in Ubuntu, it works.
• If I run AR="ar" python3 -m pip install ., it works. This was suggested over at python-pillow, as an alternative to the default use of /clang64/bin/llvm-ar

Actual behavior An error - https://github.com/radarhere/msys2/actions/runs/18629427989/job/53112005909#step:5:38

  Building wheel for msys2demo (pyproject.toml): finished with status 'error'
  error: subprocess-exited-with-error
  
  Building wheel for msys2demo (pyproject.toml) did not run successfully.
  exit code: 1
  
  [8 lines of output]
  running bdist_wheel
  running build
  running build_clib
  building 'example' library
  creating build/temp.mingw_x86_64_ucrt_llvm-cpython-312
  clang -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall -march=nocona -msahf -mtune=generic -O2 -pipe -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong -Wp,-D__USE_MINGW_ANSI_STDIO=1 -O3 -march=nocona -msahf -mtune=generic -O2 -pipe -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong -Wp,-D__USE_MINGW_ANSI_STDIO=1 -O3 -c demo.c -o build/temp.mingw_x86_64_ucrt_llvm-cpython-312/demo.o
  /clang64/bin/llvm-ar rcs build/temp.mingw_x86_64_ucrt_llvm-cpython-312/libexample.a build/temp.mingw_x86_64_ucrt_llvm-cpython-312/demo.o
  error: command '/clang64/bin/llvm-ar' failed: None
  [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
  ERROR: Failed building wheel for msys2demo

uname: MINGW64_NT-10.0-26100 Environment tested: CLANG64

Thanks. If you think this should be reported elsewhere, please let me know.

[kmilos]

x-ref https://github.com/msys2/MINGW-packages/pull/25966#issuecomment-3410866225

[lazka]

It's a bug in our Python build: https://github.com/msys2-contrib/cpython-mingw/issues/200