[BUG]

setuptools version

61.0.0

Python version

3.9

OS

Debian Unstable

Additional environment information

No response

Description

kiwisolver 1.4.0 (I haven’t checked earlier versions, but kiwisolver 1.4.0 did modernise their build, so issues with earlier versions will likely be to different code) can no build from source. I filed https://github.com/nucleic/kiwi/issues/130 with the kiwisolver developers, but it appears that setuptools 60.10.0 does work. Based on looking at https://github.com/pypa/setuptools/compare/v60.10.0...v61.0.0 and the error message that appears (see output), I think this is related to the new(?) package discovery mechanism. I’m not a kiwisolver developer, so I can’t answer questions about their build system (other than link you to the repository), but I’m filing this as it appears to be a regression (give setuptools 61 came out 10 hours ago when I wrote this).

Expected behavior

I expect pip install kiwisolver would build a wheel and install it.

How to Reproduce

1. Run pip install kiwisolver (given kiwisolver has wheels, you may need to disable using wheels to not download a pre-built wheel).

Output

      /tmp/pip-build-env-nwrt4o9m/overlay/lib/python3.9/site-packages/setuptools/config/pyprojecttoml.py:100: _ExperimentalProjectMetadata: Support for project metadata in `pyproject.toml` is still experimental and may be removed (or change) in future releases.
        warnings.warn(msg, _ExperimentalProjectMetadata)
      Install ``trove-classifiers`` to ensure proper validation. Meanwhile a list of classifiers will be downloaded from PyPI.
      error: Multiple top-level packages discovered in a flat-layout: ['py', 'kiwi'].
      
      To avoid accidental inclusion of unwanted files or directories,
      setuptools will not proceed with this build.
      
      If you are trying to create a single distribution with multiple packages
      on purpose, you should not rely on automatic discovery.
      Instead, consider the following options:
      
      1. set up custom discovery (`find` directive with `include` or `exclude`)
      2. use a `src-layout`
      3. explicitly set `py_modules` or `packages` with a list of names
      
      To find more information, look for "package discovery" on setuptools docs.

[abravalheri]

Thank you very much for reporting this.

My understanding is that unfortunately there is a clash of 2 behaviours:

To make these changes as backwards compatible as possible, I added a condition that only works for packages not using pyproject.toml that will check if ext_modules is given and then skip auto-discovery.

But, going forward my assumption was that it is very common for packages to mix both regular Python code with extensions. So if a project is using pyproject.toml for metadata, auto-discovery is always on.

I did not foresee that kiwisolver was providing metadata in both pyproject.toml and setup.py already before the latest change. Sorry for that.

@MatthieuDartiailh, one way to disable auto discovery is to explicitly set py_modules=[] in setup.py or py-modules = [] in pyproject.toml [tool.setuptools]. Would that work for you?

If that is a viable alternative, it would help a lot! I was hopping to keep the auto-discovery always on for packages using pyproject.toml…

[david-fortini]

As a quick fix, in setup.py

setuptools.setup(..,packages=[],..)

or

setuptools.setup(..,py_modules=[],..)