[BUG] ValueError when building wheel

[pkolbus]

setuptools version

57.0.0

Python version

3.6.0

OS

Windows 10

Additional environment information

No response

Description

With setuptools 57, I'm getting an exception ending with the following when testing several (private) packages via tox. This appears to occur while tox is running get_requires_for_build_wheel for the package.

A git bisect indicates this started with #2628. Notably, these packages do not have a long description, as https://packaging.python.org/specifications/core-metadata/ describes it as optional.

   ...
    File "C:\Users\kolbus\AppData\Local\Temp\pip-build-env-9rrfzn1k\overlay\Lib\site-packages\setuptools\build_meta.py", line 135, in _get_build_requires
      self.run_setup()
    File "C:\Users\kolbus\AppData\Local\Temp\pip-build-env-9rrfzn1k\overlay\Lib\site-packages\setuptools\build_meta.py", line 259, in run_setup
      self).run_setup(setup_script=setup_script)
    File "C:\Users\kolbus\AppData\Local\Temp\pip-build-env-9rrfzn1k\overlay\Lib\site-packages\setuptools\build_meta.py", line 150, in run_setup
      exec(compile(code, __file__, 'exec'), locals())
    File "setup.py", line 170, in <module>
      pkg_info = dict(line.split(": ", 1) for line in content)
  ValueError: dictionary update sequence element #30 has length 1; 2 is required
  ----------------------------------------

Expected behavior

No exception

How to Reproduce

1. TBD
2. TBD
3. TBD

Output

TBD

Code of Conduct

• I agree to follow the PSF Code of Conduct

[pkolbus]

Apologies for the noise; this is not a setuptools issue. The offending line is in my own project's setup.py.