Replace description-file setuptools metadata key with description_file in setup.cfg

[JeanChristopheMorinPerso]

Summary

Latest setuptools prints a deprecation warning as follows:

    /tmp/pip-build-env-cje71c9_/overlay/lib/python3.9/site-packages/setuptools/dist.py:697: UserWarning: Usage of dash-separated 'description-file' will not be supported in future versions. Please use the underscore name 'description_file' instead

So this PR simply replaces description-file with description_file.

[codecov-commenter]

Codecov Report

Merging #1017 (a494ea4) into master (5957ddc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1017   +/-   ##
=======================================
  Coverage   85.55%   85.55%           
=======================================
  Files         192      192           
  Lines       18317    18317           
  Branches     2056     2056           
=======================================
  Hits        15672    15672           
  Misses       2119     2119           
  Partials      526      526           

Flag	Coverage Δ
unittests	85.55% <ø> (ø)

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[meshula]

I can't find documentation, other than this, which doesn't mention the deprecation reported in the warning. https://docs.openstack.org/pbr/latest/user/features.html - our tests have all passed, including making wheels for py27, so it seems fine!

[JeanChristopheMorinPerso]

See pypa/setuptools#2588 and pypa/setuptools#1608 for more information on this warning.

[meshula]

Thanks for the links. Looks like setuptools' maintainers decided to deviate from PEP508 which states that dashes and underscores are supposed to be equivalent.

[ssteinbach]

Are the other hyphenated fields ok?

[ssteinbach]

(meaning: will we have to change the rest to underscores as well?)

[ssteinbach]

Looking through the file, it looks like a mix of hyphens and underscores. This seems fine, we can fix them as they come up. Thanks!

[JeanChristopheMorinPerso]

Looks like setuptools' maintainers decided to deviate from PEP508 which states that dashes and underscores are supposed to be equivalent.

The PEP isn't clear on that, so they decided one something, which is this warning.

Looking through the file, it looks like a mix of hyphens and underscores. This seems fine, we can fix them as they come up.

This warning should only apply to sections owned by setuptools/distutils, see pypa/setuptools#2595 (comment). So the PR I linked was a little problematic, which was fixed in pypa/setuptools#2600.

So the other sections not owned by setuptools/distutils are fine.