PEP621: Migrate setup.py config into pyproject.toml

[cclauss]

Proposed changes

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why we should accept this pull request. If it fixes a bug or resolves a feature
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PEP621 encourages the Python community to migrate away from complex setup.cfg + setup.py files by putting config data in pyproject.toml.

Migrate setup.py to setup.cfg using setuptools-py2cfg plus manual modifications.
Then migrate setup.cfg to pyproject.toml using ini2toml to do the file conversion and running validate-pyproject in pre-commit to validate the results.

• https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html
• https://packaging.python.org/en/latest/tutorials/packaging-projects/#creating-pyproject-toml

The change in tox.ini from pip install --no-binary lxml --> pip install --no-cache-dir lxml is going to be mandated by the next major release of pip and decreases our tox test runtimes from 3 or 4 minutes down to 1 or 2 minutes.

Building Python projects in this way requires dropping support for Python 3.6.

• https://devguide.python.org/versions

If this pull request is merged then required must be removed from test (3.6) and added to test (3.11).
Also, maybe remove required from flake8 and add it to pre-commit.ci?

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[codecov]

Codecov Report

Merging #770 (6e63973) into master (e043b8a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master     #770    +/-   ##
========================================
  Coverage   77.81%   77.81%            
========================================
  Files         330      330            
  Lines       10093    10093            
  Branches     1194      555   -639     
========================================
  Hits         7854     7854            
  Misses       2086     2086            
  Partials      153      153            

Flag	Coverage Δ
unittests	77.81% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
social_core/backends/loginradius.py	0.00% <ø> (ø)
social_core/backends/untappd.py	0.00% <ø> (ø)
social_core/pipeline/partial.py	100.00% <ø> (ø)

[nijel]

The change in tox.ini from pip install --no-binary lxml --> pip install --no-cache-dir lxml is going to be mandated by the next major release of pip and decreases our tox test runtimes from 3 or 4 minutes down to 1 or 2 minutes.

We really need --no-binary there, see SAML-Toolkits/python3-saml#292, #659, #738

[nijel]

This all duplicates requirements-*.txt content. Can the dependencies be specified just once?

[cclauss]

Yes, but can we push that to a separate PR? This one already touches a lot of files and tox.ini and GitHub Action caching will need to be modified when dropping requirements files.

[davidbgk]

You can generate the requirements files from the pyproject.toml one:

python3 -m piptools compile --output-file=requirements.txt pyproject.toml
python3 -m piptools compile --extra=dev --output-file=requirements-dev.txt pyproject.toml
etc