Add Python 3.10 support to _distutils_hack

[vstinner]

Get the 'Loader' abstract class from importlib.abc rather than
importlib.util.abc (alias removed in Python 3.10).

Summary of changes

Closes

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d. See documentation for details

[vstinner]

"import _distutils_hack" on Python 3.10 fails with:

Traceback (most recent call last):
  File "/home/vstinner/python/master/Doc/venv/bin/sphinx-build", line 5, in <module>
    from sphinx.cmd.build import main
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/cmd/build.py", line 25, in <module>
    from sphinx.application import Sphinx
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/application.py", line 31, in <module>
    from sphinx.config import Config
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/config.py", line 24, in <module>
    from sphinx.util import logging
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/util/__init__.py", line 39, in <module>
    from sphinx.util import smartypants  # noqa
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/util/smartypants.py", line 33, in <module>
    from sphinx.util.docutils import __version_info__ as docutils_version
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/sphinx/util/docutils.py", line 15, in <module>
    from distutils.version import LooseVersion
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 982, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 925, in _find_spec
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/_distutils_hack/__init__.py", line 74, in find_spec
    return method()
  File "/home/vstinner/python/master/Doc/venv/lib/python3.10/site-packages/_distutils_hack/__init__.py", line 79, in spec_for_distutils
    class DistutilsLoader(importlib.util.abc.Loader):
AttributeError: module 'importlib.util' has no attribute 'abc'

The "abc" submodule must be imported from importlib, not get from importlib.util.abc: https://docs.python.org/dev/library/importlib.html#module-importlib.abc

[pganssle]

@vstinner This looks good to me, though it needs a news fragment.

[vstinner]

@vstinner This looks good to me, though it needs a news fragment.

I added the changelog.d/2361.bugfix.rst file manually. Is it the expected filename and content?

Note: I failed to find a setuptools documentation explaining how to contribute to setuptools. I discovered that setuptools uses towncrier, but I failed to find a documentation explaining how to add a towncrier changelog entry :-( I'm used to blurb tool which opens a text editor and then creates the news entry.

[pganssle]

https://setuptools.readthedocs.io/en/latest/developer-guide.html

[vstinner]

https://setuptools.readthedocs.io/en/latest/developer-guide.html

Oh, thanks! It seems like "2361.bugfix.rst" is not an accepted filename, so I renamed it to "2361.change.rst". Is it better? I also squashed my commits.

[vstinner]

I may be interesting to mention https://setuptools.readthedocs.io/ and/or https://setuptools.readthedocs.io/en/latest/developer-guide.html in the README file. I can write a second PR for that, once this PR is merged. (I'm stupid and forgot to name my local branch, I abused the "master" branch. I prefer to wait until this PR is merged.)

[pganssle]

I may be interesting to mention https://setuptools.readthedocs.io/ and/or https://setuptools.readthedocs.io/en/latest/developer-guide.html in the README file. I can write a second PR for that, once this PR is merged. (I'm stupid and forgot to name my local branch, I abused the "master" branch. I prefer to wait until this PR is merged.)

Yeah, it would probably also be a good idea to rename the incredibly similar-seeming "Developer's Guide" and "Developer's Guide for Setuptools":

Probably that is best addressed as part of the #2093 revamp (though adding something to the README would be good too). It seems slightly easier in the latest iteration (though the confusing headings are still there, just more hidden).

[pradyunsg]

Thanks!

[jaraco]

I'll probably rename the changelog from change to misc so it implies an 0.0.1 bump, but good enough. Thanks Victor.

[vstinner]

Thanks Victor.

You're welcome. Good luck with fixing setuptools 50.0 regressions. I'm a strong supporter of burying distutils! So I will try to help to make it possible.