Add mypy to the pipeline

[Kludex]

• Replaces Add typing to Celery #7325
• Related to Use typing annotations in Celery (PEP 484)? #7258

Thanks @atombrella for the initial work!

This PR adds mypy to tox and to the pipeline. A couple of differences between this PR and the previous one:

• Apply mypy per file. Meaning that we can do progressive work just adding a new file to the pyproject.toml.
• Use pyproject.toml instead of mypy.ini.
• disallow_untyped_defs is True now.

This PR is intended to be minimal, so we can start working per files basis. I've reused the previous branch, so there are also some small type annotation fixes, which are not required for this PR.

[codecov]

Codecov Report

Merging #7383 (7617ec3) into master (8423c67) will decrease coverage by 0.02%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #7383      +/-   ##
==========================================
- Coverage   89.33%   89.30%   -0.03%     
==========================================
  Files         138      138              
  Lines       16781    16762      -19     
  Branches     2451     2451              
==========================================
- Hits        14991    14970      -21     
- Misses       1559     1560       +1     
- Partials      231      232       +1     

Flag	Coverage Δ
unittests	89.30% <85.71%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
celery/__main__.py	0.00% <0.00%> (ø)
celery/events/state.py	97.22% <100.00%> (-0.03%)	⬇️
celery/utils/collections.py	85.84% <100.00%> (+0.15%)	⬆️
celery/backends/asynchronous.py	67.53% <0.00%> (-2.17%)	⬇️
celery/bin/worker.py	45.31% <0.00%> (-1.47%)	⬇️
celery/result.py	96.28% <0.00%> (-0.07%)	⬇️
celery/beat.py	91.54% <0.00%> (-0.05%)	⬇️
celery/app/defaults.py	97.33% <0.00%> (ø)
celery/contrib/abortable.py	100.00% <0.00%> (ø)
... and 4 more

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[lgtm-com]

This pull request fixes 3 alerts when merging bdee5e0 into 24f22a5 - view on LGTM.com

fixed alerts:

• 1 for Non-exception in 'except' clause
• 1 for Unused import
• 1 for Module is imported with 'import' and 'import from'

[povilasb]

Nice, type hints are much appreciated when navigating the code base.
Thank you!

[Kludex]

Yep. As soon as this gets in, I'll organize a similar issue as I did on uvicorn: encode/uvicorn#998

Then we can start working on it, in an incremental way :)

[auvipy]

good job

[Kludex]

All the annotations besides __main__.py are not needed for this PR. If you want, I can remove the other ones.

[lgtm-com]

This pull request introduces 2 alerts and fixes 1 when merging e2eda10 into 24f22a5 - view on LGTM.com

new alerts:

• 1 for Unused import
• 1 for Module is imported with 'import' and 'import from'

fixed alerts:

• 1 for Unused import

[lgtm-com]

This pull request fixes 1 alert when merging 7617ec3 into 24f22a5 - view on LGTM.com

fixed alerts:

• 1 for Non-exception in 'except' clause

[Kludex]

I've just found out about this: encode/uvicorn#1437 (comment)

Might be useful for celery as well.

[Kludex]

Thanks @auvipy ! :)

I'm going to create an issue so we can organize the work towards a fully annotated celery! 🙌

[auvipy]

we can just modify this #7258

[Kludex]

@auvipy I didn't modify it because I'd like to have rights to edit. See the created issue: #7394