Add typing to Celery

[atombrella]

This is a simple bootstrap of the process, adding some types to a
few selected functions, based on comment annotations. MyPy is chosen as the
default static analyzer for the types.

It's an attempt to solve #7258 Note that the work is quite demanding.

[codecov]

Codecov Report

Merging #7325 (edd9dc4) into master (8423c67) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7325      +/-   ##
==========================================
- Coverage   89.33%   89.32%   -0.02%     
==========================================
  Files         138      138              
  Lines       16781    16781              
  Branches     2451     2451              
==========================================
- Hits        14991    14989       -2     
- Misses       1559     1561       +2     
  Partials      231      231              

Flag	Coverage Δ
unittests	89.31% <100.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
celery/events/state.py	97.25% <100.00%> (ø)
celery/utils/collections.py	85.68% <100.00%> (ø)
celery/backends/asynchronous.py	68.83% <0.00%> (-0.87%)	⬇️

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[lgtm-com]

This pull request introduces 1 alert and fixes 2 when merging edd9dc4 into 095cd78 - view on LGTM.com

new alerts:

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

fixed alerts:

• 1 for Non-exception in 'except' clause
• 1 for Unused import

[auvipy]

thanks for taking this stub, can you check the lint failures please?

[atombrella]

thanks for taking this stub, can you check the lint failures please?

Yes. I'm working on it. Have some patience ;)

[Kludex]

Is the idea here to incrementally increase typing on Celery?

If yes, wouldn't it be interesting to support file by file? We did this on uvicorn: https://github.com/encode/uvicorn/blob/8585051189f0530165e901e0c5fab57998648943/setup.cfg#L5-L43

[Kludex]

Do @atombrella you mind if I tackle the needed fixes here?

[atombrella]

Do @atombrella you mind if I tackle the needed fixes here?

Please do :) I'm currently a bit caught up on other things.

[Kludex]

I've created #7383