Support for async callbacks

[stephanm]

What do these changes do?

As mentioned in #1235 you can't use coroutines as custom callbacks. This patch tries to fix that.

Are there changes in behavior for the user?

There shouldn't be any changes for the users as sync callbacks are still supported.

Related issue number

#1235

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES/ folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example:
    Fix issue with non-ascii contents in doctest text files.

[Andrew-Chen-Wang]

Can you add a test where you receive two callbacks, one is sync and the other an async func? Plus lint with precommit. Thanks a ton! Also, pertaining to ordering, I can't actually remember my digging around of the code. In relation to your comment, dicts should be ordered now in supported Py3 versions, but I suppose it doesn't matter here 😅

[stephanm]

Yeah, no problem, I'll add the test and have a look at the linter error.
Thanks for the clarifications and the fast feedback!
TIL: Ordering is guaranteed since 3.7 :)

[codecov]

Codecov Report

Merging #1284 (359a741) into master (56d6b32) will decrease coverage by 0.02%.
The diff coverage is 96.15%.

@@            Coverage Diff             @@
##           master    #1284      +/-   ##
==========================================
- Coverage   90.66%   90.63%   -0.03%     
==========================================
  Files          21       21              
  Lines        6870     6891      +21     
  Branches      884      885       +1     
==========================================
+ Hits         6229     6246      +17     
- Misses        469      471       +2     
- Partials      172      174       +2     

Flag	Coverage Δ
unit	90.55% <96.15%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
aioredis/client.py	82.38% <85.71%> (-0.09%)	⬇️
tests/test_pubsub.py	99.27% <100.00%> (+0.03%)	⬆️
aioredis/connection.py	77.18% <0.00%> (-0.24%)	⬇️

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[stephanm]

I added a test case that uses both callback variants.

The typing problem wasn't that easy to fix.
Using something like
PubSubHandler = Callable[[Dict[str, str]], Union[None, Awaitable[None]]]
doesn't work:
aioredis/client.py:4236: error: Incompatible types in "await" (actual type "Optional[Awaitable[None]]", expected type "Awaitable[Any]") [misc]
Maybe someone who is better at this typing stuff can comment on this issue? The current variant at least works with mypy :)

[seandstewart]

Thanks for your contribution here!

Tests look good to me at this point!