warn if asyncio test requests async pytest fixture in strict mode

[jakkdl]

partially fixes pytest-dev/pytest#10839, see pytest-dev/pytest#10839 (comment)

It got a bit messy to implement, and relies on non-public API in _fixtureinfo, so I'm not 100% that this is the best way to approach it. Another approach would be to try and catch this on collection, but then you end up having to handle overriding fixtures and the like.

It's also possible that this breaks tests for end users, but if they really do want an unawaited object from a fixture they can resolve it in various ways by returning an Awaitable from their fixture.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.83%. Comparing base (575ebe1) to head (e3b30d7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pytest_asyncio/plugin.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #979      +/-   ##
==========================================
- Coverage   91.15%   90.83%   -0.33%     
==========================================
  Files           2        2              
  Lines         509      513       +4     
  Branches       64       66       +2     
==========================================
+ Hits          464      466       +2     
- Misses         27       28       +1     
- Partials       18       19       +1     

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[jakkdl]

actually, it's not that unlikely that this will break tests for some users if they're using @pytest.fixture(autouse=True) and mixing asyncio and async-but-not-asyncio tests. But... that's probably not a great thing to do.

[seifertm]

I'm loosely following the linked pytest issue. I really appreciate all the work you've put into this and I will try to support the initiative from the pytest-asyncio side.

It would be great, if you could also add a corresponding entry to docs/reference/changelog.rst, since this is a user-facing change.

[seifertm]

This looks great, thank you!

You mentioned in pytest-dev/pytest#12930 (comment) that this change may become redundant once the same check is in place in pytest. I'm generally okay with having the check in pytest-asyncio, too, at least temporarily. At some point, pytest-asyncio will bump the minimum required pytest version to a version where this check is included in pytest and we can remove it here.

I'd like to wait for a decision on your pytest PR before merging (whether you go with a deprecation or plain error), but other than that it looks good to me.

Thanks for the effort!