Use PEP-646 in stubs for asyncio

[AlexWaygood]

As with #11014, I think this will crash pytype for now -- but I'm curious to see the mypy_primer output

[AlexWaygood]

mypy_primer analysis

tornado

They're subclassing AbstractEventLoop; they'll just have to update their annotations on their subclass, unfortunately.

websockets

This is arguably a true positive: they're passing a function that expects an asyncio.Task as the first argument to call_soon(), then they're passing the result of asyncio.current_task() as the second object: https://github.com/python-websockets/websockets/blob/ec3bd2ab06278602c1d6018b476699e090036373/src/websockets/legacy/async_timeout.py#L237-L241

According to our stubs, asyncio.current_task() could return None, so mypy is right to complain here:

typeshed/stdlib/asyncio/tasks.pyi

Line 439 in aabeacf

def current_task(loop: AbstractEventLoop | None = None) -> Task[Any] | None: ...

black

I think their annotations are slightly incorrect: see psf/black#4047

discord

I think their annotations are definitely incorrect. The code in question is here: https://github.com/Rapptz/discord.py/blob/a5d03d4a1e6f4314518f6f55d8b7130ab3f4336e/discord/ext/tasks/__init__.py#L107-L119. self.future is annotated as being an asyncio.Future[None], which implies that you should only ever call self.future.set_result(None) with None, due to our annotations for asyncio.Future.set_result(). But they're passing (indirectly, via loop.call_later) self.future.set_result(True) on lines 114 and 119.

[srittau]

@AlexWaygood You marked this as ready for review, but it's still tagged as "deferred". Is the latter an oversight?

[AlexWaygood]

@AlexWaygood You marked this as ready for review, but it's still tagged as "deferred". Is the latter an oversight?

It can't be merged until pytype no longer crashes whenever we use Unpack, so in that sense it is indeed deferred. But I think the PR itself is in good condition, so there's nothing stopping you from reviewing it if you'd like to :-)

I merged main in just now because psf/black#4047 was just merged, and I wanted to double-check that it got rid of the black mypy_primer hit

[srittau]

Thanks! I really like the additional type safety that Unpack brings us. One complaint, though.

[AlexWaygood]

Oh, I thought #11120 would unblock this and #11014, but looks like I got mixed up :)

google/pytype@bbf10c1 didn't quite make it into pytype==2023.12.7 -- it'll be included in the next pytype release.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

tornado (https://github.com/tornadoweb/tornado)
+ tornado/platform/asyncio.py:705: error: Argument 3 of "add_reader" is incompatible with supertype "AbstractEventLoop"; supertype defines the argument type as "Unpack[_Ts]"  [override]
+ tornado/platform/asyncio.py:705: note: This violates the Liskov substitution principle
+ tornado/platform/asyncio.py:705: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+ tornado/platform/asyncio.py:710: error: Argument 3 of "add_writer" is incompatible with supertype "AbstractEventLoop"; supertype defines the argument type as "Unpack[_Ts]"  [override]
+ tornado/platform/asyncio.py:710: note: This violates the Liskov substitution principle
+ tornado/platform/asyncio.py:710: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides

websockets (https://github.com/aaugustin/websockets)
+ src/websockets/legacy/async_timeout.py:239: error: Argument 1 to "call_soon" of "AbstractEventLoop" has incompatible type "Callable[[Task[None]], None]"; expected "Callable[[Task[Any] | None], object]"  [arg-type]
+ src/websockets/legacy/async_timeout.py:241: error: Argument 2 to "call_at" of "AbstractEventLoop" has incompatible type "Callable[[Task[None]], None]"; expected "Callable[[Task[Any] | None], object]"  [arg-type]

discord.py (https://github.com/Rapptz/discord.py)
+ discord/ext/tasks/__init__.py:114: error: Argument 2 to "call_later" of "AbstractEventLoop" has incompatible type "Callable[[None], None]"; expected "Callable[[bool], object]"  [arg-type]
+ discord/ext/tasks/__init__.py:119: error: Argument 2 to "call_later" of "AbstractEventLoop" has incompatible type "Callable[[None], None]"; expected "Callable[[bool], object]"  [arg-type]

[AlexWaygood]

And we're there!