Collection of Generic[T] and Generic[real type] becomes Collection[object]

[crusaderky]

import asyncio
from typing import Awaitable, TypeVar

T = TypeVar("T")


async def f(aw: Awaitable[T], t: asyncio.Task[None]) -> None:
    futs = {aw, t}
    await asyncio.wait(futs)
    reveal_type(futs)

mypy 0.780 output:

9: error: Argument 1 to "wait" has incompatible type "Set[object]"; expected "Iterable[Union[Future[<nothing>], Generator[Any, None, <nothing>], Awaitable[<nothing>]]]"
10: note: Revealed type is 'builtins.set[builtins.object*]'
Found 1 error in 1 file (checked 1 source file)

Expected output:

10: note: Revealed type is 'builtins.set[Union[Awaitable[T], asyncio.Task[None]]]'

The issue disappears if I either

• replace Awaitable[T] with Awaitable[None]
• replace Task[None] with Task[Any]

This issue is not new in 0.780; however starting from 0.780 asyncio.create_task propagates the return type of its input whereas before it was returning Task[Any], so it makes the issue crop up.

[JukkaL]

Mypy can't infer a good enough type for futs. The recommended workaround is to add a type annotation for futs. This is basically an instance of #3816.