Error with Protocols and AsyncContextManager

• Are you reporting a bug, or opening a feature request?
  A bug

• Please insert below the code you are checking with mypy,

from __future__ import annotations

import asyncio
import typing as t
from contextlib import asynccontextmanager

import typing_extensions as te


class LockProto(te.Protocol):
    async def with_lock(self) -> t.AsyncContextManager[str]: ...


class Consumer:
    def __init__(self, locker: LockProto) -> None:
        self.locker = locker

    def run(self) -> None:
        async with self.locker.with_lock() as name:
            print(name)


class SockLock:
    @asynccontextmanager
    async def with_lock(self) -> t.AsyncGenerator[str, None]:
        yield 'some-string'


async def main() -> None:
    cons = Consumer(SockLock())
    await cons.run()


if __name__ == '__main__':
    asyncio.run(main())

• What is the actual behavior/output?

bug.py:18: error: "Coroutine[Any, Any, AsyncContextManager[str]]" has no attribute "__enter__"
bug.py:18: error: "Coroutine[Any, Any, AsyncContextManager[str]]" has no attribute "__exit__"
bug.py:29: error: Argument 1 to "Consumer" has incompatible type "SockLock"; expected "LockProto"
bug.py:29: note: Following member(s) of "SockLock" have conflicts:
bug.py:29: note:     Expected:
bug.py:29: note:         def with_lock(self) -> Coroutine[Any, Any, AsyncContextManager[str]]
bug.py:29: note:     Got:
bug.py:29: note:         def with_lock(*Any, **Any) -> AsyncContextManager[Any]

• What is the behavior/output you expect?
  No errors

• What are the versions of mypy and Python you are using?
  0.761

• What are the mypy flags you are using? (For example --strict-optional)
  No flags, just mypy bug.py

まず、提供された例を bug.py として保存し、報告されたバージョンでフラグを付けずに mypy bug.py を実行します。mypy が Protocol メソッド、非同期の戻り値の型、非同期コンテキストマネージャーをどのようにチェックするかを追跡します。例でエラーが発生せず、期待される型チェックの動作が維持されていれば完了です。