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

Start by saving the supplied example as bug.py and running mypy bug.py with the reported version and no flags. Trace how mypy checks Protocol methods, async return types, and async context managers. Done means the example produces no errors while preserving the expected type checking behavior.