@overload doesn't work with @asynccontextmanager

[alenzo-arch]

Bug Report

When trying to annotate overloads for an asynccontextmanager, I think mypy incorrectly reports an invalid return type.

To Reproduce

from contextlib import asynccontextmanager, contextmanager
from typing import AsyncIterator, Iterator, overload

@overload
@asynccontextmanager
async def test_async() -> AsyncIterator[int]: ...


@overload
@asynccontextmanager
async def test_async(val: int = ...) -> AsyncIterator[int]: ...


@asynccontextmanager
async def test_async(val: int = 1) -> AsyncIterator[int]:
    yield val


@overload
@contextmanager
def test_sync() -> Iterator[int]: ...


@overload
@contextmanager
def test_sync(val: int = ...) -> Iterator[int]: ...


@contextmanager
def test_sync(val: int = 1) -> Iterator[int]:
    yield val

This gives an error of "Argument 1 to "asynccontextmanager" has incompatible type "Callable[[int], Coroutine[Any, Any, AsyncIterator[int]]]"; expected "Callable[[int], AsyncIterator[Never]]"

Where the synchronous version checks fine.

Expected Behavior

I expect the async version to work the same as the sync version

Actual Behavior

Mypy reports and error

mypy test.py
test.py:5: error: Argument 1 to "asynccontextmanager" has incompatible type "Callable[[], Coroutine[Any, Any, AsyncIterator[int]]]"; expected "Callable[[], AsyncIterator[Never]]"  [arg-type]
test.py:10: error: Argument 1 to "asynccontextmanager" has incompatible type "Callable[[int], Coroutine[Any, Any, AsyncIterator[int]]]"; expected "Callable[[int], AsyncIterator[Never]]"  [arg-type]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.10.0
• Mypy command-line flags: mypy test.py
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: Python 3.11.4

[sterliakov]

Funny enough, the following typechecks (note how async disappears in overload stubs). This seems to be the same kind of problem as functions/methods and decorators: too much of "indirectly applied" stuff confuses the checker. In your original snippet, the function is "async twice": mypy thinks that it returns a Coroutine which, when awaited, produces an AsyncIterator. But this only happens when applying a decorator to overloaded definition (see the full playground, reveal_type produces a right type indeed).

from contextlib import asynccontextmanager, contextmanager
from typing import AsyncIterator, Iterator, overload

@overload
@asynccontextmanager
def test_async() -> AsyncIterator[int]: ...


@overload
@asynccontextmanager
def test_async(val: int = ...) -> AsyncIterator[int]: ...


@asynccontextmanager
async def test_async(val: int = 1) -> AsyncIterator[int]:
    yield val

(I'm posting this more like a temporary workaround, this definitely looks like a typechecker bug to me, and pyright has no objections to your snippet)

[alenzo-arch]

@sterliakov Thank for for addressing this as well as providing a temporary work around