Incompatible return types in overload

[Daenyth]

I'm trying to provide a typed interface for async_contextmanager from asyncio_extras in my codebase, and I thought I'd use an overload to address the issue of being arity-agnostic.

I tried this:

from typing import AsyncContextManager, AsyncIterator, Callable, TypeVar, overload
from asyncio_extras import async_contextmanager as _async_contextmanager  # type: ignore

A = TypeVar('A')
B = TypeVar('B')
R = TypeVar('R')

@overload
def async_contextmanager(f: Callable[[A], AsyncIterator[R]]) -> Callable[[A], AsyncContextManager[R]]:
    pass
@overload
def async_contextmanager(f: Callable[[A, B], AsyncIterator[R]]) -> Callable[[A, B], AsyncContextManager[R]]:
    pass
def async_contextmanager(f):
    return _async_contextmanager(f)

And I get

obs/async_contextmanager.py:14: error: Overloaded function signatures 1 and 2 overlap with incompatible return types
obs/async_contextmanager.py:23: error: Function is missing a type annotation

How can I provide an accurate signature here?

[ilevkivskyi]

I think this is a duplicate of #4020