"Overloaded function implementation does not accept all possible arguments"

False positive; mypy doesn't believe that Foo[T] is a subtype of T.

from typing import Union, Generic, TypeVar, overload

T = TypeVar("T")

class Foo(Generic[T]):
    pass

@overload
def expect(pattern: Foo[T]) -> None: ...

@overload
def expect(pattern: T) -> None: ...

def expect(pattern: Union[Foo[T], T]) -> None: return None

$ mypy xxx.py
xxx.py:14: error: Overloaded function implementation does not accept all possible arguments of signature 1

Note that the second overload referencing the type variable used in the first overload is necessary; if pattern: int is used instead of pattern: T in the second overload, mypy type-checks the file correctly.

Environment

• Mypy version used: 0.910
• Python version used: 3.10 and 3.7
• Operating system and version: Fedora 34

Related issues

• #11004: mypy thinks **kwargs: Union[None, int, str] overload isn't accepted by **kwargs: Any
• #9420: mypy thinks Type[T1] isn't accepted by Union[Type[T1], Type[T2]]
• #9023: same bug with two different type variables

I think that #10390 fixes this issue, but I'm not sure.

Reproduce the diagnostic in xxx.py with mypy using the overloads shown, then read related issues #10390, #11004, #9420, and #9023 to understand existing handling. Done means the valid overload implementation is accepted without the reported error and the regression is covered by the project's tests.