(🐞) No error when overload implementation has incompatible return type

from typing import overload

@overload
def foo(a: int) -> int: ...

@overload
def foo(a: float) -> int: ...

def foo(a: object) -> object:  # no error
    return object()

playground

While the strictest of solutions would be to enforce the return type be an intersection of the overload return types, that would result in being overly strict to the point of being unusable. I suggest enforcing the return type to be a union of the overloads, this is not typesafe, but is much safer than not checking it at all.

Start by reproducing the example in the linked mypy playground and trace the overload implementation return-type checking it exercises. Define done as producing a diagnostic for the incompatible implementation return type while preserving the stated intended behavior for overloads.