Unpacking an iterable with an overloaded __iter__ method leads to variable silently being inferred as Any

[AlexWaygood]

from typing import AnyStr, Generic, overload, Iterator

class Foo(Generic[AnyStr]):
    x: AnyStr
    @overload
    def __iter__(self: Foo[str]) -> Iterator[bytes]: ...
    @overload
    def __iter__(self: Foo[bytes]) -> Iterator[str]: ...
    def __iter__(self) -> Iterator[str | bytes]:
        if isinstance(self.x, str):
            yield from [b"a", b"b", b"c"]
        yield from ["a", "b", "c"]

a, b, c = Foo[str]()
reveal_type(a)  # note: Revealed type is "Any"

Mypy should have enough information here to infer that the type of a is bytes (and should probably ask for an explicit annotation if it can't infer that, rather than silently inferring Any).

Mypy version tested on

• mypy 1.2.0+dev.c245e91e1ba4d23ff28e77d08f5e103c43733bf5 (compiled: no)
• Also reproducible on mypy playground with mypy v1.0.0: https://mypy-play.net/?mypy=latest&python=3.11&gist=dde121c6575944d735d3a9a4b2dc57e3

[sobolevn]

@AlexWaygood are you working on this? Or can I take this? :)

[AlexWaygood]

Not working on it, feel free!