Mypy thinks dict[Never, Never] is a subtype of Mapping[str, object] #19641
Description
This behaves as expected: https://mypy-play.net/?mypy=latest&python=3.12&gist=8718e96550599dc3ae48a13879005762
from typing import Mapping, Never
def upcast(d: dict[Never, Never]) -> Mapping[str, object]:
return d # E: [return-value] (✅ expected)But it breaks here (due to caching?) https://mypy-play.net/?mypy=latest&python=3.12&gist=6199ba50b6b02e2350e70cb3a8ff4bba
from typing import Mapping, Never
def get[M: Mapping[str, object]](arg: M, /) -> M:
return arg
reveal_type(get({})) # dict[Never, Never] (❌ incorrect)
def upcast(d: dict[Never, Never]) -> Mapping[str, object]:
return d # <-- No error anymore 😱