Incorrect inference for types with __eq__ and no __hash__

[jorenham]

problem

class A:
    def __eq__(self, o: object, /) -> bool:
        return self is o

reveal_type(A().__hash__)  # def () -> builtins.int

https://mypy-play.net/?mypy=latest&python=3.13&flags=strict%2Clocal-partial-types&gist=2b23624b1df772175b70c08e36a6e912

yet

>>> class A:
...     def __eq__(self, o: object, /) -> bool:
...         return self is o
...         
>>> type(A.__hash__)
<class 'NoneType'>

solution

iff. class A, and only class A (i.e. excluding any base classes)

• implements __eq__, and
• does not implement __hash__

infer A.__hash__: ClassVar[None]