Type annotation on self is not enforced correctly for generic classes

[pnachum]

This code doesn't produce any type errors, but will crash at runtime when calling len with an int.

T = TypeVar('T')

class Box(Generic[T]):
    
    def __init__(self, val: T) -> None:
        self.val = val
		
    def foo(self: 'Box[str]') -> 'int':
        return len(self.val)

Box(1).foo()

Calling the foo method like this does result in a type error

Box.foo(Box(1))

[ilevkivskyi]

Hm, interesting. I think annotations on self apart from self-type-like (capturing type variable) should be prohibited.

[pnachum]

I guess that would make this scenario impossible to express until #2354 is resolved?

[elazarg]

@ilevkivskyi I think it should be allowed as long as the overloads are exhaustive.