False positive when calling object.__new__ inside __new__ with args

[li-dan]

Consider:

class A:
    def __new__(cls, x: int) -> 'A':
        return object.__new__(cls) # Argument 1 to "__new__" of "object" has incompatible type "Type[A]"; expected "Type[object]"

class B:
    def __new__(cls) -> 'B':
        return object.__new__(cls)

The object.__new__(cls) call type checks when inside a __new__ method with a single argument, but not when there are extra arguments.

The code for A is taken from testSuperWithNew, but because object.__new__ is unannotated in fixtures/__new__.pyi, the type error doesn't show up in the unit test. The discrepancy between the fixture and typeshed was noted in #3111.

[ilevkivskyi]

I think #1021 is closely related.

[msullivan]

Interestingly, the following works:

class A:
    def __new__(cls, x: int) -> 'A':
        cls2: Type[object] = cls
        return object.__new__(cls2)

[msullivan]

I think the fix for this is to make the type of cls be Type[A].

[gvanrossum]

I think the fix for this is to make the type of cls be Type[A].

(By which you mean, mypy should set it to that, right?)