object.__new__(cls) fails type check inside generic classes

[pkch]

(Based on #3111)

This fails with Argument 1 to "__new__" of "object" has incompatible type C[T]; expected "object"

T = TypeVar('T')
class C(Generic[T]):
    def __new__(cls, foo: T) -> 'C[T]':
        obj = object.__new__(cls)
        return obj
    def set(self, x: T) -> None: pass

Edit: deleted my own incorrect interpretation.

[pkch]

This also happens when __init__ is present and has non-zero arguments in the signature:

class C:
    def __init__(self, x: int) -> None:
        pass
    def __new__(cls, *args) -> 'C':
        obj = object.__new__(cls)  # E:  Argument 1 to "__new__" of "object" has incompatible type "C"; expected "object"
        return obj

However, this passes:

class C:
    def __new__(cls) -> 'C':
        obj = object.__new__(cls)
        return obj

Somehow the presence of arguments in the signature prevents mypy from matching the class object to the expected object type.

[msullivan]

#4190 is a dupe of this but I'm closing this one because that one got categorized