cls not callable inside `__class_getitem__`

[eltoder]

import typing

T = typing.TypeVar("T")

class C(typing.Generic[T]):
    def __init__(self, arg) -> None:
        self.arg = arg

    def __class_getitem__(cls, arg):
        return cls(arg)

This produces an unexpected error:

File "/home/elt/code/pytype-test/proj/cls_getitem.py", line 10, in __class_getitem__: 'C' object is not callable [not-callable]

However, if I replace cls(arg) with C(arg), the error goes away. This also works in mypy.

A second issue is that it would be nice if the type was considered indexable if it defines __class_getitem__ even if it does not inherit from Generic.