Inconsistency in metaclass/Type interaction

[msullivan]

Since #6370, we reject the following code:

from typing import Type
class Meta(type):
    pass
class Thing(metaclass=Meta):
    pass

def foo(x: Type[Thing]) -> Type[Thing]:
    assert isinstance(x, Meta)
    return x

with the error Incompatible return value type (got "Meta", expected "Type[Thing]").

Previously this worked because we thought that Meta and Type[Thing] had no overlap and so the rest of the function after the assert wasn't checked.

This caused one error in S.

The answer might be that we need to consider Type[Thing] to be a subtype of Meta?

[ilevkivskyi]

The answer might be that we need to consider Type[Thing] to be a subtype of Meta?

IIRC this is already true, we need to fix proper subtype (which is still a separate visitor, see also #3297)

Also even with proper subtype fixed, this may not help since isinstance() can widen type, see
#6386. Or maybe better proper subtype check will fix both issues.