Join of actual Class with Type[Class] results in `object`

[carljm]

This file:

from typing import Type, Optional

class Foo:
    pass

def make_foo(cls: Optional[Type[Foo]] = None) -> Foo:
    x = Foo if cls is None else cls
    reveal_type(x)
    return x()

gives the following:

typeofclass.py:10: error: Revealed type is 'builtins.object' 
typeofclass.py:11: error: "object" not callable 

This example is superficially related to #3487, in that it uses an if/else expression to make mypy perform a type join, but the distinct bug here is that joining Foo (the actual class object) with Type[Foo] should result in Type[Foo], but instead results in object.

This is related to the fact that class objects are typed as callables instead of as Type[Class].

Oddly reversing Foo if cls is None else cls to cls if cls is not None else Foo results in builtin.type instead of object, which is still wrong, but differently wrong.

Using cls or Foo results in Type[Foo].

[ilevkivskyi]

This is related to the fact that class objects are typed as callables instead of as Type[Class].

It looks like this will be easy to fix, just by adding a special case for callable types with .is_type_obj() returning True.

[ilevkivskyi]

Although original example now passes, this is because now we infer a (simplified) union from the ternary expression. I will keep this open for now.