Inheritance from nested class doesn't always work

[evhub]

I can't tell if this is the same issue as my previous issue #9238 or not, so I'm raising it separately.

On MyPy 0.780, the code

class B:
    pass

class A:
    B = B

class C(A.B):
    pass

raises

test.py:7: error: Variable "test.A.B" is not valid as a type
test.py:7: note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases
test.py:7: error: Invalid base class "A.B"
Found 2 errors in 1 file (checked 1 source file)

despite the equivalent code

class A:
    class B:
        pass

class C(A.B):
    pass

working fine.

[ilevkivskyi]

This works as intended. See my comment in #9238

[evhub]

@ilevkivskyi Is there any way to annotate the above code that would work (aside from type: ignore)? I'd like to be able to properly type-check that code.

[ilevkivskyi]

Something that may work is B = Union[B].