mypy incorrectly resolves names inside decorated methods

[beckjake]

• Are you reporting a bug, or opening a feature request?

A bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

from typing import Type

class A:
    pass

class B:
    @staticmethod
    def A() -> Type[A]:
        return A

assert A is B.A()

• What is the actual behavior/output?

$ mypy mypy_fail.py
mypy_fail.py:8: error: Function "mypy_fail.B.A" is not valid as a type
mypy_fail.py:8: note: Perhaps you need "Callable[...]" or a callback protocol?
Found 1 error in 1 file (checked 1 source file)

• What is the behavior/output you expect?

I expect this to be accepted - it works fine in python

Probably of interest: regular methods work like I expect. classmethod and property complain the same way, so I assume this has to do with decorators. For functions, I can't reproduce syntax like this that's also valid python (I get UnboundLocalErrors), so that's as far as I got with debugging.

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

mypy 0.750 and python 3.6/3.8. I also get it on git master.

• What are the mypy flags you are using? (For example --strict-optional)

No flags required

[ilevkivskyi]

This is indeed a bug. You can use a type alias as workaround:

_A = A
class B:
    @staticmethod
    def A() -> Type[_A]:
        return A

[TH3CHARLie]

There's another possible workaround:

from typing import Type

class C:
    pass

class B:
    @staticmethod
    def A() -> Type[C]:
        return C

which I confirm that at line 8, lookup_qualified will correctly lookup the node with fullname of __main__.C. However, with the failed code, the lookup result will be __main__.B.A, which caused the error. So I think we need to modify lookup_qualified to fix this. @ilevkivskyi