Abstract class properties that are classes incorrectly reported in assignments

• Are you reporting a bug, or opening a feature request?
  I believe this is a bug.

• Please insert below the code you are checking with mypy

from abc import ABC, abstractmethod
from typing import Type


class ISolution(ABC):
    @abstractmethod
    def __init__(self, b: int):
        pass

    @abstractmethod
    def func1(self, a: int) -> int:
        pass


class MySolution(ISolution):
    def __init__(self, b: int):
        self._b = b

    def func1(self, a: int) -> int:
        return a + self._b


class IHolder(ABC):
    @property
    @classmethod
    @abstractmethod
    def SolutionClass(cls) -> Type[ISolution]:
        pass

    # SolutionClass: Type[ISolution]

    @abstractmethod
    def __init__(self, c: int):
        pass

    @abstractmethod
    def cval(self) -> int:
        pass


class Main(IHolder):
    SolutionClass = MySolution

    def __init__(self, c: int):
        self._c = c

    def cval(self) -> int:
        return self._c


def check(holderclass: Type[IHolder], a: int, b: int, c: int) -> bool:
    holder = holderclass(c)
    solclass: Type[ISolution] = holderclass.SolutionClass
    return solclass(b).func1(a) == holder.cval()


print("should be true ", check(Main, 5, 5, 10))
print("should be false ", check(Main, 3, 4, 10))

• What is the actual behavior/output?

classprop.py:53: error: Incompatible types in assignment (expression has type "Callable[[], Type[ISolution]]", variable has type "Type[ISolution]")

This is referring to the line:

    solclass: Type[ISolution] = holderclass.SolutionClass

• What is the behavior/output you expect?
  No error to be reported.

Note. If you comment out

    @property
    @classmethod
    @abstractmethod
    def SolutionClass(cls) -> Type[ISolution]:
        pass

and then uncomment

    SolutionClass: Type[ISolution]

then mypy says the code is fine.

• What are the versions of mypy and Python you are using?
  mypy 0.770
  python 3.7.6

• Do you see the same issue after installing mypy from Git master?
  I'm trying to avoid dealing with that!

• What are the mypy flags you are using? (For example --strict-optional)
  None

まず、提供された抽象クラス、property、classmethod の例で診断を再現します。holderclass.SolutionClass の型推論を、注釈付きクラス属性のバージョンと比較し、その後、solclass への代入で互換性のない型が報告されなくなったことを確認します。