Mypy not detecting abstract methods returning undefined types

Bug Report

I have a class with a couple of abstract methods that return a particular custom type. That custom type is then defined right after the class. Then a global variable referencing that class is created:

To Reproduce

# test.py
from abc import ABC, abstractmethod
from typing import NamedTuple, List

class F(ABC):
    @abstractmethod
    async def m1(self) -> Result:
        pass
    
    @abstractmethod
    async def m2(self) -> Result:
        pass

class Result(NamedTuple):
    f1: str
    f2: int
    
foo: List[F] = []

> mypy --strict test.py
Success: no issues found in 1 source file

> python test.py
Traceback (most recent call last):
  File "test.py", line 4, in <module>
    class F(ABC):
  File "test.py", line 6, in F
    async def m1(self) -> Result:
NameError: name 'Result' is not defined

Expected Behavior

I would expect mypy to detect that Result is not defined before its use in class F.

Actual Behavior

Mypy is happy with the code as it is, even under --strict, while Python can't even run the code as is. Moving the declaration of Result above class F solves the problem and both Python and mypy are then happy.

Your Environment

• Mypy version used: 0.991
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.9.13

mypy --strict を実行してから Python を実行し、静的な結果と実行時の NameError を比較することで、test.py の動作を再現します。Result が宣言される前に、mypy が抽象メソッドの戻り値アノテーションをどのように解析するかを追跡します。このケースで、mypy が未定義の Result 参照を報告しつつ、有効なアノテーションを壊さなければ完了です。