deleting a class-scoped variable that shadows a global variable causes mypy to think it's undefined

To Reproduce

from typing import Callable, TypeVar

T = TypeVar("T")

x = 1


def decorate(num: int) -> Callable[[T], T]:
    def thru(it: T) -> T:
        print("decorating", it, "with", num)
        return it
    return thru


class y(object):
    @decorate(x)
    def a(self) -> None:
        ...

    x = 2

    @decorate(x)
    def b(self) -> None:
        ...

    del x

    @decorate(x)
    def c(self) -> None:
        ...

Expected Behavior

This is perfectly valid, it should not cause an error! It works at runtime.

Actual Behavior

$ mypy class_scope.py 
class_scope.py:28: error: Trying to read deleted variable 'x'
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.790
• Mypy command-line flags: all defaults
• Mypy configuration options from mypy.ini (and other config files): no mypy.ini
• Python version used: Python 3.8.5
• Operating system and version:

ProductName:	Mac OS X
ProductVersion:	10.15.7
BuildVersion:	19H2

Riproduci il problema dell’esempio class_scope.py con mypy, usando come riferimento le versioni di Python e mypy riportate. Traccia il modo in cui il checker gestisce un nome nell’ambito di una classe dopo del x, quindi aggiungi un test di regressione che mostri che l’uso successivo del decoratore non segnala una variabile non definita.