Inconsistent "Invalid Metaclass" error for classes defined within functions

Bug Report

When a class:

• is defined inside a function, and
• uses a metaclass

then it mypy will inconsistently give an Invalid metaclass error based on whether the metaclass is specified via an alias name, or the original name from when the class is defined. This behaviour occurs regardless of whether the metaclass is defined inside or outside of the function. I would have expected no error.

To Reproduce

See on mypy playground

class M(type):
    pass


def f() -> None:
    _M = M

    class C(metaclass=_M): # Error
        pass
    
    class D(metaclass=M): # OK
        pass

Actual Behavior

main.py:8: error: Invalid metaclass "_M"  [misc]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.1.1
• Python version used: 3.11

リンクされた mypy playground とネストされた関数の再現例から始め、エイリアスされたメタクラス _M と元の名前 M を比較します。無効なメタクラスのチェックを追跡し、同等のエイリアスで一貫性のない診断が生成されなくなり、例がエラーを報告しないことを確認します。