New LOAD_ATTR_CLASS_WITH_METACLASS_CHECK does not guard against __class__ reassignment

Bug description:

This was found by Codex. Consider the following:

import enum
import _testinternalcapi

class ColorMeta(enum.EnumType):
    pass

class Color(enum.IntEnum, metaclass=ColorMeta):
    RED = 1

red = Color.RED

class Descriptor(enum.IntEnum):
    RED = 1

    def __get__(self, obj, owner):
        return "descr"

def get_enum_member():
    return Color.RED

for _ in range(_testinternalcapi.SPECIALIZATION_THRESHOLD):
    assert get_enum_member() == 1

red.__class__ = Descriptor

for _ in range(_testinternalcapi.SPECIALIZATION_THRESHOLD):
    assert get_enum_member() == "descr"

This passes without specializing interpreter, but fails with. @kumaraditya303

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-149269

まず、インタープリターの特殊化ありとなしで issue の再現プログラムを実行し、LOAD_ATTR_CLASS_WITH_METACLASS_CHECK と class の再代入に注目します。リンクされている PR gh-149269 と動作を比較します。再代入後に、特殊化ありと特殊化なしの両方の実行がディスクリプターの結果を返せば完了です。