`__slots__` is incorrectly classified as an instance variable across inheritance

Bug Report

Mypy classifies __slots__ as an instance variable even though Python defines it on the class. This causes a false-positive override error when a subclass explicitly annotates __slots__ as a ClassVar.

The issue also affects plugin-generated __slots__, including slots generated by dataclasses and attrs.

To Reproduce

from dataclasses import dataclass
from typing import ClassVar


@dataclass(slots=True)
class Base:
    x: float
    y: float


class Child(Base):
    __slots__: ClassVar[tuple[()]] = ()

Run:

mypy example.py

Playground link: https://mypy-play.net/?mypy=latest&python=3.14&gist=e0e2f906ab9e0201c43d2b5cb6ff950c

Expected Behavior

Mypy should report no errors. Both generated and explicitly declared __slots__ should be treated as class variables across inheritance.

Actual Behavior

Cannot override instance variable (previously declared on base class "Base") with class variable  [misc]

A # type: ignore[misc] comment is currently required on the subclass declaration even though __slots__ is a class-level attribute.

The same inconsistent classification occurs with ordinary __slots__ declarations and attrs-generated slots.

Your Environment

• Mypy version used: 2.3.1
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.14.7

Beginne damit, den Fehler mit mypy in example.py zu reproduzieren, und verfolge dann, wie geerbte slots für gewöhnliche Deklarationen und von Plugins erzeugte Slots aus dataclasses und attrs klassifiziert werden. Füge Abdeckung für diese Fälle hinzu und überprüfe, dass mypy keinen Fehler wegen einer Überschreibung zwischen Klasse und Instanz meldet.