Slots and Generics handling broken since 2.5.3

[svenpanne]

Steps to reproduce

1. Build a venv with pylint 2.7.4 and astroid 2.5.3, e.g. via pipenv install pylint==2.7.4 astroid==2.5.3.
2. Run pylint on the following file via e.g. pipenv run pylint --disable=all --enable=assigning-non-slot broken.py:

from typing import Generic, TypeVar

T = TypeVar("T")


class Base(Generic[T]):
    __slots__ = ()


class Foo(Base[T]):
    __slots__ = ['_value']

    def __init__(self, value: T):
        # Triggers assigning-non-slot (Assigning to attribute '_value' not defined
        # in class slots), works when using Generic[T] directly as a base class.
        self._value = value

Current behavior

The steps above incorrectly trigger the assigning-non-slot check.

Expected behavior

No complaints from pylint. If you go back to astroid 2.5.2, the above works. If Foo directly inherits from Generic[T], the above works, too.

Bisecting shows that the commit cd0f896 introduced the regression. Therefore, every astroid >= 2.5.3 is buggy, as is every pylint >= 2.8.0.

python -c "from astroid import __pkginfo__; print(__pkginfo__.version)" output

As already mentioned above, the bug is present in every release containing the above commit, i.e. from 2.5.3 onwards.

[hippo91]

@svenpanne thanks for the report.