Bug report

Bug description:

While trying to test cattrs on 3.14 I ran into this issue. Here's a simple reproducer that passes on 3.13, but doesn't on 3.14.

import gc
from dataclasses import dataclass


@dataclass(slots=True)
class B:
    b: int


gc.collect()

assert [
    o for o in gc.get_objects() if hasattr(o, "__name__") and o.__name__ == "B"
] == [B]

Originally I ran into this issue with slotted attrs classes but the core problem is the same. Since slotness cannot be added to a class, dataclasses and attrs classes create a class copy with slots instead. The old class used to hang around until a GC collection happened (guess there are some reference cycles, but I never investigated thoroughly).

On 3.14, a full GC collection does not clean up the original class, causing a leak. Apart from leaking, in case of subclassing the original class will remain in the list of the parent .__subclasses__(), causing an issue.

CPython versions tested on:

3.14

Operating systems tested on:

macOS

Linked PRs

• gh-135228: Break reference cycle between class and descriptors #135230