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gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible (take 2) #137047

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@JelleZijlstra JelleZijlstra commented Jul 23, 2025

This is a redo of #136893 without relying on a hack to get to the type dictionary.

JelleZijlstra and others added 3 commits July 23, 2025 08:13
…ke the original class collectible (python#136893)

An interesting hack, but more localized in scope than python#135230.

This may be a breaking change if people intentionally keep the original class around
when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the
original class.

Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>
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Can we check that this is a Python class? Should we clear the whole class dict or set it to NULL for the case if there are more descriptors?

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Can we check that this is a Python class?

Maybe we can check that it's a heap type?

Should we clear the whole class dict or set it to NULL for the case if there are more descriptors?

I'm not aware of other descriptors that could cause problems. It's better to minimize the amount of changes we make to the class, because there are edge cases where the class is still accessible after the dataclass transformation is applied.

Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
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@encukou @serhiy-storchaka could you review again and approve if you're satisfied, so that we can get this fixed in 3.14?

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I can't find any issues in the PR; this is pretty much is the local optimum.
But, I can't tell if there will be unintended consequences. This PR feels quite risky for a RC fix.

Docs-wise: the notes/comments shouldn't imply that the original class is guaranteed to be garbage collected -- something else could still keep it alive.

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