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Add a codemod for dataclass changes in 3.11 #1257

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Add a codemod for dataclass changes in 3.11 #1257

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@zsol zsol commented Dec 7, 2024

Add a codemod for dataclass changes in 3.11

Python 3.11 changed the field default mutability check for dataclasses to only allow defaults which are hashable.

This codemod helps with the migration by changing all default values that aren't obviously hashable to use default_factory instead.

Note: it's impossible to accurately determine if a particular expression produces a hashable value in a codemod, so the codemod significantly over-approximates what's unhashable.

@facebook-github-bot facebook-github-bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Dec 7, 2024
@zsol zsol marked this pull request as ready for review December 7, 2024 15:19
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Is it too cumbersome to identify zero-args-calls used as mutable defaults and drop the lambda in those cases?
Similarly for empty list/dict literals, using list / dict instead of the lambda

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zsol commented Dec 7, 2024

@itamaro no, not at all. If you wanna take a stab at it, feel free to commandeer this PR :)

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itamaro commented Dec 7, 2024

If you wanna take a stab at it, feel free to commandeer this PR :)

don't have the time right now, and it's useful enough to merge as is!
we can iterate on it in future PRs.

Python 3.11 changed the field default mutability check for dataclasses to only allow defaults which are hashable.

This codemod helps with the migration by changing all default values that aren't obviously hashable to use `default_factory` instead.

Note: it's impossible to accurately determine if a particular expression produces a hashable value in a codemod, so the codemod significantly over-approximates what's unhashable.
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