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[flake8-bugbear] Fix panic on match subjects (B031) - #27781
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…ect (B031) The `Stmt::Match` arm pushed an empty branch-counter frame before visiting the subject, so a group usage in the subject unwrapped `last_mut()` on the empty frame and panicked. Visit the subject first: it is evaluated unconditionally, so it belongs to the enclosing count, and a subsequent usage in a case body is still flagged. Fixes astral-sh#26624
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ntBre
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Thanks, this looks good to me overall. I just had one suggestion to treat If statements similarly and a small nit about a comment.
The comment on the `match` subject fix referenced a panic that no longer exists after the fix; trim it to the first sentence per review feedback. Also extend the same "visit unconditionally-evaluated expression before pushing branch counters" pattern to `if` statement tests, which are evaluated unconditionally just like a `match` subject. Previously the test's usage was attributed to the `if` branch's counter, causing a false negative when the group was reused in the `else` branch (or another elif branch).
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Trimmed the comment to the first sentence, and extended the unconditional-visit-then-track-counters pattern to |
flake8-bugbear] Fix B031 panic on match subjectsflake8-bugbear] Fix panic on match subjects (B031)
ntBre
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August 28, 2026 20:56
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Thanks! |
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Fixes #26624