Add check for redundant non-capturing groups (W129) - #59
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Flag (?:...) groups that can be removed without changing the match. Unquantified concatenation is associative, so the group boundary is invisible: (?:ab) -> ab, x(?:ab)y -> xaby, (?:a) -> a. A quantified group is redundant only when it wraps a single atom: (?:a)+ -> a+, (?:[abc])+ -> [abc]+. Load-bearing groups are left alone: a bare alternation keeps the group for precedence unless it is the whole pattern (x(?:a|b)y stays, (?:a|b) -> a|b), quantifiers over multiple atoms ((?:ab)+) or over an alternation ((?:a|b)+), and stacked quantifiers ((?:a+)+, which would otherwise merge into the illegal a++). Includes unit tests for the single-atom, concatenation, whole-pattern alternation and no-flag cases.
thatch
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Jul 31, 2026
This is the second time independent PRs collided on the same message id (126 across #52/#53/#54, now 129 across #55-#59). Statically walk each check_/bygroups_check_/groups_check_ function's source for its 'num' assignment and assert none repeat, so a future collision fails CI instead of silently shipping ambiguous warning codes.
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Flag (?:...) groups that can be removed without changing the match. Unquantified concatenation is associative, so the group boundary is invisible: (?:ab) -> ab, x(?:ab)y -> xaby, (?:a) -> a. A quantified group is redundant only when it wraps a single atom: (?:a)+ -> a+, (?:[abc])+ -> [abc]+.
Load-bearing groups are left alone: a bare alternation keeps the group for precedence unless it is the whole pattern (x(?:a|b)y stays, (?:a|b) -> a|b), quantifiers over multiple atoms ((?:ab)+) or over an alternation ((?:a|b)+), and stacked quantifiers ((?:a+)+, which would otherwise merge into the illegal a++).
Includes unit tests for the single-atom, concatenation, whole-pattern alternation and no-flag cases.