Add check for redundant lookarounds over assertions - #54
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Flag zero-width lookarounds that wrap a single boundary/anchor assertion, since a lookaround over a zero-width assertion is just the assertion itself: (?=\b)/(?<=\b) -> \b, (?<=^) -> ^, (?=$) -> $, etc. (?!\b)/(?<!\b) -> \B (\b is the only anchor with a named negation) Negative lookarounds over other anchors have no simple replacement and are left alone, as are lookarounds wrapping more than a bare assertion. This is the anti-pattern cleaned up in pygments/pygments#3192. New checker 126 (check_redundant_lookaround), with tests.
thatch
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Jul 31, 2026
This is the second time independent PRs collided on the same message id (126 across #52/#53/#54, now 129 across #55-#59). Statically walk each check_/bygroups_check_/groups_check_ function's source for its 'num' assignment and assert none repeat, so a future collision fails CI instead of silently shipping ambiguous warning codes.
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Flag zero-width lookarounds that wrap a single boundary/anchor assertion, since a lookaround over a zero-width assertion is just the assertion itself:
(?=\b)/(?<=\b) -> \b, (?<=^) -> ^, (?=$) -> $, etc.
(?!\b)/(?<!\b) -> \B (\b is the only anchor with a named negation)
Negative lookarounds over other anchors have no simple replacement and are left alone, as are lookarounds wrapping more than a bare assertion.
This is the anti-pattern cleaned up in pygments/pygments#3192.
New checker 126 (check_redundant_lookaround), with tests.