[6.4] Fix forward progress check for lookahead, attempt 2#869
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When a quantified concatenation begins with a lookaround group, the forward progress checker fails to skip over the assertion's child subtree, leaving the analysis cursor misaligned and leading to false positives. This change skips the lookaround's child subtree, matching the treatment added for nullable quantifications in #851.
parkera
approved these changes
Jul 22, 2026
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Cherry-pick of #866 and #867 to the 6.4 branch (actually the 6.4 branch this time, unlike #868).
Fixes an issue that was introduced in this release, where some patterns with lookaheads can lead to compiled regexes that do not terminate when matching.
Changes the runtime compilation of regex patterns into byte code for patterns with lookaheads.
RegexBuilder infinite loop when nullable capture starts with NegativeLookahead #865
rdar://179763689
Fix forward progress detection for lookaround groups #866
Add'l testing for lookahead forward prog detection #867
Very low.
Existing and new unit tests.
@stephentyrone