Fix optional lookahead capture semantics #9
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Per ECMAScript spec, when an optional group matches but with zero-width (e.g., contains only a lookahead), captures inside should be undefined. This is because a zero-width optional match is equivalent to skipping the group entirely. Implementation: - Add new RESET_IF_NO_ADV opcode that resets captures if position unchanged - In compiler, detect optional groups with zero-width bodies (e.g., lookaheads) - Emit SET_POS before and RESET_IF_NO_ADV after such bodies - In VM, handle the new opcode to conditionally reset captures This fixes the following tests: - test_optional_lookahead_no_match - test_repeated_optional_lookahead
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Per ECMAScript spec, when an optional group matches but with zero-width
(e.g., contains only a lookahead), captures inside should be undefined.
This is because a zero-width optional match is equivalent to skipping
the group entirely.
Implementation:
This fixes the following tests:
Claude Code transcript: https://gistpreview.github.io/?65d1a6449a8077c59946435f485121bf/index.html