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<regex>: Fix matching of loops with context-dependent empty matches and bounded number of repetitions #5820

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Merged
merged 2 commits into from
Nov 5, 2025
Merged

<regex>: Fix matching of loops with context-dependent empty matches and bounded number of repetitions #5820

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3870c0f
`<regex>`: Fix matching of loops with context-dependent empty matches…
muellerj2 Nov 1, 2025
6957a9b
Cite bug number in comment.
StephanTLavavej Nov 3, 2025
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10 changes: 7 additions & 3 deletions stl/inc/regex
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Original file line number Diff line number Diff line change
Expand Up @@ -4096,11 +4096,15 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_frame_idx = _Frame_idx;
if (_Progress) {
++_Sav._Loop_idx;
} else { // try only one more match after an empty match

// optimization: try only one more match after an empty match
// if there is no maximum number of reps
if (!_Progress && _Nr->_Max < 0) {
_Sav._Loop_idx = _Nr->_Min;
} else {
++_Sav._Loop_idx;
}

_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Sav._Group_first),
_Tgt_state._Grp_valid.end(), false);
_Next = _Nr->_Next;
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8 changes: 8 additions & 0 deletions tests/std/tests/VSO_0000000_regex_use/test.cpp
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Expand Up @@ -2263,6 +2263,13 @@ void test_gh_5792() {
g_regexTester.should_match("bc", "(?:(?!ab))+bc");
}

void test_gh_5797() {
// GH-5797: <regex>: Loops with bounded number of repetitions and context-dependent empty alternative are mishandled
g_regexTester.should_match("bc", "(?:b|c|(?=bc)){3}");
g_regexTester.should_match("bc", "(^|b|c){3}");
g_regexTester.should_match("bc", "(^|b|c){3}", regex_constants::extended);
}

void test_gh_5798() {
// GH-5798: <regex>: Process generic loops non-recursively.
// This extends our test coverage on non-simple loops,
Expand Down Expand Up @@ -2401,6 +2408,7 @@ int main() {
test_gh_5774();
test_gh_5790();
test_gh_5792();
test_gh_5797();
test_gh_5798();

return g_regexTester.result();
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