microsoft · StephanTLavavej · Mar 24, 2025 · Jan 2, 2025 · Jan 7, 2025 · Jan 14, 2025
@@ -1640,11 +1640,12 @@ public:
 
         if (_Matches) { // copy results to _Matches
             _Matches->_Resize(_Get_ncap());
+            const auto& _Result = _Longest ? _Res : _Tgt_state;
             for (unsigned int _Idx = 0; _Idx < _Get_ncap(); ++_Idx) { // copy submatch _Idx
-                if (_Res._Grp_valid[_Idx]) { // copy successful match
+                if (_Result._Grp_valid[_Idx]) { // copy successful match
                     _Matches->_At(_Idx).matched = true;
-                    _Matches->_At(_Idx).first   = _Res._Grps[_Idx]._Begin;
-                    _Matches->_At(_Idx).second  = _Res._Grps[_Idx]._End;
+                    _Matches->_At(_Idx).first   = _Result._Grps[_Idx]._Begin;
+                    _Matches->_At(_Idx).second  = _Result._Grps[_Idx]._End;
                 } else { // copy failed match
                     _Matches->_At(_Idx).matched = false;
                     _Matches->_At(_Idx).first   = _End;
@@ -3290,6 +3291,20 @@ bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Do_rep(_Node_rep* _Node, bool _Gr
             _Psav->_Loop_iter = _STD addressof(_Cur_iter);
             _Matched0         = _Match_pat(_Node->_Next);
         }
+    } else if (_Longest) { // longest, try any number of repetitions
+
+        // match with no further repetition
+        _Matched0 = _Match_pat(_Node->_End_rep->_Next);
+        // match with at least one more repetition if last repetition made progress
+        if (_Progress) {
+            _Tgt_state        = _St;
+            _Psav->_Loop_idx  = _Init_idx + 1;
+            _Psav->_Loop_iter = _STD addressof(_Cur_iter);
+
+            if (_Match_pat(_Node->_Next)) { // always call _Match_pat, even when _Matched0 is already true
+                _Matched0 = true;
+            }
+        }
     } else if (!_Greedy) { // not greedy, favor minimum number of reps
         _Matched0 = _Match_pat(_Node->_End_rep->_Next);
         if (!_Matched0 && _Progress) { // tail failed, try another rep
@@ -3450,16 +3465,24 @@ bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Do_class(_Node_base* _Nx) { // ap
 }
 
 template <class _BidIt, class _Elem, class _RxTraits, class _It>
-bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Better_match() { // check for better match under UNIX rules
+bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Better_match() { // check for better match under leftmost-longest rule
     for (unsigned int _Ix = 0; _Ix < _Get_ncap(); ++_Ix) { // check each capture group
-        if (_Res._Grp_valid[_Ix] && _Tgt_state._Grp_valid[_Ix]) {
+        // any match (even an empty one) is better than no match at all
+        if (_Res._Grp_valid[_Ix] != _Tgt_state._Grp_valid[_Ix]) {
+            return _Tgt_state._Grp_valid[_Ix];
+        }
+
+        if (_Res._Grp_valid[_Ix]) { // now known to be equal to _Tgt_state._Grp_valid[_Ix], no need to test both
+            // if both groups are matched, prefer the leftmost one
             if (_Res._Grps[_Ix]._Begin != _Tgt_state._Grps[_Ix]._Begin) {
                 return _STD distance(_Begin, _Res._Grps[_Ix]._Begin)
-                     < _STD distance(_Begin, _Tgt_state._Grps[_Ix]._Begin);
+                     > _STD distance(_Begin, _Tgt_state._Grps[_Ix]._Begin);
             }
 
+            // if both groups start at the same position, prefer the longer one
             if (_Res._Grps[_Ix]._End != _Tgt_state._Grps[_Ix]._End) {
-                return _STD distance(_Begin, _Res._Grps[_Ix]._End) < _STD distance(_Begin, _Tgt_state._Grps[_Ix]._End);
+                return _STD distance(_Res._Grps[_Ix]._Begin, _Res._Grps[_Ix]._End)
+                     < _STD distance(_Tgt_state._Grps[_Ix]._Begin, _Tgt_state._Grps[_Ix]._End);
             }
         }
     }
@@ -3678,7 +3701,7 @@ bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Match_pat(_Node_base* _Nx) { // c
                     && _Begin == _Tgt_state._Cur)
                 || (_Full && _Tgt_state._Cur != _End)) {
                 _Failed = true;
-            } else if (!_Matched || _Better_match()) { // record successful match
+            } else if (_Longest && (!_Matched || _Better_match())) { // record successful match
                 _Res     = _Tgt_state;
                 _Matched = true;
             }

@@ -2,9 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #pragma once
+#include <cstddef>
 #include <cstdio>
+#include <initializer_list>
 #include <regex>
 #include <string>
+#include <utility>
 
 class regex_fixture {
     int regex_test_result = 0;
@@ -241,6 +244,93 @@ class test_regex {
             fixture->fail_regex();
         }
     }
+
+    void should_search_match_capture_groups(const std::string& subject, const std::string& expected,
+        const std::regex_constants::match_flag_type match_flags,
+        std::initializer_list<std::pair<std::ptrdiff_t, std::ptrdiff_t>> capture_groups) const {
+        std::smatch mr;
+        try {
+            const bool search_result = std::regex_search(subject, mr, r, match_flags);
+            if (!search_result || mr[0] != expected) {
+                printf(R"(Expected regex_search("%s", regex("%s", 0x%X), 0x%X) to find "%s", )", subject.c_str(),
+                    pattern.c_str(), static_cast<unsigned int>(syntax), static_cast<unsigned int>(match_flags),
+                    expected.c_str());
+                if (search_result) {
+                    printf(R"(but it matched "%s")"
+                           "\n",
+                        mr.str().c_str());
+                } else {
+                    puts("but it failed to match");
+                }
+
+                fixture->fail_regex();
+            } else if (capture_groups.size() + 1 != mr.size()) {
+                printf(R"(Expected regex_search("%s", regex("%s", 0x%X), 0x%X) to match %zu capture groups in "%s", )",
+                    subject.c_str(), pattern.c_str(), static_cast<unsigned int>(syntax),
+                    static_cast<unsigned int>(match_flags), capture_groups.size() + 1, expected.c_str());
+                printf(R"(but it matched %zu groups)"
+                       "\n",
+                    mr.size());
+                fixture->fail_regex();
+            } else {
+                bool submatches_success = true;
+                for (std::size_t i = 1U; i < mr.size(); ++i) {
+                    const auto& expected_capture = capture_groups.begin()[i - 1];
+                    const auto& actual_capture   = mr[i];
+                    if (expected_capture.first == -1) {
+                        if (actual_capture.matched) {
+                            submatches_success = false;
+                            break;
+                        }
+                    } else if (!actual_capture.matched || actual_capture.first != (mr[0].first + expected_capture.first)
+                               || actual_capture.second != (mr[0].first + expected_capture.second)) {
+                        submatches_success = false;
+                        break;
+                    }
+                }
+                if (!submatches_success) {
+                    printf(R"(Expected regex_search("%s", regex("%s", 0x%X), 0x%X) to find capture groups {)",
+                        subject.c_str(), pattern.c_str(), static_cast<unsigned int>(syntax),
+                        static_cast<unsigned int>(match_flags));
+
+                    bool initial = true;
+                    for (const auto& expected_capture : capture_groups) {
+                        std::string capture = "(unmatched)";
+                        if (expected_capture.first != -1) {
+                            capture.assign(mr[0].first + expected_capture.first, mr[0].first + expected_capture.second);
+                        }
+                        printf(R"(%s"%s" [%td %td])", initial ? "" : ", ", capture.c_str(), expected_capture.first,
+                            expected_capture.second);
+                        initial = false;
+                    }
+                    printf(R"(} in "%s", but found {)", expected.c_str());
+
+                    initial = true;
+                    for (std::size_t i = 1U; i < mr.size(); ++i) {
+                        const auto& actual_capture = mr[i];
+                        std::string capture        = "(unmatched)";
+                        std::ptrdiff_t first       = -1;
+                        std::ptrdiff_t last        = -1;
+                        if (actual_capture.matched) {
+                            capture = actual_capture.str();
+                            first   = actual_capture.first - mr[0].first;
+                            last    = actual_capture.second - mr[0].first;
+                        }
+                        printf(R"(%s"%s" [%td %td])", initial ? "" : ", ", capture.c_str(), first, last);
+                        initial = false;
+                    }
+                    printf("}\n");
+                    fixture->fail_regex();
+                }
+            }
+        } catch (const std::regex_error& e) {
+            printf(R"(Failed to regex_search("%s", regex("%s", 0x%X), 0x%X): regex_error: "%s")"
+                   "\n",
+                subject.c_str(), pattern.c_str(), static_cast<unsigned int>(syntax),
+                static_cast<unsigned int>(match_flags), e.what());
+            fixture->fail_regex();
+        }
+    }
 };
 
 class test_wregex {

@@ -558,6 +558,84 @@ void test_construction_from_nullptr_and_zero() {
     }
 }
 
+void test_gh_731() {
+    // GH-731 <regex>: Incorrect behavior for capture groups
+    // GH-996: regex_search behaves incorrectly when the regex contains R"(\[)"
+
+    // Several bugs were fixed in ECMAScript (depth-first) and POSIX (leftmost-longest) matching rules.
+    {
+        const test_regex ecma_regex(&g_regexTester, R"((A+)\s*(B+)?\s*B*)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("AAA BBB", "AAA BBB", match_default, {{0, 3}, {4, 7}});
+    }
+    for (syntax_option_type option : {extended, egrep, awk}) {
+        const test_regex posix_regex(&g_regexTester, R"((A+)[[:space:]]*(B+)?[[:space:]]*B*)", option);
+        posix_regex.should_search_match_capture_groups("AAA BBB", "AAA BBB", match_default, {{0, 3}, {4, 7}});
+    }
+
+    {
+        const test_regex ecma_regex(&g_regexTester, ".*(cat|concatenate)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("WXconcatenateYZ", "WXconcat", match_default, {{5, 8}});
+    }
+    for (syntax_option_type option : {extended, egrep, awk}) {
+        const test_regex posix_regex(&g_regexTester, ".*(cat|concatenate)", option);
+        posix_regex.should_search_match_capture_groups("WXconcatenateYZ", "WXconcatenate", match_default, {{2, 13}});
+    }
+
+    {
+        const test_regex ecma_regex(&g_regexTester, "(aa|aabaac|ba|b|c)*", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("aabaac", "aaba", match_default, {{2, 4}});
+    }
+    for (syntax_option_type option : {extended, egrep, awk}) {
+        const test_regex posix_regex(&g_regexTester, "(aa|aabaac|ba|b|c)*", option);
+        posix_regex.should_search_match_capture_groups("aabaac", "aabaac", match_default, {{0, 6}});
+    }
+
+    {
+        const test_regex ecma_regex(&g_regexTester, ".*(a|bacc|baccc)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("ddbacccd", "ddba", match_default, {{3, 4}});
+    }
+    {
+        const test_regex ecma_regex(&g_regexTester, ".*?(a|bacc|baccc)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("ddbacccd", "ddbacc", match_default, {{2, 6}});
+    }
+    for (syntax_option_type option : {extended, egrep, awk}) {
+        const test_regex posix_regex(&g_regexTester, ".*(a|bacc|baccc)", option);
+        posix_regex.should_search_match_capture_groups("ddbacccd", "ddbaccc", match_default, {{2, 7}});
+    }
+
+    {
+        const test_regex ecma_regex(&g_regexTester, R"(^[[:blank:]]*#([^\n]*\\[[:space:]]+)*[^\n]*)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);",
+            "#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);", match_default, {{30, 42}});
+    }
+    {
+        const test_regex awk_regex(&g_regexTester, R"(^[[:blank:]]*#([^\n]*\\[[:space:]]+)*[^\n]*)", awk);
+        awk_regex.should_search_match_capture_groups("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);",
+            "#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);", match_default, {{28, 42}});
+    }
+    {
+        const test_regex extended_regex(&g_regexTester, "^[[:blank:]]*#([^\n]*\\\\[[:space:]]+)*[^\n]*", extended);
+        extended_regex.should_search_match_capture_groups("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);",
+            "#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);", match_default, {{28, 42}});
+    }
+
+    {
+        const test_regex ecma_regex(&g_regexTester, "(ab*)*(ce|bbceef)", ECMAScript);
+        ecma_regex.should_search_match_capture_groups("aababbbceef", "aababbbce", match_default, {{3, 7}, {7, 9}});
+    }
+    for (syntax_option_type option : {extended, egrep, awk}) {
+        const test_regex posix_regex(&g_regexTester, "(ab*)*(ce|bbceef)", option);
+        posix_regex.should_search_match_capture_groups("aababbbceef", "aababbbceef", match_default, {{3, 5}, {5, 11}});
+    }
+
+    {
+        // GH-996 test case
+        const test_regex ecma_regex(&g_regexTester, R"( *((<<)|(\[)|(.+)))", ECMAScript);
+        ecma_regex.should_search_match_capture_groups(
+            " [<</Category/Export>>]>>", " [", match_default, {{1, 2}, {-1, -1}, {1, 2}, {-1, -1}});
+    }
+}
+
 void test_gh_993() {
     // GH-993 regex::icase is not handled correctly for some input.
     {
@@ -775,6 +853,7 @@ int main() {
     test_VSO_225160_match_eol_flag();
     test_VSO_226914_word_boundaries();
     test_construction_from_nullptr_and_zero();
+    test_gh_731();
     test_gh_993();
     test_gh_4995();
     test_gh_5058();

@@ -659,7 +659,7 @@ static const regex_test tests[] = {
     {__LINE__, T("a[a-z]\\{2,4\\}"), T("abcdefghi"), "1 0 5", BASIC | GREP},
     {__LINE__, T("a[a-z]{2,4}?"), T("abcdefghi"), "1 0 3", ECMA},
     {__LINE__, T("(aa|aabaac|ba|b|c)*"), T("aabaac"), "2 0 4 2 4", ECMA},
-    {__LINE__, T("(aa|aabaac|ba|b|c)*"), T("aabaac"), "2 0 6 5 6", EEA},
+    {__LINE__, T("(aa|aabaac|ba|b|c)*"), T("aabaac"), "2 0 6 0 6", EEA},
     {__LINE__, T("(z)((a+)?(b+)?(c))*"), T("zaacbbbcac"), "6 0 10 0 1 8 10 8 9 -1 -1 9 10", ECMA},
     {__LINE__, T("(a*)b\\1+"), T("baaaac"), "2 0 1 0 0", ECMA},
     {__LINE__, T("(?=(a+))"), T("baaabac"), "2 1 1 1 4", ECMA},
@@ -774,7 +774,9 @@ static const regex_test tests[] = {
     {__LINE__, T("^[[:blank:]]*#([^\\n]*\\\\[[:space:]]+)*[^\\n]*"), T("#define some_symbol(x) #x"), "2 0 25 -1 -1",
         ECMA | AWK},
     {__LINE__, T("^[[:blank:]]*#([^\\n]*\\\\[[:space:]]+)*[^\\n]*"),
-        T("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);"), "2 0 53 30 42", ECMA | AWK},
+        T("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);"), "2 0 53 30 42", ECMA},
+    {__LINE__, T("^[[:blank:]]*#([^\\n]*\\\\[[:space:]]+)*[^\\n]*"),
+        T("#define some_symbol(x) \\  \r\n  cat();\\\r\n   printf(#x);"), "2 0 53 28 42", AWK},
 };
 
 static STD string check_matches(