<regex>: Fix regex_error when matching a repeated pattern containing a lookahead assertion (#5793)

Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: muellerj2

stl/inc/regex

@@ -3521,7 +3521,7 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Find_first_inner_capture
 
         case _N_assert:
         case _N_neg_assert:
-            if (_Find_first_inner_capture_group(static_cast<_Node_assert*>(_Nx), _Loop_state)) {
+            if (_Find_first_inner_capture_group(static_cast<_Node_assert*>(_Nx)->_Child, _Loop_state)) {
                 _Found_group = true;
                 _Nx          = nullptr;
             }

tests/std/tests/VSO_0000000_regex_use/test.cpp

@@ -2223,6 +2223,15 @@ void test_gh_5790() {
     }
 }
 
+void test_gh_5792() {
+    // GH-5792: <regex>: regex_match() throws regex_error(error_stack)
+    // when a repeated pattern contains a lookahead assertion
+    g_regexTester.should_match("", "(?:(?=ab))*");
+    g_regexTester.should_match("", "(?:(?!ab))*");
+    g_regexTester.should_not_match("bc", "(?:(?=ab))+bc");
+    g_regexTester.should_match("bc", "(?:(?!ab))+bc");
+}
+
 int main() {
     test_dev10_449367_case_insensitivity_should_work();
     test_dev11_462743_regex_collate_should_not_disable_regex_icase();
@@ -2276,6 +2285,7 @@ int main() {
     test_gh_5672();
     test_gh_5774();
     test_gh_5790();
+    test_gh_5792();
 
     return g_regexTester.result();
 }