<regex>: Properly parse dollar anchors in basic and grep mode (#5362)

muellerj2 · StephanTLavavej · web-flow · commit 13f1f16260aa · 2025-04-09T20:09:41.000-07:00
Co-authored-by: Stephan T. Lavavej &lt;stl@microsoft.com&gt;
diff --git a/stl/inc/regex b/stl/inc/regex
@@ -1721,7 +1721,7 @@ private:
     // lexing
     [[noreturn]] void _Error(regex_constants::error_type);
 
-    bool _Is_esc() const;
+    bool _Is_esc(_FwdIt) const;
     void _Trans();
     void _Next();
     void _Expect(_Meta_type, regex_constants::error_type);
@@ -3875,8 +3875,7 @@ template <class _FwdIt, class _Elem, class _RxTraits>
 }
 
 template <class _FwdIt, class _Elem, class _RxTraits>
-bool _Parser<_FwdIt, _Elem, _RxTraits>::_Is_esc() const { // assumes _Pat != _End
-    _FwdIt _Ch0 = _Pat;
+bool _Parser<_FwdIt, _Elem, _RxTraits>::_Is_esc(_FwdIt _Ch0) const { // assumes _Ch0 != _End
     return ++_Ch0 != _End
         && ((!(_L_flags & _L_nex_grp) && (*_Ch0 == _Meta_lpar || *_Ch0 == _Meta_rpar))
             || (!(_L_flags & _L_nex_rep) && (*_Ch0 == _Meta_lbr || *_Ch0 == _Meta_rbr)));
@@ -3897,7 +3896,7 @@ void _Parser<_FwdIt, _Elem, _RxTraits>::_Trans() { // map character to meta-char
     }
     switch (_Char) { // handle special cases
     case _Meta_esc:
-        if (_Is_esc()) { // replace escape sequence
+        if (_Is_esc(_Pat)) { // replace escape sequence
             _FwdIt _Ch0 = _Pat;
             _Mchar      = static_cast<_Meta_type>(_Char = *++_Ch0);
         }
@@ -3941,9 +3940,28 @@ void _Parser<_FwdIt, _Elem, _RxTraits>::_Trans() { // map character to meta-char
 
     case _Meta_dlr:
         { // check if $ is special
-            _FwdIt _Ch0 = _Pat;
-            if ((_L_flags & _L_anch_rstr) && ++_Ch0 != _End && *_Ch0 != _Meta_nl) {
-                _Mchar = _Meta_chr;
+            _FwdIt _Next = _Pat;
+            if ((_L_flags & _L_anch_rstr) && ++_Next != _End) {
+                const bool _Escaped = *_Next == _Meta_esc && _Is_esc(_Next);
+                if (_Escaped) {
+                    ++_Next;
+                }
+
+                // Only the basic and grep grammars set _L_anch_rstr, so _L_alt_pipe and _L_nex_grp must be unset.
+                // Therefore, we don't need to handle "dollar followed by pipe '|' for alternation"
+                // or "dollar followed by non-escaped right parenthesis ')' closing a group" below.
+                _STL_INTERNAL_CHECK((_L_flags & (_L_alt_pipe | _L_nex_grp)) == 0);
+
+                const _Elem _Ch = *_Next;
+                const bool _Is_end_of_alternative =
+                    ((_L_flags & _L_alt_nl) && _Ch == _Meta_nl
+                        && _Disj_count == 0) // dollar followed by newline '\n' for alternation
+                    || (_Escaped && _Ch == _Meta_rpar
+                        && _Disj_count != 0); // dollar followed by (escaped) right parenthesis ')' closing a group
+
+                if (!_Is_end_of_alternative) {
+                    _Mchar = _Meta_chr;
+                }
             }
 
             break;
@@ -3972,7 +3990,7 @@ void _Parser<_FwdIt, _Elem, _RxTraits>::_Trans() { // map character to meta-char
 template <class _FwdIt, class _Elem, class _RxTraits>
 void _Parser<_FwdIt, _Elem, _RxTraits>::_Next() { // advance to next input character
     if (_Pat != _End) { // advance
-        if (*_Pat == _Meta_esc && _Is_esc()) {
+        if (*_Pat == _Meta_esc && _Is_esc(_Pat)) {
             ++_Pat;
         }
 
diff --git a/tests/std/tests/VSO_0000000_regex_use/test.cpp b/tests/std/tests/VSO_0000000_regex_use/test.cpp
@@ -1031,7 +1031,6 @@ void test_gh_5165_grep() {
         middle_nl_with_caret.should_search_fail("^a");
         middle_nl_with_caret.should_search_fail("ca");
         middle_nl_with_caret.should_search_fail("^b");
-        middle_nl_with_caret.should_search_fail("ca");
         middle_nl_with_caret.should_search_fail("cb");
     }
     {
@@ -1171,6 +1170,196 @@ void test_gh_5253() {
     g_regexTester.should_not_match("a", "()*");
 }
 
+void test_gh_5362_syntax_option(const syntax_option_type basic_or_grep) {
+    {
+        const test_regex ending_anchor(&g_regexTester, "meo[wW]$", basic_or_grep);
+        ending_anchor.should_search_match("kitten_meow", "meow");
+        ending_anchor.should_search_fail("homeowner");
+    }
+    {
+        const test_regex middle_anchor(&g_regexTester, "me$o[wW]", basic_or_grep);
+        middle_anchor.should_search_fail("kitten_meow");
+        middle_anchor.should_search_fail("homeowner");
+        middle_anchor.should_search_match("home$owner", "me$ow");
+    }
+    {
+        const test_regex double_dollars(&g_regexTester, "meo[wW]$$", basic_or_grep);
+        double_dollars.should_search_fail("kitten_meow");
+        double_dollars.should_search_fail("homeowner");
+        double_dollars.should_search_match("kitten_meow$", "meow$");
+        double_dollars.should_search_fail("kitten_meow$$");
+        double_dollars.should_search_fail("homeow$ner");
+        double_dollars.should_search_fail("homeow$$ner");
+    }
+
+    g_regexTester.should_not_match("me$ow", R"(\(me$\)o[wW])", basic_or_grep);
+    g_regexTester.should_not_match("meow", R"(\(me$\)o[wW])", basic_or_grep);
+
+    {
+        const test_regex singlegroup_anchor(&g_regexTester, R"(\(meo[wW]$\))", basic_or_grep);
+        singlegroup_anchor.should_search_match("kitten_meow", "meow");
+        singlegroup_anchor.should_search_fail("kitten_meow$");
+        singlegroup_anchor.should_search_fail("homeowner");
+        singlegroup_anchor.should_search_fail("homeow$ner");
+    }
+    {
+        const test_regex suffixedgroup_anchor(&g_regexTester, R"(\(meo[wW]$\).*)", basic_or_grep);
+        suffixedgroup_anchor.should_search_match("kitten_meow", "meow");
+        suffixedgroup_anchor.should_search_fail("kitten_meow$");
+        suffixedgroup_anchor.should_search_fail("homeowner");
+        suffixedgroup_anchor.should_search_fail("homeow$ner");
+    }
+    {
+        const test_regex firstgroup_anchor(&g_regexTester, R"(\(meo[wW]$\)\(.*\))", basic_or_grep);
+        firstgroup_anchor.should_search_match("kitten_meow", "meow");
+        firstgroup_anchor.should_search_fail("kitten_meow$");
+        firstgroup_anchor.should_search_fail("homeowner");
+        firstgroup_anchor.should_search_fail("homeow$ner");
+    }
+    {
+        const test_regex nested_anchor(&g_regexTester, R"(\(\(meo[wW]$\)$\).*)", basic_or_grep);
+        nested_anchor.should_search_match("kitten_meow", "meow");
+        nested_anchor.should_search_fail("kitten_meow$");
+        nested_anchor.should_search_fail("kitten_meow$$");
+        nested_anchor.should_search_fail("homeowner");
+        nested_anchor.should_search_fail("homeow$ner");
+        nested_anchor.should_search_fail("homeow$$ner");
+    }
+    {
+        const test_regex double_dollars(&g_regexTester, R"(\(meo[wW]$$\).*)", basic_or_grep);
+        double_dollars.should_search_fail("kitten_meow");
+        double_dollars.should_search_match("kitten_meow$", "meow$");
+        double_dollars.should_search_fail("kitten_meow$$");
+        double_dollars.should_search_fail("homeowner");
+        double_dollars.should_search_fail("homeow$ner");
+        double_dollars.should_search_fail("homeow$$ner");
+    }
+
+    // Validate that there is no special behavior near bars,
+    // as they are alternation operators in regex modes other than basic or grep.
+    {
+        const test_regex middle_bar(&g_regexTester, "a|a$", basic_or_grep);
+        middle_bar.should_search_match("a|a", "a|a");
+        middle_bar.should_search_fail("a|a$");
+        middle_bar.should_search_fail("a|ab");
+        middle_bar.should_search_fail("a");
+    }
+    {
+        const test_regex group_middle_bar(&g_regexTester, R"(\(a|a\)$)", basic_or_grep);
+        group_middle_bar.should_search_match("a|a", "a|a");
+        group_middle_bar.should_search_fail("a|a$");
+        group_middle_bar.should_search_fail("a|ab");
+        group_middle_bar.should_search_fail("a");
+    }
+    {
+        const test_regex middle_bar_with_dollar(&g_regexTester, "a$|b$", basic_or_grep);
+        middle_bar_with_dollar.should_search_match("a$|b", "a$|b");
+        middle_bar_with_dollar.should_search_fail("a|b");
+        middle_bar_with_dollar.should_search_fail("a$|b$");
+        middle_bar_with_dollar.should_search_fail("a$|bc");
+        middle_bar_with_dollar.should_search_fail("a");
+        middle_bar_with_dollar.should_search_fail("b");
+    }
+    {
+        const test_regex group_middle_bar_with_dollar(&g_regexTester, R"(\(a$|b\)$)", basic_or_grep);
+        group_middle_bar_with_dollar.should_search_match("a$|b", "a$|b");
+        group_middle_bar_with_dollar.should_search_fail("a|b");
+        group_middle_bar_with_dollar.should_search_fail("a$|b$");
+        group_middle_bar_with_dollar.should_search_fail("a$|bc");
+        group_middle_bar_with_dollar.should_search_fail("a");
+        group_middle_bar_with_dollar.should_search_fail("b");
+    }
+}
+
+void test_gh_5362_basic() {
+    // test cases specific for basic regular expressions
+    {
+        const test_regex middle_nl(&g_regexTester, "a\na$", basic);
+        middle_nl.should_search_match("a\na", "a\na");
+        middle_nl.should_search_fail("a\na$");
+        middle_nl.should_search_fail("a\nab");
+        middle_nl.should_search_fail("a");
+    }
+    {
+        const test_regex group_middle_nl(&g_regexTester, "\\(a\na\\)$", basic);
+        group_middle_nl.should_search_match("a\na", "a\na");
+        group_middle_nl.should_search_fail("a\na$");
+        group_middle_nl.should_search_fail("a\nab");
+        group_middle_nl.should_search_fail("a");
+    }
+    {
+        const test_regex middle_nl_with_dollar(&g_regexTester, "a$\nb$", basic);
+        middle_nl_with_dollar.should_search_match("a$\nb", "a$\nb");
+        middle_nl_with_dollar.should_search_fail("a\nb");
+        middle_nl_with_dollar.should_search_fail("a$\nb$");
+        middle_nl_with_dollar.should_search_fail("a$\nbc");
+        middle_nl_with_dollar.should_search_fail("a");
+        middle_nl_with_dollar.should_search_fail("b");
+    }
+    {
+        const test_regex group_middle_nl_with_dollar(&g_regexTester, "\\(a$\nb\\)$", basic);
+        group_middle_nl_with_dollar.should_search_match("a$\nb", "a$\nb");
+        group_middle_nl_with_dollar.should_search_fail("a\nb");
+        group_middle_nl_with_dollar.should_search_fail("a$\nb$");
+        group_middle_nl_with_dollar.should_search_fail("a$\nbc");
+        group_middle_nl_with_dollar.should_search_fail("a");
+        group_middle_nl_with_dollar.should_search_fail("b");
+    }
+}
+
+void test_gh_5362_grep() {
+    // test cases specific for grep mode
+    {
+        const test_regex middle_nl(&g_regexTester, "a\na$", grep);
+        middle_nl.should_search_match("a\na$", "a");
+        middle_nl.should_search_match("a\nab", "a");
+        middle_nl.should_search_match("a", "a");
+        middle_nl.should_search_fail("b");
+    }
+    {
+        // This regular expression is not accepted by POSIX grep, but currently the regex parser does not reject it.
+        // If the parser is changed to reject it, adjust this test case.
+        const test_regex group_middle_nl(&g_regexTester, "\\(a\na\\)$", grep);
+        group_middle_nl.should_search_match("a\na", "a\na");
+        group_middle_nl.should_search_fail("a\na$");
+        group_middle_nl.should_search_fail("a\nac");
+        group_middle_nl.should_search_fail("a");
+    }
+    {
+        const test_regex middle_nl_with_dollar(&g_regexTester, "a$\nb$", grep);
+        middle_nl_with_dollar.should_search_match("a$\nb", "b");
+        middle_nl_with_dollar.should_search_match("a\nb", "a");
+        middle_nl_with_dollar.should_search_match("ba", "a");
+        middle_nl_with_dollar.should_search_match("a", "a");
+        middle_nl_with_dollar.should_search_match("b", "b");
+        middle_nl_with_dollar.should_search_match("ab", "b");
+        middle_nl_with_dollar.should_search_fail("a$");
+        middle_nl_with_dollar.should_search_fail("ac");
+        middle_nl_with_dollar.should_search_fail("b$");
+        middle_nl_with_dollar.should_search_fail("bc");
+    }
+    {
+        // This regular expression is not accepted by POSIX grep, but currently the regex parser does not reject it.
+        // If the parser is changed to reject it, adjust this test case.
+        const test_regex group_middle_nl_with_dollar(&g_regexTester, "\\(a$\nb\\)$", grep);
+        group_middle_nl_with_dollar.should_search_match("a$\nb", "a$\nb");
+        group_middle_nl_with_dollar.should_search_fail("a\nb");
+        group_middle_nl_with_dollar.should_search_fail("a$\nb$");
+        group_middle_nl_with_dollar.should_search_fail("a$\nbc");
+        group_middle_nl_with_dollar.should_search_fail("a");
+        group_middle_nl_with_dollar.should_search_fail("b");
+    }
+}
+
+void test_gh_5362() {
+    // GH-5362: `<regex>`: Properly parse dollar anchors in basic and grep mode
+    test_gh_5362_syntax_option(basic);
+    test_gh_5362_syntax_option(grep);
+
+    test_gh_5362_basic();
+    test_gh_5362_grep();
+}
+
 int main() {
     test_dev10_449367_case_insensitivity_should_work();
     test_dev11_462743_regex_collate_should_not_disable_regex_icase();
@@ -1208,6 +1397,7 @@ int main() {
     test_gh_5192();
     test_gh_5214();
     test_gh_5253();
+    test_gh_5362();
 
     return g_regexTester.result();
 }
