[libcxx-commits] [libcxx] [libc++] Fix `regex_search` to match `$` alone with `match_default` flag (PR #78845)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Sanjay Marreddi (SanjayMarreddi)

<details>
<summary>Changes</summary>

Using `regex_search` with the regex_constant `match_default` and a simple regex pattern `$` is expected to match general strings such as _"a", "ab", "abc"..._ at `[last, last)` positions.  But, the current implementation fails to do so.

Fixes #<!-- -->75042


---
Full diff: https://github.com/llvm/llvm-project/pull/78845.diff


2 Files Affected:

- (modified) libcxx/include/regex (+8) 
- (modified) libcxx/test/std/re/re.const/re.matchflag/match_not_eol.pass.cpp (+28) 


``````````diff
diff --git a/libcxx/include/regex b/libcxx/include/regex
index b575a267583b5f..48af5b8b57fd64 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -5124,6 +5124,14 @@ bool basic_regex<_CharT, _Traits>::__search(
       }
       __m.__matches_.assign(__m.size(), __m.__unmatched_);
     }
+    __m.__matches_.assign(__m.size(), __m.__unmatched_);
+    if (__match_at_start(__first, __last, __m, __flags, false)) {
+      __m.__prefix_.second  = __m[0].first;
+      __m.__prefix_.matched = __m.__prefix_.first != __m.__prefix_.second;
+      __m.__suffix_.first   = __m[0].second;
+      __m.__suffix_.matched = __m.__suffix_.first != __m.__suffix_.second;
+      return true;
+    }
   }
   __m.__matches_.clear();
   return false;
diff --git a/libcxx/test/std/re/re.const/re.matchflag/match_not_eol.pass.cpp b/libcxx/test/std/re/re.const/re.matchflag/match_not_eol.pass.cpp
index edeea517d2537a..a696d815dda5a8 100644
--- a/libcxx/test/std/re/re.const/re.matchflag/match_not_eol.pass.cpp
+++ b/libcxx/test/std/re/re.const/re.matchflag/match_not_eol.pass.cpp
@@ -47,5 +47,33 @@ int main(int, char**)
     assert( std::regex_search(target, re, std::regex_constants::match_not_eol));
     }
 
+    {
+      std::string target = "foo";
+      std::regex re("$");
+      assert(std::regex_search(target, re));
+      assert(!std::regex_search(target, re, std::regex_constants::match_not_eol));
+
+      std::smatch match;
+      assert(std::regex_search(target, match, re));
+      assert(match.position(0) == 3);
+      assert(match.length(0) == 0);
+      assert(!std::regex_search(target, match, re, std::regex_constants::match_not_eol));
+      assert(match.length(0) == 0);
+    }
+
+    {
+      std::string target = "foo";
+      std::regex re("$");
+      assert(!std::regex_match(target, re));
+      assert(!std::regex_match(target, re, std::regex_constants::match_not_eol));
+    }
+
+    {
+      std::string target = "a";
+      std::regex re{"^b*$"};
+      assert(!std::regex_search(target, re));
+      assert(!std::regex_search(target, re, std::regex_constants::match_not_eol));
+    }
+
   return 0;
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/78845