[libcxx-commits] [libcxx] Revert "[libc++] Fix `regex_search` to match `$` alone with `match_default` flag" (PR #78349)

[Sanjay Marreddi via libcxx-commits]

https://github.com/SanjayMarreddi created https://github.com/llvm/llvm-project/pull/78349

The behavior of `std::regex_search` for patterns anchored both to the start and to the end of the input went wrong after merging #77256 . Patterns like `"^b*$"` started matching the strings such as `"a"`, which is not expected. 

Reverts the PR: #77256

>From cf7b32b74031e121c30532777096bafef48134c7 Mon Sep 17 00:00:00 2001
From: SanjayMarreddi <sanjay.mareddi at gmail.com>
Date: Tue, 16 Jan 2024 21:16:30 +0000
Subject: [PATCH] Revert "[libc++] Fix `regex_search` to match `$` alone with
 `match_default` flag"

This reverts commit 8badd8a06d2f92cd46f6333fa4cf4d908a789c21.
---
 libcxx/include/regex                               |  3 ---
 .../re.const/re.matchflag/match_not_eol.pass.cpp   | 14 --------------
 2 files changed, 17 deletions(-)

diff --git a/libcxx/include/regex b/libcxx/include/regex
index 0761d9de54a95c..b575a267583b5f 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -1889,9 +1889,6 @@ void __r_anchor_multiline<_CharT>::__exec(__state& __s) const {
   if (__s.__current_ == __s.__last_ && !(__s.__flags_ & regex_constants::match_not_eol)) {
     __s.__do_   = __state::__accept_but_not_consume;
     __s.__node_ = this->first();
-  } else if (__s.__current_ == __s.__first_ && !(__s.__flags_ & regex_constants::match_not_eol)) {
-    __s.__do_   = __state::__accept_but_not_consume;
-    __s.__node_ = this->first();
   } else if (__multiline_ && std::__is_eol(*__s.__current_)) {
     __s.__do_   = __state::__accept_but_not_consume;
     __s.__node_ = this->first();
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 ce00d6ee79fc85..edeea517d2537a 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
@@ -47,19 +47,5 @@ int main(int, char**)
     assert( std::regex_search(target, re, std::regex_constants::match_not_eol));
     }
 
-    {
-      std::string target = "foo";
-      std::regex re("$");
-      assert(std::regex_search(target, re));
-      assert(!std::regex_search(target, re, std::regex_constants::match_not_eol));
-    }
-
-    {
-      std::string target = "foo";
-      std::regex re("$");
-      assert(!std::regex_match(target, re));
-      assert(!std::regex_match(target, re, std::regex_constants::match_not_eol));
-    }
-
   return 0;
 }