William Fisher:  A bug in __lookahead::exec causes /(?=^)b/ to match ab. When  makes a recursive call to , it passes true for the value of . This causes a beginning-of-line anchor (^) inside a lookahead assertion to match anywhere in the text.  This fixes http://llvm.org/bugs/show_bug.cgi?id=11118

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@185196 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/regex b/include/regex
index 27c7ecf..75c61db 100644
--- a/include/regex
+++ b/include/regex
@@ -2921,7 +2921,7 @@
     bool __matched = __exp_.__match_at_start_ecma(__s.__current_, __s.__last_,
                                                   __m,
                                                   __s.__flags_ | regex_constants::match_continuous,
-                                                  true);
+                                                  __s.__at_first_ && __s.__current_ == __s.__first_);
     if (__matched != __invert_)
     {
         __s.__do_ = __state::__accept_but_not_consume;