Bill Fisher: This patch fixes a bug where regex_iterator doesn't indicate when it's restarting in the middle of a string. This bug causes /^a/ to match in the middle of the string "aaaaaaa", during iteration.

My patch uses  to communicate when  is false.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@185950 91177308-0d34-0410-b5e6-96231b3b80d8

include/regex

@@ -5773,7 +5773,8 @@ basic_regex<_CharT, _Traits>::__search(
 {
     __m.__init(1 + mark_count(), __first, __last,
                                     __flags & regex_constants::__no_update_pos);
-    if (__match_at_start(__first, __last, __m, __flags, true))
+    if (__match_at_start(__first, __last, __m, __flags, 
+                                    !(__flags & regex_constants::__no_update_pos)))
     {
         __m.__prefix_.second = __m[0].first;
         __m.__prefix_.matched = __m.__prefix_.first != __m.__prefix_.second;

test/re/re.alg/re.alg.search/no_update_pos.pass.cpp

@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <regex>
+
+// template <class BidirectionalIterator, class Allocator, class charT, class traits>
+//     bool
+//     regex_search(BidirectionalIterator first, BidirectionalIterator last,
+//                  match_results<BidirectionalIterator, Allocator>& m,
+//                  const basic_regex<charT, traits>& e,
+//                  regex_constants::match_flag_type flags = regex_constants::match_default);
+
+#include <regex>
+#include <cassert>
+
+int main()
+{
+    // Iterating over /^a/ should yield one instance at the beginning
+    // of the text.
+
+    const char *text = "aaa\naa";
+    std::regex re{"^a"};
+    std::cregex_iterator it{text, text+6, re};
+    std::cregex_iterator end{};
+
+    assert(it->str() == "a");
+    assert(it->position(0) == 0);
+    assert(it->length(0) == 1);
+
+    ++it;
+    assert(it == end);
+}