libstdc++: Implement LWG 561 for std::inserter

libstdc++-v3/ChangeLog:

	* include/bits/stl_iterator.h (inserter): Do not deduce
	iterator type (LWG 561).
	* testsuite/24_iterators/insert_iterator/dr561.cc: New test.

2 files changed, 50 insertions, 6 deletions

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 08e25d8..f0cf4c5 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -931,13 +931,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inserter(_Container& __x, std::__detail::__range_iter_t<_Container> __i)
     { return insert_iterator<_Container>(__x, __i); }
 #else
-  template<typename _Container, typename _Iterator>
+  template<typename _Container>
     inline insert_iterator<_Container>
-    inserter(_Container& __x, _Iterator __i)
-    {
-      return insert_iterator<_Container>(__x,
-					 typename _Container::iterator(__i));
-    }
+    inserter(_Container& __x, typename _Container::iterator __i)
+    { return insert_iterator<_Container>(__x, __i); }
 #endif
 
   // @} group iterators
diff --git a/libstdc++-v3/testsuite/24_iterators/insert_iterator/dr561.cc b/libstdc++-v3/testsuite/24_iterators/insert_iterator/dr561.cc
new file mode 100644
index 0000000..1753399
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/insert_iterator/dr561.cc
@@ -0,0 +1,47 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+// Example from https://wg21.link/lwg561
+
+#include <iterator>
+#include <string>
+
+namespace my
+{
+
+template <class String>
+struct my_type {};
+
+struct my_container
+{
+template <class String>
+void push_back(const my_type<String>&);
+};
+
+template <class String>
+void inserter(const my_type<String>& m, my_container& c) {c.push_back(m);}
+
+}  // my
+
+int main()
+{
+    my::my_container c;
+    my::my_type<std::string> m;
+    inserter(m, c);
+}