[gcc r9-9386] libstdc++: Implement LWG 561 for std::inserter

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:0022a0364907fbddce38fd7e7c156bf35c83e09e

commit r9-9386-g0022a0364907fbddce38fd7e7c156bf35c83e09e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 27 23:55:48 2020 +0000

    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.
    
    (cherry picked from commit 2203a80a72cb582364245b6997d0724a5f84e062)

Diff:
---
 libstdc++-v3/include/bits/stl_iterator.h           |  9 ++---
 .../24_iterators/insert_iterator/dr561.cc          | 47 ++++++++++++++++++++++
 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 c743215c83e..ee04a4e35c8 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -757,13 +757,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  template parameter deduction, making the compiler match the correct
    *  types for you.
   */
-  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); }
 
   /// @} 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 00000000000..17533990983
--- /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);
+}