Fix std::wbuffer_convert::sync()

	* include/bits/locale_conv.h (wbuffer_convert::sync): Fix condition.
	* testsuite/22_locale/conversions/buffer/2.cc: New.

From-SVN: r249255

libstdc++-v3/ChangeLog

 2017-06-16  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/bits/locale_conv.h (wbuffer_convert::sync): Fix condition.
+	* testsuite/22_locale/conversions/buffer/2.cc: New.
+
 	PR libstdc++/81092
 	* acinclude.m4: Bump libtool_VERSION.
 	* config/abi/post/i386-linux-gnu/baseline_symbols.txt: Update.

libstdc++-v3/include/bits/locale_conv.h

@@ -375,7 +375,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
     protected:
       int
       sync()
-      { return _M_buf && _M_conv_put() && _M_buf->pubsync() ? 0 : -1; }
+      { return _M_buf && _M_conv_put() && !_M_buf->pubsync() ? 0 : -1; }
 
       typename _Wide_streambuf::int_type
       overflow(typename _Wide_streambuf::int_type __out)

libstdc++-v3/testsuite/22_locale/conversions/buffer/2.cc

+// Copyright (C) 2017 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 run { target c++11 } }
+
+#include <locale>
+#include <sstream>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  struct Cvt : std::codecvt<char, char, std::mbstate_t> { };
+  std::stringstream ss;
+  std::wbuffer_convert<Cvt, char> cvt(ss.rdbuf());
+  auto p = ss.std::ios::rdbuf(&cvt);
+  ss << "hello";
+  VERIFY( ss.flush().good() );
+  ss.std::ios::rdbuf(p);
+}
+
+int main()
+{
+  test01();
+}