libstdc++: LWG 3313 join_view::iterator::operator-- is incorrectly constrained

libstdc++-v3/ChangeLog:

	LWG 3313 join_view::_Iterator::operator-- is incorrectly constrained
	* include/std/ranges (join_view::_Iterator::operator--): Require that
	range_reference_t<_Base> models common_range.
	* testsuite/std/ranges/adaptors/lwg3313_neg.cc: New test.

libstdc++-v3/ChangeLog

 2020-02-25  Patrick Palka  <ppalka@redhat.com>
 
+	LWG 3313 join_view::_Iterator::operator-- is incorrectly constrained
+	* include/std/ranges (join_view::_Iterator::operator--): Require that
+	range_reference_t<_Base> models common_range.
+	* testsuite/std/ranges/adaptors/lwg3313_neg.cc: New test.
+
 	LWG 3301 transform_view::_Iterator has incorrect iterator_category
 	* include/std/ranges (transform_view::_Iterator::_S_iter_cat): Adjust
 	determination of iterator_category as per LWG 3301.

libstdc++-v3/include/std/ranges

@@ -2399,6 +2399,7 @@ namespace views
 	  operator--()
 	    requires _S_ref_is_glvalue && bidirectional_range<_Base>
 	      && bidirectional_range<range_reference_t<_Base>>
+	      && common_range<range_reference_t<_Base>>
 	  {
 	    if (_M_outer == ranges::end(_M_parent->_M_base))
 	      _M_inner = ranges::end(*--_M_outer);
@@ -2412,6 +2413,7 @@ namespace views
 	  operator--(int)
 	    requires _S_ref_is_glvalue && bidirectional_range<_Base>
 	      && bidirectional_range<range_reference_t<_Base>>
+	      && common_range<range_reference_t<_Base>>
 	  {
 	    auto __tmp = *this;
 	    --*this;

libstdc++-v3/testsuite/std/ranges/adaptors/lwg3313_neg.cc

+// 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-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <array>
+#include <iterator>
+#include <ranges>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+void
+test01()
+{
+  int x[] = {1};
+  auto rx = ranges::subrange{std::counted_iterator(x,1), std::default_sentinel};
+  std::array<decltype(rx), 5> y = {rx, rx, rx, rx, rx,};
+  auto v = y | views::join;
+  auto i = v.begin();
+  ++i;
+  ++i;
+  --i; // { dg-error "no match" }
+  i--; // { dg-error "" }
+}