From 7f0f108309a881fe9e84a9c0b9a6f13b24a7886e Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Mon, 24 Feb 2020 17:01:29 -0500
Subject: [PATCH] libstdc++: LWG 3292 iota_view is under-constrained

libstdc++-v3/ChangeLog:

	LWG 3292 iota_view is under-constrained
	* include/std/ranges (iota_view): Require that _Winc models semiregular
	  as per LWG 3292.
	* testsuite/std/ranges/iota/lwg3292_neg.cc: New test.
---
 libstdc++-v3/ChangeLog                        |  7 ++++
 libstdc++-v3/include/std/ranges               |  1 +
 .../testsuite/std/ranges/iota/lwg3292_neg.cc  | 40 +++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/iota/lwg3292_neg.cc

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 2adf9cba26f..046d50de6d1 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2020-02-25  Patrick Palka  <ppalka@redhat.com>
+
+	LWG 3292 iota_view is under-constrained
+	* include/std/ranges (iota_view): Require that _Winc models semiregular
+	  as per LWG 3292.
+	* testsuite/std/ranges/iota/lwg3292_neg.cc: New test.
+
 2020-02-25  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/ranges_algobase.h (__copy_or_move): Do not use memmove
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 0b2057c9661..ab8fbaca38f 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -615,6 +615,7 @@ namespace ranges
   template<weakly_incrementable _Winc,
 	   semiregular _Bound = unreachable_sentinel_t>
     requires std::__detail::__weakly_eq_cmp_with<_Winc, _Bound>
+      && semiregular<_Winc>
     class iota_view : public view_interface<iota_view<_Winc, _Bound>>
     {
     private:
diff --git a/libstdc++-v3/testsuite/std/ranges/iota/lwg3292_neg.cc b/libstdc++-v3/testsuite/std/ranges/iota/lwg3292_neg.cc
new file mode 100644
index 00000000000..80c392729b3
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/iota/lwg3292_neg.cc
@@ -0,0 +1,40 @@
+// 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 <sstream>
+#include <ranges>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+void
+test01()
+{
+  std::istringstream s("1 2 3 4 5");
+  auto v = ranges::istream_view<int>(s);
+  auto i = v.begin();
+  static_assert(!std::semiregular<decltype(i)>);
+  auto o = views::iota(std::move(i));
+  static_assert(false); // { dg-error "" }
+}
+
+// { dg-prune-output "no match" }
+// { dg-prune-output "deduction failed" }
+// { dg-prune-output "constraint failure" }
-- 
2.30.2