From: Patrick Palka <ppalka@redhat.com>
Date: Mon, 12 Oct 2020 17:46:24 +0000 (-0400)
Subject: libstdc++: Apply proposed resolution for LWG 3450
X-Git-Tag: releases/gcc-10.3.0~734
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d445a86968459e837a3653f8d81bc03f1f3e2e15;p=thirdparty%2Fgcc.git

libstdc++: Apply proposed resolution for LWG 3450

libstdc++-v3/ChangeLog:

	* include/std/ranges (take_while_view::begin): Constrain the
	const overload further as per LWG 3450.
	(take_while_view::end): Likewise.
	* testsuite/std/ranges/adaptors/take_while.cc: Add test for LWG
	3450.

(cherry picked from commit c5aad5a41838dbfd29ff114692ff9533b52746b4)
---

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 98aa0d6a7c86..23f7d9e32b1f 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2202,6 +2202,7 @@ namespace views
 
       constexpr auto
       begin() const requires range<const _Vp>
+	&& indirect_unary_predicate<const _Pred, iterator_t<const _Vp>>
       { return ranges::begin(_M_base); }
 
       constexpr auto
@@ -2211,6 +2212,7 @@ namespace views
 
       constexpr auto
       end() const requires range<const _Vp>
+	&& indirect_unary_predicate<const _Pred, iterator_t<const _Vp>>
       { return _Sentinel<true>(ranges::end(_M_base),
 			       std::__addressof(*_M_pred)); }
     };
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/take_while.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/take_while.cc
index d587127b97eb..48771397f1d8 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/take_while.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/take_while.cc
@@ -70,10 +70,20 @@ test03()
   b = ranges::end(v);
 }
 
+void
+test04()
+{
+  // LWG 3450
+  auto v = views::single(1) | views::take_while([](int& x) { return true;});
+  static_assert(ranges::range<decltype(v)>);
+  static_assert(!ranges::range<decltype(v) const>);
+}
+
 int
 main()
 {
   test01();
   test02();
   test03();
+  test04();
 }