LWG 3050 Fix cv-qualification of convertibility constraints

Backport from mainline
2018-06-18  Jonathan Wakely  <jwakely@redhat.com>

	* include/std/chrono (duration, operator*, operator/, operator%): Use
	const-qualified type as source type in is_convertible constraints.
	* testsuite/20_util/duration/arithmetic/dr3050.cc: New.
	* testsuite/20_util/duration/cons/dr3050.cc: New.
	* testsuite/20_util/duration/literals/range.cc: Rename to...
	* testsuite/20_util/duration/literals/range_neg.cc: Here. Adjust
	dg-error lineno.

git-svn-id: https://gcc.gnu.org/svn/gcc/branches/gcc-7-branch@262412 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 45 insertions, 3 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 772c62fce40..c0b4c5fccba 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,6 +1,18 @@
 2018-07-04  Jonathan Wakely  <jwakely@redhat.com>
 
 	Backport from mainline
+	2018-06-18  Jonathan Wakely  <jwakely@redhat.com>
+
+	LWG 3050 Fix cv-qualification of convertibility constraints
+	* include/std/chrono (duration, operator*, operator/, operator%): Use
+	const-qualified type as source type in is_convertible constraints.
+	* testsuite/20_util/duration/arithmetic/dr3050.cc: New.
+	* testsuite/20_util/duration/cons/dr3050.cc: New.
+	* testsuite/20_util/duration/literals/range.cc: Rename to...
+	* testsuite/20_util/duration/literals/range_neg.cc: Here. Adjust
+	dg-error lineno.
+
+	Backport from mainline
 	2018-06-13  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/86127
diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index 5d0151857e7..2138ff027e4 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -318,8 +318,10 @@ _GLIBCXX_END_NAMESPACE_VERSION
 	// constexpr copy constructor will be ill-formed.
 	duration(const duration&) = default;
 
+	// _GLIBCXX_RESOLVE_LIB_DEFECTS
+	// 3050. Conversion specification problem in chrono::duration
 	template<typename _Rep2, typename = typename
-	       enable_if<is_convertible<_Rep2, rep>::value
+	       enable_if<is_convertible<const _Rep2&, rep>::value
 			 && (treat_as_floating_point<rep>::value
 			     || !treat_as_floating_point<_Rep2>::value)>::type>
 	  constexpr explicit duration(const _Rep2& __rep)
@@ -463,8 +465,12 @@ _GLIBCXX_END_NAMESPACE_VERSION
 	return __cd(__cd(__lhs).count() - __cd(__rhs).count());
       }
 
+    // SFINAE helper to obtain common_type<_Rep1, _Rep2> only if _Rep2
+    // is implicitly convertible to it.
+    // _GLIBCXX_RESOLVE_LIB_DEFECTS
+    // 3050. Conversion specification problem in chrono::duration constructor
     template<typename _Rep1, typename _Rep2, bool =
-	     is_convertible<_Rep2,
+	     is_convertible<const _Rep2&,
 			    typename common_type<_Rep1, _Rep2>::type>::value>
       struct __common_rep_type { };
 
diff --git a/libstdc++-v3/testsuite/20_util/duration/cons/dr3050.cc b/libstdc++-v3/testsuite/20_util/duration/cons/dr3050.cc
new file mode 100644
index 00000000000..a4f57a38c30
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/duration/cons/dr3050.cc
@@ -0,0 +1,24 @@
+// Copyright (C) 2018 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 } }
+
+#include <chrono>
+
+struct X { operator int64_t() /* not const */; };
+static_assert(!std::is_constructible<std::chrono::seconds, X>::value,
+	      "LWG 3050");
diff --git a/libstdc++-v3/testsuite/20_util/duration/literals/range.cc b/libstdc++-v3/testsuite/20_util/duration/literals/range_neg.cc
index 531b53c42ec..bccff767ef7 100644
--- a/libstdc++-v3/testsuite/20_util/duration/literals/range.cc
+++ b/libstdc++-v3/testsuite/20_util/duration/literals/range_neg.cc
@@ -26,6 +26,6 @@ test01()
 
   // std::numeric_limits<int64_t>::max() == 9223372036854775807;
   auto h = 9223372036854775808h;
-  // { dg-error "cannot be represented" "" { target *-*-* } 893 }
+  // { dg-error "cannot be represented" "" { target *-*-* } 899 }
 }
 // { dg-prune-output "in constexpr expansion" } // needed for -O0