[PATCH] LWG 3050 Fix cv-qualification of convertibility constraints

[Jonathan Wakely]

This issue hasn't been voted into the working draft yet, but it's been
approved by LWG and is obviously correct.

	* 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.

Tested powerpc64le-linux, committed to trunk.


-------------- next part --------------
commit c34782c185f06d10d64625e64ea70dd9819de10c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jun 18 17:56:11 2018 +0100

    LWG 3050 Fix cv-qualification of convertibility constraints
    
            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.

diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index b3a0cb2087d..d6d9dcae411 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -325,8 +325,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	duration(const duration&) = default;
 
+	// _GLIBCXX_RESOLVE_LIB_DEFECTS
+	// 3050. Conversion specification problem in chrono::duration
 	template<typename _Rep2, typename = _Require<
-		 is_convertible<_Rep2, rep>,
+		 is_convertible<const _Rep2&, rep>,
 		 __or_<__is_float<rep>, __not_<__is_float<_Rep2>>>>>
 	  constexpr explicit duration(const _Rep2& __rep)
 	  : __r(static_cast<rep>(__rep)) { }
@@ -471,10 +473,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     // 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,
 	     typename _CRep = typename common_type<_Rep1, _Rep2>::type>
-      using __common_rep_t
-	= typename enable_if<is_convertible<_Rep2, _CRep>::value, _CRep>::type;
+      using __common_rep_t = typename
+	enable_if<is_convertible<const _Rep2&, _CRep>::value, _CRep>::type;
 
     template<typename _Rep1, typename _Period, typename _Rep2>
       constexpr duration<__common_rep_t<_Rep1, _Rep2>, _Period>
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
similarity index 94%
rename from libstdc++-v3/testsuite/20_util/duration/literals/range.cc
rename to libstdc++-v3/testsuite/20_util/duration/literals/range_neg.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 *-*-* } 894 }
+  // { dg-error "cannot be represented" "" { target *-*-* } 898 }
 }
 // { dg-prune-output "in constexpr expansion" } // needed for -O0