PR libstdc++/81468 constrain std::chrono::time_point constructor

PR libstdc++/81468
	* include/std/chrono (time_point(const time_point<_Dur2>&)): Add
	missing constraint from LWG DR 1177.
	* testsuite/20_util/duration/cons/dr1177.cc: New.
	* testsuite/20_util/time_point/cons/81468.cc: New.
	* testsuite/20_util/duration/literals/range.cc: Update dg-error line.

From-SVN: r252090

libstdc++-v3/ChangeLog

@@ -1,5 +1,12 @@
 2017-09-13  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/81468
+	* include/std/chrono (time_point(const time_point<_Dur2>&)): Add
+	missing constraint from LWG DR 1177.
+	* testsuite/20_util/duration/cons/dr1177.cc: New.
+	* testsuite/20_util/time_point/cons/81468.cc: New.
+	* testsuite/20_util/duration/literals/range.cc: Update dg-error line.
+
 	* doc/doxygen/mainpage.html: Fix broken URLs.
 
 	PR libstdc++/81835

libstdc++-v3/include/std/chrono

@@ -622,7 +622,8 @@ _GLIBCXX_END_NAMESPACE_VERSION
 	{ }
 
 	// conversions
-	template<typename _Dur2>
+	template<typename _Dur2,
+		 typename = _Require<is_convertible<_Dur2, _Dur>>>
 	  constexpr time_point(const time_point<clock, _Dur2>& __t)
 	  : __d(__t.time_since_epoch())
 	  { }

libstdc++-v3/testsuite/20_util/duration/cons/dr1177.cc

@@ -0,0 +1,41 @@
+// Copyright (C) 2017 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>
+#include <type_traits>
+
+using namespace std;
+using namespace std::chrono;
+
+// DR 1177
+static_assert(is_constructible<duration<float>, duration<double>>{},
+    "can convert duration with one floating point rep to another");
+static_assert(is_constructible<duration<float>, duration<int>>{},
+    "can convert duration with integral rep to one with floating point rep");
+static_assert(!is_constructible<duration<int>, duration<float>>{},
+    "cannot convert duration with floating point rep to one with integral rep");
+static_assert(is_constructible<duration<int>, duration<long>>{},
+    "can convert duration with one integral rep to another");
+
+static_assert(!is_constructible<duration<int>, duration<int, ratio<2,3>>>{},
+    "cannot convert duration to one with different period");
+static_assert(is_constructible<duration<float>, duration<int, ratio<2,3>>>{},
+    "unless it has a floating-point representation");
+static_assert(is_constructible<duration<float>, duration<int, ratio<1,3>>>{},
+    "or a period that is an integral multiple of the original");

libstdc++-v3/testsuite/20_util/duration/literals/range.cc

@@ -26,6 +26,6 @@ test01()
 
   // std::numeric_limits<int64_t>::max() == 9223372036854775807;
   auto h = 9223372036854775808h;
-  // { dg-error "cannot be represented" "" { target *-*-* } 892 }
+  // { dg-error "cannot be represented" "" { target *-*-* } 893 }
 }
 // { dg-prune-output "in constexpr expansion" } // needed for -O0

libstdc++-v3/testsuite/20_util/time_point/cons/81468.cc

@@ -0,0 +1,34 @@
+// Copyright (C) 2017 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>
+#include <type_traits>
+
+using namespace std;
+using namespace std::chrono;
+
+template <class Duration>
+    using sys_time = time_point<system_clock, Duration>;
+
+static_assert(is_constructible<sys_time<milliseconds>, sys_time<seconds>>{},
+    "Can construct time_point from one with lower precision duration");
+
+// PR libstdc++/81468 - DR 1177
+static_assert(!is_constructible<sys_time<seconds>, sys_time<milliseconds>>{},
+    "Cannot construct time_point from one with higher precision duration");