--- /dev/null
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+// 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/>.
+
+// PR libstdc++/97613
+// Test year_month_weekday to sys_days conversion for extreme values of index().
+
+#include <chrono>
+
+void
+test01()
+{
+ using namespace std::chrono;
+ using ymd = year_month_day;
+
+ static_assert(ymd{sys_days{2020y/January/Sunday[0]}} == 2019y/December/29);
+ static_assert(ymd{sys_days{2020y/January/Monday[0]}} == 2019y/December/30);
+ static_assert(ymd{sys_days{2020y/January/Tuesday[0]}} == 2019y/December/31);
+ static_assert(ymd{sys_days{2020y/January/Wednesday[0]}} == 2019y/December/25);
+ static_assert(ymd{sys_days{2020y/January/Thursday[0]}} == 2019y/December/26);
+ static_assert(ymd{sys_days{2020y/January/Friday[0]}} == 2019y/December/27);
+ static_assert(ymd{sys_days{2020y/January/Saturday[0]}} == 2019y/December/28);
+
+ static_assert((2020y).is_leap());
+ static_assert(ymd{sys_days{2020y/March/Sunday[0]}} == 2020y/February/23);
+ static_assert(ymd{sys_days{2020y/March/Monday[0]}} == 2020y/February/24);
+ static_assert(ymd{sys_days{2020y/March/Tuesday[0]}} == 2020y/February/25);
+ static_assert(ymd{sys_days{2020y/March/Wednesday[0]}} == 2020y/February/26);
+ static_assert(ymd{sys_days{2020y/March/Thursday[0]}} == 2020y/February/27);
+ static_assert(ymd{sys_days{2020y/March/Friday[0]}} == 2020y/February/28);
+ static_assert(ymd{sys_days{2020y/March/Saturday[0]}} == 2020y/February/29);
+
+ static_assert(!(2019y).is_leap());
+ static_assert(ymd{sys_days{2019y/March/Sunday[0]}} == 2019y/February/24);
+ static_assert(ymd{sys_days{2019y/March/Monday[0]}} == 2019y/February/25);
+ static_assert(ymd{sys_days{2019y/March/Tuesday[0]}} == 2019y/February/26);
+ static_assert(ymd{sys_days{2019y/March/Wednesday[0]}} == 2019y/February/27);
+ static_assert(ymd{sys_days{2019y/March/Thursday[0]}} == 2019y/February/28);
+ static_assert(ymd{sys_days{2019y/March/Friday[0]}} == 2019y/February/22);
+ static_assert(ymd{sys_days{2019y/March/Saturday[0]}} == 2019y/February/23);
+
+ static_assert(ymd{sys_days{2020y/December/Sunday[5]}} == 2021y/January/3);
+ static_assert(ymd{sys_days{2020y/December/Monday[5]}} == 2021y/January/4);
+ static_assert(ymd{sys_days{2020y/December/Tuesday[5]}} == 2020y/December/29);
+ static_assert(ymd{sys_days{2020y/December/Wednesday[5]}} == 2020y/December/30);
+ static_assert(ymd{sys_days{2020y/December/Thursday[5]}} == 2020y/December/31);
+ static_assert(ymd{sys_days{2020y/December/Friday[5]}} == 2021y/January/1);
+ static_assert(ymd{sys_days{2020y/December/Saturday[5]}} == 2021y/January/2);
+}