[libcxx-commits] [libcxx] [libc++] Add missing C++20 [time.point.arithmetic] (PR #143165)

[Hristo Hristov via libcxx-commits]

================
@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <chrono>
+
+// time_point
+
+// constexpr time_point& operator++();
+
+#include <chrono>
+#include <cassert>
+
+#include "test_macros.h"
+
+constexpr bool constexpr_test() {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t(Duration(5));
+  return (++t).time_since_epoch() == Duration(6);
+}
+
+int main(int, char**) {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t(Duration(3));
+  std::chrono::time_point<Clock, Duration>& tref = ++t;
+  assert(&tref == &t);
+  assert(t.time_since_epoch() == Duration(4));
+
+  static_assert(constexpr_test());
----------------
Zingam wrote:

```suggestion
  test();
  static_assert(test());
```

This is the common pattern used to use a single constexpr function to test the non-constexpr and constexpr cases.

https://github.com/llvm/llvm-project/pull/143165