[libc++] Add missing C++20 [time.point.arithmetic]

[maflcko]

This was part of https://wg21.link/p0355r7, but apparently never implemented.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: None (maflcko)

Changes

This was part of https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0355r7.html, but apparently never implemented.

---

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

6 Files Affected:

• (modified) libcxx/include/__chrono/time_point.h (+13)
• (modified) libcxx/include/chrono (+5)
• (added) libcxx/test/std/time/time.point/time.point.arithmetic/op_++.pass.cpp (+39)
• (added) libcxx/test/std/time/time.point/time.point.arithmetic/op_++int.pass.cpp (+40)
• (added) libcxx/test/std/time/time.point/time.point.arithmetic/op_--.pass.cpp (+39)
• (added) libcxx/test/std/time/time.point/time.point.arithmetic/op_--int.pass.cpp (+40)

diff --git a/libcxx/include/__chrono/time_point.h b/libcxx/include/__chrono/time_point.h
index 6b866b882f89a..36be0759b6b8c 100644
--- a/libcxx/include/__chrono/time_point.h
+++ b/libcxx/include/__chrono/time_point.h
@@ -58,6 +58,19 @@ class time_point {
 
   // arithmetic
 
+#if _LIBCPP_STD_VER >= 20
+  _LIBCPP_HIDE_FROM_ABI constexpr time_point& operator++() {
+    ++__d_;
+    return *this;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr time_point operator++(int) { return time_point(__d_++); }
+  _LIBCPP_HIDE_FROM_ABI constexpr time_point& operator--() {
+    --__d_;
+    return *this;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr time_point operator--(int) { return time_point(__d_--); }
+#endif // _LIBCPP_STD_VER >= 20
+
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 time_point& operator+=(const duration& __d) {
     __d_ += __d;
     return *this;
diff --git a/libcxx/include/chrono b/libcxx/include/chrono
index cd9b98872083e..82e99a31bcc9f 100644
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -132,6 +132,11 @@ public:
 
     // arithmetic
 
+    constexpr time_point& operator++();    // C++20
+    constexpr time_point  operator++(int); // C++20
+    constexpr time_point& operator--();    // C++20
+    constexpr time_point  operator--(int); // C++20
+
     time_point& operator+=(const duration& d); // constexpr in C++17
     time_point& operator-=(const duration& d); // constexpr in C++17
 
diff --git a/libcxx/test/std/time/time.point/time.point.arithmetic/op_++.pass.cpp b/libcxx/test/std/time/time.point/time.point.arithmetic/op_++.pass.cpp
new file mode 100644
index 0000000000000..dad50d09ed8b0
--- /dev/null
+++ b/libcxx/test/std/time/time.point/time.point.arithmetic/op_++.pass.cpp
@@ -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());
+
+  return 0;
+}
diff --git a/libcxx/test/std/time/time.point/time.point.arithmetic/op_++int.pass.cpp b/libcxx/test/std/time/time.point/time.point.arithmetic/op_++int.pass.cpp
new file mode 100644
index 0000000000000..c517ff9516bdc
--- /dev/null
+++ b/libcxx/test/std/time/time.point/time.point.arithmetic/op_++int.pass.cpp
@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++(int);
+
+#include <chrono>
+#include <cassert>
+
+#include "test_macros.h"
+
+constexpr bool test_constexpr() {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t1(Duration(3));
+  std::chrono::time_point<Clock, Duration> t2 = t1++;
+  return t1.time_since_epoch() == Duration(4) && t2.time_since_epoch() == Duration(3);
+}
+
+int main(int, char**) {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t1(Duration(3));
+  std::chrono::time_point<Clock, Duration> t2 = t1++;
+  assert(t1.time_since_epoch() == Duration(4));
+  assert(t2.time_since_epoch() == Duration(3));
+
+  static_assert(test_constexpr());
+
+  return 0;
+}
diff --git a/libcxx/test/std/time/time.point/time.point.arithmetic/op_--.pass.cpp b/libcxx/test/std/time/time.point/time.point.arithmetic/op_--.pass.cpp
new file mode 100644
index 0000000000000..7b55f747d06c7
--- /dev/null
+++ b/libcxx/test/std/time/time.point/time.point.arithmetic/op_--.pass.cpp
@@ -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(4);
+}
+
+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(2));
+
+  static_assert(constexpr_test());
+
+  return 0;
+}
diff --git a/libcxx/test/std/time/time.point/time.point.arithmetic/op_--int.pass.cpp b/libcxx/test/std/time/time.point/time.point.arithmetic/op_--int.pass.cpp
new file mode 100644
index 0000000000000..6dfa03c154f57
--- /dev/null
+++ b/libcxx/test/std/time/time.point/time.point.arithmetic/op_--int.pass.cpp
@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// 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--(int);
+
+#include <chrono>
+#include <cassert>
+
+#include "test_macros.h"
+
+constexpr bool test_constexpr() {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t1(Duration(3));
+  std::chrono::time_point<Clock, Duration> t2 = t1--;
+  return t1.time_since_epoch() == Duration(2) && t2.time_since_epoch() == Duration(3);
+}
+
+int main(int, char**) {
+  typedef std::chrono::system_clock Clock;
+  typedef std::chrono::milliseconds Duration;
+  std::chrono::time_point<Clock, Duration> t1(Duration(3));
+  std::chrono::time_point<Clock, Duration> t2 = t1--;
+  assert(t1.time_since_epoch() == Duration(2));
+  assert(t2.time_since_epoch() == Duration(3));
+
+  static_assert(test_constexpr());
+
+  return 0;
+}

[maflcko]

Further references:

• P0355R7: Extending chrono to Calendars and Time Zones #99982
• https://eel.is/c++draft/time.point#arithmetic
• https://en.cppreference.com/w/cpp/chrono/time_point/operator_inc_dec.html
• https://godbolt.org/z/KzYvxKf9o

[Zingam]

LGTM with the remaining comments, which I think should be addressed.

[Zingam]

LGTM. Thank you.
Let's wait for a library maintainer to approve (and merge) the PR.