[libc++][spaceship] Implement operator<=> for duration

Implements parts of [[ https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1614r2.html | P1614R2 ]]
Implemented `operator<=>` for `std::chrono::duration`

Reviewed By: #libc, Mordante

Differential Revision: https://reviews.llvm.org/D145881

libcxx/docs/Status/SpaceshipProjects.csv

@@ -52,7 +52,7 @@ Section,Description,Dependencies,Assignee,Complete
 | `[range.iota.iterator] <https://wg21.link/range.iota.iterator>`_,| `ranges::iota_view::iterator <https://reviews.llvm.org/D110774>`_,[concepts.cmp],Arthur O'Dwyer,|Complete|
 | `[range.transform.iterator] <https://wg21.link/range.transform.iterator>`_,| `ranges::transform_view::iterator <https://reviews.llvm.org/D110774>`_,[concepts.cmp],Arthur O'Dwyer,|Complete|
 | `[range.elements.iterator] <https://wg21.link/range.elements.iterator>`_,| ranges::elements_view::iterator,[concepts.cmp],Hui Xie,|Complete|
-| `[time.duration.comparisons] <https://wg21.link/time.duration.comparisons>`_, "chrono::duration", None, Mark de Wever, |Not Started|
+| `[time.duration.comparisons] <https://wg21.link/time.duration.comparisons>`_, `chrono::duration <https://reviews.llvm.org/D145881>`_, None, Hristo Hristov, |Complete|
 | `[time.point.comparisons] <https://wg21.link/time.point.comparisons>`_, "chrono::time_point", None, Mark de Wever, |Not Started|
 "| `[time.cal.day.nonmembers] <https://wg21.link/time.cal.day.nonmembers>`_
 | `[time.cal.month.nonmembers] <https://wg21.link/time.cal.month.nonmembers>`_

libcxx/include/__chrono/duration.h

@@ -10,6 +10,8 @@
 #ifndef _LIBCPP___CHRONO_DURATION_H
 #define _LIBCPP___CHRONO_DURATION_H
 
+#include <__compare/ordering.h>
+#include <__compare/three_way_comparable.h>
 #include <__config>
 #include <__type_traits/common_type.h>
 #include <__type_traits/enable_if.h>
@@ -343,6 +345,8 @@ operator==(const duration<_Rep1, _Period1>& __lhs, const duration<_Rep2, _Period
     return __duration_eq<duration<_Rep1, _Period1>, duration<_Rep2, _Period2> >()(__lhs, __rhs);
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 // Duration !=
 
 template <class _Rep1, class _Period1, class _Rep2, class _Period2>
@@ -354,6 +358,8 @@ operator!=(const duration<_Rep1, _Period1>& __lhs, const duration<_Rep2, _Period
     return !(__lhs == __rhs);
 }
 
+#endif // _LIBCPP_STD_VER <= 17
+
 // Duration <
 
 template <class _LhsDuration, class _RhsDuration>
@@ -417,6 +423,20 @@ operator>=(const duration<_Rep1, _Period1>& __lhs, const duration<_Rep2, _Period
     return !(__lhs < __rhs);
 }
 
+#if _LIBCPP_STD_VER >= 20
+
+template<class _Rep1, class _Period1, class _Rep2, class _Period2>
+  requires three_way_comparable<common_type_t<_Rep1, _Rep2>>
+_LIBCPP_HIDE_FROM_ABI
+constexpr auto operator<=>(const duration<_Rep1, _Period1>& __lhs,
+                           const duration<_Rep2, _Period2>& __rhs)
+{
+    using _Ct = common_type_t<duration<_Rep1, _Period1>, duration<_Rep2, _Period2>>;
+    return _Ct(__lhs).count() <=> _Ct(__rhs).count();
+}
+
+#endif // _LIBCPP_STD_VER >= 20
+
 // Duration +
 
 template <class _Rep1, class _Period1, class _Rep2, class _Period2>

libcxx/include/chrono

@@ -182,7 +182,7 @@ template <class Rep1, class Period1, class Rep2, class Period2>
    bool operator==(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
-   bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
+   bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); // removed in C++20
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
    bool operator< (const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
@@ -195,6 +195,10 @@ template <class Rep1, class Period1, class Rep2, class Period2>
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
    bool operator>=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
+template<class Rep1, class Period1, class Rep2, class Period2>
+  requires three_way_comparable<typename CT::rep>
+  constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
+                             const duration<Rep2, Period2>& rhs);                           // since C++20
 
 // duration_cast
 template <class ToDuration, class Rep, class Period>

libcxx/test/std/time/time.duration/time.duration.comparisons/compare.three_way.pass.cpp

@@ -0,0 +1,77 @@
+//===----------------------------------------------------------------------===//
+//
+// 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>
+
+// duration
+
+// template<class Rep1, class Period1, class Rep2, class Period2>
+//     requires ThreeWayComparable<typename CT::rep>
+//   constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
+//                              const duration<Rep2, Period2>& rhs);
+
+#include <cassert>
+#include <chrono>
+#include <ratio>
+
+#include "test_comparisons.h"
+
+constexpr bool test() {
+  {
+    std::chrono::seconds s1(3);
+    std::chrono::seconds s2(3);
+    assert((s1 <=> s2) == std::strong_ordering::equal);
+    assert(testOrder(s1, s2, std::strong_ordering::equal));
+  }
+  {
+    std::chrono::seconds s1(3);
+    std::chrono::seconds s2(4);
+    assert((s1 <=> s2) == std::strong_ordering::less);
+    assert(testOrder(s1, s2, std::strong_ordering::less));
+  }
+  {
+    std::chrono::milliseconds s1(3);
+    std::chrono::microseconds s2(3000);
+    assert((s1 <=> s2) == std::strong_ordering::equal);
+    assert(testOrder(s1, s2, std::strong_ordering::equal));
+  }
+  {
+    std::chrono::milliseconds s1(3);
+    std::chrono::microseconds s2(4000);
+    assert((s1 <=> s2) == std::strong_ordering::less);
+    assert(testOrder(s1, s2, std::strong_ordering::less));
+  }
+  {
+    std::chrono::duration<int, std::ratio<2, 3>> s1(9);
+    std::chrono::duration<int, std::ratio<3, 5>> s2(10);
+    assert((s1 <=> s2) == std::strong_ordering::equal);
+    assert(testOrder(s1, s2, std::strong_ordering::equal));
+  }
+  {
+    std::chrono::duration<int, std::ratio<2, 3>> s1(10);
+    std::chrono::duration<int, std::ratio<3, 5>> s2(9);
+    assert((s1 <=> s2) == std::strong_ordering::greater);
+    assert(testOrder(s1, s2, std::strong_ordering::greater));
+  }
+  {
+    std::chrono::duration<int, std::ratio<2, 3>> s1(9);
+    std::chrono::duration<double, std::ratio<3, 5>> s2(10.1);
+    assert((s1 <=> s2) == std::strong_ordering::less);
+    assert(testOrder(s1, s2, std::strong_ordering::less));
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+  static_assert(test());
+  return 0;
+}