[libc++] [P1614] Implement std::compare_three_way_result.

Differential Revision: https://reviews.llvm.org/D103581

libcxx/include/CMakeLists.txt

@@ -98,6 +98,7 @@ set(files
   __bsd_locale_defaults.h
   __bsd_locale_fallbacks.h
   __compare/common_comparison_category.h
+  __compare/compare_three_way_result.h
   __compare/ordering.h
   __concepts/arithmetic.h
   __concepts/assignable.h

libcxx/include/__compare/compare_three_way_result.h

@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
+#define _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
+
+#include <__config>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+template<class, class, class>
+struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result { };
+
+template<class _Tp, class _Up>
+struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result<_Tp, _Up, decltype(
+  declval<__make_const_lvalue_ref<_Tp>>() <=> declval<__make_const_lvalue_ref<_Up>>(), void()
+)> {
+    using type = decltype(declval<__make_const_lvalue_ref<_Tp>>() <=> declval<__make_const_lvalue_ref<_Up>>());
+};
+
+template<class _Tp, class _Up = _Tp>
+struct _LIBCPP_TEMPLATE_VIS compare_three_way_result : __compare_three_way_result<_Tp, _Up, void> { };
+
+template<class _Tp, class _Up = _Tp>
+using compare_three_way_result_t = typename compare_three_way_result<_Tp, _Up>::type;
+
+#endif // _LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H

libcxx/include/compare

@@ -35,6 +35,12 @@ namespace std {
   template<class... Ts>
     using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
 
+  // [cmp.result], result of three-way comparison
+  template<class T, class U = T> struct compare_three_way_result;
+
+  template<class T, class U = T>
+    using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
+
   // [cmp.alg], comparison algorithms
   template<class T> constexpr strong_ordering strong_order(const T& a, const T& b);
   template<class T> constexpr weak_ordering weak_order(const T& a, const T& b);
@@ -121,6 +127,7 @@ namespace std {
 */
 
 #include <__compare/common_comparison_category.h>
+#include <__compare/compare_three_way_result.h>
 #include <__compare/ordering.h>
 #include <__config>
 #include <type_traits>

libcxx/include/module.modulemap

@@ -361,6 +361,7 @@ module std [system] {
 
     module __compare {
       module common_comparison_category { private header "__compare/common_comparison_category.h" }
+      module compare_three_way_result   { private header "__compare/compare_three_way_result.h"   }
       module ordering                   { private header "__compare/ordering.h"                   }
     }
   }

libcxx/test/libcxx/diagnostics/detail.headers/compare/compare_three_way_result.module.verify.cpp

@@ -0,0 +1,16 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__compare/compare_three_way_result.h'}}
+#include <__compare/compare_three_way_result.h>

libcxx/test/std/language.support/cmp/cmp.result/compare_three_way_result.compile.pass.cpp

@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// UNSUPPORTED: libcpp-no-concepts
+
+// <compare>
+
+// template<class T, class U = T> struct compare_three_way_result;
+// template<class T, class U = T>
+//   using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;
+
+#include <compare>
+
+#include "test_macros.h"
+
+template<class T>
+concept has_no_nested_type = !requires { typename T::type; };
+
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<int>, std::strong_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<float>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<unsigned>, std::strong_ordering);
+
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<int, int>, std::strong_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<int, float>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<float, int>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<float, float>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<float, unsigned>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<unsigned, float>, std::partial_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<unsigned, unsigned>, std::strong_ordering);
+
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const int&>, std::strong_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const int&, int>, std::strong_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const int*>, std::strong_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const int*, int*>, std::strong_ordering);
+
+static_assert(has_no_nested_type<std::compare_three_way_result<void>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<void, void>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<int, void>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<int, int*>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<int, unsigned>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<unsigned, int>>);
+
+struct A {
+    float operator<=>(const A&) const;  // a non-comparison-category type is OK
+};
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<A>, float);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<A, A>, float);
+
+struct B {
+    using T = int(&)();
+    T operator<=>(const B&) const;  // no decay takes place either
+};
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<B>, int(&)());
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<B, B>, int(&)());
+
+struct C {
+    std::strong_ordering operator<=>(C&);  // C isn't const-comparable
+};
+static_assert(has_no_nested_type<std::compare_three_way_result<C>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<C&>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<C&&>>);
+
+static_assert(has_no_nested_type<std::compare_three_way_result<C, C>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<C&, C&>>);
+static_assert(has_no_nested_type<std::compare_three_way_result<C&&, C&&>>);
+
+struct D {
+    std::strong_ordering operator<=>(D&) &;
+    std::strong_ordering operator<=>(D&&) &&;
+    std::weak_ordering operator<=>(const D&) const&;  // comparison is always done by const&
+    std::strong_ordering operator<=>(const D&&) const&&;
+};
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D&&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const D&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const D&&>, std::weak_ordering);
+
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D, D>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D&, D&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<D&&, D&&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const D&, const D&>, std::weak_ordering);
+ASSERT_SAME_TYPE(std::compare_three_way_result_t<const D&&, const D&&>, std::weak_ordering);