[libc++] Implement `operator<=>` for `error_{code,condition}`

[avogelsgesang]

Summary

Implements part of P1614R2 "The Mothership has Landed"

[avogelsgesang]

Update review link and fix synopsis in test files

[Mordante]

LGTM module some nits.

libcxx/include/system_error

457

461

Please format the new code so return is placed properly.

[avogelsgesang]

address comments. waiting for CI before landing this

libcxx/docs/Status/SpaceshipProjects.csv

 | `weak_order_fallback <https://reviews.llvm.org/D111514>`_
 | `partial_order_fallback <https://reviews.llvm.org/D111514>`_",None,Arthur O'Dwyer,|Complete| [#note-strongorder]_
 | `[alg.three.way] <https://wg21.link/alg.three.way>`_,| `lexicographical_compare_three_way <https://reviews.llvm.org/D80902>`_,[comparisons.three.way],Christopher Di Bella,|In Progress|
 | `[type.info] <https://wg21.link/type.info>`_,| `typeinfo <https://reviews.llvm.org/D130853>`_,None,Adrian Vogelsgesang,|Complete|
 | `[coroutine.handle.compare] <https://wg21.link/coroutine.handle.compare>`_,| `coroutine_handle <https://reviews.llvm.org/D109433>`_,[comparisons.three.way],Chuanqi Xu,|Complete|
 | `[pairs.spec] <https://wg21.link/pairs.spec>`_,| `pair <https://reviews.llvm.org/D107721>`_,[expos.only.func],Kent Ross,|Complete|
 | `[syserr.errcat.nonvirtuals] <https://wg21.link/syserr.errcat.nonvirtuals>`_,| `error_category <https://reviews.llvm.org/D131363>`_,[comparisons.three.way],Adrian Vogelsgesang,|Complete|
 | `[syserr.compare] <https://wg21.link/syserr.compare>`_,"| `error_code <https://reviews.llvm.org/D131371>`_
-| `error_condition <https://reviews.llvm.org/D131371>`_",None,Adrian Vogelsgesang,|In Progress|
+| `error_condition <https://reviews.llvm.org/D131371>`_",None,Adrian Vogelsgesang,|Complete|
 | `[tuple.rel] <https://wg21.link/tuple.rel>`_,| `tuple <https://reviews.llvm.org/D108250>`_,[expos.only.func],Kent Ross,|Complete|
 "| `[optional.relops] <https://wg21.link/optional.relops>`_
 | `[optional.nullops] <https://wg21.link/optional.nullops>`_
 | `[optional.comp.with.t] <https://wg21.link/optional.comp.with.t>`_","| optional
 | nullopt",None,Kent Ross,|In Progress|
 "| `[variant.relops] <https://wg21.link/variant.relops>`_
 | `[variant.monostate.relops] <https://wg21.link/variant.monostate.relops>`_","| `monostate <https://reviews.llvm.org/D131372>`_
 | `variant <https://reviews.llvm.org/D131372>`_",None,Kent Ross,|Complete|

libcxx/include/system_error

public:
     int value() const noexcept;
     const error_category& category() const noexcept;
     error_condition default_error_condition() const noexcept;
     string message() const;
     explicit operator bool() const noexcept;
 };
 
 // non-member functions:
-bool operator<(const error_code& lhs, const error_code& rhs) noexcept;
 template <class charT, class traits>
     basic_ostream<charT,traits>&
     operator<<(basic_ostream<charT,traits>& os, const error_code& ec);
 
 class error_condition
 {
 public:
     // constructors:
public:
 
     // observers:
     int value() const noexcept;
     const error_category& category() const noexcept;
     string message() const noexcept;
     explicit operator bool() const noexcept;
 };
 
-bool operator<(const error_condition& lhs, const error_condition& rhs) noexcept;
-
 class system_error
     : public runtime_error
 {
 public:
     system_error(error_code ec, const string& what_arg);
     system_error(error_code ec, const char* what_arg);
     system_error(error_code ec);
     system_error(int ev, const error_category& ecat, const string& what_arg);
     system_error(int ev, const error_category& ecat, const char* what_arg);
     system_error(int ev, const error_category& ecat);
 
     const error_code& code() const noexcept;
     const char* what() const noexcept;
 };
 
 template <> struct is_error_condition_enum<errc>
     : true_type { }
 
 error_code make_error_code(errc e) noexcept;
 error_condition make_error_condition(errc e) noexcept;
 
 // Comparison operators:
 bool operator==(const error_code& lhs, const error_code& rhs) noexcept;
 bool operator==(const error_code& lhs, const error_condition& rhs) noexcept;
-bool operator==(const error_condition& lhs, const error_code& rhs) noexcept;
+bool operator==(const error_condition& lhs, const error_code& rhs) noexcept;                  // removed in C++20
 bool operator==(const error_condition& lhs, const error_condition& rhs) noexcept;
-bool operator!=(const error_code& lhs, const error_code& rhs) noexcept;
-bool operator!=(const error_code& lhs, const error_condition& rhs) noexcept;
-bool operator!=(const error_condition& lhs, const error_code& rhs) noexcept;
-bool operator!=(const error_condition& lhs, const error_condition& rhs) noexcept;
+bool operator!=(const error_code& lhs, const error_code& rhs) noexcept;                       // removed in C++20
+bool operator!=(const error_code& lhs, const error_condition& rhs) noexcept;                  // removed in C++20
+bool operator!=(const error_condition& lhs, const error_code& rhs) noexcept;                  // removed in C++20
+bool operator!=(const error_condition& lhs, const error_condition& rhs) noexcept;             // removed in C++20
+bool operator<(const error_condition& lhs, const error_condition& rhs) noexcept;              // removed in C++20
+bool operator<(const error_code& lhs, const error_code& rhs) noexcept;                        // removed in C++20
+strong_ordering operator<=>(const error_code& lhs, const error_code& rhs) noexcept;           // C++20
+strong_ordering operator<=>(const error_condition& lhs, const error_condition& rhs) noexcept; // C++20
 
 template <> struct hash<std::error_code>;
 template <> struct hash<std::error_condition>;
 
 }  // std
 
 */
 

 
 inline _LIBCPP_INLINE_VISIBILITY
 error_condition
 make_error_condition(errc __e) _NOEXCEPT
 {
     return error_condition(static_cast<int>(__e), generic_category());
 }
 
-inline _LIBCPP_INLINE_VISIBILITY
-bool
-operator<(const error_condition& __x, const error_condition& __y) _NOEXCEPT
-{
-    return __x.category() < __y.category()
-        || (__x.category() == __y.category() && __x.value() < __y.value());
-}
-
 // error_code
 
 class _LIBCPP_TYPE_VIS error_code
 {
     int __val_;
     const error_category* __cat_;
 public:
     _LIBCPP_INLINE_VISIBILITY

 error_code
 make_error_code(errc __e) _NOEXCEPT
 {
     return error_code(static_cast<int>(__e), generic_category());
 }
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
-operator<(const error_code& __x, const error_code& __y) _NOEXCEPT
-{
-    return __x.category() < __y.category()
-        || (__x.category() == __y.category() && __x.value() < __y.value());
-}
-
-inline _LIBCPP_INLINE_VISIBILITY
-bool
 operator==(const error_code& __x, const error_code& __y) _NOEXCEPT
 {
     return __x.category() == __y.category() && __x.value() == __y.value();
 }
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator==(const error_code& __x, const error_condition& __y) _NOEXCEPT
 {
     return __x.category().equivalent(__x.value(), __y)
         || __y.category().equivalent(__x, __y.value());
 }
 
+#if _LIBCPP_STD_VER <= 17
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator==(const error_condition& __x, const error_code& __y) _NOEXCEPT
 {
     return __y == __x;
 }
+#endif
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator==(const error_condition& __x, const error_condition& __y) _NOEXCEPT
 {
     return __x.category() == __y.category() && __x.value() == __y.value();
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const error_code& __x, const error_code& __y) _NOEXCEPT
 {return !(__x == __y);}
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const error_code& __x, const error_condition& __y) _NOEXCEPT
 {return !(__x == __y);}
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const error_condition& __x, const error_code& __y) _NOEXCEPT
 {return !(__x == __y);}
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const error_condition& __x, const error_condition& __y) _NOEXCEPT
 {return !(__x == __y);}
 
+inline _LIBCPP_INLINE_VISIBILITY
+bool
+operator<(const error_condition& __x, const error_condition& __y) _NOEXCEPT
+{
+    return __x.category() < __y.category()
+        || (__x.category() == __y.category() && __x.value() < __y.value());
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+bool
+operator<(const error_code& __x, const error_code& __y) _NOEXCEPT
+{
+    return __x.category() < __y.category()
+        || (__x.category() == __y.category() && __x.value() < __y.value());
+}
+
+#else // _LIBCPP_STD_VER <= 17
+
+inline _LIBCPP_HIDE_FROM_ABI strong_ordering
+operator<=>(const error_code& __x, const error_code& __y) noexcept
+{
+    if (auto __c = __x.category() <=> __y.category(); __c != 0)
+        return __c;
+    return __x.value() <=> __y.value();
+}
+
+inline _LIBCPP_HIDE_FROM_ABI strong_ordering
+operator<=>(const error_condition& __x, const error_condition& __y) noexcept
+{
+    if (auto __c = __x.category() <=> __y.category(); __c != 0)
+       return __c;
+    return __x.value() <=> __y.value();
+}
+
+#endif // _LIBCPP_STD_VER <= 17
+
 template <>
 struct _LIBCPP_TEMPLATE_VIS hash<error_code>
     : public __unary_function<error_code, size_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     size_t operator()(const error_code& __ec) const _NOEXCEPT
     {
         return static_cast<size_t>(__ec.value());

libcxx/test/std/diagnostics/syserr/syserr.compare/cmp_error_code.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <system_error>
+
+// class error_code
+
+// strong_ordering operator<=>(const error_code& lhs, const error_code& rhs) noexcept
+
+#include <system_error>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_comparisons.h"
+
+int main(int, char**) {
+  AssertOrderAreNoexcept<std::error_code>();
+  AssertOrderReturn<std::strong_ordering, std::error_code>();
+
+  // Same error category
+  std::error_code ec1a = std::error_code(1, std::generic_category());
+  std::error_code ec1b = std::error_code(1, std::generic_category());
+  std::error_code ec2  = std::error_code(2, std::generic_category());
+
+  assert(testOrder(ec1a, ec1b, std::strong_ordering::equal));
+  assert(testOrder(ec1a, ec2, std::strong_ordering::less));
+
+  // Different error category
+  const std::error_code& ec3 = std::error_code(2, std::system_category());
+
+  bool isLess = ec2 < ec3;
+  assert(testOrder(ec2, ec3, isLess ? std::strong_ordering::less : std::strong_ordering::greater));
+
+  return 0;
+}

libcxx/test/std/diagnostics/syserr/syserr.compare/cmp_error_condition.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <system_error>
+
+// class error_condition
+
+// strong_ordering operator<=>(const error_condition& lhs, const error_condition& rhs) noexcept
+
+#include <system_error>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_comparisons.h"
+
+int main(int, char**) {
+  AssertOrderAreNoexcept<std::error_condition>();
+  AssertOrderReturn<std::strong_ordering, std::error_condition>();
+
+  // Same error category
+  std::error_condition ec1a = std::error_condition(1, std::generic_category());
+  std::error_condition ec1b = std::error_condition(1, std::generic_category());
+  std::error_condition ec2  = std::error_condition(2, std::generic_category());
+
+  assert(testOrder(ec1a, ec1b, std::strong_ordering::equal));
+  assert(testOrder(ec1a, ec2, std::strong_ordering::less));
+
+  // Different error category
+  const std::error_condition& ec3 = std::error_condition(2, std::system_category());
+
+  bool isLess = ec2 < ec3;
+  assert(testOrder(ec2, ec3, isLess ? std::strong_ordering::less : std::strong_ordering::greater));
+
+  return 0;
+}