[libc++] Adds (to|from)_chars_result operator==.

[Mordante]

Summary

Implements part of P1614 The Mothership has Landed.

[Mordante]

Remove some tabs.

[• Quuxplusone]

LGTM!

libcxx/docs/Status/SpaceshipProjects.csv

 | `[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
 | variant",None,Kent Ross,|In Progress|
 | `[unique.ptr.special] <https://wg21.link/unique.ptr.special>`_,| unique_ptr,[comparisons.three.way],Unassigned,|Not Started|
 | `[util.smartptr.shared.cmp] <https://wg21.link/util.smartptr.shared.cmp>`_,| shared_ptr,[comparisons.three.way],Unassigned,|Not Started|
 | `[type.index.members] <https://wg21.link/type.index.members>`_,| type_index,None,Unassigned,|Not Started|
+| `[charconv.syn] <https://wg21.link/charconv.syn>`_,| to_chars_result,None,Mark de Wever,|Complete|
+| `[charconv.syn] <https://wg21.link/charconv.syn>`_,| from_chars_result,None,Mark de Wever,|Complete|
 | `[stacktrace.entry.cmp] <https://wg21.link/stacktrace.entry.cmp>`_,| stacktrace_entry,None,Unassigned,|Not Started|
 | `[stacktrace.basic.cmp] <https://wg21.link/stacktrace.basic.cmp>`_,| basic_stacktrace,[alg.three.way],Unassigned,|Not Started|
 | `[string.cmp] <https://wg21.link/string.cmp>`_,| `basic_string <https://reviews.llvm.org/D80895>`_,None,Christopher Di Bella,|In Progress|
 | `[string.view.comparison] <https://wg21.link/string.view.comparison>`_,| `basic_string_view <https://reviews.llvm.org/D80891>`_,None,Christopher Di Bella,|In Progress|
 | `[array.syn] <https://wg21.link/array.syn>`_ (`general <https://wg21.link/container.requirements.general#14>`_),| array,[expos.only.func],Unassigned,|Not Started|
 | `[deque.syn] <https://wg21.link/deque.syn>`_ (`general <https://wg21.link/container.requirements.general#14>`_),| deque,[expos.only.func],Unassigned,|Not Started|
 | `[forward.list.syn] <https://wg21.link/forward.list.syn>`_ (`general <https://wg21.link/container.requirements.general#14>`_),| forward_list,[expos.only.func],Unassigned,|Not Started|
 | `[list.syn] <https://wg21.link/list.syn>`_ (`general <https://wg21.link/container.requirements.general#14>`_),| list,[expos.only.func],Unassigned,|Not Started|

libcxx/include/__charconv/from_chars_result.h

 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_CXX03_LANG
 
 struct _LIBCPP_TYPE_VIS from_chars_result
 {
     const char* ptr;
     errc ec;
+#  if _LIBCPP_STD_VER > 17
+    _LIBCPP_HIDE_FROM_ABI friend bool operator==(const from_chars_result&, const from_chars_result&) = default;
+#  endif
 };
 
 #endif // _LIBCPP_CXX03_LANG
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHARCONV_FROM_CHARS_RESULT_H

libcxx/include/__charconv/to_chars_result.h

 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_CXX03_LANG
 
 struct _LIBCPP_TYPE_VIS to_chars_result
 {
     char* ptr;
     errc ec;
+#  if _LIBCPP_STD_VER > 17
+    _LIBCPP_HIDE_FROM_ABI friend bool operator==(const to_chars_result&, const to_chars_result&) = default;
+#  endif
 };
 
 #endif // _LIBCPP_CXX03_LANG
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHARCONV_TO_CHARS_RESULT_H

libcxx/include/charconv

enum class chars_format {
     hex = unspecified,
     general = fixed | scientific
   };
 
   // 23.20.2, primitive numerical output conversion
   struct to_chars_result {
     char* ptr;
     errc ec;
+    friend bool operator==(const to_chars_result&, const to_chars_result&) = default; // since C++20
   };
 
   to_chars_result to_chars(char* first, char* last, see below value,
                            int base = 10);
   to_chars_result to_chars(char* first, char* last, bool value,
                            int base = 10) = delete;
 
   to_chars_result to_chars(char* first, char* last, float value);
to_chars_result to_chars(char* first, char* last, double value,
                            chars_format fmt, int precision);
   to_chars_result to_chars(char* first, char* last, long double value,
                            chars_format fmt, int precision);
 
   // 23.20.3, primitive numerical input conversion
   struct from_chars_result {
     const char* ptr;
     errc ec;
+    friend bool operator==(const from_chars_result&, const from_chars_result&) = default; // since C++20
   };
 
   from_chars_result from_chars(const char* first, const char* last,
                                see below& value, int base = 10);
 
   from_chars_result from_chars(const char* first, const char* last,
                                float& value,
                                chars_format fmt = chars_format::general);

libcxx/test/std/utilities/charconv/charconv.syn/from_chars_result.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
+// UNSUPPORTED: libcpp-no-concepts
+
+// <charconv>
+
+// struct from_chars_result
+//   friend bool operator==(const from_chars_result&, const from_chars_result&) = default;
+
+#include <charconv>
+
+#include <cassert>
+#include <compare>
+#include <concepts>
+
+#include "test_macros.h"
+
+constexpr bool test() {
+  std::from_chars_result lhs{nullptr, std::errc{}};
+  std::from_chars_result rhs{nullptr, std::errc{}};
+  assert(lhs == rhs);
+  assert(!(lhs != rhs));
+
+  return true;
+}
+
+int main(int, char**) {
+  static_assert(std::equality_comparable<std::from_chars_result>);
+  static_assert(!std::totally_ordered<std::from_chars_result>);
+  static_assert(!std::three_way_comparable<std::from_chars_result>);
+
+  assert(test());
+  static_assert(test());
+
+  return 0;
+}

libcxx/test/std/utilities/charconv/charconv.syn/to_chars_result.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
+// UNSUPPORTED: libcpp-no-concepts
+
+// <charconv>
+
+// struct to_chars_result
+//   friend bool operator==(const to_chars_result&, const to_chars_result&) = default;
+
+#include <charconv>
+
+#include <cassert>
+#include <compare>
+#include <concepts>
+
+#include "test_macros.h"
+
+constexpr bool test() {
+  std::to_chars_result lhs{nullptr, std::errc{}};
+  std::to_chars_result rhs{nullptr, std::errc{}};
+  assert(lhs == rhs);
+  assert(!(lhs != rhs));
+
+  return true;
+}
+
+int main(int, char**) {
+  static_assert(std::equality_comparable<std::to_chars_result>);
+  static_assert(!std::totally_ordered<std::to_chars_result>);
+  static_assert(!std::three_way_comparable<std::to_chars_result>);
+
+  assert(test());
+  static_assert(test());
+
+  return 0;
+}