Restoring authorship annotation for Andrey Khalyavin <halyavin@gmail.com>. Commit 2 of 2.

1 files changed, 776 insertions, 776 deletions

diff --git a/contrib/libs/cxxsupp/libcxx/include/format b/contrib/libs/cxxsupp/libcxx/include/format
index f37f5194ab..19f642716b 100644
--- a/contrib/libs/cxxsupp/libcxx/include/format
+++ b/contrib/libs/cxxsupp/libcxx/include/format
@@ -1,776 +1,776 @@
-// -*- C++ -*- 
-//===--------------------------- format -----------------------------------===// 
-// 
-// 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_FORMAT 
-#define _LIBCPP_FORMAT 
- 
-/* 
- 
-namespace std { 
-  // [format.context], class template basic_format_context 
-  template<class Out, class charT> 
-  class basic_format_context { 
-    basic_format_args<basic_format_context> args_;      // exposition only 
-    Out out_;                                           // exposition only 
- 
-  public: 
-    using iterator = Out; 
-    using char_type = charT; 
-    template<class T> using formatter_type = formatter<T, charT>; 
- 
-    basic_format_arg<basic_format_context> arg(size_t id) const; 
-    std::locale locale(); 
- 
-    iterator out(); 
-    void advance_to(iterator it); 
-  }; 
-  using format_context = basic_format_context<unspecified, char>; 
-  using wformat_context = basic_format_context<unspecified, wchar_t>; 
- 
-  // [format.args], class template basic_format_args 
-  template<class Context> 
-  class basic_format_args { 
-    size_t size_;                               // exposition only 
-    const basic_format_arg<Context>* data_;     // exposition only 
- 
-  public: 
-    basic_format_args() noexcept; 
- 
-    template<class... Args> 
-      basic_format_args(const format-arg-store<Context, Args...>& store) noexcept; 
- 
-    basic_format_arg<Context> get(size_t i) const noexcept; 
-  }; 
-  using format_args = basic_format_args<format_context>; 
-  using wformat_args = basic_format_args<wformat_context>; 
- 
- 
-  template<class Out, class charT> 
-    using format_args_t = basic_format_args<basic_format_context<Out, charT>>; 
- 
-  // [format.functions], formatting functions 
-  template<class... Args> 
-    string format(string_view fmt, const Args&... args); 
-  template<class... Args> 
-    wstring format(wstring_view fmt, const Args&... args); 
-  template<class... Args> 
-    string format(const locale& loc, string_view fmt, const Args&... args); 
-  template<class... Args> 
-    wstring format(const locale& loc, wstring_view fmt, const Args&... args); 
- 
-  string vformat(string_view fmt, format_args args); 
-  wstring vformat(wstring_view fmt, wformat_args args); 
-  string vformat(const locale& loc, string_view fmt, format_args args); 
-  wstring vformat(const locale& loc, wstring_view fmt, wformat_args args); 
- 
-  template<class Out, class... Args> 
-    Out format_to(Out out, string_view fmt, const Args&... args); 
-  template<class Out, class... Args> 
-    Out format_to(Out out, wstring_view fmt, const Args&... args); 
-  template<class Out, class... Args> 
-    Out format_to(Out out, const locale& loc, string_view fmt, const Args&... args); 
-  template<class Out, class... Args> 
-    Out format_to(Out out, const locale& loc, wstring_view fmt, const Args&... args); 
- 
-  template<class Out> 
-    Out vformat_to(Out out, string_view fmt, 
-                   format_args_t<type_identity_t<Out>, char> args); 
-  template<class Out> 
-    Out vformat_to(Out out, wstring_view fmt, 
-                   format_args_t<type_identity_t<Out>, wchar_t> args); 
-  template<class Out> 
-    Out vformat_to(Out out, const locale& loc, string_view fmt, 
-                   format_args_t<type_identity_t<Out>, char> args); 
-  template<class Out> 
-    Out vformat_to(Out out, const locale& loc, wstring_view fmt, 
-                   format_args_t<type_identity_t<Out>, wchar_t> args); 
- 
-  template<class Out> struct format_to_n_result { 
-    Out out; 
-    iter_difference_t<Out> size; 
-  }; 
- 
- template<class Out, class... Args> 
-    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, 
-                                        string_view fmt, const Args&... args); 
-  template<class Out, class... Args> 
-    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, 
-                                        wstring_view fmt, const Args&... args); 
-  template<class Out, class... Args> 
-    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, 
-                                        const locale& loc, string_view fmt, 
-                                        const Args&... args); 
-  template<class Out, class... Args> 
-    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, 
-                                        const locale& loc, wstring_view fmt, 
-                                        const Args&... args); 
- 
-  template<class... Args> 
-    size_t formatted_size(string_view fmt, const Args&... args); 
-  template<class... Args> 
-    size_t formatted_size(wstring_view fmt, const Args&... args); 
-  template<class... Args> 
-    size_t formatted_size(const locale& loc, string_view fmt, const Args&... args); 
-  template<class... Args> 
-    size_t formatted_size(const locale& loc, wstring_view fmt, const Args&... args); 
- 
-  // [format.formatter], formatter 
-  template<> struct formatter<char, char>; 
-  template<> struct formatter<char, wchar_t>; 
-  template<> struct formatter<wchar_t, wchar_t>; 
- 
-  template<> struct formatter<charT*, charT>; 
-  template<> struct formatter<const charT*, charT>; 
-  template<size_t N> struct formatter<const charT[N], charT>; 
-  template<class traits, class Allocator> 
-    struct formatter<basic_string<charT, traits, Allocator>, charT>; 
-  template<class traits> 
-    struct formatter<basic_string_view<charT, traits>, charT>; 
- 
-  // [format.parse.ctx], class template basic_format_parse_context 
-  template<class charT> 
-  class basic_format_parse_context { 
-  public: 
-    using char_type = charT; 
-    using const_iterator = typename basic_string_view<charT>::const_iterator; 
-    using iterator = const_iterator; 
- 
-  private: 
-    iterator begin_;                                    // exposition only 
-    iterator end_;                                      // exposition only 
-    enum indexing { unknown, manual, automatic };       // exposition only 
-    indexing indexing_;                                 // exposition only 
-    size_t next_arg_id_;                                // exposition only 
-    size_t num_args_;                                   // exposition only 
- 
-  public: 
-    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt, 
-                                                  size_t num_args = 0) noexcept; 
-    basic_format_parse_context(const basic_format_parse_context&) = delete; 
-    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete; 
- 
-    constexpr const_iterator begin() const noexcept; 
-    constexpr const_iterator end() const noexcept; 
-    constexpr void advance_to(const_iterator it); 
- 
-    constexpr size_t next_arg_id(); 
-    constexpr void check_arg_id(size_t id); 
-  }; 
-  using format_parse_context = basic_format_parse_context<char>; 
-  using wformat_parse_context = basic_format_parse_context<wchar_t>; 
- 
-  // [format.arguments], arguments 
-  // [format.arg], class template basic_format_arg 
-  template<class Context> 
-  class basic_format_arg { 
-  public: 
-    class handle; 
- 
-  private: 
-    using char_type = typename Context::char_type;                              // exposition only 
- 
-    variant<monostate, bool, char_type, 
-            int, unsigned int, long long int, unsigned long long int, 
-            float, double, long double, 
-            const char_type*, basic_string_view<char_type>, 
-            const void*, handle> value;                                         // exposition only 
- 
-    template<class T> explicit basic_format_arg(const T& v) noexcept;           // exposition only 
-    explicit basic_format_arg(float n) noexcept;                                // exposition only 
-    explicit basic_format_arg(double n) noexcept;                               // exposition only 
-    explicit basic_format_arg(long double n) noexcept;                          // exposition only 
-    explicit basic_format_arg(const char_type* s);                              // exposition only 
- 
-    template<class traits> 
-      explicit basic_format_arg( 
-        basic_string_view<char_type, traits> s) noexcept;                       // exposition only 
- 
-    template<class traits, class Allocator> 
-      explicit basic_format_arg( 
-        const basic_string<char_type, traits, Allocator>& s) noexcept;          // exposition only 
- 
-    explicit basic_format_arg(nullptr_t) noexcept;                              // exposition only 
- 
-    template<class T> 
-      explicit basic_format_arg(const T* p) noexcept;                           // exposition only 
- 
-  public: 
-    basic_format_arg() noexcept; 
- 
-    explicit operator bool() const noexcept; 
-  }; 
- 
-  template<class Visitor, class Context> 
-    see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg); 
- 
-  // [format.arg.store], class template format-arg-store 
-  template<class Context, class... Args> 
-  struct format-arg-store {      // exposition only 
-    array<basic_format_arg<Context>, sizeof...(Args)> args; 
-  }; 
- 
-  template<class Context = format_context, class... Args> 
-    format-arg-store<Context, Args...> 
-      make_format_args(const Args&... args); 
-  template<class... Args> 
-    format-arg-store<wformat_context, Args...> 
-      make_wformat_args(const Args&... args); 
- 
-  // [format.error], class format_error 
-  class format_error : public runtime_error { 
-  public: 
-    explicit format_error(const string& what_arg); 
-    explicit format_error(const char* what_arg); 
-  }; 
- 
-  // [format.parse.ctx], class template basic_format_parse_context 
-  template<class charT> 
-  class basic_format_parse_context { 
-  public: 
-    using char_type = charT; 
-    using const_iterator = typename basic_string_view<charT>::const_iterator; 
-    using iterator = const_iterator; 
- 
-  private: 
-    iterator begin_;                                    // exposition only 
-    iterator end_;                                      // exposition only 
-    enum indexing { unknown, manual, automatic };       // exposition only 
-    indexing indexing_;                                 // exposition only 
-    size_t next_arg_id_;                                // exposition only 
-    size_t num_args_;                                   // exposition only 
- 
-  public: 
-    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt, 
-                                                  size_t num_args = 0) noexcept; 
-    basic_format_parse_context(const basic_format_parse_context&) = delete; 
-    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete; 
- 
-    constexpr const_iterator begin() const noexcept; 
-    constexpr const_iterator end() const noexcept; 
-    constexpr void advance_to(const_iterator it); 
- 
-    constexpr size_t next_arg_id(); 
-    constexpr void check_arg_id(size_t id); 
-  }; 
-  using format_parse_context = basic_format_parse_context<char>; 
-  using wformat_parse_context = basic_format_parse_context<wchar_t>; 
-} 
- 
-*/ 
- 
-// Make sure all feature-test macros are available. 
-#include <version> 
-// Enable the contents of the header only when libc++ was built with LIBCXX_ENABLE_INCOMPLETE_FEATURES. 
-#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT) 
- 
-#include <__config> 
-#include <__debug> 
-#include <__format/format_arg.h> 
-#include <__format/format_args.h> 
-#include <__format/format_context.h> 
-#include <__format/format_error.h> 
-#include <__format/format_fwd.h> 
-#include <__format/format_parse_context.h> 
-#include <__format/format_string.h> 
-#include <__format/formatter.h> 
-#include <__format/formatter_bool.h> 
-#include <__format/formatter_char.h> 
-#include <__format/formatter_integer.h> 
-#include <__format/formatter_string.h> 
-#include <__format/parser_std_format_spec.h> 
-#include <__variant/monostate.h> 
-#include <array> 
-#include <concepts> 
-#include <string> 
-#include <string_view> 
-#include <type_traits> 
- 
-#ifndef _LIBCPP_HAS_NO_LOCALIZATION 
-#include <locale> 
-#endif 
- 
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 
-#pragma GCC system_header 
-#endif 
- 
-_LIBCPP_PUSH_MACROS 
-#include <__undef_macros> 
- 
-_LIBCPP_BEGIN_NAMESPACE_STD 
- 
-#if _LIBCPP_STD_VER > 17 
- 
-// TODO FMT Remove this once we require compilers with proper C++20 support. 
-// If the compiler has no concepts support, the format header will be disabled. 
-// Without concepts support enable_if needs to be used and that too much effort 
-// to support compilers with partial C++20 support. 
-#if !defined(_LIBCPP_HAS_NO_CONCEPTS) 
- 
-// TODO FMT Evaluate which templates should be external templates. This 
-// improves the efficiency of the header. However since the header is still 
-// under heavy development and not all classes are stable it makes no sense 
-// to do this optimization now. 
- 
-using format_args = basic_format_args<format_context>; 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-using wformat_args = basic_format_args<wformat_context>; 
-#endif 
- 
-template <class _OutIt, class _CharT> 
-using format_args_t = basic_format_args<basic_format_context<_OutIt, _CharT>>; 
- 
-template <class _Context, class... _Args> 
-struct _LIBCPP_TEMPLATE_VIS __format_arg_store { 
-  // TODO FMT Use a built-in array. 
-  array<basic_format_arg<_Context>, sizeof...(_Args)> __args; 
-}; 
- 
-template <class _Context = format_context, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI __format_arg_store<_Context, _Args...> 
-make_format_args(const _Args&... __args) { 
-  return {basic_format_arg<_Context>(__args)...}; 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI __format_arg_store<wformat_context, _Args...> 
-make_wformat_args(const _Args&... __args) { 
-  return _VSTD::make_format_args<wformat_context>(__args...); 
-} 
-#endif 
- 
-namespace __format { 
- 
-template <class _Tp, class _CharT> 
-requires(is_arithmetic_v<_Tp> && 
-         !same_as<_Tp, bool>) struct _LIBCPP_HIDE_FROM_ABI 
-    __formatter_arithmetic { 
-  _LIBCPP_HIDE_FROM_ABI 
-  auto parse(auto& __parse_ctx) -> decltype(__parse_ctx.begin()) { 
-    // TODO FMT Implement 
-    return __parse_ctx.begin(); 
-  } 
- 
-  _LIBCPP_HIDE_FROM_ABI 
-  auto format(_Tp __value, auto& __ctx) -> decltype(__ctx.out()) { 
-    return __handle_format(__value, __ctx); 
-  } 
- 
-private: 
-  template <class _Uv> 
-  _LIBCPP_HIDDEN static string 
-  __convert(_Uv __value) requires(same_as<_CharT, char>) { 
-    return _VSTD::to_string(__value); 
-  } 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-  template <class _Uv> 
-  _LIBCPP_HIDDEN static wstring 
-  __convert(_Uv __value) requires(same_as<_CharT, wchar_t>) { 
-    return _VSTD::to_wstring(__value); 
-  } 
-#endif 
- 
-  template <class _Uv> 
-  _LIBCPP_HIDDEN auto __handle_format(_Uv __value, auto& __ctx) 
-      -> decltype(__ctx.out()) 
-  { 
-    // TODO FMT Implement using formatting arguments 
-    // TODO FMT Improve PoC since using std::to_string is inefficient. 
-    // Note the code doesn't use std::string::iterator since the unit tests 
-    // test with debug iterators and they fail with strings created from 
-    // std::to_string. 
-    auto __str = __convert(__value); 
-    auto __out_it = __ctx.out(); 
-    for (size_t __i = 0, __e = __str.size(); __i != __e; ++__i) 
-      *__out_it++ = __str[__i]; 
-    return __out_it; 
-  } 
-}; 
-} // namespace __format 
- 
-// These specializations are helper stubs and not proper formatters. 
-// TODO FMT Implement the proper formatter specializations. 
- 
-// Floating point types. 
-// TODO FMT There are no replacements for the floating point stubs due to not 
-// having floating point support in std::to_chars yet. These stubs aren't 
-// removed since they are useful for developing the real versions. 
-// Ultimately the stubs should be implemented properly and this code can be 
-// removed. 
-#if 0 
-template <class _CharT> 
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<float, _CharT> 
-    : public __format::__formatter_arithmetic<float, _CharT> {}; 
-template <class _CharT> 
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT 
-    formatter<double, _CharT> 
-    : public __format::__formatter_arithmetic<double, _CharT> {}; 
-template <class _CharT> 
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT 
-    formatter<long double, _CharT> 
-    : public __format::__formatter_arithmetic<long double, _CharT> {}; 
-#endif 
- 
-namespace __format { 
- 
-template <class _CharT, class _ParseCtx, class _Ctx> 
-_LIBCPP_HIDE_FROM_ABI const _CharT* 
-__handle_replacement_field(const _CharT* __begin, const _CharT* __end, 
-                           _ParseCtx& __parse_ctx, _Ctx& __ctx) { 
-  __format::__parse_number_result __r = 
-      __format::__parse_arg_id(__begin, __end, __parse_ctx); 
- 
-  switch (*__r.__ptr) { 
-  case _CharT(':'): 
-    // The arg-id has a format-specifier, advance the input to the format-spec. 
-    __parse_ctx.advance_to(__r.__ptr + 1); 
-    break; 
-  case _CharT('}'): 
-    // The arg-id has no format-specifier. 
-    __parse_ctx.advance_to(__r.__ptr); 
-    break; 
-  default: 
-    __throw_format_error( 
-        "The replacement field arg-id should terminate at a ':' or '}'"); 
-  } 
- 
-  _VSTD::visit_format_arg( 
-      [&](auto __arg) { 
-        if constexpr (same_as<decltype(__arg), monostate>) 
-          __throw_format_error("Argument index out of bounds"); 
-        else { 
-          formatter<decltype(__arg), _CharT> __formatter; 
-          __parse_ctx.advance_to(__formatter.parse(__parse_ctx)); 
-          __ctx.advance_to(__formatter.format(__arg, __ctx)); 
-        } 
-      }, 
-      __ctx.arg(__r.__value)); 
- 
-  __begin = __parse_ctx.begin(); 
-  if (__begin == __end || *__begin != _CharT('}')) 
-    __throw_format_error("The replacement field misses a terminating '}'"); 
- 
-  return ++__begin; 
-} 
- 
-template <class _ParseCtx, class _Ctx> 
-_LIBCPP_HIDE_FROM_ABI typename _Ctx::iterator 
-__vformat_to(_ParseCtx&& __parse_ctx, _Ctx&& __ctx) { 
-  using _CharT = typename _ParseCtx::char_type; 
-  static_assert(same_as<typename _Ctx::char_type, _CharT>); 
- 
-  const _CharT* __begin = __parse_ctx.begin(); 
-  const _CharT* __end = __parse_ctx.end(); 
-  typename _Ctx::iterator __out_it = __ctx.out(); 
-  while (__begin != __end) { 
-    switch (*__begin) { 
-    case _CharT('{'): 
-      ++__begin; 
-      if (__begin == __end) 
-        __throw_format_error("The format string terminates at a '{'"); 
- 
-      if (*__begin != _CharT('{')) [[likely]] { 
-        __ctx.advance_to(_VSTD::move(__out_it)); 
-        __begin = 
-            __handle_replacement_field(__begin, __end, __parse_ctx, __ctx); 
-        __out_it = __ctx.out(); 
- 
-        // The output is written and __begin points to the next character. So 
-        // start the next iteration. 
-        continue; 
-      } 
-      // The string is an escape character. 
-      break; 
- 
-    case _CharT('}'): 
-      ++__begin; 
-      if (__begin == __end || *__begin != _CharT('}')) 
-        __throw_format_error( 
-            "The format string contains an invalid escape sequence"); 
- 
-      break; 
-    } 
- 
-    // Copy the character to the output verbatim. 
-    *__out_it++ = *__begin++; 
-  } 
-  return __out_it; 
-} 
- 
-} // namespace __format 
- 
-template <class _OutIt, class _CharT> 
-requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt 
-    __vformat_to(_OutIt __out_it, basic_string_view<_CharT> __fmt, 
-                 format_args_t<type_identity_t<_OutIt>, _CharT> __args) { 
-  return __format::__vformat_to( 
-      basic_format_parse_context{__fmt, __args.__size()}, 
-      _VSTD::__format_context_create(_VSTD::move(__out_it), __args)); 
-} 
- 
-template <output_iterator<const char&> _OutIt> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-vformat_to(_OutIt __out_it, string_view __fmt, 
-           format_args_t<type_identity_t<_OutIt>, char> __args) { 
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-vformat_to(_OutIt __out_it, wstring_view __fmt, 
-           format_args_t<type_identity_t<_OutIt>, wchar_t> __args) { 
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args); 
-} 
-#endif 
- 
-template <output_iterator<const char&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-format_to(_OutIt __out_it, string_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat_to( 
-      _VSTD::move(__out_it), __fmt, 
-      _VSTD::make_format_args<basic_format_context<_OutIt, char>>(__args...)); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-format_to(_OutIt __out_it, wstring_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat_to( 
-      _VSTD::move(__out_it), __fmt, 
-      _VSTD::make_format_args<basic_format_context<_OutIt, wchar_t>>( 
-          __args...)); 
-} 
-#endif 
- 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string 
-vformat(string_view __fmt, format_args __args) { 
-  string __res; 
-  _VSTD::vformat_to(_VSTD::back_inserter(__res), __fmt, __args); 
-  return __res; 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring 
-vformat(wstring_view __fmt, wformat_args __args) { 
-  wstring __res; 
-  _VSTD::vformat_to(_VSTD::back_inserter(__res), __fmt, __args); 
-  return __res; 
-} 
-#endif 
- 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string 
-format(string_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...)); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring 
-format(wstring_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...)); 
-} 
-#endif 
- 
-template <class _OutIt> 
-struct _LIBCPP_TEMPLATE_VIS format_to_n_result { 
-  _OutIt out; 
-  iter_difference_t<_OutIt> size; 
-}; 
- 
-template <output_iterator<const char&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt> 
-format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, string_view __fmt, 
-            const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  string __str = _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...)); 
-  iter_difference_t<_OutIt> __s = __str.size(); 
-  iter_difference_t<_OutIt> __m = 
-      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s); 
-  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it)); 
-  return {_VSTD::move(__out_it), __s}; 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt> 
-format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, wstring_view __fmt, 
-            const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  wstring __str = _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...)); 
-  iter_difference_t<_OutIt> __s = __str.size(); 
-  iter_difference_t<_OutIt> __m = 
-      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s); 
-  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it)); 
-  return {_VSTD::move(__out_it), __s}; 
-} 
-#endif 
- 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t 
-formatted_size(string_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  return _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...)).size(); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t 
-formatted_size(wstring_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  return _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...)).size(); 
-} 
-#endif 
- 
-#ifndef _LIBCPP_HAS_NO_LOCALIZATION 
- 
-template <class _OutIt, class _CharT> 
-requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt 
-    __vformat_to(_OutIt __out_it, locale __loc, basic_string_view<_CharT> __fmt, 
-                 format_args_t<type_identity_t<_OutIt>, _CharT> __args) { 
-  return __format::__vformat_to( 
-      basic_format_parse_context{__fmt, __args.__size()}, 
-      _VSTD::__format_context_create(_VSTD::move(__out_it), __args, 
-                                     _VSTD::move(__loc))); 
-} 
- 
-template <output_iterator<const char&> _OutIt> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-vformat_to(_OutIt __out_it, locale __loc, string_view __fmt, 
-           format_args_t<type_identity_t<_OutIt>, char> __args) { 
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt, 
-                             __args); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt 
-vformat_to(_OutIt __out_it, locale __loc, wstring_view __fmt, 
-           format_args_t<type_identity_t<_OutIt>, wchar_t> __args) { 
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt, 
-                             __args); 
-} 
-#endif 
- 
-template <output_iterator<const char&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt format_to( 
-    _OutIt __out_it, locale __loc, string_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat_to( 
-      _VSTD::move(__out_it), _VSTD::move(__loc), __fmt, 
-      _VSTD::make_format_args<basic_format_context<_OutIt, char>>(__args...)); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt format_to( 
-    _OutIt __out_it, locale __loc, wstring_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat_to( 
-      _VSTD::move(__out_it), _VSTD::move(__loc), __fmt, 
-      _VSTD::make_format_args<basic_format_context<_OutIt, wchar_t>>( 
-          __args...)); 
-} 
-#endif 
- 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string 
-vformat(locale __loc, string_view __fmt, format_args __args) { 
-  string __res; 
-  _VSTD::vformat_to(_VSTD::back_inserter(__res), _VSTD::move(__loc), __fmt, 
-                    __args); 
-  return __res; 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring 
-vformat(locale __loc, wstring_view __fmt, wformat_args __args) { 
-  wstring __res; 
-  _VSTD::vformat_to(_VSTD::back_inserter(__res), _VSTD::move(__loc), __fmt, 
-                    __args); 
-  return __res; 
-} 
-#endif 
- 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string 
-format(locale __loc, string_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                        _VSTD::make_format_args(__args...)); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring 
-format(locale __loc, wstring_view __fmt, const _Args&... __args) { 
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                        _VSTD::make_wformat_args(__args...)); 
-} 
-#endif 
- 
-template <output_iterator<const char&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt> 
-format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, locale __loc, 
-            string_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  string __str = _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                                _VSTD::make_format_args(__args...)); 
-  iter_difference_t<_OutIt> __s = __str.size(); 
-  iter_difference_t<_OutIt> __m = 
-      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s); 
-  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it)); 
-  return {_VSTD::move(__out_it), __s}; 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <output_iterator<const wchar_t&> _OutIt, class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt> 
-format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, locale __loc, 
-            wstring_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  wstring __str = _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                                 _VSTD::make_wformat_args(__args...)); 
-  iter_difference_t<_OutIt> __s = __str.size(); 
-  iter_difference_t<_OutIt> __m = 
-      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s); 
-  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it)); 
-  return {_VSTD::move(__out_it), __s}; 
-} 
-#endif 
- 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t 
-formatted_size(locale __loc, string_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                        _VSTD::make_format_args(__args...)) 
-      .size(); 
-} 
- 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS 
-template <class... _Args> 
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t 
-formatted_size(locale __loc, wstring_view __fmt, const _Args&... __args) { 
-  // TODO FMT Improve PoC: using std::string is inefficient. 
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt, 
-                        _VSTD::make_wformat_args(__args...)) 
-      .size(); 
-} 
-#endif 
- 
-#endif // _LIBCPP_HAS_NO_LOCALIZATION 
- 
-#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS) 
-#endif //_LIBCPP_STD_VER > 17 
- 
-_LIBCPP_END_NAMESPACE_STD 
- 
-_LIBCPP_POP_MACROS 
- 
-#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT) 
- 
-#endif // _LIBCPP_FORMAT 
+// -*- C++ -*-
+//===--------------------------- format -----------------------------------===//
+//
+// 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_FORMAT
+#define _LIBCPP_FORMAT
+
+/*
+
+namespace std {
+  // [format.context], class template basic_format_context
+  template<class Out, class charT>
+  class basic_format_context {
+    basic_format_args<basic_format_context> args_;      // exposition only
+    Out out_;                                           // exposition only
+
+  public:
+    using iterator = Out;
+    using char_type = charT;
+    template<class T> using formatter_type = formatter<T, charT>;
+
+    basic_format_arg<basic_format_context> arg(size_t id) const;
+    std::locale locale();
+
+    iterator out();
+    void advance_to(iterator it);
+  };
+  using format_context = basic_format_context<unspecified, char>;
+  using wformat_context = basic_format_context<unspecified, wchar_t>;
+
+  // [format.args], class template basic_format_args
+  template<class Context>
+  class basic_format_args {
+    size_t size_;                               // exposition only
+    const basic_format_arg<Context>* data_;     // exposition only
+
+  public:
+    basic_format_args() noexcept;
+
+    template<class... Args>
+      basic_format_args(const format-arg-store<Context, Args...>& store) noexcept;
+
+    basic_format_arg<Context> get(size_t i) const noexcept;
+  };
+  using format_args = basic_format_args<format_context>;
+  using wformat_args = basic_format_args<wformat_context>;
+
+
+  template<class Out, class charT>
+    using format_args_t = basic_format_args<basic_format_context<Out, charT>>;
+
+  // [format.functions], formatting functions
+  template<class... Args>
+    string format(string_view fmt, const Args&... args);
+  template<class... Args>
+    wstring format(wstring_view fmt, const Args&... args);
+  template<class... Args>
+    string format(const locale& loc, string_view fmt, const Args&... args);
+  template<class... Args>
+    wstring format(const locale& loc, wstring_view fmt, const Args&... args);
+
+  string vformat(string_view fmt, format_args args);
+  wstring vformat(wstring_view fmt, wformat_args args);
+  string vformat(const locale& loc, string_view fmt, format_args args);
+  wstring vformat(const locale& loc, wstring_view fmt, wformat_args args);
+
+  template<class Out, class... Args>
+    Out format_to(Out out, string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, wstring_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, const locale& loc, string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, const locale& loc, wstring_view fmt, const Args&... args);
+
+  template<class Out>
+    Out vformat_to(Out out, string_view fmt,
+                   format_args_t<type_identity_t<Out>, char> args);
+  template<class Out>
+    Out vformat_to(Out out, wstring_view fmt,
+                   format_args_t<type_identity_t<Out>, wchar_t> args);
+  template<class Out>
+    Out vformat_to(Out out, const locale& loc, string_view fmt,
+                   format_args_t<type_identity_t<Out>, char> args);
+  template<class Out>
+    Out vformat_to(Out out, const locale& loc, wstring_view fmt,
+                   format_args_t<type_identity_t<Out>, wchar_t> args);
+
+  template<class Out> struct format_to_n_result {
+    Out out;
+    iter_difference_t<Out> size;
+  };
+
+ template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        wstring_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        const locale& loc, string_view fmt,
+                                        const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        const locale& loc, wstring_view fmt,
+                                        const Args&... args);
+
+  template<class... Args>
+    size_t formatted_size(string_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(wstring_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(const locale& loc, string_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(const locale& loc, wstring_view fmt, const Args&... args);
+
+  // [format.formatter], formatter
+  template<> struct formatter<char, char>;
+  template<> struct formatter<char, wchar_t>;
+  template<> struct formatter<wchar_t, wchar_t>;
+
+  template<> struct formatter<charT*, charT>;
+  template<> struct formatter<const charT*, charT>;
+  template<size_t N> struct formatter<const charT[N], charT>;
+  template<class traits, class Allocator>
+    struct formatter<basic_string<charT, traits, Allocator>, charT>;
+  template<class traits>
+    struct formatter<basic_string_view<charT, traits>, charT>;
+
+  // [format.parse.ctx], class template basic_format_parse_context
+  template<class charT>
+  class basic_format_parse_context {
+  public:
+    using char_type = charT;
+    using const_iterator = typename basic_string_view<charT>::const_iterator;
+    using iterator = const_iterator;
+
+  private:
+    iterator begin_;                                    // exposition only
+    iterator end_;                                      // exposition only
+    enum indexing { unknown, manual, automatic };       // exposition only
+    indexing indexing_;                                 // exposition only
+    size_t next_arg_id_;                                // exposition only
+    size_t num_args_;                                   // exposition only
+
+  public:
+    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt,
+                                                  size_t num_args = 0) noexcept;
+    basic_format_parse_context(const basic_format_parse_context&) = delete;
+    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;
+
+    constexpr const_iterator begin() const noexcept;
+    constexpr const_iterator end() const noexcept;
+    constexpr void advance_to(const_iterator it);
+
+    constexpr size_t next_arg_id();
+    constexpr void check_arg_id(size_t id);
+  };
+  using format_parse_context = basic_format_parse_context<char>;
+  using wformat_parse_context = basic_format_parse_context<wchar_t>;
+
+  // [format.arguments], arguments
+  // [format.arg], class template basic_format_arg
+  template<class Context>
+  class basic_format_arg {
+  public:
+    class handle;
+
+  private:
+    using char_type = typename Context::char_type;                              // exposition only
+
+    variant<monostate, bool, char_type,
+            int, unsigned int, long long int, unsigned long long int,
+            float, double, long double,
+            const char_type*, basic_string_view<char_type>,
+            const void*, handle> value;                                         // exposition only
+
+    template<class T> explicit basic_format_arg(const T& v) noexcept;           // exposition only
+    explicit basic_format_arg(float n) noexcept;                                // exposition only
+    explicit basic_format_arg(double n) noexcept;                               // exposition only
+    explicit basic_format_arg(long double n) noexcept;                          // exposition only
+    explicit basic_format_arg(const char_type* s);                              // exposition only
+
+    template<class traits>
+      explicit basic_format_arg(
+        basic_string_view<char_type, traits> s) noexcept;                       // exposition only
+
+    template<class traits, class Allocator>
+      explicit basic_format_arg(
+        const basic_string<char_type, traits, Allocator>& s) noexcept;          // exposition only
+
+    explicit basic_format_arg(nullptr_t) noexcept;                              // exposition only
+
+    template<class T>
+      explicit basic_format_arg(const T* p) noexcept;                           // exposition only
+
+  public:
+    basic_format_arg() noexcept;
+
+    explicit operator bool() const noexcept;
+  };
+
+  template<class Visitor, class Context>
+    see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+
+  // [format.arg.store], class template format-arg-store
+  template<class Context, class... Args>
+  struct format-arg-store {      // exposition only
+    array<basic_format_arg<Context>, sizeof...(Args)> args;
+  };
+
+  template<class Context = format_context, class... Args>
+    format-arg-store<Context, Args...>
+      make_format_args(const Args&... args);
+  template<class... Args>
+    format-arg-store<wformat_context, Args...>
+      make_wformat_args(const Args&... args);
+
+  // [format.error], class format_error
+  class format_error : public runtime_error {
+  public:
+    explicit format_error(const string& what_arg);
+    explicit format_error(const char* what_arg);
+  };
+
+  // [format.parse.ctx], class template basic_format_parse_context
+  template<class charT>
+  class basic_format_parse_context {
+  public:
+    using char_type = charT;
+    using const_iterator = typename basic_string_view<charT>::const_iterator;
+    using iterator = const_iterator;
+
+  private:
+    iterator begin_;                                    // exposition only
+    iterator end_;                                      // exposition only
+    enum indexing { unknown, manual, automatic };       // exposition only
+    indexing indexing_;                                 // exposition only
+    size_t next_arg_id_;                                // exposition only
+    size_t num_args_;                                   // exposition only
+
+  public:
+    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt,
+                                                  size_t num_args = 0) noexcept;
+    basic_format_parse_context(const basic_format_parse_context&) = delete;
+    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;
+
+    constexpr const_iterator begin() const noexcept;
+    constexpr const_iterator end() const noexcept;
+    constexpr void advance_to(const_iterator it);
+
+    constexpr size_t next_arg_id();
+    constexpr void check_arg_id(size_t id);
+  };
+  using format_parse_context = basic_format_parse_context<char>;
+  using wformat_parse_context = basic_format_parse_context<wchar_t>;
+}
+
+*/
+
+// Make sure all feature-test macros are available.
+#include <version>
+// Enable the contents of the header only when libc++ was built with LIBCXX_ENABLE_INCOMPLETE_FEATURES.
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+
+#include <__config>
+#include <__debug>
+#include <__format/format_arg.h>
+#include <__format/format_args.h>
+#include <__format/format_context.h>
+#include <__format/format_error.h>
+#include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
+#include <__format/format_string.h>
+#include <__format/formatter.h>
+#include <__format/formatter_bool.h>
+#include <__format/formatter_char.h>
+#include <__format/formatter_integer.h>
+#include <__format/formatter_string.h>
+#include <__format/parser_std_format_spec.h>
+#include <__variant/monostate.h>
+#include <array>
+#include <concepts>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+#include <locale>
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+#if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+// TODO FMT Evaluate which templates should be external templates. This
+// improves the efficiency of the header. However since the header is still
+// under heavy development and not all classes are stable it makes no sense
+// to do this optimization now.
+
+using format_args = basic_format_args<format_context>;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wformat_args = basic_format_args<wformat_context>;
+#endif
+
+template <class _OutIt, class _CharT>
+using format_args_t = basic_format_args<basic_format_context<_OutIt, _CharT>>;
+
+template <class _Context, class... _Args>
+struct _LIBCPP_TEMPLATE_VIS __format_arg_store {
+  // TODO FMT Use a built-in array.
+  array<basic_format_arg<_Context>, sizeof...(_Args)> __args;
+};
+
+template <class _Context = format_context, class... _Args>
+_LIBCPP_HIDE_FROM_ABI __format_arg_store<_Context, _Args...>
+make_format_args(const _Args&... __args) {
+  return {basic_format_arg<_Context>(__args)...};
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI __format_arg_store<wformat_context, _Args...>
+make_wformat_args(const _Args&... __args) {
+  return _VSTD::make_format_args<wformat_context>(__args...);
+}
+#endif
+
+namespace __format {
+
+template <class _Tp, class _CharT>
+requires(is_arithmetic_v<_Tp> &&
+         !same_as<_Tp, bool>) struct _LIBCPP_HIDE_FROM_ABI
+    __formatter_arithmetic {
+  _LIBCPP_HIDE_FROM_ABI
+  auto parse(auto& __parse_ctx) -> decltype(__parse_ctx.begin()) {
+    // TODO FMT Implement
+    return __parse_ctx.begin();
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  auto format(_Tp __value, auto& __ctx) -> decltype(__ctx.out()) {
+    return __handle_format(__value, __ctx);
+  }
+
+private:
+  template <class _Uv>
+  _LIBCPP_HIDDEN static string
+  __convert(_Uv __value) requires(same_as<_CharT, char>) {
+    return _VSTD::to_string(__value);
+  }
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+  template <class _Uv>
+  _LIBCPP_HIDDEN static wstring
+  __convert(_Uv __value) requires(same_as<_CharT, wchar_t>) {
+    return _VSTD::to_wstring(__value);
+  }
+#endif
+
+  template <class _Uv>
+  _LIBCPP_HIDDEN auto __handle_format(_Uv __value, auto& __ctx)
+      -> decltype(__ctx.out())
+  {
+    // TODO FMT Implement using formatting arguments
+    // TODO FMT Improve PoC since using std::to_string is inefficient.
+    // Note the code doesn't use std::string::iterator since the unit tests
+    // test with debug iterators and they fail with strings created from
+    // std::to_string.
+    auto __str = __convert(__value);
+    auto __out_it = __ctx.out();
+    for (size_t __i = 0, __e = __str.size(); __i != __e; ++__i)
+      *__out_it++ = __str[__i];
+    return __out_it;
+  }
+};
+} // namespace __format
+
+// These specializations are helper stubs and not proper formatters.
+// TODO FMT Implement the proper formatter specializations.
+
+// Floating point types.
+// TODO FMT There are no replacements for the floating point stubs due to not
+// having floating point support in std::to_chars yet. These stubs aren't
+// removed since they are useful for developing the real versions.
+// Ultimately the stubs should be implemented properly and this code can be
+// removed.
+#if 0
+template <class _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<float, _CharT>
+    : public __format::__formatter_arithmetic<float, _CharT> {};
+template <class _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
+    formatter<double, _CharT>
+    : public __format::__formatter_arithmetic<double, _CharT> {};
+template <class _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
+    formatter<long double, _CharT>
+    : public __format::__formatter_arithmetic<long double, _CharT> {};
+#endif
+
+namespace __format {
+
+template <class _CharT, class _ParseCtx, class _Ctx>
+_LIBCPP_HIDE_FROM_ABI const _CharT*
+__handle_replacement_field(const _CharT* __begin, const _CharT* __end,
+                           _ParseCtx& __parse_ctx, _Ctx& __ctx) {
+  __format::__parse_number_result __r =
+      __format::__parse_arg_id(__begin, __end, __parse_ctx);
+
+  switch (*__r.__ptr) {
+  case _CharT(':'):
+    // The arg-id has a format-specifier, advance the input to the format-spec.
+    __parse_ctx.advance_to(__r.__ptr + 1);
+    break;
+  case _CharT('}'):
+    // The arg-id has no format-specifier.
+    __parse_ctx.advance_to(__r.__ptr);
+    break;
+  default:
+    __throw_format_error(
+        "The replacement field arg-id should terminate at a ':' or '}'");
+  }
+
+  _VSTD::visit_format_arg(
+      [&](auto __arg) {
+        if constexpr (same_as<decltype(__arg), monostate>)
+          __throw_format_error("Argument index out of bounds");
+        else {
+          formatter<decltype(__arg), _CharT> __formatter;
+          __parse_ctx.advance_to(__formatter.parse(__parse_ctx));
+          __ctx.advance_to(__formatter.format(__arg, __ctx));
+        }
+      },
+      __ctx.arg(__r.__value));
+
+  __begin = __parse_ctx.begin();
+  if (__begin == __end || *__begin != _CharT('}'))
+    __throw_format_error("The replacement field misses a terminating '}'");
+
+  return ++__begin;
+}
+
+template <class _ParseCtx, class _Ctx>
+_LIBCPP_HIDE_FROM_ABI typename _Ctx::iterator
+__vformat_to(_ParseCtx&& __parse_ctx, _Ctx&& __ctx) {
+  using _CharT = typename _ParseCtx::char_type;
+  static_assert(same_as<typename _Ctx::char_type, _CharT>);
+
+  const _CharT* __begin = __parse_ctx.begin();
+  const _CharT* __end = __parse_ctx.end();
+  typename _Ctx::iterator __out_it = __ctx.out();
+  while (__begin != __end) {
+    switch (*__begin) {
+    case _CharT('{'):
+      ++__begin;
+      if (__begin == __end)
+        __throw_format_error("The format string terminates at a '{'");
+
+      if (*__begin != _CharT('{')) [[likely]] {
+        __ctx.advance_to(_VSTD::move(__out_it));
+        __begin =
+            __handle_replacement_field(__begin, __end, __parse_ctx, __ctx);
+        __out_it = __ctx.out();
+
+        // The output is written and __begin points to the next character. So
+        // start the next iteration.
+        continue;
+      }
+      // The string is an escape character.
+      break;
+
+    case _CharT('}'):
+      ++__begin;
+      if (__begin == __end || *__begin != _CharT('}'))
+        __throw_format_error(
+            "The format string contains an invalid escape sequence");
+
+      break;
+    }
+
+    // Copy the character to the output verbatim.
+    *__out_it++ = *__begin++;
+  }
+  return __out_it;
+}
+
+} // namespace __format
+
+template <class _OutIt, class _CharT>
+requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt
+    __vformat_to(_OutIt __out_it, basic_string_view<_CharT> __fmt,
+                 format_args_t<type_identity_t<_OutIt>, _CharT> __args) {
+  return __format::__vformat_to(
+      basic_format_parse_context{__fmt, __args.__size()},
+      _VSTD::__format_context_create(_VSTD::move(__out_it), __args));
+}
+
+template <output_iterator<const char&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+vformat_to(_OutIt __out_it, string_view __fmt,
+           format_args_t<type_identity_t<_OutIt>, char> __args) {
+  return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args);
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+vformat_to(_OutIt __out_it, wstring_view __fmt,
+           format_args_t<type_identity_t<_OutIt>, wchar_t> __args) {
+  return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args);
+}
+#endif
+
+template <output_iterator<const char&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+format_to(_OutIt __out_it, string_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat_to(
+      _VSTD::move(__out_it), __fmt,
+      _VSTD::make_format_args<basic_format_context<_OutIt, char>>(__args...));
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+format_to(_OutIt __out_it, wstring_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat_to(
+      _VSTD::move(__out_it), __fmt,
+      _VSTD::make_format_args<basic_format_context<_OutIt, wchar_t>>(
+          __args...));
+}
+#endif
+
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string
+vformat(string_view __fmt, format_args __args) {
+  string __res;
+  _VSTD::vformat_to(_VSTD::back_inserter(__res), __fmt, __args);
+  return __res;
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
+vformat(wstring_view __fmt, wformat_args __args) {
+  wstring __res;
+  _VSTD::vformat_to(_VSTD::back_inserter(__res), __fmt, __args);
+  return __res;
+}
+#endif
+
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string
+format(string_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...));
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
+format(wstring_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...));
+}
+#endif
+
+template <class _OutIt>
+struct _LIBCPP_TEMPLATE_VIS format_to_n_result {
+  _OutIt out;
+  iter_difference_t<_OutIt> size;
+};
+
+template <output_iterator<const char&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
+format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, string_view __fmt,
+            const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  string __str = _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...));
+  iter_difference_t<_OutIt> __s = __str.size();
+  iter_difference_t<_OutIt> __m =
+      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s);
+  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it));
+  return {_VSTD::move(__out_it), __s};
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
+format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, wstring_view __fmt,
+            const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  wstring __str = _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...));
+  iter_difference_t<_OutIt> __s = __str.size();
+  iter_difference_t<_OutIt> __m =
+      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s);
+  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it));
+  return {_VSTD::move(__out_it), __s};
+}
+#endif
+
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
+formatted_size(string_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  return _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...)).size();
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
+formatted_size(wstring_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  return _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...)).size();
+}
+#endif
+
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+
+template <class _OutIt, class _CharT>
+requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt
+    __vformat_to(_OutIt __out_it, locale __loc, basic_string_view<_CharT> __fmt,
+                 format_args_t<type_identity_t<_OutIt>, _CharT> __args) {
+  return __format::__vformat_to(
+      basic_format_parse_context{__fmt, __args.__size()},
+      _VSTD::__format_context_create(_VSTD::move(__out_it), __args,
+                                     _VSTD::move(__loc)));
+}
+
+template <output_iterator<const char&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+vformat_to(_OutIt __out_it, locale __loc, string_view __fmt,
+           format_args_t<type_identity_t<_OutIt>, char> __args) {
+  return _VSTD::__vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt,
+                             __args);
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
+vformat_to(_OutIt __out_it, locale __loc, wstring_view __fmt,
+           format_args_t<type_identity_t<_OutIt>, wchar_t> __args) {
+  return _VSTD::__vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt,
+                             __args);
+}
+#endif
+
+template <output_iterator<const char&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt format_to(
+    _OutIt __out_it, locale __loc, string_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat_to(
+      _VSTD::move(__out_it), _VSTD::move(__loc), __fmt,
+      _VSTD::make_format_args<basic_format_context<_OutIt, char>>(__args...));
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt format_to(
+    _OutIt __out_it, locale __loc, wstring_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat_to(
+      _VSTD::move(__out_it), _VSTD::move(__loc), __fmt,
+      _VSTD::make_format_args<basic_format_context<_OutIt, wchar_t>>(
+          __args...));
+}
+#endif
+
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string
+vformat(locale __loc, string_view __fmt, format_args __args) {
+  string __res;
+  _VSTD::vformat_to(_VSTD::back_inserter(__res), _VSTD::move(__loc), __fmt,
+                    __args);
+  return __res;
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
+vformat(locale __loc, wstring_view __fmt, wformat_args __args) {
+  wstring __res;
+  _VSTD::vformat_to(_VSTD::back_inserter(__res), _VSTD::move(__loc), __fmt,
+                    __args);
+  return __res;
+}
+#endif
+
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string
+format(locale __loc, string_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                        _VSTD::make_format_args(__args...));
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
+format(locale __loc, wstring_view __fmt, const _Args&... __args) {
+  return _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                        _VSTD::make_wformat_args(__args...));
+}
+#endif
+
+template <output_iterator<const char&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
+format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, locale __loc,
+            string_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  string __str = _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                                _VSTD::make_format_args(__args...));
+  iter_difference_t<_OutIt> __s = __str.size();
+  iter_difference_t<_OutIt> __m =
+      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s);
+  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it));
+  return {_VSTD::move(__out_it), __s};
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <output_iterator<const wchar_t&> _OutIt, class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
+format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, locale __loc,
+            wstring_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  wstring __str = _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                                 _VSTD::make_wformat_args(__args...));
+  iter_difference_t<_OutIt> __s = __str.size();
+  iter_difference_t<_OutIt> __m =
+      _VSTD::clamp(__n, iter_difference_t<_OutIt>(0), __s);
+  __out_it = _VSTD::copy_n(__str.begin(), __m, _VSTD::move(__out_it));
+  return {_VSTD::move(__out_it), __s};
+}
+#endif
+
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
+formatted_size(locale __loc, string_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  return _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                        _VSTD::make_format_args(__args...))
+      .size();
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class... _Args>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
+formatted_size(locale __loc, wstring_view __fmt, const _Args&... __args) {
+  // TODO FMT Improve PoC: using std::string is inefficient.
+  return _VSTD::vformat(_VSTD::move(__loc), __fmt,
+                        _VSTD::make_wformat_args(__args...))
+      .size();
+}
+#endif
+
+#endif // _LIBCPP_HAS_NO_LOCALIZATION
+
+#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+
+#endif // _LIBCPP_FORMAT