[libc++][format] Granularizes the format header.

[Mordante]

Summary

Moves the last pieces of code to its own header.

[Mordante]

Fixes CI.

[Mordante]

Attempts to fix the CI.

[Mordante]

Attempts to fix the CI.

[Mordante]

Attempts to fix CI.

[ldionne]

libcxx/include/__format/format_functions.h

797

This removal seems to be the issue on macOS backdeployment.

I think basically <format> never worked on back-deployment targets. We should look into this as a separate effort -- we shouldn't be getting compilation errors if we just try to include e.g. <chrono> with -fexperimental-library on a back-deployment target, which I think is probably the case right now. I think investigating this would be trying to remove this in run-buildbot:

# TODO: Enable experimental features during back-deployment -- right now some of the availability
#       annotations are incorrect, leading to test failures that could be avoided.
PARAMS+=";enable_experimental=False"

[Mordante]

Attempts to fix CI based on observations while with @ldionne.

libcxx/include/CMakeLists.txt

set(files
   __format/concepts.h
   __format/enable_insertable.h
   __format/extended_grapheme_cluster_table.h
   __format/format_arg.h
   __format/format_arg_store.h
   __format/format_args.h
   __format/format_context.h
   __format/format_error.h
+  __format/format_functions.h
   __format/format_fwd.h
   __format/format_parse_context.h
   __format/format_string.h
   __format/format_to_n_result.h
   __format/formatter.h
   __format/formatter_bool.h
   __format/formatter_char.h
   __format/formatter_floating_point.h

libcxx/include/__format/format_functions.h

 // -*- 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
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP_FORMAT
-#define _LIBCPP_FORMAT
+#ifndef _LIBCPP___FORMAT_FORMAT_FUNCTIONS
+#define _LIBCPP___FORMAT_FORMAT_FUNCTIONS
 
-/*
-
-namespace std {
-  // [format.context], class template basic_format_context
-  template<class Out, class charT> class basic_format_context;
-  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;
-  using format_args = basic_format_args<format_context>;
-  using wformat_args = basic_format_args<wformat_context>;
-
-  // [format.fmt.string], class template basic_format_string
-  template<class charT, class... Args>
-    struct basic_format_string {                                // since C++23, exposition only before C++23
-    private:
-      basic_string_view<charT> str;                             // exposition only
-
-    public:
-      template<class T> consteval basic_format_string(const T& s);
-
-      constexpr basic_string_view<charT> get() const noexcept { return str; }
-    };
-  template<class... Args>
-    using format_string =                                       // since C++23, exposition only before C++23
-      basic_format_string<char, type_identity_t<Args>...>;
-  template<class... Args>
-    using wformat_string =                                      // since C++23, exposition only before C++23
-      basic_format_string<wchar_t, type_identity_t<Args>...>;
-
-  // [format.functions], formatting functions
-  template<class... Args>
-    string format(format-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    wstring format(wformat-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    string format(const locale& loc, format-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    wstring format(const locale& loc, wformat-string<Args...> fmt, 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, format-string<Args...> fmt, Args&&... args);
-  template<class Out, class... Args>
-    Out format_to(Out out, wformat-string<Args...> fmt, Args&&... args);
-  template<class Out, class... Args>
-    Out format_to(Out out, const locale& loc, format-string<Args...> fmt, Args&&... args);
-  template<class Out, class... Args>
-    Out format_to(Out out, const locale& loc, wformat-string<Args...> fmt, Args&&... args);
-
-  template<class Out>
-    Out vformat_to(Out out, string_view fmt, format_args args);
-  template<class Out>
-    Out vformat_to(Out out, wstring_view fmt, wformat_args args);
-  template<class Out>
-    Out vformat_to(Out out, const locale& loc, string_view fmt,
-                   format_args char> args);
-  template<class Out>
-    Out vformat_to(Out out, const locale& loc, wstring_view fmt,
-                   wformat_args 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,
-                                        format-string<Args...> fmt, Args&&... args);
-  template<class Out, class... Args>
-    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
-                                        wformat-string<Args...> fmt, 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, format-string<Args...> fmt,
-                                        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, wformat-string<Args...> fmt,
-                                        Args&&... args);
-
-  template<class... Args>
-    size_t formatted_size(format-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    size_t formatted_size(wformat-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    size_t formatted_size(const locale& loc, format-string<Args...> fmt, Args&&... args);
-  template<class... Args>
-    size_t formatted_size(const locale& loc, wformat-string<Args...> fmt, Args&&... args);
-
-  // [format.formatter], formatter
-  template<class T, class charT = char> struct formatter;
-
-  // [format.parse.ctx], class template basic_format_parse_context
-  template<class charT> class basic_format_parse_context;
-  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;
-
-  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
-
-  template<class Context = format_context, class... Args>
-    format-arg-store<Context, Args...>
-      make_format_args(Args&&... args);
-  template<class... Args>
-    format-arg-store<wformat_context, Args...>
-      make_wformat_args(Args&&... args);
-
-  // [format.error], class format_error
-  class format_error;
-}
-
-*/
-
-#include <__assert> // all public C++ headers provide the assertion handler
-// Make sure all feature-test macros are available.
+// TODO FMT This is added to fix Apple back-deployment.
 #include <version>
-// Enable the contents of the header only when libc++ was built with experimental features enabled.
 #if !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
 #include <__algorithm/clamp.h>
+#include <__availability>
+#include <__concepts/convertible_to.h>
+#include <__concepts/same_as.h>
 #include <__config>
 #include <__debug>
 #include <__format/buffer.h>
-#include <__format/concepts.h>
-#include <__format/enable_insertable.h>
 #include <__format/format_arg.h>
 #include <__format/format_arg_store.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/format_to_n_result.h>
 #include <__format/formatter.h>
 #include <__format/formatter_bool.h>
 #include <__format/formatter_char.h>
 #include <__format/formatter_floating_point.h>
 #include <__format/formatter_integer.h>
 #include <__format/formatter_pointer.h>
 #include <__format/formatter_string.h>
 #include <__format/parser_std_format_spec.h>
-#include <__format/unicode.h>
 #include <__iterator/back_insert_iterator.h>
 #include <__iterator/incrementable_traits.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_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-// TODO FMT Move the implementation in this file to its own granular headers.
-
 // 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>;

 _LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
 formatted_size(locale __loc, wformat_string<_Args...> __fmt, _Args&&... __args) {
   return _VSTD::__vformatted_size(_VSTD::move(__loc), __fmt.get(), basic_format_args{_VSTD::make_wformat_args(__args...)});
 }
 #endif
 
 #endif // _LIBCPP_HAS_NO_LOCALIZATION
 
+
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
-#endif // _LIBCPP_FORMAT
+#endif // _LIBCPP___FORMAT_FORMAT_FUNCTIONS

libcxx/include/format

 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 // Make sure all feature-test macros are available.
 #include <version>
 // Enable the contents of the header only when libc++ was built with experimental features enabled.
 #if !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
-#include <__algorithm/clamp.h>
 #include <__config>
-#include <__debug>
 #include <__format/buffer.h>
 #include <__format/concepts.h>
 #include <__format/enable_insertable.h>
 #include <__format/format_arg.h>
 #include <__format/format_arg_store.h>
 #include <__format/format_args.h>
 #include <__format/format_context.h>
 #include <__format/format_error.h>
+#include <__format/format_functions.h>
 #include <__format/format_fwd.h>
 #include <__format/format_parse_context.h>
 #include <__format/format_string.h>
 #include <__format/format_to_n_result.h>
 #include <__format/formatter.h>
 #include <__format/formatter_bool.h>
 #include <__format/formatter_char.h>
 #include <__format/formatter_floating_point.h>
 #include <__format/formatter_integer.h>
 #include <__format/formatter_pointer.h>
 #include <__format/formatter_string.h>
 #include <__format/parser_std_format_spec.h>
 #include <__format/unicode.h>
-#include <__iterator/back_insert_iterator.h>
-#include <__iterator/incrementable_traits.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_BEGIN_NAMESPACE_STD
-
-#if _LIBCPP_STD_VER > 17
-
-// TODO FMT Move the implementation in this file to its own granular headers.
-
-// 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 _Context = format_context, class... _Args>
-_LIBCPP_HIDE_FROM_ABI __format_arg_store<_Context, _Args...> make_format_args(_Args&&... __args) {
-  return _VSTD::__format_arg_store<_Context, _Args...>(__args...);
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-_LIBCPP_HIDE_FROM_ABI __format_arg_store<wformat_context, _Args...> make_wformat_args(_Args&&... __args) {
-  return _VSTD::__format_arg_store<wformat_context, _Args...>(__args...);
-}
-#endif
-
-namespace __format {
-
-/// Helper class parse and handle argument.
-///
-/// When parsing a handle which is not enabled the code is ill-formed.
-/// This helper uses the parser of the appropriate formatter for the stored type.
-template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS __compile_time_handle {
-public:
-  _LIBCPP_HIDE_FROM_ABI
-  constexpr void __parse(basic_format_parse_context<_CharT>& __parse_ctx) const { __parse_(__parse_ctx); }
-
-  template <class _Tp>
-  _LIBCPP_HIDE_FROM_ABI constexpr void __enable() {
-    __parse_ = [](basic_format_parse_context<_CharT>& __parse_ctx) {
-      formatter<_Tp, _CharT> __f;
-      __parse_ctx.advance_to(__f.parse(__parse_ctx));
-    };
-  }
-
-  // Before calling __parse the proper handler needs to be set with __enable.
-  // The default handler isn't a core constant expression.
-  _LIBCPP_HIDE_FROM_ABI constexpr __compile_time_handle()
-      : __parse_([](basic_format_parse_context<_CharT>&) { __throw_format_error("Not a handle"); }) {}
-
-private:
-  void (*__parse_)(basic_format_parse_context<_CharT>&);
-};
-
-// Dummy format_context only providing the parts used during constant
-// validation of the basic_format_string.
-template <class _CharT>
-struct _LIBCPP_TEMPLATE_VIS __compile_time_basic_format_context {
-public:
-  using char_type = _CharT;
-
-  _LIBCPP_HIDE_FROM_ABI constexpr explicit __compile_time_basic_format_context(
-      const __arg_t* __args, const __compile_time_handle<_CharT>* __handles, size_t __size)
-      : __args_(__args), __handles_(__handles), __size_(__size) {}
-
-  // During the compile-time validation nothing needs to be written.
-  // Therefore all operations of this iterator are a NOP.
-  struct iterator {
-    _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator=(_CharT) { return *this; }
-    _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator*() { return *this; }
-    _LIBCPP_HIDE_FROM_ABI constexpr iterator operator++(int) { return *this; }
-  };
-
-  _LIBCPP_HIDE_FROM_ABI constexpr __arg_t arg(size_t __id) const {
-    if (__id >= __size_)
-      __throw_format_error("Argument index out of bounds");
-    return __args_[__id];
-  }
-
-  _LIBCPP_HIDE_FROM_ABI constexpr const __compile_time_handle<_CharT>& __handle(size_t __id) const {
-    if (__id >= __size_)
-      __throw_format_error("Argument index out of bounds");
-    return __handles_[__id];
-  }
-
-  _LIBCPP_HIDE_FROM_ABI constexpr iterator out() { return {}; }
-  _LIBCPP_HIDE_FROM_ABI constexpr void advance_to(iterator) {}
-
-private:
-  const __arg_t* __args_;
-  const __compile_time_handle<_CharT>* __handles_;
-  size_t __size_;
-};
-
-_LIBCPP_HIDE_FROM_ABI
-constexpr void __compile_time_validate_integral(__arg_t __type) {
-  switch (__type) {
-  case __arg_t::__int:
-  case __arg_t::__long_long:
-  case __arg_t::__i128:
-  case __arg_t::__unsigned:
-  case __arg_t::__unsigned_long_long:
-  case __arg_t::__u128:
-    return;
-
-  default:
-    __throw_format_error("Argument isn't an integral type");
-  }
-}
-
-// _HasPrecision does the formatter have a precision?
-template <class _CharT, class _Tp, bool _HasPrecision = false>
-_LIBCPP_HIDE_FROM_ABI constexpr void
-__compile_time_validate_argument(basic_format_parse_context<_CharT>& __parse_ctx,
-                                 __compile_time_basic_format_context<_CharT>& __ctx) {
-  formatter<_Tp, _CharT> __formatter;
-  __parse_ctx.advance_to(__formatter.parse(__parse_ctx));
-  // [format.string.std]/7
-  // ... If the corresponding formatting argument is not of integral type, or
-  // its value is negative for precision or non-positive for width, an
-  // exception of type format_error is thrown.
-  //
-  // Validate whether the arguments are integrals.
-  if (__formatter.__parser_.__width_as_arg_)
-    __format::__compile_time_validate_integral(__ctx.arg(__formatter.__parser_.__width_));
-
-  if constexpr (_HasPrecision)
-    if (__formatter.__parser_.__precision_as_arg_)
-      __format::__compile_time_validate_integral(__ctx.arg(__formatter.__parser_.__precision_));
-}
-
-template <class _CharT>
-_LIBCPP_HIDE_FROM_ABI constexpr void __compile_time_visit_format_arg(basic_format_parse_context<_CharT>& __parse_ctx,
-                                                                     __compile_time_basic_format_context<_CharT>& __ctx,
-                                                                     __arg_t __type) {
-  switch (__type) {
-  case __arg_t::__none:
-    __throw_format_error("Invalid argument");
-  case __arg_t::__boolean:
-    return __format::__compile_time_validate_argument<_CharT, bool>(__parse_ctx, __ctx);
-  case __arg_t::__char_type:
-    return __format::__compile_time_validate_argument<_CharT, _CharT>(__parse_ctx, __ctx);
-  case __arg_t::__int:
-    return __format::__compile_time_validate_argument<_CharT, int>(__parse_ctx, __ctx);
-  case __arg_t::__long_long:
-    return __format::__compile_time_validate_argument<_CharT, long long>(__parse_ctx, __ctx);
-  case __arg_t::__i128:
-#      ifndef _LIBCPP_HAS_NO_INT128
-    return __format::__compile_time_validate_argument<_CharT, __int128_t>(__parse_ctx, __ctx);
-#      else
-    __throw_format_error("Invalid argument");
-#      endif
-    return;
-  case __arg_t::__unsigned:
-    return __format::__compile_time_validate_argument<_CharT, unsigned>(__parse_ctx, __ctx);
-  case __arg_t::__unsigned_long_long:
-    return __format::__compile_time_validate_argument<_CharT, unsigned long long>(__parse_ctx, __ctx);
-  case __arg_t::__u128:
-#      ifndef _LIBCPP_HAS_NO_INT128
-    return __format::__compile_time_validate_argument<_CharT, __uint128_t>(__parse_ctx, __ctx);
-#      else
-    __throw_format_error("Invalid argument");
-#      endif
-    return;
-  case __arg_t::__float:
-    return __format::__compile_time_validate_argument<_CharT, float, true>(__parse_ctx, __ctx);
-  case __arg_t::__double:
-    return __format::__compile_time_validate_argument<_CharT, double, true>(__parse_ctx, __ctx);
-  case __arg_t::__long_double:
-    return __format::__compile_time_validate_argument<_CharT, long double, true>(__parse_ctx, __ctx);
-  case __arg_t::__const_char_type_ptr:
-    return __format::__compile_time_validate_argument<_CharT, const _CharT*, true>(__parse_ctx, __ctx);
-  case __arg_t::__string_view:
-    return __format::__compile_time_validate_argument<_CharT, basic_string_view<_CharT>, true>(__parse_ctx, __ctx);
-  case __arg_t::__ptr:
-    return __format::__compile_time_validate_argument<_CharT, const void*>(__parse_ctx, __ctx);
-  case __arg_t::__handle:
-    __throw_format_error("Handle should use __compile_time_validate_handle_argument");
-  }
-  __throw_format_error("Invalid argument");
-}
-
-template <class _CharT, class _ParseCtx, class _Ctx>
-_LIBCPP_HIDE_FROM_ABI constexpr 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);
-
-  bool __parse = *__r.__ptr == _CharT(':');
-  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 '}'");
-  }
-
-  if constexpr (same_as<_Ctx, __compile_time_basic_format_context<_CharT>>) {
-    __arg_t __type = __ctx.arg(__r.__value);
-    if (__type == __arg_t::__handle)
-      __ctx.__handle(__r.__value).__parse(__parse_ctx);
-    else
-        __format::__compile_time_visit_format_arg(__parse_ctx, __ctx, __type);
-  } else
-    _VSTD::visit_format_arg(
-        [&](auto __arg) {
-          if constexpr (same_as<decltype(__arg), monostate>)
-            __throw_format_error("Argument index out of bounds");
-          else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Ctx>::handle>)
-            __arg.format(__parse_ctx, __ctx);
-          else {
-            formatter<decltype(__arg), _CharT> __formatter;
-            if (__parse)
-              __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 constexpr 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 _CharT, class... _Args>
-struct _LIBCPP_TEMPLATE_VIS basic_format_string {
-  template <class _Tp>
-    requires convertible_to<const _Tp&, basic_string_view<_CharT>>
-  consteval basic_format_string(const _Tp& __str) : __str_{__str} {
-    __format::__vformat_to(basic_format_parse_context<_CharT>{__str_, sizeof...(_Args)},
-                           _Context{__types_.data(), __handles_.data(), sizeof...(_Args)});
-  }
-
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT constexpr basic_string_view<_CharT> get() const noexcept {
-    return __str_;
-  }
-
-private:
-  basic_string_view<_CharT> __str_;
-
-  using _Context = __format::__compile_time_basic_format_context<_CharT>;
-
-  static constexpr array<__format::__arg_t, sizeof...(_Args)> __types_{
-      __format::__determine_arg_t<_Context, remove_cvref_t<_Args>>()...};
-
-  // TODO FMT remove this work-around when the AIX ICE has been resolved.
-#    if defined(_AIX) && defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER < 1400
-  template <class _Tp>
-  static constexpr __format::__compile_time_handle<_CharT> __get_handle() {
-    __format::__compile_time_handle<_CharT> __handle;
-    if (__format::__determine_arg_t<_Context, _Tp>() == __format::__arg_t::__handle)
-      __handle.template __enable<_Tp>();
-
-    return __handle;
-  }
-
-  static constexpr array<__format::__compile_time_handle<_CharT>, sizeof...(_Args)> __handles_{
-      __get_handle<_Args>()...};
-#    else
-  static constexpr array<__format::__compile_time_handle<_CharT>, sizeof...(_Args)> __handles_{[] {
-    using _Tp = remove_cvref_t<_Args>;
-    __format::__compile_time_handle<_CharT> __handle;
-    if (__format::__determine_arg_t<_Context, _Tp>() == __format::__arg_t::__handle)
-      __handle.template __enable<_Tp>();
-
-    return __handle;
-  }()...};
-#    endif
-};
-
-template <class... _Args>
-using format_string = basic_format_string<char, type_identity_t<_Args>...>;
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-using wformat_string = basic_format_string<wchar_t, type_identity_t<_Args>...>;
-#endif
-
-template <class _OutIt, class _CharT, class _FormatOutIt>
-requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt
-    __vformat_to(
-        _OutIt __out_it, basic_string_view<_CharT> __fmt,
-        basic_format_args<basic_format_context<_FormatOutIt, _CharT>> __args) {
-  if constexpr (same_as<_OutIt, _FormatOutIt>)
-    return _VSTD::__format::__vformat_to(
-        basic_format_parse_context{__fmt, __args.__size()},
-        _VSTD::__format_context_create(_VSTD::move(__out_it), __args));
-  else {
-    __format::__format_buffer<_OutIt, _CharT> __buffer{_VSTD::move(__out_it)};
-    _VSTD::__format::__vformat_to(
-        basic_format_parse_context{__fmt, __args.__size()},
-        _VSTD::__format_context_create(__buffer.__make_output_iterator(),
-                                       __args));
-    return _VSTD::move(__buffer).__out_it();
-  }
-}
-
-// The function is _LIBCPP_ALWAYS_INLINE since the compiler is bad at inlining
-// https://reviews.llvm.org/D110499#inline-1180704
-// TODO FMT Evaluate whether we want to file a Clang bug report regarding this.
-template <output_iterator<const char&> _OutIt>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-vformat_to(_OutIt __out_it, string_view __fmt, format_args __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_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-vformat_to(_OutIt __out_it, wstring_view __fmt, wformat_args __args) {
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args);
-}
-#endif
-
-template <output_iterator<const char&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-format_to(_OutIt __out_it, format_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat_to(_VSTD::move(__out_it), __fmt.get(),
-                           _VSTD::make_format_args(__args...));
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <output_iterator<const wchar_t&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-format_to(_OutIt __out_it, wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat_to(_VSTD::move(__out_it), __fmt.get(),
-                           _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-_LIBCPP_ALWAYS_INLINE 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
-_LIBCPP_ALWAYS_INLINE 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_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string format(format_string<_Args...> __fmt,
-                                                                                      _Args&&... __args) {
-  return _VSTD::vformat(__fmt.get(), _VSTD::make_format_args(__args...));
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
-format(wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat(__fmt.get(), _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-template <class _Context, class _OutIt, class _CharT>
-_LIBCPP_HIDE_FROM_ABI format_to_n_result<_OutIt> __vformat_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n,
-                                                                basic_string_view<_CharT> __fmt,
-                                                                basic_format_args<_Context> __args) {
-  __format::__format_to_n_buffer<_OutIt, _CharT> __buffer{_VSTD::move(__out_it), __n};
-  _VSTD::__format::__vformat_to(basic_format_parse_context{__fmt, __args.__size()},
-                                _VSTD::__format_context_create(__buffer.__make_output_iterator(), __args));
-  return _VSTD::move(__buffer).__result();
-}
-
-template <output_iterator<const char&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
-format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, format_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::__vformat_to_n<format_context>(_VSTD::move(__out_it), __n, __fmt.get(), _VSTD::make_format_args(__args...));
-}
-
-#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, wformat_string<_Args...> __fmt,
-            _Args&&... __args) {
-  return _VSTD::__vformat_to_n<wformat_context>(_VSTD::move(__out_it), __n, __fmt.get(), _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-template <class _CharT>
-_LIBCPP_HIDE_FROM_ABI size_t __vformatted_size(basic_string_view<_CharT> __fmt, auto __args) {
-  __format::__formatted_size_buffer<_CharT> __buffer;
-  _VSTD::__format::__vformat_to(basic_format_parse_context{__fmt, __args.__size()},
-                                _VSTD::__format_context_create(__buffer.__make_output_iterator(), __args));
-  return _VSTD::move(__buffer).__result();
-}
-
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
-formatted_size(format_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::__vformatted_size(__fmt.get(), basic_format_args{_VSTD::make_format_args(__args...)});
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
-formatted_size(wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::__vformatted_size(__fmt.get(), basic_format_args{_VSTD::make_wformat_args(__args...)});
-}
-#endif
-
-#ifndef _LIBCPP_HAS_NO_LOCALIZATION
-
-template <class _OutIt, class _CharT, class _FormatOutIt>
-requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt
-    __vformat_to(
-        _OutIt __out_it, locale __loc, basic_string_view<_CharT> __fmt,
-        basic_format_args<basic_format_context<_FormatOutIt, _CharT>> __args) {
-  if constexpr (same_as<_OutIt, _FormatOutIt>)
-    return _VSTD::__format::__vformat_to(
-        basic_format_parse_context{__fmt, __args.__size()},
-        _VSTD::__format_context_create(_VSTD::move(__out_it), __args,
-                                       _VSTD::move(__loc)));
-  else {
-    __format::__format_buffer<_OutIt, _CharT> __buffer{_VSTD::move(__out_it)};
-    _VSTD::__format::__vformat_to(
-        basic_format_parse_context{__fmt, __args.__size()},
-        _VSTD::__format_context_create(__buffer.__make_output_iterator(),
-                                       __args, _VSTD::move(__loc)));
-    return _VSTD::move(__buffer).__out_it();
-  }
-}
-
-template <output_iterator<const char&> _OutIt>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt vformat_to(
-    _OutIt __out_it, locale __loc, string_view __fmt, format_args __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_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt vformat_to(
-    _OutIt __out_it, locale __loc, wstring_view __fmt, wformat_args __args) {
-  return _VSTD::__vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt,
-                             __args);
-}
-#endif
-
-template <output_iterator<const char&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-format_to(_OutIt __out_it, locale __loc, format_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt.get(),
-                           _VSTD::make_format_args(__args...));
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <output_iterator<const wchar_t&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT _OutIt
-format_to(_OutIt __out_it, locale __loc, wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat_to(_VSTD::move(__out_it), _VSTD::move(__loc), __fmt.get(),
-                           _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-_LIBCPP_ALWAYS_INLINE 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
-_LIBCPP_ALWAYS_INLINE 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_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT string format(locale __loc,
-                                                                                      format_string<_Args...> __fmt,
-                                                                                      _Args&&... __args) {
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt.get(),
-                        _VSTD::make_format_args(__args...));
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
-format(locale __loc, wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::vformat(_VSTD::move(__loc), __fmt.get(),
-                        _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-template <class _Context, class _OutIt, class _CharT>
-_LIBCPP_HIDE_FROM_ABI format_to_n_result<_OutIt> __vformat_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n,
-                                                                locale __loc, basic_string_view<_CharT> __fmt,
-                                                                basic_format_args<_Context> __args) {
-  __format::__format_to_n_buffer<_OutIt, _CharT> __buffer{_VSTD::move(__out_it), __n};
-  _VSTD::__format::__vformat_to(
-      basic_format_parse_context{__fmt, __args.__size()},
-      _VSTD::__format_context_create(__buffer.__make_output_iterator(), __args, _VSTD::move(__loc)));
-  return _VSTD::move(__buffer).__result();
-}
-
-template <output_iterator<const char&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _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, format_string<_Args...> __fmt,
-            _Args&&... __args) {
-  return _VSTD::__vformat_to_n<format_context>(_VSTD::move(__out_it), __n, _VSTD::move(__loc), __fmt.get(),
-                                               _VSTD::make_format_args(__args...));
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <output_iterator<const wchar_t&> _OutIt, class... _Args>
-_LIBCPP_ALWAYS_INLINE _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, wformat_string<_Args...> __fmt,
-            _Args&&... __args) {
-  return _VSTD::__vformat_to_n<wformat_context>(_VSTD::move(__out_it), __n, _VSTD::move(__loc), __fmt.get(),
-                                                _VSTD::make_wformat_args(__args...));
-}
-#endif
-
-template <class _CharT>
-_LIBCPP_HIDE_FROM_ABI size_t __vformatted_size(locale __loc, basic_string_view<_CharT> __fmt, auto __args) {
-  __format::__formatted_size_buffer<_CharT> __buffer;
-  _VSTD::__format::__vformat_to(
-      basic_format_parse_context{__fmt, __args.__size()},
-      _VSTD::__format_context_create(__buffer.__make_output_iterator(), __args, _VSTD::move(__loc)));
-  return _VSTD::move(__buffer).__result();
-}
-
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
-formatted_size(locale __loc, format_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::__vformatted_size(_VSTD::move(__loc), __fmt.get(), basic_format_args{_VSTD::make_format_args(__args...)});
-}
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-template <class... _Args>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT size_t
-formatted_size(locale __loc, wformat_string<_Args...> __fmt, _Args&&... __args) {
-  return _VSTD::__vformatted_size(_VSTD::move(__loc), __fmt.get(), basic_format_args{_VSTD::make_wformat_args(__args...)});
-}
-#endif
-
-#endif // _LIBCPP_HAS_NO_LOCALIZATION
-
-#endif //_LIBCPP_STD_VER > 17
-
-_LIBCPP_END_NAMESPACE_STD
-
 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
 #endif // _LIBCPP_FORMAT

libcxx/include/module.modulemap.in

module __format {
       module format_arg_store                { private header "__format/format_arg_store.h" }
       module format_args                     { private header "__format/format_args.h" }
       module format_context {
         private header "__format/format_context.h"
         export optional
         export locale
       }
       module format_error                    { private header "__format/format_error.h" }
+      module format_functions                { private header "__format/format_functions.h" }
       module format_fwd                      { private header "__format/format_fwd.h" }
       module format_parse_context            { private header "__format/format_parse_context.h" }
       module format_string                   { private header "__format/format_string.h" }
-      module format_to_n_result              { private header "__format/format_to_n_result.h" }
+      module format_to_n_result {
+        private header "__format/format_to_n_result.h"
+        export iterator.__iterator.incrementable_traits
+      }
       module formatter                       { private header "__format/formatter.h" }
       module formatter_bool                  { private header "__format/formatter_bool.h" }
       module formatter_char                  { private header "__format/formatter_char.h" }
       module formatter_floating_point        { private header "__format/formatter_floating_point.h" }
       module formatter_integer               { private header "__format/formatter_integer.h" }
       module formatter_integral              { private header "__format/formatter_integral.h" }
       module formatter_output                { private header "__format/formatter_output.h" }
       module formatter_pointer               { private header "__format/formatter_pointer.h" }

libcxx/test/libcxx/private_headers.verify.cpp

 #include <__format/concepts.h> // expected-error@*:* {{use of private header from outside its module: '__format/concepts.h'}}
 #include <__format/enable_insertable.h> // expected-error@*:* {{use of private header from outside its module: '__format/enable_insertable.h'}}
 #include <__format/extended_grapheme_cluster_table.h> // expected-error@*:* {{use of private header from outside its module: '__format/extended_grapheme_cluster_table.h'}}
 #include <__format/format_arg.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_arg.h'}}
 #include <__format/format_arg_store.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_arg_store.h'}}
 #include <__format/format_args.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_args.h'}}
 #include <__format/format_context.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_context.h'}}
 #include <__format/format_error.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_error.h'}}
+#include <__format/format_functions.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_functions.h'}}
 #include <__format/format_fwd.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_fwd.h'}}
 #include <__format/format_parse_context.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_parse_context.h'}}
 #include <__format/format_string.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_string.h'}}
 #include <__format/format_to_n_result.h> // expected-error@*:* {{use of private header from outside its module: '__format/format_to_n_result.h'}}
 #include <__format/formatter.h> // expected-error@*:* {{use of private header from outside its module: '__format/formatter.h'}}
 #include <__format/formatter_bool.h> // expected-error@*:* {{use of private header from outside its module: '__format/formatter_bool.h'}}
 #include <__format/formatter_char.h> // expected-error@*:* {{use of private header from outside its module: '__format/formatter_char.h'}}
 #include <__format/formatter_floating_point.h> // expected-error@*:* {{use of private header from outside its module: '__format/formatter_floating_point.h'}}