[libc++][NFC] Move basic_format_parse_context to its own header.

[Mordante]

Summary

This is a preparation to split the format header in smaller parts for the
upcoming patches.

Depends on D101723

[zoecarver]

I guess I looked at these in the wrong order 😁

WDYT about merging this and D101723 into one file, they seem small enough. That being said, I'd be OK with two headers, especially if either is expected to grow.

[Mordante]

Both headers are complete. I separated them since they are defined in different sections of the standard. I don't object against moving them together. Since I think both classes are used everywhere in the std::format. Do you have a suggestion for a name, I have __format/basic.h, but that doesn't feel great.

[Mordante]

Rebased to fix applying D93593.

libcxx/include/CMakeLists.txt

 set(files
   __availability
   __bit_reference
   __bits
   __bsd_locale_defaults.h
   __bsd_locale_fallbacks.h
   __config
   __debug
   __errc
   __format/format_error.h
+  __format/format_parse_context.h
   __function_like.h
   __functional_03
   __functional_base
   __functional_base_03
   __hash_table
   __iterator/advance.h
   __iterator/concepts.h
   __iterator/incrementable_traits.h

libcxx/include/__format/format_parse_context.h

 // -*- 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.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>;
-}
-
-*/
+#ifndef _LIBCPP___FORMAT_FORMAT_PARSE_CONTEXT_H
+#define _LIBCPP___FORMAT_FORMAT_PARSE_CONTEXT_H
 
 #include <__config>
 #include <__format/format_error.h>
 #include <string_view>
-#include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC 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) && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if !defined(_LIBCPP_HAS_NO_CONCEPTS) &&                                       \
+    !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
 
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS basic_format_parse_context {
 public:
   using char_type = _CharT;
-  using const_iterator =
-      typename basic_string_view<_CharT>::const_iterator;
+  using const_iterator = typename basic_string_view<_CharT>::const_iterator;
   using iterator = const_iterator;
 
-public:
   _LIBCPP_INLINE_VISIBILITY
-  constexpr explicit basic_format_parse_context(
-      basic_string_view<_CharT> __fmt, size_t __num_args = 0) noexcept
+  constexpr explicit basic_format_parse_context(basic_string_view<_CharT> __fmt,
+                                                size_t __num_args = 0) noexcept
       : __begin_(__fmt.begin()),
         __end_(__fmt.end()),
         __indexing_(__unknown),
         __next_arg_id_(0),
         __num_args_(__num_args) {}
 
   basic_format_parse_context(const basic_format_parse_context&) = delete;
   basic_format_parse_context&
private:
   size_t __next_arg_id_;
   size_t __num_args_;
 };
 
 using format_parse_context = basic_format_parse_context<char>;
 using wformat_parse_context = basic_format_parse_context<wchar_t>;
 
 #endif // !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
-#endif // _LIBCPP_FORMAT
+#endif // _LIBCPP___FORMAT_FORMAT_PARSE_CONTEXT_H

libcxx/include/format

namespace std {
   using format_parse_context = basic_format_parse_context<char>;
   using wformat_parse_context = basic_format_parse_context<wchar_t>;
 }
 
 */
 
 #include <__config>
 #include <__format/format_error.h>
-#include <string_view>
+#include <__format/format_parse_context.h>
 #include <version>
 
 #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) && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
-
-template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS basic_format_parse_context {
-public:
-  using char_type = _CharT;
-  using const_iterator =
-      typename basic_string_view<_CharT>::const_iterator;
-  using iterator = const_iterator;
-
-public:
-  _LIBCPP_INLINE_VISIBILITY
-  constexpr explicit basic_format_parse_context(
-      basic_string_view<_CharT> __fmt, size_t __num_args = 0) noexcept
-      : __begin_(__fmt.begin()),
-        __end_(__fmt.end()),
-        __indexing_(__unknown),
-        __next_arg_id_(0),
-        __num_args_(__num_args) {}
-
-  basic_format_parse_context(const basic_format_parse_context&) = delete;
-  basic_format_parse_context&
-  operator=(const basic_format_parse_context&) = delete;
-
-  _LIBCPP_INLINE_VISIBILITY constexpr const_iterator begin() const noexcept {
-    return __begin_;
-  }
-  _LIBCPP_INLINE_VISIBILITY constexpr const_iterator end() const noexcept {
-    return __end_;
-  }
-  _LIBCPP_INLINE_VISIBILITY constexpr void advance_to(const_iterator __it) {
-    __begin_ = __it;
-  }
-
-  _LIBCPP_INLINE_VISIBILITY constexpr size_t next_arg_id() {
-    if (__indexing_ == __manual)
-      __throw_format_error("Using automatic argument numbering in manual "
-                           "argument numbering mode");
-
-    if (__indexing_ == __unknown)
-      __indexing_ = __automatic;
-    return __next_arg_id_++;
-  }
-  _LIBCPP_INLINE_VISIBILITY constexpr void check_arg_id(size_t __id) {
-    if (__indexing_ == __automatic)
-      __throw_format_error("Using manual argument numbering in automatic "
-                           "argument numbering mode");
-
-    if (__indexing_ == __unknown)
-      __indexing_ = __manual;
-
-    // Throws an exception to make the expression a non core constant
-    // expression as required by:
-    // [format.parse.ctx]/11
-    //   Remarks: Call expressions where id >= num_args_ are not core constant
-    //   expressions ([expr.const]).
-    // Note: the Throws clause [format.parse.ctx]/10 doesn't specify the
-    // behavior when id >= num_args_.
-    if (is_constant_evaluated() && __id >= __num_args_)
-      __throw_format_error("Argument index outside the valid range");
-  }
-
-private:
-  iterator __begin_;
-  iterator __end_;
-  enum _Indexing { __unknown, __manual, __automatic };
-  _Indexing __indexing_;
-  size_t __next_arg_id_;
-  size_t __num_args_;
-};
-
-using format_parse_context = basic_format_parse_context<char>;
-using wformat_parse_context = basic_format_parse_context<wchar_t>;
-
-#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
 #endif //_LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_FORMAT