Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__format/buffer.h

@@ -0,0 +1,643 @@
+// -*- 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_BUFFER_H
+#define _LIBCPP___FORMAT_BUFFER_H
+
+#include <__algorithm/copy_n.h>
+#include <__algorithm/fill_n.h>
+#include <__algorithm/max.h>
+#include <__algorithm/min.h>
+#include <__algorithm/ranges_copy_n.h>
+#include <__algorithm/transform.h>
+#include <__algorithm/unwrap_iter.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/enable_insertable.h>
+#include <__format/format_to_n_result.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__iterator/concepts.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/wrap_iter.h>
+#include <__memory/addressof.h>
+#include <__memory/allocate_at_least.h>
+#include <__memory/allocator_traits.h>
+#include <__memory/construct_at.h>
+#include <__memory/ranges_construct_at.h>
+#include <__memory/uninitialized_algorithms.h>
+#include <__type_traits/add_pointer.h>
+#include <__type_traits/conditional.h>
+#include <__utility/exception_guard.h>
+#include <__utility/move.h>
+#include <cstddef>
+#include <string_view>
+
+#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 >= 20
+
+namespace __format {
+
+/// A "buffer" that handles writing to the proper iterator.
+///
+/// This helper is used together with the @ref back_insert_iterator to offer
+/// type-erasure for the formatting functions. This reduces the number to
+/// template instantiations.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __output_buffer {
+public:
+  using value_type = _CharT;
+
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI explicit __output_buffer(_CharT* __ptr, size_t __capacity, _Tp* __obj)
+      : __ptr_(__ptr),
+        __capacity_(__capacity),
+        __flush_([](_CharT* __p, size_t __n, void* __o) { static_cast<_Tp*>(__o)->__flush(__p, __n); }),
+        __obj_(__obj) {}
+
+  _LIBCPP_HIDE_FROM_ABI void __reset(_CharT* __ptr, size_t __capacity) {
+    __ptr_ = __ptr;
+    __capacity_ = __capacity;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return std::back_insert_iterator{*this}; }
+
+  // Used in std::back_insert_iterator.
+  _LIBCPP_HIDE_FROM_ABI void push_back(_CharT __c) {
+    __ptr_[__size_++] = __c;
+
+    // Profiling showed flushing after adding is more efficient than flushing
+    // when entering the function.
+    if (__size_ == __capacity_)
+      __flush();
+  }
+
+  /// Copies the input __str to the buffer.
+  ///
+  /// Since some of the input is generated by std::to_chars, there needs to be a
+  /// conversion when _CharT is wchar_t.
+  template <__fmt_char_type _InCharT>
+  _LIBCPP_HIDE_FROM_ABI void __copy(basic_string_view<_InCharT> __str) {
+    // When the underlying iterator is a simple iterator the __capacity_ is
+    // infinite. For a string or container back_inserter it isn't. This means
+    // adding a large string the the buffer can cause some overhead. In that
+    // case a better approach could be:
+    // - flush the buffer
+    // - container.append(__str.begin(), __str.end());
+    // The same holds true for the fill.
+    // For transform it might be slightly harder, however the use case for
+    // transform is slightly less common; it converts hexadecimal values to
+    // upper case. For integral these strings are short.
+    // TODO FMT Look at the improvements above.
+    size_t __n = __str.size();
+
+    __flush_on_overflow(__n);
+    if (__n <= __capacity_) {
+      _VSTD::copy_n(__str.data(), __n, _VSTD::addressof(__ptr_[__size_]));
+      __size_ += __n;
+      return;
+    }
+
+    // The output doesn't fit in the internal buffer.
+    // Copy the data in "__capacity_" sized chunks.
+    _LIBCPP_ASSERT(__size_ == 0, "the buffer should be flushed by __flush_on_overflow");
+    const _InCharT* __first = __str.data();
+    do {
+      size_t __chunk = _VSTD::min(__n, __capacity_);
+      _VSTD::copy_n(__first, __chunk, _VSTD::addressof(__ptr_[__size_]));
+      __size_ = __chunk;
+      __first += __chunk;
+      __n -= __chunk;
+      __flush();
+    } while (__n);
+  }
+
+  /// A std::transform wrapper.
+  ///
+  /// Like @ref __copy it may need to do type conversion.
+  template <__fmt_char_type _InCharT, class _UnaryOperation>
+  _LIBCPP_HIDE_FROM_ABI void __transform(const _InCharT* __first, const _InCharT* __last, _UnaryOperation __operation) {
+    _LIBCPP_ASSERT(__first <= __last, "not a valid range");
+
+    size_t __n = static_cast<size_t>(__last - __first);
+    __flush_on_overflow(__n);
+    if (__n <= __capacity_) {
+      _VSTD::transform(__first, __last, _VSTD::addressof(__ptr_[__size_]), _VSTD::move(__operation));
+      __size_ += __n;
+      return;
+    }
+
+    // The output doesn't fit in the internal buffer.
+    // Transform the data in "__capacity_" sized chunks.
+    _LIBCPP_ASSERT(__size_ == 0, "the buffer should be flushed by __flush_on_overflow");
+    do {
+      size_t __chunk = _VSTD::min(__n, __capacity_);
+      _VSTD::transform(__first, __first + __chunk, _VSTD::addressof(__ptr_[__size_]), __operation);
+      __size_ = __chunk;
+      __first += __chunk;
+      __n -= __chunk;
+      __flush();
+    } while (__n);
+  }
+
+  /// A \c fill_n wrapper.
+  _LIBCPP_HIDE_FROM_ABI void __fill(size_t __n, _CharT __value) {
+    __flush_on_overflow(__n);
+    if (__n <= __capacity_) {
+      _VSTD::fill_n(_VSTD::addressof(__ptr_[__size_]), __n, __value);
+      __size_ += __n;
+      return;
+    }
+
+    // The output doesn't fit in the internal buffer.
+    // Fill the buffer in "__capacity_" sized chunks.
+    _LIBCPP_ASSERT(__size_ == 0, "the buffer should be flushed by __flush_on_overflow");
+    do {
+      size_t __chunk = _VSTD::min(__n, __capacity_);
+      _VSTD::fill_n(_VSTD::addressof(__ptr_[__size_]), __chunk, __value);
+      __size_ = __chunk;
+      __n -= __chunk;
+      __flush();
+    } while (__n);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush() {
+    __flush_(__ptr_, __size_, __obj_);
+    __size_ = 0;
+  }
+
+private:
+  _CharT* __ptr_;
+  size_t __capacity_;
+  size_t __size_{0};
+  void (*__flush_)(_CharT*, size_t, void*);
+  void* __obj_;
+
+  /// Flushes the buffer when the output operation would overflow the buffer.
+  ///
+  /// A simple approach for the overflow detection would be something along the
+  /// lines:
+  /// \code
+  /// // The internal buffer is large enough.
+  /// if (__n <= __capacity_) {
+  ///   // Flush when we really would overflow.
+  ///   if (__size_ + __n >= __capacity_)
+  ///     __flush();
+  ///   ...
+  /// }
+  /// \endcode
+  ///
+  /// This approach works for all cases but one:
+  /// A __format_to_n_buffer_base where \ref __enable_direct_output is true.
+  /// In that case the \ref __capacity_ of the buffer changes during the first
+  /// \ref __flush. During that operation the output buffer switches from its
+  /// __writer_ to its __storage_. The \ref __capacity_ of the former depends
+  /// on the value of n, of the latter is a fixed size. For example:
+  /// - a format_to_n call with a 10'000 char buffer,
+  /// - the buffer is filled with 9'500 chars,
+  /// - adding 1'000 elements would overflow the buffer so the buffer gets
+  ///   changed and the \ref __capacity_ decreases from 10'000 to
+  ///   __buffer_size (256 at the time of writing).
+  ///
+  /// This means that the \ref __flush for this class may need to copy a part of
+  /// the internal buffer to the proper output. In this example there will be
+  /// 500 characters that need this copy operation.
+  ///
+  /// Note it would be more efficient to write 500 chars directly and then swap
+  /// the buffers. This would make the code more complex and \ref format_to_n is
+  /// not the most common use case. Therefore the optimization isn't done.
+  _LIBCPP_HIDE_FROM_ABI void __flush_on_overflow(size_t __n) {
+    if (__size_ + __n >= __capacity_)
+      __flush();
+  }
+};
+
+/// A storage using an internal buffer.
+///
+/// This storage is used when writing a single element to the output iterator
+/// is expensive.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __internal_storage {
+public:
+  _LIBCPP_HIDE_FROM_ABI _CharT* __begin() { return __buffer_; }
+
+  static constexpr size_t __buffer_size = 256 / sizeof(_CharT);
+
+private:
+  _CharT __buffer_[__buffer_size];
+};
+
+/// A storage writing directly to the storage.
+///
+/// This requires the storage to be a contiguous buffer of \a _CharT.
+/// Since the output is directly written to the underlying storage this class
+/// is just an empty class.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __direct_storage {};
+
+template <class _OutIt, class _CharT>
+concept __enable_direct_output = __fmt_char_type<_CharT> &&
+    (same_as<_OutIt, _CharT*>
+#ifndef _LIBCPP_ENABLE_DEBUG_MODE
+     || same_as<_OutIt, __wrap_iter<_CharT*>>
+#endif
+    );
+
+/// Write policy for directly writing to the underlying output.
+template <class _OutIt, __fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __writer_direct {
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __writer_direct(_OutIt __out_it)
+      : __out_it_(__out_it) {}
+
+  _LIBCPP_HIDE_FROM_ABI _OutIt __out_it() { return __out_it_; }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT*, size_t __n) {
+    // _OutIt can be a __wrap_iter<CharT*>. Therefore the original iterator
+    // is adjusted.
+    __out_it_ += __n;
+  }
+
+private:
+  _OutIt __out_it_;
+};
+
+/// Write policy for copying the buffer to the output.
+template <class _OutIt, __fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __writer_iterator {
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __writer_iterator(_OutIt __out_it)
+      : __out_it_{_VSTD::move(__out_it)} {}
+
+  _LIBCPP_HIDE_FROM_ABI _OutIt __out_it() && { return std::move(__out_it_); }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) {
+    __out_it_ = std::ranges::copy_n(__ptr, __n, std::move(__out_it_)).out;
+  }
+
+private:
+  _OutIt __out_it_;
+};
+
+/// Concept to see whether a \a _Container is insertable.
+///
+/// The concept is used to validate whether multiple calls to a
+/// \ref back_insert_iterator can be replace by a call to \c _Container::insert.
+///
+/// \note a \a _Container needs to opt-in to the concept by specializing
+/// \ref __enable_insertable.
+template <class _Container>
+concept __insertable =
+    __enable_insertable<_Container> && __fmt_char_type<typename _Container::value_type> &&
+    requires(_Container& __t, add_pointer_t<typename _Container::value_type> __first,
+             add_pointer_t<typename _Container::value_type> __last) { __t.insert(__t.end(), __first, __last); };
+
+/// Extract the container type of a \ref back_insert_iterator.
+template <class _It>
+struct _LIBCPP_TEMPLATE_VIS __back_insert_iterator_container {
+  using type = void;
+};
+
+template <__insertable _Container>
+struct _LIBCPP_TEMPLATE_VIS __back_insert_iterator_container<back_insert_iterator<_Container>> {
+  using type = _Container;
+};
+
+/// Write policy for inserting the buffer in a container.
+template <class _Container>
+class _LIBCPP_TEMPLATE_VIS __writer_container {
+public:
+  using _CharT = typename _Container::value_type;
+
+  _LIBCPP_HIDE_FROM_ABI explicit __writer_container(back_insert_iterator<_Container> __out_it)
+      : __container_{__out_it.__get_container()} {}
+
+  _LIBCPP_HIDE_FROM_ABI auto __out_it() { return std::back_inserter(*__container_); }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) {
+    __container_->insert(__container_->end(), __ptr, __ptr + __n);
+  }
+
+private:
+  _Container* __container_;
+};
+
+/// Selects the type of the writer used for the output iterator.
+template <class _OutIt, class _CharT>
+class _LIBCPP_TEMPLATE_VIS __writer_selector {
+  using _Container = typename __back_insert_iterator_container<_OutIt>::type;
+
+public:
+  using type = conditional_t<!same_as<_Container, void>, __writer_container<_Container>,
+                             conditional_t<__enable_direct_output<_OutIt, _CharT>, __writer_direct<_OutIt, _CharT>,
+                                           __writer_iterator<_OutIt, _CharT>>>;
+};
+
+/// The generic formatting buffer.
+template <class _OutIt, __fmt_char_type _CharT>
+requires(output_iterator<_OutIt, const _CharT&>) class _LIBCPP_TEMPLATE_VIS
+    __format_buffer {
+  using _Storage =
+      conditional_t<__enable_direct_output<_OutIt, _CharT>,
+                    __direct_storage<_CharT>, __internal_storage<_CharT>>;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __format_buffer(_OutIt __out_it)
+    requires(same_as<_Storage, __internal_storage<_CharT>>)
+      : __output_(__storage_.__begin(), __storage_.__buffer_size, this), __writer_(_VSTD::move(__out_it)) {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit __format_buffer(_OutIt __out_it) requires(
+      same_as<_Storage, __direct_storage<_CharT>>)
+      : __output_(_VSTD::__unwrap_iter(__out_it), size_t(-1), this),
+        __writer_(_VSTD::move(__out_it)) {}
+
+  _LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return __output_.__make_output_iterator(); }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) { __writer_.__flush(__ptr, __n); }
+
+  _LIBCPP_HIDE_FROM_ABI _OutIt __out_it() && {
+    __output_.__flush();
+    return _VSTD::move(__writer_).__out_it();
+  }
+
+private:
+  _LIBCPP_NO_UNIQUE_ADDRESS _Storage __storage_;
+  __output_buffer<_CharT> __output_;
+  typename __writer_selector<_OutIt, _CharT>::type __writer_;
+};
+
+/// A buffer that counts the number of insertions.
+///
+/// Since \ref formatted_size only needs to know the size, the output itself is
+/// discarded.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __formatted_size_buffer {
+public:
+  _LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return __output_.__make_output_iterator(); }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(const _CharT*, size_t __n) { __size_ += __n; }
+
+  _LIBCPP_HIDE_FROM_ABI size_t __result() && {
+    __output_.__flush();
+    return __size_;
+  }
+
+private:
+  __internal_storage<_CharT> __storage_;
+  __output_buffer<_CharT> __output_{__storage_.__begin(), __storage_.__buffer_size, this};
+  size_t __size_{0};
+};
+
+/// The base of a buffer that counts and limits the number of insertions.
+template <class _OutIt, __fmt_char_type _CharT, bool>
+  requires(output_iterator<_OutIt, const _CharT&>)
+struct _LIBCPP_TEMPLATE_VIS __format_to_n_buffer_base {
+  using _Size = iter_difference_t<_OutIt>;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __format_to_n_buffer_base(_OutIt __out_it, _Size __max_size)
+      : __writer_(_VSTD::move(__out_it)), __max_size_(_VSTD::max(_Size(0), __max_size)) {}
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) {
+    if (_Size(__size_) <= __max_size_)
+      __writer_.__flush(__ptr, _VSTD::min(_Size(__n), __max_size_ - __size_));
+    __size_ += __n;
+  }
+
+protected:
+  __internal_storage<_CharT> __storage_;
+  __output_buffer<_CharT> __output_{__storage_.__begin(), __storage_.__buffer_size, this};
+  typename __writer_selector<_OutIt, _CharT>::type __writer_;
+
+  _Size __max_size_;
+  _Size __size_{0};
+};
+
+/// The base of a buffer that counts and limits the number of insertions.
+///
+/// This version is used when \c __enable_direct_output<_OutIt, _CharT> == true.
+///
+/// This class limits the size available to the direct writer so it will not
+/// exceed the maximum number of code units.
+template <class _OutIt, __fmt_char_type _CharT>
+  requires(output_iterator<_OutIt, const _CharT&>)
+class _LIBCPP_TEMPLATE_VIS __format_to_n_buffer_base<_OutIt, _CharT, true> {
+  using _Size = iter_difference_t<_OutIt>;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __format_to_n_buffer_base(_OutIt __out_it, _Size __max_size)
+      : __output_(_VSTD::__unwrap_iter(__out_it), __max_size, this),
+        __writer_(_VSTD::move(__out_it)),
+        __max_size_(__max_size) {
+    if (__max_size <= 0) [[unlikely]]
+      __output_.__reset(__storage_.__begin(), __storage_.__buffer_size);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) {
+    // A __flush to the direct writer happens in the following occasions:
+    // - The format function has written the maximum number of allowed code
+    //   units. At this point it's no longer valid to write to this writer. So
+    //   switch to the internal storage. This internal storage doesn't need to
+    //   be written anywhere so the __flush for that storage writes no output.
+    // - Like above, but the next "mass write" operation would overflow the
+    //   buffer. In that case the buffer is pre-emptively switched. The still
+    //   valid code units will be written separately.
+    // - The format_to_n function is finished. In this case there's no need to
+    //   switch the buffer, but for simplicity the buffers are still switched.
+    // When the __max_size <= 0 the constructor already switched the buffers.
+    if (__size_ == 0 && __ptr != __storage_.__begin()) {
+      __writer_.__flush(__ptr, __n);
+      __output_.__reset(__storage_.__begin(), __storage_.__buffer_size);
+    } else if (__size_ < __max_size_) {
+      // Copies a part of the internal buffer to the output up to n characters.
+      // See __output_buffer<_CharT>::__flush_on_overflow for more information.
+      _Size __s = _VSTD::min(_Size(__n), __max_size_ - __size_);
+      std::copy_n(__ptr, __s, __writer_.__out_it());
+      __writer_.__flush(__ptr, __s);
+    }
+
+    __size_ += __n;
+  }
+
+protected:
+  __internal_storage<_CharT> __storage_;
+  __output_buffer<_CharT> __output_;
+  __writer_direct<_OutIt, _CharT> __writer_;
+
+  _Size __max_size_;
+  _Size __size_{0};
+};
+
+/// The buffer that counts and limits the number of insertions.
+template <class _OutIt, __fmt_char_type _CharT>
+  requires(output_iterator<_OutIt, const _CharT&>)
+struct _LIBCPP_TEMPLATE_VIS __format_to_n_buffer final
+    : public __format_to_n_buffer_base< _OutIt, _CharT, __enable_direct_output<_OutIt, _CharT>> {
+  using _Base = __format_to_n_buffer_base<_OutIt, _CharT, __enable_direct_output<_OutIt, _CharT>>;
+  using _Size = iter_difference_t<_OutIt>;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __format_to_n_buffer(_OutIt __out_it, _Size __max_size)
+      : _Base(_VSTD::move(__out_it), __max_size) {}
+  _LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return this->__output_.__make_output_iterator(); }
+
+  _LIBCPP_HIDE_FROM_ABI format_to_n_result<_OutIt> __result() && {
+    this->__output_.__flush();
+    return {_VSTD::move(this->__writer_).__out_it(), this->__size_};
+  }
+};
+
+// A dynamically growing buffer intended to be used for retargeting a context.
+//
+// P2286 Formatting ranges adds range formatting support. It allows the user to
+// specify the minimum width for the entire formatted range.  The width of the
+// range is not known until the range is formatted. Formatting is done to an
+// output_iterator so there's no guarantee it would be possible to add the fill
+// to the front of the output. Instead the range is formatted to a temporary
+// buffer and that buffer is formatted as a string.
+//
+// There is an issue with that approach, the format context used in
+// std::formatter<T>::format contains the output iterator used as part of its
+// type. So using this output iterator means there needs to be a new format
+// context and the format arguments need to be retargeted to the new context.
+// This retargeting is done by a basic_format_context specialized for the
+// __iterator of this container.
+//
+// This class uses its own buffer management, since using vector
+// would lead to a circular include with formatter for vector<bool>.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __retarget_buffer {
+  using _Alloc = allocator<_CharT>;
+
+public:
+  using value_type = _CharT;
+
+  struct __iterator {
+    using difference_type = ptrdiff_t;
+
+    _LIBCPP_HIDE_FROM_ABI constexpr explicit __iterator(__retarget_buffer& __buffer)
+        : __buffer_(std::addressof(__buffer)) {}
+    _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator=(const _CharT& __c) {
+      __buffer_->push_back(__c);
+      return *this;
+    }
+    _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator=(_CharT&& __c) {
+      __buffer_->push_back(__c);
+      return *this;
+    }
+
+    _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator*() { return *this; }
+    _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() { return *this; }
+    _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator++(int) { return *this; }
+    __retarget_buffer* __buffer_;
+  };
+
+  __retarget_buffer(const __retarget_buffer&)            = delete;
+  __retarget_buffer& operator=(const __retarget_buffer&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI explicit __retarget_buffer(size_t __size_hint) {
+    auto __result = std::__allocate_at_least(__alloc_, __size_hint ? __size_hint : 256 / sizeof(_CharT));
+    __ptr_        = __result.ptr;
+    __capacity_   = __result.count;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI ~__retarget_buffer() {
+    ranges::destroy_n(__ptr_, __size_);
+    allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __capacity_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI __iterator __make_output_iterator() { return __iterator{*this}; }
+
+  _LIBCPP_HIDE_FROM_ABI void push_back(_CharT __c) {
+    std::construct_at(__ptr_ + __size_, __c);
+    ++__size_;
+
+    if (__size_ == __capacity_)
+      __grow_buffer();
+  }
+
+  template <__fmt_char_type _InCharT>
+  _LIBCPP_HIDE_FROM_ABI void __copy(basic_string_view<_InCharT> __str) {
+    size_t __n = __str.size();
+    if (__size_ + __n >= __capacity_)
+      // Push_back requires the buffer to have room for at least one character.
+      __grow_buffer(__size_ + __n + 1);
+
+    std::uninitialized_copy_n(__str.data(), __n, __ptr_ + __size_);
+    __size_ += __n;
+  }
+
+  template <__fmt_char_type _InCharT, class _UnaryOperation>
+  _LIBCPP_HIDE_FROM_ABI void __transform(const _InCharT* __first, const _InCharT* __last, _UnaryOperation __operation) {
+    _LIBCPP_ASSERT(__first <= __last, "not a valid range");
+
+    size_t __n = static_cast<size_t>(__last - __first);
+    if (__size_ + __n >= __capacity_)
+      // Push_back requires the buffer to have room for at least one character.
+      __grow_buffer(__size_ + __n + 1);
+
+    std::uninitialized_default_construct_n(__ptr_ + __size_, __n);
+    std::transform(__first, __last, __ptr_ + __size_, std::move(__operation));
+    __size_ += __n;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI void __fill(size_t __n, _CharT __value) {
+    if (__size_ + __n >= __capacity_)
+      // Push_back requires the buffer to have room for at least one character.
+      __grow_buffer(__size_ + __n + 1);
+
+    std::uninitialized_fill_n(__ptr_ + __size_, __n, __value);
+    __size_ += __n;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI basic_string_view<_CharT> __view() { return {__ptr_, __size_}; }
+
+private:
+  _LIBCPP_HIDE_FROM_ABI void __grow_buffer() { __grow_buffer(__capacity_ * 1.6); }
+
+  _LIBCPP_HIDE_FROM_ABI void __grow_buffer(size_t __capacity) {
+    _LIBCPP_ASSERT(__capacity > __capacity_, "the buffer must grow");
+    auto __result = std::__allocate_at_least(__alloc_, __capacity);
+    auto __guard  = std::__make_exception_guard([&] {
+      allocator_traits<_Alloc>::deallocate(__alloc_, __result.ptr, __result.count);
+    });
+    // This shouldn't throw, but just to be safe. Not that at -O1 this
+    // guard is optimized away so there is no runtime overhead.
+    std::uninitialized_move_n(__ptr_, __size_, __result.ptr);
+    __guard.__complete();
+    ranges::destroy_n(__ptr_, __size_);
+    allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __capacity_);
+
+    __ptr_      = __result.ptr;
+    __capacity_ = __result.count;
+  }
+  _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
+  _CharT* __ptr_;
+  size_t __capacity_;
+  size_t __size_{0};
+};
+
+} // namespace __format
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___FORMAT_BUFFER_H

third_party/libcxx/__format/concepts.h

@@ -0,0 +1,76 @@
+// -*- 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_CONCEPTS_H
+#define _LIBCPP___FORMAT_CONCEPTS_H
+
+#include <__concepts/same_as.h>
+#include <__concepts/semiregular.h>
+#include <__config>
+#include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
+#include <__type_traits/is_specialization.h>
+#include <__utility/pair.h>
+#include <tuple>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+/// The character type specializations of \ref formatter.
+template <class _CharT>
+concept __fmt_char_type =
+    same_as<_CharT, char>
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+    || same_as<_CharT, wchar_t>
+#  endif
+    ;
+
+// The output iterator isn't specified. A formatter should accept any
+// output_iterator. This iterator is a minimal iterator to test the concept.
+// (Note testing for (w)format_context would be a valid choice, but requires
+// selecting the proper one depending on the type of _CharT.)
+template <class _CharT>
+using __fmt_iter_for = _CharT*;
+
+template <class _Tp, class _CharT>
+concept __formattable =
+    (semiregular<formatter<remove_cvref_t<_Tp>, _CharT>>) &&
+    requires(formatter<remove_cvref_t<_Tp>, _CharT> __f,
+             const formatter<remove_cvref_t<_Tp>, _CharT> __cf,
+             _Tp __t,
+             basic_format_context<__fmt_iter_for<_CharT>, _CharT> __fc,
+             basic_format_parse_context<_CharT> __pc) {
+      { __f.parse(__pc) } -> same_as<typename basic_format_parse_context<_CharT>::iterator>;
+      { __cf.format(__t, __fc) } -> same_as<__fmt_iter_for<_CharT>>;
+    };
+
+#  if _LIBCPP_STD_VER >= 23
+template <class _Tp, class _CharT>
+concept formattable = __formattable<_Tp, _CharT>;
+
+// [tuple.like] defines a tuple-like exposition only concept. This concept is
+// not related to that. Therefore it uses a different name for the concept.
+//
+// TODO FMT Add a test to validate we fail when using that concept after P2165
+// has been implemented.
+template <class _Tp>
+concept __fmt_pair_like =
+    __is_specialization_v<_Tp, pair> || (__is_specialization_v<_Tp, tuple> && tuple_size_v<_Tp> == 2);
+
+#  endif //_LIBCPP_STD_VER >= 23
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_CONCEPTS_H

third_party/libcxx/__format/container_adaptor.h

@@ -0,0 +1,71 @@
+// -*- 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_CONTAINER_ADAPTOR_H
+#define _LIBCPP___FORMAT_CONTAINER_ADAPTOR_H
+
+#include <__availability>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/formatter.h>
+#include <__format/range_default_formatter.h>
+#include <__ranges/all.h>
+#include <__ranges/ref_view.h>
+#include <__type_traits/is_const.h>
+#include <__type_traits/maybe_const.h>
+#include <queue>
+#include <stack>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+// [container.adaptors.format] only specifies the library should provide the
+// formatter specializations, not which header should provide them.
+// Since <format> includes a lot of headers, add these headers here instead of
+// adding more dependencies like, locale, optinal, string, tuple, etc. to the
+// adaptor headers. To use the format functions users already include <format>.
+
+template <class _Adaptor, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_container_adaptor {
+private:
+  using __maybe_const_container = __fmt_maybe_const<typename _Adaptor::container_type, _CharT>;
+  using __maybe_const_adaptor   = __maybe_const<is_const_v<__maybe_const_container>, _Adaptor>;
+  formatter<ranges::ref_view<__maybe_const_container>, _CharT> __underlying_;
+
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return __underlying_.parse(__ctx);
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(__maybe_const_adaptor& __adaptor, _FormatContext& __ctx) const {
+    return __underlying_.format(__adaptor.__get_container(), __ctx);
+  }
+};
+
+template <class _CharT, class _Tp, formattable<_CharT> _Container>
+struct _LIBCPP_TEMPLATE_VIS formatter<queue<_Tp, _Container>, _CharT>
+    : public __formatter_container_adaptor<queue<_Tp, _Container>, _CharT> {};
+
+template <class _CharT, class _Tp, class _Container, class _Compare>
+struct _LIBCPP_TEMPLATE_VIS formatter<priority_queue<_Tp, _Container, _Compare>, _CharT>
+    : public __formatter_container_adaptor<priority_queue<_Tp, _Container, _Compare>, _CharT> {};
+
+template <class _CharT, class _Tp, formattable<_CharT> _Container>
+struct _LIBCPP_TEMPLATE_VIS formatter<stack<_Tp, _Container>, _CharT>
+    : public __formatter_container_adaptor<stack<_Tp, _Container>, _CharT> {};
+
+#endif //_LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_CONTAINER_ADAPTOR_H

third_party/libcxx/__format/enable_insertable.h

@@ -0,0 +1,35 @@
+// -*- 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_ENABLE_INSERTABLE_H
+#define _LIBCPP___FORMAT_ENABLE_INSERTABLE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __format {
+
+/// Opt-in to enable \ref __insertable for a \a _Container.
+template <class _Container>
+inline constexpr bool __enable_insertable = false;
+
+} // namespace __format
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_ENABLE_INSERTABLE_H

third_party/libcxx/__format/format_arg.h

@@ -0,0 +1,305 @@
+// -*- 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_FORMAT_ARG_H
+#define _LIBCPP___FORMAT_FORMAT_ARG_H
+
+#include <__assert>
+#include <__concepts/arithmetic.h>
+#include <__config>
+#include <__format/format_error.h>
+#include <__format/format_fwd.h>
+#include <__format/format_parse_context.h>
+#include <__functional/invoke.h>
+#include <__memory/addressof.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/is_const.h>
+#include <__utility/declval.h>
+#include <__utility/forward.h>
+#include <__utility/unreachable.h>
+#include <__variant/monostate.h>
+#include <string>
+#include <string_view>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __format {
+/// The type stored in @ref basic_format_arg.
+///
+/// @note The 128-bit types are unconditionally in the list to avoid the values
+/// of the enums to depend on the availability of 128-bit integers.
+///
+/// @note The value is stored as a 5-bit value in the __packed_arg_t_bits. This
+/// limits the maximum number of elements to 32.
+/// When modifying update the test
+/// test/libcxx/utilities/format/format.arguments/format.arg/arg_t.compile.pass.cpp
+/// It could be packed in 4-bits but that means a new type directly becomes an
+/// ABI break. The packed type is 64-bit so this reduces the maximum number of
+/// packed elements from 16 to 12.
+///
+/// @note Some members of this enum are an extension. These extensions need
+/// special behaviour in visit_format_arg. There they need to be wrapped in a
+/// handle to satisfy the user observable behaviour. The internal function
+/// __visit_format_arg doesn't do this wrapping. So in the format functions
+/// this function is used to avoid unneeded overhead.
+enum class _LIBCPP_ENUM_VIS __arg_t : uint8_t {
+  __none,
+  __boolean,
+  __char_type,
+  __int,
+  __long_long,
+  __i128, // extension
+  __unsigned,
+  __unsigned_long_long,
+  __u128, // extension
+  __float,
+  __double,
+  __long_double,
+  __const_char_type_ptr,
+  __string_view,
+  __ptr,
+  __handle
+};
+
+inline constexpr unsigned __packed_arg_t_bits = 5;
+inline constexpr uint8_t __packed_arg_t_mask = 0x1f;
+
+inline constexpr unsigned __packed_types_storage_bits = 64;
+inline constexpr unsigned __packed_types_max = __packed_types_storage_bits / __packed_arg_t_bits;
+
+_LIBCPP_HIDE_FROM_ABI
+constexpr bool __use_packed_format_arg_store(size_t __size) { return __size <= __packed_types_max; }
+
+_LIBCPP_HIDE_FROM_ABI
+constexpr __arg_t __get_packed_type(uint64_t __types, size_t __id) {
+  _LIBCPP_ASSERT(__id <= __packed_types_max, "");
+
+  if (__id > 0)
+    __types >>= __id * __packed_arg_t_bits;
+
+  return static_cast<__format::__arg_t>(__types & __packed_arg_t_mask);
+}
+
+} // namespace __format
+
+// This function is not user obervable, so it can directly use the non-standard
+// types of the "variant". See __arg_t for more details.
+template <class _Visitor, class _Context>
+_LIBCPP_HIDE_FROM_ABI decltype(auto)
+__visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+  switch (__arg.__type_) {
+  case __format::__arg_t::__none:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__monostate_);
+  case __format::__arg_t::__boolean:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__boolean_);
+  case __format::__arg_t::__char_type:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__char_type_);
+  case __format::__arg_t::__int:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__int_);
+  case __format::__arg_t::__long_long:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
+  case __format::__arg_t::__i128:
+#  ifndef _LIBCPP_HAS_NO_INT128
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+#  else
+    __libcpp_unreachable();
+#  endif
+  case __format::__arg_t::__unsigned:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__unsigned_);
+  case __format::__arg_t::__unsigned_long_long:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
+  case __format::__arg_t::__u128:
+#  ifndef _LIBCPP_HAS_NO_INT128
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+#  else
+    __libcpp_unreachable();
+#  endif
+  case __format::__arg_t::__float:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__float_);
+  case __format::__arg_t::__double:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__double_);
+  case __format::__arg_t::__long_double:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__long_double_);
+  case __format::__arg_t::__const_char_type_ptr:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__const_char_type_ptr_);
+  case __format::__arg_t::__string_view:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__string_view_);
+  case __format::__arg_t::__ptr:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), __arg.__value_.__ptr_);
+  case __format::__arg_t::__handle:
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis),
+                         typename basic_format_arg<_Context>::handle{__arg.__value_.__handle_});
+  }
+
+  __libcpp_unreachable();
+}
+
+/// Contains the values used in basic_format_arg.
+///
+/// This is a separate type so it's possible to store the values and types in
+/// separate arrays.
+template <class _Context>
+class __basic_format_arg_value {
+  using _CharT = typename _Context::char_type;
+
+public:
+  /// Contains the implementation for basic_format_arg::handle.
+  struct __handle {
+    template <class _Tp>
+    _LIBCPP_HIDE_FROM_ABI explicit __handle(_Tp&& __v) noexcept
+        : __ptr_(_VSTD::addressof(__v)),
+          __format_([](basic_format_parse_context<_CharT>& __parse_ctx, _Context& __ctx, const void* __ptr) {
+            using _Dp = remove_cvref_t<_Tp>;
+            using _Formatter = typename _Context::template formatter_type<_Dp>;
+            constexpr bool __const_formattable =
+                requires { _Formatter().format(std::declval<const _Dp&>(), std::declval<_Context&>()); };
+            using _Qp = conditional_t<__const_formattable, const _Dp, _Dp>;
+
+            static_assert(__const_formattable || !is_const_v<remove_reference_t<_Tp>>, "Mandated by [format.arg]/18");
+
+            _Formatter __f;
+            __parse_ctx.advance_to(__f.parse(__parse_ctx));
+            __ctx.advance_to(__f.format(*const_cast<_Qp*>(static_cast<const _Dp*>(__ptr)), __ctx));
+          }) {}
+
+    const void* __ptr_;
+    void (*__format_)(basic_format_parse_context<_CharT>&, _Context&, const void*);
+  };
+
+  union {
+    monostate __monostate_;
+    bool __boolean_;
+    _CharT __char_type_;
+    int __int_;
+    unsigned __unsigned_;
+    long long __long_long_;
+    unsigned long long __unsigned_long_long_;
+#  ifndef _LIBCPP_HAS_NO_INT128
+    __int128_t __i128_;
+    __uint128_t __u128_;
+#  endif
+    float __float_;
+    double __double_;
+    long double __long_double_;
+    const _CharT* __const_char_type_ptr_;
+    basic_string_view<_CharT> __string_view_;
+    const void* __ptr_;
+    __handle __handle_;
+  };
+
+  // These constructors contain the exact storage type used. If adjustments are
+  // required, these will be done in __create_format_arg.
+
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value() noexcept : __monostate_() {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(bool __value) noexcept : __boolean_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(_CharT __value) noexcept : __char_type_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(int __value) noexcept : __int_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned __value) noexcept : __unsigned_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long long __value) noexcept : __long_long_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(unsigned long long __value) noexcept
+      : __unsigned_long_long_(__value) {}
+#  ifndef _LIBCPP_HAS_NO_INT128
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__int128_t __value) noexcept : __i128_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__uint128_t __value) noexcept : __u128_(__value) {}
+#  endif
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(float __value) noexcept : __float_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(double __value) noexcept : __double_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(long double __value) noexcept : __long_double_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const _CharT* __value) noexcept : __const_char_type_ptr_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(basic_string_view<_CharT> __value) noexcept
+      : __string_view_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(const void* __value) noexcept : __ptr_(__value) {}
+  _LIBCPP_HIDE_FROM_ABI __basic_format_arg_value(__handle __value) noexcept
+      // TODO FMT Investigate why it doesn't work without the forward.
+      : __handle_(std::forward<__handle>(__value)) {}
+};
+
+template <class _Context>
+class _LIBCPP_TEMPLATE_VIS basic_format_arg {
+public:
+  class _LIBCPP_TEMPLATE_VIS handle;
+
+  _LIBCPP_HIDE_FROM_ABI basic_format_arg() noexcept
+      : __type_{__format::__arg_t::__none} {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept {
+    return __type_ != __format::__arg_t::__none;
+  }
+
+private:
+  using char_type = typename _Context::char_type;
+
+  // TODO FMT Implement constrain [format.arg]/4
+  // Constraints: The template specialization
+  //   typename Context::template formatter_type<T>
+  // meets the Formatter requirements ([formatter.requirements]).  The extent
+  // to which an implementation determines that the specialization meets the
+  // Formatter requirements is unspecified, except that as a minimum the
+  // expression
+  //   typename Context::template formatter_type<T>()
+  //    .format(declval<const T&>(), declval<Context&>())
+  // shall be well-formed when treated as an unevaluated operand.
+
+public:
+  __basic_format_arg_value<_Context> __value_;
+  __format::__arg_t __type_;
+
+  _LIBCPP_HIDE_FROM_ABI explicit basic_format_arg(__format::__arg_t __type,
+                                                  __basic_format_arg_value<_Context> __value) noexcept
+      : __value_(__value), __type_(__type) {}
+};
+
+template <class _Context>
+class _LIBCPP_TEMPLATE_VIS basic_format_arg<_Context>::handle {
+public:
+  _LIBCPP_HIDE_FROM_ABI
+  void format(basic_format_parse_context<char_type>& __parse_ctx, _Context& __ctx) const {
+    __handle_.__format_(__parse_ctx, __ctx, __handle_.__ptr_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI explicit handle(typename __basic_format_arg_value<_Context>::__handle& __handle) noexcept
+      : __handle_(__handle) {}
+
+private:
+  typename __basic_format_arg_value<_Context>::__handle& __handle_;
+};
+
+// This function is user facing, so it must wrap the non-standard types of
+// the "variant" in a handle to stay conforming. See __arg_t for more details.
+template <class _Visitor, class _Context>
+_LIBCPP_HIDE_FROM_ABI decltype(auto)
+visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+  switch (__arg.__type_) {
+#  ifndef _LIBCPP_HAS_NO_INT128
+  case __format::__arg_t::__i128: {
+    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+  }
+
+  case __format::__arg_t::__u128: {
+    typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+    return _VSTD::invoke(_VSTD::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+  }
+#  endif
+  default:
+    return _VSTD::__visit_format_arg(_VSTD::forward<_Visitor>(__vis), __arg);
+  }
+}
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_ARG_H

third_party/libcxx/__format/format_arg_store.h

@@ -0,0 +1,254 @@
+// -*- 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_FORMAT_ARG_STORE_H
+#define _LIBCPP___FORMAT_FORMAT_ARG_STORE_H
+
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_arg.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/extent.h>
+#include <__type_traits/is_same.h>
+#include <__utility/forward.h>
+#include <string>
+#include <string_view>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __format {
+
+/// \returns The @c __arg_t based on the type of the formatting argument.
+///
+/// \pre \c __formattable<_Tp, typename _Context::char_type>
+template <class _Context, class _Tp>
+consteval __arg_t __determine_arg_t();
+
+// Boolean
+template <class, same_as<bool> _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__boolean;
+}
+
+// Char
+template <class _Context, same_as<typename _Context::char_type> _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__char_type;
+}
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class _Context, class _CharT>
+  requires(same_as<typename _Context::char_type, wchar_t> && same_as<_CharT, char>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__char_type;
+}
+#  endif
+
+// Signed integers
+template <class, __libcpp_signed_integer _Tp>
+consteval __arg_t __determine_arg_t() {
+  if constexpr (sizeof(_Tp) <= sizeof(int))
+    return __arg_t::__int;
+  else if constexpr (sizeof(_Tp) <= sizeof(long long))
+    return __arg_t::__long_long;
+#  ifndef _LIBCPP_HAS_NO_INT128
+  else if constexpr (sizeof(_Tp) == sizeof(__int128_t))
+    return __arg_t::__i128;
+#  endif
+  else
+    static_assert(sizeof(_Tp) == 0, "an unsupported signed integer was used");
+}
+
+// Unsigned integers
+template <class, __libcpp_unsigned_integer _Tp>
+consteval __arg_t __determine_arg_t() {
+  if constexpr (sizeof(_Tp) <= sizeof(unsigned))
+    return __arg_t::__unsigned;
+  else if constexpr (sizeof(_Tp) <= sizeof(unsigned long long))
+    return __arg_t::__unsigned_long_long;
+#  ifndef _LIBCPP_HAS_NO_INT128
+  else if constexpr (sizeof(_Tp) == sizeof(__uint128_t))
+    return __arg_t::__u128;
+#  endif
+  else
+    static_assert(sizeof(_Tp) == 0, "an unsupported unsigned integer was used");
+}
+
+// Floating-point
+template <class, same_as<float> _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__float;
+}
+template <class, same_as<double> _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__double;
+}
+template <class, same_as<long double> _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__long_double;
+}
+
+// Char pointer
+template <class _Context, class _Tp>
+  requires(same_as<typename _Context::char_type*, _Tp> || same_as<const typename _Context::char_type*, _Tp>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__const_char_type_ptr;
+}
+
+// Char array
+template <class _Context, class _Tp>
+  requires(is_array_v<_Tp> && same_as<_Tp, typename _Context::char_type[extent_v<_Tp>]>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__string_view;
+}
+
+// String view
+template <class _Context, class _Tp>
+  requires(same_as<typename _Context::char_type, typename _Tp::value_type> &&
+           same_as<_Tp, basic_string_view<typename _Tp::value_type, typename _Tp::traits_type>>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__string_view;
+}
+
+// String
+template <class _Context, class _Tp>
+  requires(
+      same_as<typename _Context::char_type, typename _Tp::value_type> &&
+      same_as<_Tp, basic_string<typename _Tp::value_type, typename _Tp::traits_type, typename _Tp::allocator_type>>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__string_view;
+}
+
+// Pointers
+template <class, class _Ptr>
+  requires(same_as<_Ptr, void*> || same_as<_Ptr, const void*> || same_as<_Ptr, nullptr_t>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__ptr;
+}
+
+// Handle
+//
+// Note this version can't be constrained avoiding ambiguous overloads.
+// That means it can be instantiated by disabled formatters. To solve this, a
+// constrained version for not formattable formatters is added.
+template <class _Context, class _Tp>
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__handle;
+}
+
+// The overload for not formattable types allows triggering the static
+// assertion below.
+template <class _Context, class _Tp>
+  requires(!__formattable<_Tp, typename _Context::char_type>)
+consteval __arg_t __determine_arg_t() {
+  return __arg_t::__none;
+}
+
+template <class _Context, class _Tp>
+_LIBCPP_HIDE_FROM_ABI basic_format_arg<_Context> __create_format_arg(_Tp&& __value) noexcept {
+  constexpr __arg_t __arg = __determine_arg_t<_Context, remove_cvref_t<_Tp>>();
+  static_assert(__arg != __arg_t::__none, "the supplied type is not formattable");
+
+  // Not all types can be used to directly initialize the
+  // __basic_format_arg_value.  First handle all types needing adjustment, the
+  // final else requires no adjustment.
+  if constexpr (__arg == __arg_t::__char_type)
+    // On some platforms initializing a wchar_t from a char is a narrowing
+    // conversion.
+    return basic_format_arg<_Context>{__arg, static_cast<typename _Context::char_type>(__value)};
+  else if constexpr (__arg == __arg_t::__int)
+    return basic_format_arg<_Context>{__arg, static_cast<int>(__value)};
+  else if constexpr (__arg == __arg_t::__long_long)
+    return basic_format_arg<_Context>{__arg, static_cast<long long>(__value)};
+  else if constexpr (__arg == __arg_t::__unsigned)
+    return basic_format_arg<_Context>{__arg, static_cast<unsigned>(__value)};
+  else if constexpr (__arg == __arg_t::__unsigned_long_long)
+    return basic_format_arg<_Context>{__arg, static_cast<unsigned long long>(__value)};
+  else if constexpr (__arg == __arg_t::__string_view)
+    // Using std::size on a character array will add the NUL-terminator to the size.
+    if constexpr (is_array_v<remove_cvref_t<_Tp>>)
+      return basic_format_arg<_Context>{
+          __arg, basic_string_view<typename _Context::char_type>{__value, extent_v<remove_cvref_t<_Tp>> - 1}};
+    else
+      // When the _Traits or _Allocator are different an implicit conversion will
+      // fail.
+      return basic_format_arg<_Context>{
+          __arg, basic_string_view<typename _Context::char_type>{__value.data(), __value.size()}};
+  else if constexpr (__arg == __arg_t::__ptr)
+    return basic_format_arg<_Context>{__arg, static_cast<const void*>(__value)};
+  else if constexpr (__arg == __arg_t::__handle)
+    return basic_format_arg<_Context>{
+        __arg, typename __basic_format_arg_value<_Context>::__handle{_VSTD::forward<_Tp>(__value)}};
+  else
+    return basic_format_arg<_Context>{__arg, __value};
+}
+
+template <class _Context, class... _Args>
+_LIBCPP_HIDE_FROM_ABI void __create_packed_storage(uint64_t& __types, __basic_format_arg_value<_Context>* __values,
+                                                   _Args&&... __args) noexcept {
+  int __shift = 0;
+  (
+      [&] {
+        basic_format_arg<_Context> __arg = __format::__create_format_arg<_Context>(__args);
+        if (__shift != 0)
+          __types |= static_cast<uint64_t>(__arg.__type_) << __shift;
+        else
+          // Assigns the initial value.
+          __types = static_cast<uint64_t>(__arg.__type_);
+        __shift += __packed_arg_t_bits;
+        *__values++ = __arg.__value_;
+      }(),
+      ...);
+}
+
+template <class _Context, class... _Args>
+_LIBCPP_HIDE_FROM_ABI void __store_basic_format_arg(basic_format_arg<_Context>* __data, _Args&&... __args) noexcept {
+  ([&] { *__data++ = __format::__create_format_arg<_Context>(__args); }(), ...);
+}
+
+template <class _Context, size_t N>
+struct __packed_format_arg_store {
+  __basic_format_arg_value<_Context> __values_[N];
+  uint64_t __types_;
+};
+
+template <class _Context, size_t N>
+struct __unpacked_format_arg_store {
+  basic_format_arg<_Context> __args_[N];
+};
+
+} // namespace __format
+
+template <class _Context, class... _Args>
+struct _LIBCPP_TEMPLATE_VIS __format_arg_store {
+  _LIBCPP_HIDE_FROM_ABI
+  __format_arg_store(_Args&... __args) noexcept {
+    if constexpr (sizeof...(_Args) != 0) {
+      if constexpr (__format::__use_packed_format_arg_store(sizeof...(_Args)))
+        __format::__create_packed_storage(__storage.__types_, __storage.__values_, __args...);
+      else
+        __format::__store_basic_format_arg<_Context>(__storage.__args_, __args...);
+    }
+  }
+
+  using _Storage = conditional_t<__format::__use_packed_format_arg_store(sizeof...(_Args)),
+                                 __format::__packed_format_arg_store<_Context, sizeof...(_Args)>,
+                                 __format::__unpacked_format_arg_store<_Context, sizeof...(_Args)>>;
+
+  _Storage __storage;
+};
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_ARG_STORE_H

third_party/libcxx/__format/format_args.h

@@ -0,0 +1,82 @@
+// -*- 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_FORMAT_ARGS_H
+#define _LIBCPP___FORMAT_FORMAT_ARGS_H
+
+#include <__availability>
+#include <__config>
+#include <__format/format_arg.h>
+#include <__format/format_arg_store.h>
+#include <__format/format_fwd.h>
+#include <cstddef>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _Context>
+class _LIBCPP_TEMPLATE_VIS basic_format_args {
+public:
+  basic_format_args() noexcept = default;
+
+  template <class... _Args>
+  _LIBCPP_HIDE_FROM_ABI basic_format_args(const __format_arg_store<_Context, _Args...>& __store) noexcept
+      : __size_(sizeof...(_Args)) {
+    if constexpr (sizeof...(_Args) != 0) {
+      if constexpr (__format::__use_packed_format_arg_store(sizeof...(_Args))) {
+        __values_ = __store.__storage.__values_;
+        __types_ = __store.__storage.__types_;
+      } else
+        __args_ = __store.__storage.__args_;
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  basic_format_arg<_Context> get(size_t __id) const noexcept {
+    if (__id >= __size_)
+      return basic_format_arg<_Context>{};
+
+    if (__format::__use_packed_format_arg_store(__size_))
+      return basic_format_arg<_Context>{__format::__get_packed_type(__types_, __id), __values_[__id]};
+
+    return __args_[__id];
+  }
+
+  _LIBCPP_HIDE_FROM_ABI size_t __size() const noexcept { return __size_; }
+
+private:
+  size_t __size_{0};
+  // [format.args]/5
+  // [Note 1: Implementations are encouraged to optimize the representation of
+  // basic_format_args for small number of formatting arguments by storing
+  // indices of type alternatives separately from values and packing the
+  // former. - end note]
+  union {
+    struct {
+      const __basic_format_arg_value<_Context>* __values_;
+      uint64_t __types_;
+    };
+    const basic_format_arg<_Context>* __args_;
+  };
+};
+
+template <class _Context, class... _Args>
+basic_format_args(__format_arg_store<_Context, _Args...>) -> basic_format_args<_Context>;
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_ARGS_H

third_party/libcxx/__format/format_context.h

@@ -0,0 +1,222 @@
+// -*- 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_FORMAT_CONTEXT_H
+#define _LIBCPP___FORMAT_FORMAT_CONTEXT_H
+
+#include <__availability>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/buffer.h>
+#include <__format/format_arg.h>
+#include <__format/format_arg_store.h>
+#include <__format/format_args.h>
+#include <__format/format_error.h>
+#include <__format/format_fwd.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__iterator/concepts.h>
+#include <__memory/addressof.h>
+#include <__utility/move.h>
+#include <__variant/monostate.h>
+#include <cstddef>
+
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+#include <locale>
+#include <optional>
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _OutIt, class _CharT>
+requires output_iterator<_OutIt, const _CharT&>
+class _LIBCPP_TEMPLATE_VIS basic_format_context;
+
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+/**
+ * Helper to create a basic_format_context.
+ *
+ * This is needed since the constructor is private.
+ */
+template <class _OutIt, class _CharT>
+_LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
+__format_context_create(
+    _OutIt __out_it,
+    basic_format_args<basic_format_context<_OutIt, _CharT>> __args,
+    optional<_VSTD::locale>&& __loc = nullopt) {
+  return _VSTD::basic_format_context(_VSTD::move(__out_it), __args, _VSTD::move(__loc));
+}
+#else
+template <class _OutIt, class _CharT>
+_LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
+__format_context_create(
+    _OutIt __out_it,
+    basic_format_args<basic_format_context<_OutIt, _CharT>> __args) {
+  return _VSTD::basic_format_context(_VSTD::move(__out_it), __args);
+}
+#endif
+
+using format_context =
+    basic_format_context<back_insert_iterator<__format::__output_buffer<char>>,
+                         char>;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wformat_context = basic_format_context<
+    back_insert_iterator<__format::__output_buffer<wchar_t>>, wchar_t>;
+#endif
+
+template <class _OutIt, class _CharT>
+requires output_iterator<_OutIt, const _CharT&>
+class
+    // clang-format off
+    _LIBCPP_TEMPLATE_VIS
+    _LIBCPP_PREFERRED_NAME(format_context)
+    _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wformat_context))
+    // clang-format on
+    basic_format_context {
+public:
+  using iterator = _OutIt;
+  using char_type = _CharT;
+  template <class _Tp>
+  using formatter_type = formatter<_Tp, _CharT>;
+
+  _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context>
+  arg(size_t __id) const noexcept {
+    return __args_.get(__id);
+  }
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  _LIBCPP_HIDE_FROM_ABI _VSTD::locale locale() {
+    if (!__loc_)
+      __loc_ = _VSTD::locale{};
+    return *__loc_;
+  }
+#endif
+  _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
+  _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
+
+private:
+  iterator __out_it_;
+  basic_format_args<basic_format_context> __args_;
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+
+  // The Standard doesn't specify how the locale is stored.
+  // [format.context]/6
+  // std::locale locale();
+  //   Returns: The locale passed to the formatting function if the latter
+  //   takes one, and std::locale() otherwise.
+  // This is done by storing the locale of the constructor in this optional. If
+  // locale() is called and the optional has no value the value will be created.
+  // This allows the implementation to lazily create the locale.
+  // TODO FMT Validate whether lazy creation is the best solution.
+  optional<_VSTD::locale> __loc_;
+
+  template <class __OutIt, class __CharT>
+  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
+  __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>,
+                          optional<_VSTD::locale>&&);
+
+  // Note: the Standard doesn't specify the required constructors.
+  _LIBCPP_HIDE_FROM_ABI
+  explicit basic_format_context(_OutIt __out_it,
+                                basic_format_args<basic_format_context> __args,
+                                optional<_VSTD::locale>&& __loc)
+      : __out_it_(_VSTD::move(__out_it)), __args_(__args),
+        __loc_(_VSTD::move(__loc)) {}
+#else
+  template <class __OutIt, class __CharT>
+  friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
+      __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>);
+
+  _LIBCPP_HIDE_FROM_ABI
+  explicit basic_format_context(_OutIt __out_it,
+                                basic_format_args<basic_format_context> __args)
+      : __out_it_(_VSTD::move(__out_it)), __args_(__args) {}
+#endif
+};
+
+// A specialization for __retarget_buffer
+//
+// See __retarget_buffer for the motivation for this specialization.
+//
+// This context holds a reference to the instance of the basic_format_context
+// that is retargeted. It converts a formatting argument when it is requested
+// during formatting. It is expected that the usage of the arguments is rare so
+// the lookups are not expected to be used often. An alternative would be to
+// convert all elements during construction.
+//
+// The elements of the retargets context are only used when an underlying
+// formatter uses a locale specific formatting or an formatting argument is
+// part for the format spec. For example
+//   format("{:256:{}}", input, 8);
+// Here the width of an element in input is determined dynamically.
+// Note when the top-level element has no width the retargeting is not needed.
+template <class _CharT>
+class _LIBCPP_TEMPLATE_VIS
+    basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> {
+public:
+  using iterator  = typename __format::__retarget_buffer<_CharT>::__iterator;
+  using char_type = _CharT;
+  template <class _Tp>
+  using formatter_type = formatter<_Tp, _CharT>;
+
+  template <class _Context>
+  _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(iterator __out_it, _Context& __ctx)
+      : __out_it_(std::move(__out_it)),
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+        __loc_([](void* __c) { return static_cast<_Context*>(__c)->locale(); }),
+#  endif
+        __ctx_(std::addressof(__ctx)),
+        __arg_([](void* __c, size_t __id) {
+          return std::visit_format_arg(
+              [&](auto __arg) -> basic_format_arg<basic_format_context> {
+                if constexpr (same_as<decltype(__arg), monostate>)
+                  return {};
+                else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
+                  // At the moment it's not possible for formatting to use a re-targeted handle.
+                  // TODO FMT add this when support is needed.
+                  std::__throw_format_error("Re-targeting handle not supported");
+                else
+                  return basic_format_arg<basic_format_context>{
+                      __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
+                      __basic_format_arg_value<basic_format_context>(__arg)};
+              },
+              static_cast<_Context*>(__c)->arg(__id));
+        }) {
+  }
+
+  _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
+    return __arg_(__ctx_, __id);
+  }
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  _LIBCPP_HIDE_FROM_ABI _VSTD::locale locale() { return __loc_(__ctx_); }
+#  endif
+  _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
+  _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
+
+private:
+  iterator __out_it_;
+
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  std::locale (*__loc_)(void* __ctx);
+#  endif
+
+  void* __ctx_;
+  basic_format_arg<basic_format_context> (*__arg_)(void* __ctx, size_t __id);
+};
+
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(basic_format_context);
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_CONTEXT_H

third_party/libcxx/__format/format_error.h

@@ -0,0 +1,52 @@
+// -*- 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_FORMAT_ERROR_H
+#define _LIBCPP___FORMAT_FORMAT_ERROR_H
+
+#include <__config>
+#include <cstdlib>
+#include <stdexcept>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wweak-vtables")
+class _LIBCPP_EXCEPTION_ABI format_error : public runtime_error {
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit format_error(const string& __s)
+      : runtime_error(__s) {}
+  _LIBCPP_HIDE_FROM_ABI explicit format_error(const char* __s)
+      : runtime_error(__s) {}
+  _LIBCPP_HIDE_FROM_ABI_VIRTUAL
+  ~format_error() noexcept override = default;
+};
+_LIBCPP_DIAGNOSTIC_POP
+
+_LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void
+__throw_format_error(const char* __s) {
+#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
+  throw format_error(__s);
+#else
+  (void)__s;
+  _VSTD::abort();
+#endif
+}
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_ERROR_H

third_party/libcxx/__format/format_functions.h

@@ -0,0 +1,677 @@
+// -*- 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_FORMAT_FUNCTIONS
+#define _LIBCPP___FORMAT_FORMAT_FUNCTIONS
+
+#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/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_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 <__iterator/back_insert_iterator.h>
+#include <__iterator/concepts.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/readable_traits.h> // iter_value_t
+#include <__variant/monostate.h>
+#include <array>
+#include <string>
+#include <string_view>
+
+#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 >= 20
+
+// 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:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr void __parse(_ParseContext& __ctx) const {
+    __parse_(__ctx);
+  }
+
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI constexpr void __enable() {
+    __parse_ = [](basic_format_parse_context<_CharT>& __ctx) {
+      formatter<_Tp, _CharT> __f;
+      __ctx.advance_to(__f.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>&) { std::__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_)
+      std::__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_)
+      std::__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_;
+};
+
+// [format.string.std]/8
+// If { arg-idopt } is used in a width or precision, the value of the
+// corresponding formatting argument is used in its place. If the
+// corresponding formatting argument is not of standard signed or unsigned
+// integer type, or its value is negative for precision or non-positive for
+// width, an exception of type format_error is thrown.
+//
+// _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) {
+  auto __validate_type = [](__arg_t __type) {
+    // LWG3720 originally allowed "signed or unsigned integer types", however
+    // the final version explicitly changed it to "*standard* signed or unsigned
+    // integer types". It's trivial to use 128-bit integrals in libc++'s
+    // implementation, but other implementations may not implement it.
+    // (Using a width or precision, that does not fit in 64-bits, sounds very
+    // unlikely in real world code.)
+    switch (__type) {
+    case __arg_t::__int:
+    case __arg_t::__long_long:
+    case __arg_t::__unsigned:
+    case __arg_t::__unsigned_long_long:
+      return;
+
+    default:
+      std::__throw_format_error("Replacement argument isn't a standard signed or unsigned integer type");
+    }
+  };
+
+  formatter<_Tp, _CharT> __formatter;
+  __parse_ctx.advance_to(__formatter.parse(__parse_ctx));
+  if (__formatter.__parser_.__width_as_arg_)
+    __validate_type(__ctx.arg(__formatter.__parser_.__width_));
+
+  if constexpr (_HasPrecision)
+    if (__formatter.__parser_.__precision_as_arg_)
+      __validate_type(__ctx.arg(__formatter.__parser_.__precision_));
+}
+
+// This function is not user facing, so it can directly use the non-standard types of the "variant".
+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:
+    std::__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
+    std::__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
+    std::__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:
+    std::__throw_format_error("Handle should use __compile_time_validate_handle_argument");
+  }
+  std::__throw_format_error("Invalid argument");
+}
+
+template <contiguous_iterator _Iterator, class _ParseCtx, class _Ctx>
+_LIBCPP_HIDE_FROM_ABI constexpr _Iterator
+__handle_replacement_field(_Iterator __begin, _Iterator __end,
+                           _ParseCtx& __parse_ctx, _Ctx& __ctx) {
+  using _CharT = iter_value_t<_Iterator>;
+  __format::__parse_number_result __r = __format::__parse_arg_id(__begin, __end, __parse_ctx);
+
+  bool __parse = *__r.__last == _CharT(':');
+  switch (*__r.__last) {
+  case _CharT(':'):
+    // The arg-id has a format-specifier, advance the input to the format-spec.
+    __parse_ctx.advance_to(__r.__last + 1);
+    break;
+  case _CharT('}'):
+    // The arg-id has no format-specifier.
+    __parse_ctx.advance_to(__r.__last);
+    break;
+  default:
+    std::__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::__none)
+      std::__throw_format_error("Argument index out of bounds");
+    else if (__type == __arg_t::__handle)
+      __ctx.__handle(__r.__value).__parse(__parse_ctx);
+    else if (__parse)
+      __format::__compile_time_visit_format_arg(__parse_ctx, __ctx, __type);
+  } else
+    _VSTD::__visit_format_arg(
+        [&](auto __arg) {
+          if constexpr (same_as<decltype(__arg), monostate>)
+            std::__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('}'))
+    std::__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>);
+
+  auto __begin = __parse_ctx.begin();
+  auto __end = __parse_ctx.end();
+  typename _Ctx::iterator __out_it = __ctx.out();
+  while (__begin != __end) {
+    switch (*__begin) {
+    case _CharT('{'):
+      ++__begin;
+      if (__begin == __end)
+        std::__throw_format_error("The format string terminates at a '{'");
+
+      if (*__begin != _CharT('{')) [[likely]] {
+        __ctx.advance_to(_VSTD::move(__out_it));
+        __begin =
+            __format::__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('}'))
+        std::__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 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 _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 _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 _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 _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
+
+// TODO FMT This needs to be a template or std::to_chars(floating-point) availability markup
+// fires too eagerly, see http://llvm.org/PR61563.
+template <class = void>
+_LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI 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
+// TODO FMT This needs to be a template or std::to_chars(floating-point) availability markup
+// fires too eagerly, see http://llvm.org/PR61563.
+template <class = void>
+_LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI 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 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 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 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 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 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 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 _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 _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 _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 _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
+
+// TODO FMT This needs to be a template or std::to_chars(floating-point) availability markup
+// fires too eagerly, see http://llvm.org/PR61563.
+template <class = void>
+_LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI 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
+// TODO FMT This needs to be a template or std::to_chars(floating-point) availability markup
+// fires too eagerly, see http://llvm.org/PR61563.
+template <class = void>
+_LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI 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 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 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 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 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 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 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 >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_FUNCTIONS

third_party/libcxx/__format/format_fwd.h

@@ -0,0 +1,39 @@
+// -*- 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_FORMAT_FWD_H
+#define _LIBCPP___FORMAT_FORMAT_FWD_H
+
+#include <__availability>
+#include <__config>
+#include <__iterator/concepts.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _Context>
+class _LIBCPP_TEMPLATE_VIS basic_format_arg;
+
+template <class _OutIt, class _CharT>
+  requires output_iterator<_OutIt, const _CharT&>
+class _LIBCPP_TEMPLATE_VIS basic_format_context;
+
+template <class _Tp, class _CharT = char>
+struct _LIBCPP_TEMPLATE_VIS formatter;
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_FWD_H

third_party/libcxx/__format/format_parse_context.h

@@ -0,0 +1,113 @@
+// -*- 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_FORMAT_PARSE_CONTEXT_H
+#define _LIBCPP___FORMAT_FORMAT_PARSE_CONTEXT_H
+
+#include <__config>
+#include <__format/format_error.h>
+#include <__type_traits/is_constant_evaluated.h>
+#include <string_view>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+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;
+
+  _LIBCPP_HIDE_FROM_ABI
+  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_HIDE_FROM_ABI constexpr const_iterator begin() const noexcept {
+    return __begin_;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr const_iterator end() const noexcept {
+    return __end_;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void advance_to(const_iterator __it) {
+    __begin_ = __it;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr size_t next_arg_id() {
+    if (__indexing_ == __manual)
+      std::__throw_format_error("Using automatic argument numbering in manual argument numbering mode");
+
+    if (__indexing_ == __unknown)
+      __indexing_ = __automatic;
+
+    // Throws an exception to make the expression a non core constant
+    // expression as required by:
+    // [format.parse.ctx]/8
+    //   Remarks: Let cur-arg-id be the value of next_arg_id_ prior to this
+    //   call. Call expressions where cur-arg-id >= num_args_ is true are not
+    //   core constant expressions (7.7 [expr.const]).
+    // Note: the Throws clause [format.parse.ctx]/9 doesn't specify the
+    // behavior when id >= num_args_.
+    if (is_constant_evaluated() && __next_arg_id_ >= __num_args_)
+      std::__throw_format_error("Argument index outside the valid range");
+
+    return __next_arg_id_++;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void check_arg_id(size_t __id) {
+    if (__indexing_ == __automatic)
+      std::__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_)
+      std::__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_;
+};
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(basic_format_parse_context);
+
+using format_parse_context = basic_format_parse_context<char>;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wformat_parse_context = basic_format_parse_context<wchar_t>;
+#endif
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_PARSE_CONTEXT_H

third_party/libcxx/__format/format_string.h

@@ -0,0 +1,167 @@
+// -*- 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_FORMAT_STRING_H
+#define _LIBCPP___FORMAT_FORMAT_STRING_H
+
+#include <__assert>
+#include <__config>
+#include <__format/format_error.h>
+#include <__iterator/concepts.h>
+#include <__iterator/readable_traits.h> // iter_value_t
+#include <cstddef>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __format {
+
+template <contiguous_iterator _Iterator>
+struct _LIBCPP_TEMPLATE_VIS __parse_number_result {
+  _Iterator __last;
+  uint32_t __value;
+};
+
+template <contiguous_iterator _Iterator>
+__parse_number_result(_Iterator, uint32_t) -> __parse_number_result<_Iterator>;
+
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_number(_Iterator __begin, _Iterator __end);
+
+/**
+ * The maximum value of a numeric argument.
+ *
+ * This is used for:
+ * * arg-id
+ * * width as value or arg-id.
+ * * precision as value or arg-id.
+ *
+ * The value is compatible with the maximum formatting width and precision
+ * using the `%*` syntax on a 32-bit system.
+ */
+inline constexpr uint32_t __number_max = INT32_MAX;
+
+namespace __detail {
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_zero(_Iterator __begin, _Iterator, auto& __parse_ctx) {
+  __parse_ctx.check_arg_id(0);
+  return {++__begin, 0}; // can never be larger than the maximum.
+}
+
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_automatic(_Iterator __begin, _Iterator, auto& __parse_ctx) {
+  size_t __value = __parse_ctx.next_arg_id();
+  _LIBCPP_ASSERT(__value <= __number_max,
+                 "Compilers don't support this number of arguments");
+
+  return {__begin, uint32_t(__value)};
+}
+
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_manual(_Iterator __begin, _Iterator __end, auto& __parse_ctx) {
+  __parse_number_result<_Iterator> __r = __format::__parse_number(__begin, __end);
+  __parse_ctx.check_arg_id(__r.__value);
+  return __r;
+}
+
+} // namespace __detail
+
+/**
+ * Parses a number.
+ *
+ * The number is used for the 31-bit values @em width and @em precision. This
+ * allows a maximum value of 2147483647.
+ */
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_number(_Iterator __begin, _Iterator __end_input) {
+  using _CharT = iter_value_t<_Iterator>;
+  static_assert(__format::__number_max == INT32_MAX,
+                "The algorithm is implemented based on this value.");
+  /*
+   * Limit the input to 9 digits, otherwise we need two checks during every
+   * iteration:
+   * - Are we at the end of the input?
+   * - Does the value exceed width of an uint32_t? (Switching to uint64_t would
+   *   have the same issue, but with a higher maximum.)
+   */
+  _Iterator __end = __end_input - __begin > 9 ? __begin + 9 : __end_input;
+  uint32_t __value = *__begin - _CharT('0');
+  while (++__begin != __end) {
+    if (*__begin < _CharT('0') || *__begin > _CharT('9'))
+      return {__begin, __value};
+
+    __value = __value * 10 + *__begin - _CharT('0');
+  }
+
+  if (__begin != __end_input && *__begin >= _CharT('0') &&
+      *__begin <= _CharT('9')) {
+
+    /*
+     * There are more than 9 digits, do additional validations:
+     * - Does the 10th digit exceed the maximum allowed value?
+     * - Are there more than 10 digits?
+     * (More than 10 digits always overflows the maximum.)
+     */
+    uint64_t __v = uint64_t(__value) * 10 + *__begin++ - _CharT('0');
+    if (__v > __number_max ||
+        (__begin != __end_input && *__begin >= _CharT('0') &&
+         *__begin <= _CharT('9')))
+      std::__throw_format_error("The numeric value of the format-spec is too large");
+
+    __value = __v;
+  }
+
+  return {__begin, __value};
+}
+
+/**
+ * Multiplexer for all parse functions.
+ *
+ * The parser will return a pointer beyond the last consumed character. This
+ * should be the closing '}' of the arg-id.
+ */
+template <contiguous_iterator _Iterator>
+_LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
+__parse_arg_id(_Iterator __begin, _Iterator __end, auto& __parse_ctx) {
+  using _CharT = iter_value_t<_Iterator>;
+  switch (*__begin) {
+  case _CharT('0'):
+    return __detail::__parse_zero(__begin, __end, __parse_ctx);
+
+  case _CharT(':'):
+    // This case is conditionally valid. It's allowed in an arg-id in the
+    // replacement-field, but not in the std-format-spec. The caller can
+    // provide a better diagnostic, so accept it here unconditionally.
+  case _CharT('}'):
+    return __detail::__parse_automatic(__begin, __end, __parse_ctx);
+  }
+  if (*__begin < _CharT('0') || *__begin > _CharT('9'))
+    std::__throw_format_error("The arg-id of the format-spec starts with an invalid character");
+
+  return __detail::__parse_manual(__begin, __end, __parse_ctx);
+}
+
+} // namespace __format
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_STRING_H

third_party/libcxx/__format/format_to_n_result.h

@@ -0,0 +1,35 @@
+// -*- 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_FORMAT_TO_N_RESULT_H
+#define _LIBCPP___FORMAT_FORMAT_TO_N_RESULT_H
+
+#include <__config>
+#include <__iterator/incrementable_traits.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _OutIt>
+struct _LIBCPP_TEMPLATE_VIS format_to_n_result {
+  _OutIt out;
+  iter_difference_t<_OutIt> size;
+};
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(format_to_n_result);
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_TO_N_RESULT_H

third_party/libcxx/__format/formatter.h

@@ -0,0 +1,54 @@
+// -*- 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_FORMATTER_H
+#define _LIBCPP___FORMAT_FORMATTER_H
+
+#include <__availability>
+#include <__config>
+#include <__format/format_fwd.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+/// The default formatter template.
+///
+/// [format.formatter.spec]/5
+/// If F is a disabled specialization of formatter, these values are false:
+/// - is_default_constructible_v<F>,
+/// - is_copy_constructible_v<F>,
+/// - is_move_constructible_v<F>,
+/// - is_copy_assignable<F>, and
+/// - is_move_assignable<F>.
+template <class _Tp, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter {
+  formatter() = delete;
+  formatter(const formatter&) = delete;
+  formatter& operator=(const formatter&) = delete;
+};
+
+#  if _LIBCPP_STD_VER >= 23
+
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI constexpr void __set_debug_format(_Tp& __formatter) {
+  if constexpr (requires { __formatter.set_debug_format(); })
+    __formatter.set_debug_format();
+}
+
+#  endif // _LIBCPP_STD_VER >= 23
+#endif   // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_H

third_party/libcxx/__format/formatter_bool.h

@@ -0,0 +1,79 @@
+// -*- 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_FORMATTER_BOOL_H
+#define _LIBCPP___FORMAT_FORMATTER_BOOL_H
+
+#include <__algorithm/copy.h>
+#include <__availability>
+#include <__config>
+#include <__debug>
+#include <__format/concepts.h>
+#include <__format/format_error.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/parser_std_format_spec.h>
+#include <__utility/unreachable.h>
+#include <string_view>
+
+#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 >= 20
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<bool, _CharT> {
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_bool(__parser_);
+    return __result;
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(bool __value, _FormatContext& __ctx) const {
+    switch (__parser_.__type_) {
+    case __format_spec::__type::__default:
+    case __format_spec::__type::__string:
+      return __formatter::__format_bool(__value, __ctx, __parser_.__get_parsed_std_specifications(__ctx));
+
+    case __format_spec::__type::__binary_lower_case:
+    case __format_spec::__type::__binary_upper_case:
+    case __format_spec::__type::__octal:
+    case __format_spec::__type::__decimal:
+    case __format_spec::__type::__hexadecimal_lower_case:
+    case __format_spec::__type::__hexadecimal_upper_case:
+      // Promotes bool to an integral type. This reduces the number of
+      // instantiations of __format_integer reducing code size.
+      return __formatter::__format_integer(
+          static_cast<unsigned>(__value), __ctx, __parser_.__get_parsed_std_specifications(__ctx));
+
+    default:
+      _LIBCPP_ASSERT(false, "The parse function should have validated the type");
+      __libcpp_unreachable();
+    }
+  }
+
+  __format_spec::__parser<_CharT> __parser_;
+};
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_BOOL_H

third_party/libcxx/__format/formatter_char.h

@@ -0,0 +1,95 @@
+// -*- 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_FORMATTER_CHAR_H
+#define _LIBCPP___FORMAT_FORMATTER_CHAR_H
+
+#include <__availability>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/is_signed.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_char {
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_char(__parser_);
+    return __result;
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT __value, _FormatContext& __ctx) const {
+    if (__parser_.__type_ == __format_spec::__type::__default || __parser_.__type_ == __format_spec::__type::__char)
+      return __formatter::__format_char(__value, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
+
+#  if _LIBCPP_STD_VER >= 23
+    if (__parser_.__type_ == __format_spec::__type::__debug)
+      return __formatter::__format_escaped_char(__value, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
+#  endif
+
+    if constexpr (sizeof(_CharT) <= sizeof(int))
+      // Promotes _CharT to an integral type. This reduces the number of
+      // instantiations of __format_integer reducing code size.
+      return __formatter::__format_integer(
+          static_cast<conditional_t<is_signed_v<_CharT>, int, unsigned>>(__value),
+          __ctx,
+          __parser_.__get_parsed_std_specifications(__ctx));
+    else
+      return __formatter::__format_integer(__value, __ctx, __parser_.__get_parsed_std_specifications(__ctx));
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(char __value, _FormatContext& __ctx) const
+    requires(same_as<_CharT, wchar_t>)
+  {
+    return format(static_cast<wchar_t>(__value), __ctx);
+  }
+
+#  if _LIBCPP_STD_VER >= 23
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_debug_format() { __parser_.__type_ = __format_spec::__type::__debug; }
+#  endif
+
+  __format_spec::__parser<_CharT> __parser_;
+};
+
+template <>
+struct _LIBCPP_TEMPLATE_VIS formatter<char, char> : public __formatter_char<char> {};
+
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <>
+struct _LIBCPP_TEMPLATE_VIS formatter<char, wchar_t> : public __formatter_char<wchar_t> {};
+
+template <>
+struct _LIBCPP_TEMPLATE_VIS formatter<wchar_t, wchar_t> : public __formatter_char<wchar_t> {
+};
+
+#  endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_CHAR_H

third_party/libcxx/__format/formatter_floating_point.h

@@ -0,0 +1,761 @@
+// -*- 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_FORMATTER_FLOATING_POINT_H
+#define _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H
+
+#include <__algorithm/copy_n.h>
+#include <__algorithm/find.h>
+#include <__algorithm/max.h>
+#include <__algorithm/min.h>
+#include <__algorithm/rotate.h>
+#include <__algorithm/transform.h>
+#include <__charconv/chars_format.h>
+#include <__charconv/to_chars_floating_point.h>
+#include <__charconv/to_chars_result.h>
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__memory/allocator.h>
+#include <__system_error/errc.h>
+#include <__type_traits/conditional.h>
+#include <__utility/move.h>
+#include <__utility/unreachable.h>
+#include <cmath>
+#include <cstddef>
+
+#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 >= 20
+
+namespace __formatter {
+
+template <floating_point _Tp>
+_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value) {
+  to_chars_result __r = _VSTD::to_chars(__first, __last, __value);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  return __r.ptr;
+}
+
+template <floating_point _Tp>
+_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, chars_format __fmt) {
+  to_chars_result __r = _VSTD::to_chars(__first, __last, __value, __fmt);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  return __r.ptr;
+}
+
+template <floating_point _Tp>
+_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, chars_format __fmt, int __precision) {
+  to_chars_result __r = _VSTD::to_chars(__first, __last, __value, __fmt, __precision);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  return __r.ptr;
+}
+
+// https://en.cppreference.com/w/cpp/language/types#cite_note-1
+// float             min subnormal: +/-0x1p-149   max: +/- 3.402,823,4 10^38
+// double            min subnormal: +/-0x1p-1074  max  +/- 1.797,693,134,862,315,7 10^308
+// long double (x86) min subnormal: +/-0x1p-16446 max: +/- 1.189,731,495,357,231,765,021 10^4932
+//
+// The maximum number of digits required for the integral part is based on the
+// maximum's value power of 10. Every power of 10 requires one additional
+// decimal digit.
+// The maximum number of digits required for the fractional part is based on
+// the minimal subnormal hexadecimal output's power of 10. Every division of a
+// fraction's binary 1 by 2, requires one additional decimal digit.
+//
+// The maximum size of a formatted value depends on the selected output format.
+// Ignoring the fact the format string can request a precision larger than the
+// values maximum required, these values are:
+//
+// sign                    1 code unit
+// __max_integral
+// radix point             1 code unit
+// __max_fractional
+// exponent character      1 code unit
+// sign                    1 code unit
+// __max_fractional_value
+// -----------------------------------
+// total                   4 code units extra required.
+//
+// TODO FMT Optimize the storage to avoid storing digits that are known to be zero.
+// https://www.exploringbinary.com/maximum-number-of-decimal-digits-in-binary-floating-point-numbers/
+
+// TODO FMT Add long double specialization when to_chars has proper long double support.
+template <class _Tp>
+struct __traits;
+
+template <floating_point _Fp>
+_LIBCPP_HIDE_FROM_ABI constexpr size_t __float_buffer_size(int __precision) {
+  using _Traits = __traits<_Fp>;
+  return 4 + _Traits::__max_integral + __precision + _Traits::__max_fractional_value;
+}
+
+template <>
+struct __traits<float> {
+  static constexpr int __max_integral = 38;
+  static constexpr int __max_fractional = 149;
+  static constexpr int __max_fractional_value = 3;
+  static constexpr size_t __stack_buffer_size = 256;
+
+  static constexpr int __hex_precision_digits = 3;
+};
+
+template <>
+struct __traits<double> {
+  static constexpr int __max_integral = 308;
+  static constexpr int __max_fractional = 1074;
+  static constexpr int __max_fractional_value = 4;
+  static constexpr size_t __stack_buffer_size = 1024;
+
+  static constexpr int __hex_precision_digits = 4;
+};
+
+/// Helper class to store the conversion buffer.
+///
+/// Depending on the maxium size required for a value, the buffer is allocated
+/// on the stack or the heap.
+template <floating_point _Fp>
+class _LIBCPP_TEMPLATE_VIS __float_buffer {
+  using _Traits = __traits<_Fp>;
+
+public:
+  // TODO FMT Improve this constructor to do a better estimate.
+  // When using a scientific formatting with a precision of 6 a stack buffer
+  // will always suffice. At the moment that isn't important since floats and
+  // doubles use a stack buffer, unless the precision used in the format string
+  // is large.
+  // When supporting long doubles the __max_integral part becomes 4932 which
+  // may be too much for some platforms. For these cases a better estimate is
+  // required.
+  explicit _LIBCPP_HIDE_FROM_ABI __float_buffer(int __precision)
+      : __precision_(__precision != -1 ? __precision : _Traits::__max_fractional) {
+
+    // When the precision is larger than _Traits::__max_fractional the digits in
+    // the range (_Traits::__max_fractional, precision] will contain the value
+    // zero. There's no need to request to_chars to write these zeros:
+    // - When the value is large a temporary heap buffer needs to be allocated.
+    // - When to_chars writes the values they need to be "copied" to the output:
+    //   - char: std::fill on the output iterator is faster than std::copy.
+    //   - wchar_t: same argument as char, but additional std::copy won't work.
+    //     The input is always a char buffer, so every char in the buffer needs
+    //     to be converted from a char to a wchar_t.
+    if (__precision_ > _Traits::__max_fractional) {
+      __num_trailing_zeros_ = __precision_ - _Traits::__max_fractional;
+      __precision_ = _Traits::__max_fractional;
+    }
+
+    __size_ = __formatter::__float_buffer_size<_Fp>(__precision_);
+    if (__size_ > _Traits::__stack_buffer_size)
+      // The allocated buffer's contents don't need initialization.
+      __begin_ = allocator<char>{}.allocate(__size_);
+    else
+      __begin_ = __buffer_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI ~__float_buffer() {
+    if (__size_ > _Traits::__stack_buffer_size)
+      allocator<char>{}.deallocate(__begin_, __size_);
+  }
+  _LIBCPP_HIDE_FROM_ABI __float_buffer(const __float_buffer&) = delete;
+  _LIBCPP_HIDE_FROM_ABI __float_buffer& operator=(const __float_buffer&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI char* begin() const { return __begin_; }
+  _LIBCPP_HIDE_FROM_ABI char* end() const { return __begin_ + __size_; }
+
+  _LIBCPP_HIDE_FROM_ABI int __precision() const { return __precision_; }
+  _LIBCPP_HIDE_FROM_ABI int __num_trailing_zeros() const { return __num_trailing_zeros_; }
+  _LIBCPP_HIDE_FROM_ABI void __remove_trailing_zeros() { __num_trailing_zeros_ = 0; }
+  _LIBCPP_HIDE_FROM_ABI void __add_trailing_zeros(int __zeros) { __num_trailing_zeros_ += __zeros; }
+
+private:
+  int __precision_;
+  int __num_trailing_zeros_{0};
+  size_t __size_;
+  char* __begin_;
+  char __buffer_[_Traits::__stack_buffer_size];
+};
+
+struct __float_result {
+  /// Points at the beginning of the integral part in the buffer.
+  ///
+  /// When there's no sign character this points at the start of the buffer.
+  char* __integral;
+
+  /// Points at the radix point, when not present it's the same as \ref __last.
+  char* __radix_point;
+
+  /// Points at the exponent character, when not present it's the same as \ref __last.
+  char* __exponent;
+
+  /// Points beyond the last written element in the buffer.
+  char* __last;
+};
+
+/// Finds the position of the exponent character 'e' at the end of the buffer.
+///
+/// Assuming there is an exponent the input will terminate with
+/// eSdd and eSdddd (S = sign, d = digit)
+///
+/// \returns a pointer to the exponent or __last when not found.
+constexpr inline _LIBCPP_HIDE_FROM_ABI char* __find_exponent(char* __first, char* __last) {
+  ptrdiff_t __size = __last - __first;
+  if (__size >= 4) {
+    __first = __last - _VSTD::min(__size, ptrdiff_t(6));
+    for (; __first != __last - 3; ++__first) {
+      if (*__first == 'e')
+        return __first;
+    }
+  }
+  return __last;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_default(const __float_buffer<_Fp>& __buffer, _Tp __value,
+                                                             char* __integral) {
+  __float_result __result;
+  __result.__integral = __integral;
+  __result.__last     = __formatter::__to_buffer(__integral, __buffer.end(), __value);
+
+  __result.__exponent = __formatter::__find_exponent(__result.__integral, __result.__last);
+
+  // Constrains:
+  // - There's at least one decimal digit before the radix point.
+  // - The radix point, when present, is placed before the exponent.
+  __result.__radix_point = _VSTD::find(__result.__integral + 1, __result.__exponent, '.');
+
+  // When the radix point isn't found its position is the exponent instead of
+  // __result.__last.
+  if (__result.__radix_point == __result.__exponent)
+    __result.__radix_point = __result.__last;
+
+  // clang-format off
+  _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
+                 (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
+                 (__result.__exponent == __result.__last || *__result.__exponent == 'e'),
+                 "Post-condition failure.");
+  // clang-format on
+
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_hexadecimal_lower_case(const __float_buffer<_Fp>& __buffer,
+                                                                            _Tp __value, int __precision,
+                                                                            char* __integral) {
+  __float_result __result;
+  __result.__integral = __integral;
+  if (__precision == -1)
+    __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex);
+  else
+    __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::hex, __precision);
+
+  // H = one or more hex-digits
+  // S = sign
+  // D = one or more decimal-digits
+  // When the fractional part is zero and no precision the output is 0p+0
+  // else the output is                                              0.HpSD
+  // So testing the second position can differentiate between these two cases.
+  char* __first = __integral + 1;
+  if (*__first == '.') {
+    __result.__radix_point = __first;
+    // One digit is the minimum
+    // 0.hpSd
+    //       ^-- last
+    //     ^---- integral = end of search
+    // ^-------- start of search
+    // 0123456
+    //
+    // Four digits is the maximum
+    // 0.hpSdddd
+    //          ^-- last
+    //        ^---- integral = end of search
+    //    ^-------- start of search
+    // 0123456789
+    static_assert(__traits<_Fp>::__hex_precision_digits <= 4, "Guard against possible underflow.");
+
+    char* __last = __result.__last - 2;
+    __first = __last - __traits<_Fp>::__hex_precision_digits;
+    __result.__exponent = _VSTD::find(__first, __last, 'p');
+  } else {
+    __result.__radix_point = __result.__last;
+    __result.__exponent = __first;
+  }
+
+  // clang-format off
+  _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
+                 (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
+                 (__result.__exponent != __result.__last && *__result.__exponent == 'p'),
+                 "Post-condition failure.");
+  // clang-format on
+
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_hexadecimal_upper_case(const __float_buffer<_Fp>& __buffer,
+                                                                            _Tp __value, int __precision,
+                                                                            char* __integral) {
+  __float_result __result =
+      __formatter::__format_buffer_hexadecimal_lower_case(__buffer, __value, __precision, __integral);
+  _VSTD::transform(__result.__integral, __result.__exponent, __result.__integral, __hex_to_upper);
+  *__result.__exponent = 'P';
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_scientific_lower_case(const __float_buffer<_Fp>& __buffer,
+                                                                           _Tp __value, int __precision,
+                                                                           char* __integral) {
+  __float_result __result;
+  __result.__integral = __integral;
+  __result.__last =
+      __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::scientific, __precision);
+
+  char* __first = __integral + 1;
+  _LIBCPP_ASSERT(__first != __result.__last, "No exponent present");
+  if (*__first == '.') {
+    __result.__radix_point = __first;
+    __result.__exponent    = __formatter::__find_exponent(__first + 1, __result.__last);
+  } else {
+    __result.__radix_point = __result.__last;
+    __result.__exponent = __first;
+  }
+
+  // clang-format off
+  _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
+                 (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
+                 (__result.__exponent != __result.__last && *__result.__exponent == 'e'),
+                 "Post-condition failure.");
+  // clang-format on
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_scientific_upper_case(const __float_buffer<_Fp>& __buffer,
+                                                                           _Tp __value, int __precision,
+                                                                           char* __integral) {
+  __float_result __result =
+      __formatter::__format_buffer_scientific_lower_case(__buffer, __value, __precision, __integral);
+  *__result.__exponent = 'E';
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_fixed(const __float_buffer<_Fp>& __buffer, _Tp __value,
+                                                           int __precision, char* __integral) {
+  __float_result __result;
+  __result.__integral = __integral;
+  __result.__last     = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::fixed, __precision);
+
+  // When there's no precision there's no radix point.
+  // Else the radix point is placed at __precision + 1 from the end.
+  // By converting __precision to a bool the subtraction can be done
+  // unconditionally.
+  __result.__radix_point = __result.__last - (__precision + bool(__precision));
+  __result.__exponent = __result.__last;
+
+  // clang-format off
+  _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
+                 (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
+                 (__result.__exponent == __result.__last),
+                 "Post-condition failure.");
+  // clang-format on
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_general_lower_case(__float_buffer<_Fp>& __buffer, _Tp __value,
+                                                                        int __precision, char* __integral) {
+
+  __buffer.__remove_trailing_zeros();
+
+  __float_result __result;
+  __result.__integral = __integral;
+  __result.__last = __formatter::__to_buffer(__integral, __buffer.end(), __value, chars_format::general, __precision);
+
+  char* __first = __integral + 1;
+  if (__first == __result.__last) {
+    __result.__radix_point = __result.__last;
+    __result.__exponent = __result.__last;
+  } else {
+    __result.__exponent = __formatter::__find_exponent(__first, __result.__last);
+    if (__result.__exponent != __result.__last)
+      // In scientific mode if there's a radix point it will always be after
+      // the first digit. (This is the position __first points at).
+      __result.__radix_point = *__first == '.' ? __first : __result.__last;
+    else {
+      // In fixed mode the algorithm truncates trailing spaces and possibly the
+      // radix point. There's no good guess for the position of the radix point
+      // therefore scan the output after the first digit.
+      __result.__radix_point = _VSTD::find(__first, __result.__last, '.');
+    }
+  }
+
+  // clang-format off
+  _LIBCPP_ASSERT((__result.__integral != __result.__last) &&
+                 (__result.__radix_point == __result.__last || *__result.__radix_point == '.') &&
+                 (__result.__exponent == __result.__last || *__result.__exponent == 'e'),
+                 "Post-condition failure.");
+  // clang-format on
+
+  return __result;
+}
+
+template <class _Fp, class _Tp>
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer_general_upper_case(__float_buffer<_Fp>& __buffer, _Tp __value,
+                                                                        int __precision, char* __integral) {
+  __float_result __result = __formatter::__format_buffer_general_lower_case(__buffer, __value, __precision, __integral);
+  if (__result.__exponent != __result.__last)
+    *__result.__exponent = 'E';
+  return __result;
+}
+
+/// Fills the buffer with the data based on the requested formatting.
+///
+/// This function, when needed, turns the characters to upper case and
+/// determines the "interesting" locations which are returned to the caller.
+///
+/// This means the caller never has to convert the contents of the buffer to
+/// upper case or search for radix points and the location of the exponent.
+/// This gives a bit of overhead. The original code didn't do that, but due
+/// to the number of possible additional work needed to turn this number to
+/// the proper output the code was littered with tests for upper cases and
+/// searches for radix points and exponents.
+/// - When a precision larger than the type's precision is selected
+///   additional zero characters need to be written before the exponent.
+/// - alternate form needs to add a radix point when not present.
+/// - localization needs to do grouping in the integral part.
+template <class _Fp, class _Tp>
+// TODO FMT _Fp should just be _Tp when to_chars has proper long double support.
+_LIBCPP_HIDE_FROM_ABI __float_result __format_buffer(
+    __float_buffer<_Fp>& __buffer,
+    _Tp __value,
+    bool __negative,
+    bool __has_precision,
+    __format_spec::__sign __sign,
+    __format_spec::__type __type) {
+  char* __first = __formatter::__insert_sign(__buffer.begin(), __negative, __sign);
+  switch (__type) {
+  case __format_spec::__type::__default:
+    if (__has_precision)
+      return __formatter::__format_buffer_general_lower_case(__buffer, __value, __buffer.__precision(), __first);
+    else
+      return __formatter::__format_buffer_default(__buffer, __value, __first);
+
+  case __format_spec::__type::__hexfloat_lower_case:
+    return __formatter::__format_buffer_hexadecimal_lower_case(
+        __buffer, __value, __has_precision ? __buffer.__precision() : -1, __first);
+
+  case __format_spec::__type::__hexfloat_upper_case:
+    return __formatter::__format_buffer_hexadecimal_upper_case(
+        __buffer, __value, __has_precision ? __buffer.__precision() : -1, __first);
+
+  case __format_spec::__type::__scientific_lower_case:
+    return __formatter::__format_buffer_scientific_lower_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__scientific_upper_case:
+    return __formatter::__format_buffer_scientific_upper_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__fixed_lower_case:
+  case __format_spec::__type::__fixed_upper_case:
+    return __formatter::__format_buffer_fixed(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__general_lower_case:
+    return __formatter::__format_buffer_general_lower_case(__buffer, __value, __buffer.__precision(), __first);
+
+  case __format_spec::__type::__general_upper_case:
+    return __formatter::__format_buffer_general_upper_case(__buffer, __value, __buffer.__precision(), __first);
+
+  default:
+    _LIBCPP_ASSERT(false, "The parser should have validated the type");
+    __libcpp_unreachable();
+  }
+}
+
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+template <class _OutIt, class _Fp, class _CharT>
+_LIBCPP_HIDE_FROM_ABI _OutIt __format_locale_specific_form(
+    _OutIt __out_it,
+    const __float_buffer<_Fp>& __buffer,
+    const __float_result& __result,
+    _VSTD::locale __loc,
+    __format_spec::__parsed_specifications<_CharT> __specs) {
+  const auto& __np = std::use_facet<numpunct<_CharT>>(__loc);
+  string __grouping = __np.grouping();
+  char* __first = __result.__integral;
+  // When no radix point or exponent are present __last will be __result.__last.
+  char* __last = _VSTD::min(__result.__radix_point, __result.__exponent);
+
+  ptrdiff_t __digits = __last - __first;
+  if (!__grouping.empty()) {
+    if (__digits <= __grouping[0])
+      __grouping.clear();
+    else
+      __grouping = __formatter::__determine_grouping(__digits, __grouping);
+  }
+
+  ptrdiff_t __size =
+      __result.__last - __buffer.begin() + // Formatted string
+      __buffer.__num_trailing_zeros() +    // Not yet rendered zeros
+      __grouping.size() -                  // Grouping contains one
+      !__grouping.empty();                 // additional character
+
+  __formatter::__padding_size_result __padding    = {0, 0};
+  bool __zero_padding                             = __specs.__alignment_ == __format_spec::__alignment::__zero_padding;
+  if (__size < __specs.__width_) {
+    if (__zero_padding) {
+      __specs.__alignment_ = __format_spec::__alignment::__right;
+      __specs.__fill_.__data[0] = _CharT('0');
+    }
+
+    __padding = __formatter::__padding_size(__size, __specs.__width_, __specs.__alignment_);
+  }
+
+  // sign and (zero padding or alignment)
+  if (__zero_padding && __first != __buffer.begin())
+    *__out_it++ = *__buffer.begin();
+  __out_it = __formatter::__fill(_VSTD::move(__out_it), __padding.__before_, __specs.__fill_);
+  if (!__zero_padding && __first != __buffer.begin())
+    *__out_it++ = *__buffer.begin();
+
+  // integral part
+  if (__grouping.empty()) {
+    __out_it = __formatter::__copy(__first, __digits, _VSTD::move(__out_it));
+  } else {
+    auto __r = __grouping.rbegin();
+    auto __e = __grouping.rend() - 1;
+    _CharT __sep = __np.thousands_sep();
+    // The output is divided in small groups of numbers to write:
+    // - A group before the first separator.
+    // - A separator and a group, repeated for the number of separators.
+    // - A group after the last separator.
+    // This loop achieves that process by testing the termination condition
+    // midway in the loop.
+    while (true) {
+      __out_it = __formatter::__copy(__first, *__r, _VSTD::move(__out_it));
+      __first += *__r;
+
+      if (__r == __e)
+        break;
+
+      ++__r;
+      *__out_it++ = __sep;
+    }
+  }
+
+  // fractional part
+  if (__result.__radix_point != __result.__last) {
+    *__out_it++ = __np.decimal_point();
+    __out_it    = __formatter::__copy(__result.__radix_point + 1, __result.__exponent, _VSTD::move(__out_it));
+    __out_it    = __formatter::__fill(_VSTD::move(__out_it), __buffer.__num_trailing_zeros(), _CharT('0'));
+  }
+
+  // exponent
+  if (__result.__exponent != __result.__last)
+    __out_it = __formatter::__copy(__result.__exponent, __result.__last, _VSTD::move(__out_it));
+
+  // alignment
+  return __formatter::__fill(_VSTD::move(__out_it), __padding.__after_, __specs.__fill_);
+}
+#  endif // _LIBCPP_HAS_NO_LOCALIZATION
+
+template <class _OutIt, class _CharT>
+_LIBCPP_HIDE_FROM_ABI _OutIt __format_floating_point_non_finite(
+    _OutIt __out_it, __format_spec::__parsed_specifications<_CharT> __specs, bool __negative, bool __isnan) {
+  char __buffer[4];
+  char* __last = __formatter::__insert_sign(__buffer, __negative, __specs.__std_.__sign_);
+
+  // to_chars can return inf, infinity, nan, and nan(n-char-sequence).
+  // The format library requires inf and nan.
+  // All in one expression to avoid dangling references.
+  bool __upper_case =
+      __specs.__std_.__type_ == __format_spec::__type::__hexfloat_upper_case ||
+      __specs.__std_.__type_ == __format_spec::__type::__scientific_upper_case ||
+      __specs.__std_.__type_ == __format_spec::__type::__fixed_upper_case ||
+      __specs.__std_.__type_ == __format_spec::__type::__general_upper_case;
+  __last = _VSTD::copy_n(&("infnanINFNAN"[6 * __upper_case + 3 * __isnan]), 3, __last);
+
+  // [format.string.std]/13
+  // A zero (0) character preceding the width field pads the field with
+  // leading zeros (following any indication of sign or base) to the field
+  // width, except when applied to an infinity or NaN.
+  if (__specs.__alignment_ == __format_spec::__alignment::__zero_padding)
+    __specs.__alignment_ = __format_spec::__alignment::__right;
+
+  return __formatter::__write(__buffer, __last, _VSTD::move(__out_it), __specs);
+}
+
+template <floating_point _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_floating_point(_Tp __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
+  bool __negative = _VSTD::signbit(__value);
+
+  if (!_VSTD::isfinite(__value)) [[unlikely]]
+    return __formatter::__format_floating_point_non_finite(__ctx.out(), __specs, __negative, _VSTD::isnan(__value));
+
+  // Depending on the std-format-spec string the sign and the value
+  // might not be outputted together:
+  // - zero-padding may insert additional '0' characters.
+  // Therefore the value is processed as a non negative value.
+  // The function @ref __insert_sign will insert a '-' when the value was
+  // negative.
+
+  if (__negative)
+    __value = -__value;
+
+  // TODO FMT _Fp should just be _Tp when to_chars has proper long double support.
+  using _Fp = conditional_t<same_as<_Tp, long double>, double, _Tp>;
+  // Force the type of the precision to avoid -1 to become an unsigned value.
+  __float_buffer<_Fp> __buffer(__specs.__precision_);
+  __float_result __result = __formatter::__format_buffer(
+      __buffer, __value, __negative, (__specs.__has_precision()), __specs.__std_.__sign_, __specs.__std_.__type_);
+
+  if (__specs.__std_.__alternate_form_) {
+    if (__result.__radix_point == __result.__last) {
+      *__result.__last++ = '.';
+
+      // When there is an exponent the point needs to be moved before the
+      // exponent. When there's no exponent the rotate does nothing. Since
+      // rotate tests whether the operation is a nop, call it unconditionally.
+      _VSTD::rotate(__result.__exponent, __result.__last - 1, __result.__last);
+      __result.__radix_point = __result.__exponent;
+
+      // The radix point is always placed before the exponent.
+      // - No exponent needs to point to the new last.
+      // - An exponent needs to move one position to the right.
+      // So it's safe to increment the value unconditionally.
+      ++__result.__exponent;
+    }
+
+    // [format.string.std]/6
+    //   In addition, for g and G conversions, trailing zeros are not removed
+    //   from the result.
+    //
+    // If the type option for a floating-point type is none it may use the
+    // general formatting, but it's not a g or G conversion. So in that case
+    // the formatting should not append trailing zeros.
+    bool __is_general = __specs.__std_.__type_ == __format_spec::__type::__general_lower_case ||
+                        __specs.__std_.__type_ == __format_spec::__type::__general_upper_case;
+
+    if (__is_general) {
+      // https://en.cppreference.com/w/c/io/fprintf
+      // Let P equal the precision if nonzero, 6 if the precision is not
+      // specified, or 1 if the precision is 0. Then, if a conversion with
+      // style E would have an exponent of X:
+      int __p = _VSTD::max(1, (__specs.__has_precision() ? __specs.__precision_ : 6));
+      if (__result.__exponent == __result.__last)
+        // if P > X >= -4, the conversion is with style f or F and precision P - 1 - X.
+        // By including the radix point it calculates P - (1 + X)
+        __p -= __result.__radix_point - __result.__integral;
+      else
+        // otherwise, the conversion is with style e or E and precision P - 1.
+        --__p;
+
+      ptrdiff_t __precision = (__result.__exponent - __result.__radix_point) - 1;
+      if (__precision < __p)
+        __buffer.__add_trailing_zeros(__p - __precision);
+    }
+  }
+
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  if (__specs.__std_.__locale_specific_form_)
+    return __formatter::__format_locale_specific_form(__ctx.out(), __buffer, __result, __ctx.locale(), __specs);
+#  endif
+
+  ptrdiff_t __size         = __result.__last - __buffer.begin();
+  int __num_trailing_zeros = __buffer.__num_trailing_zeros();
+  if (__size + __num_trailing_zeros >= __specs.__width_) {
+    if (__num_trailing_zeros && __result.__exponent != __result.__last)
+      // Insert trailing zeros before exponent character.
+      return __formatter::__copy(
+          __result.__exponent,
+          __result.__last,
+          __formatter::__fill(__formatter::__copy(__buffer.begin(), __result.__exponent, __ctx.out()),
+                              __num_trailing_zeros,
+                              _CharT('0')));
+
+    return __formatter::__fill(
+        __formatter::__copy(__buffer.begin(), __result.__last, __ctx.out()), __num_trailing_zeros, _CharT('0'));
+  }
+
+  auto __out_it = __ctx.out();
+  char* __first = __buffer.begin();
+  if (__specs.__alignment_ == __format_spec::__alignment ::__zero_padding) {
+    // When there is a sign output it before the padding. Note the __size
+    // doesn't need any adjustment, regardless whether the sign is written
+    // here or in __formatter::__write.
+    if (__first != __result.__integral)
+      *__out_it++ = *__first++;
+    // After the sign is written, zero padding is the same a right alignment
+    // with '0'.
+    __specs.__alignment_ = __format_spec::__alignment::__right;
+    __specs.__fill_.__data[0] = _CharT('0');
+  }
+
+  if (__num_trailing_zeros)
+    return __formatter::__write_using_trailing_zeros(
+        __first, __result.__last, _VSTD::move(__out_it), __specs, __size, __result.__exponent, __num_trailing_zeros);
+
+  return __formatter::__write(__first, __result.__last, _VSTD::move(__out_it), __specs, __size);
+}
+
+} // namespace __formatter
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_floating_point {
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_floating_point);
+    __format_spec::__process_parsed_floating_point(__parser_);
+    return __result;
+  }
+
+  template <floating_point _Tp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_Tp __value, _FormatContext& __ctx) const {
+    return __formatter::__format_floating_point(__value, __ctx, __parser_.__get_parsed_std_specifications(__ctx));
+  }
+
+  __format_spec::__parser<_CharT> __parser_;
+};
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<float, _CharT>
+    : public __formatter_floating_point<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<double, _CharT>
+    : public __formatter_floating_point<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<long double, _CharT>
+    : public __formatter_floating_point<_CharT> {};
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___FORMAT_FORMATTER_FLOATING_POINT_H

third_party/libcxx/__format/formatter_integer.h

@@ -0,0 +1,107 @@
+// -*- 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_FORMATTER_INTEGER_H
+#define _LIBCPP___FORMAT_FORMATTER_INTEGER_H
+
+#include <__availability>
+#include <__concepts/arithmetic.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__type_traits/is_same.h>
+#include <__type_traits/make_32_64_or_128_bit.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+    _LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+    template <__fmt_char_type _CharT>
+    struct _LIBCPP_TEMPLATE_VIS __formatter_integer {
+
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
+    __format_spec::__process_parsed_integer(__parser_);
+    return __result;
+  }
+
+  template <integral _Tp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_Tp __value, _FormatContext& __ctx) const {
+    __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
+
+    if (__specs.__std_.__type_ == __format_spec::__type::__char)
+      return __formatter::__format_char(__value, __ctx.out(), __specs);
+
+    using _Type = __make_32_64_or_128_bit_t<_Tp>;
+    static_assert(!is_same<_Type, void>::value, "unsupported integral type used in __formatter_integer::__format");
+
+    // Reduce the number of instantiation of the integer formatter
+    return __formatter::__format_integer(static_cast<_Type>(__value), __ctx, __specs);
+  }
+
+  __format_spec::__parser<_CharT> __parser_;
+};
+
+// Signed integral types.
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<signed char, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<short, _CharT> : public __formatter_integer<_CharT> {
+};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<int, _CharT> : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<long, _CharT> : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<long long, _CharT>
+    : public __formatter_integer<_CharT> {};
+#  ifndef _LIBCPP_HAS_NO_INT128
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<__int128_t, _CharT>
+    : public __formatter_integer<_CharT> {};
+#  endif
+
+// Unsigned integral types.
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<unsigned char, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<unsigned short, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<unsigned, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<unsigned long, _CharT>
+    : public __formatter_integer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<unsigned long long, _CharT>
+    : public __formatter_integer<_CharT> {};
+#  ifndef _LIBCPP_HAS_NO_INT128
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<__uint128_t, _CharT>
+    : public __formatter_integer<_CharT> {};
+#  endif
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_INTEGER_H

third_party/libcxx/__format/formatter_integral.h

@@ -0,0 +1,368 @@
+// -*- 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_FORMATTER_INTEGRAL_H
+#define _LIBCPP___FORMAT_FORMATTER_INTEGRAL_H
+
+#include <__charconv/to_chars_integral.h>
+#include <__charconv/to_chars_result.h>
+#include <__charconv/traits.h>
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_error.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__system_error/errc.h>
+#include <__type_traits/make_unsigned.h>
+#include <__utility/unreachable.h>
+#include <array>
+#include <limits>
+#include <string>
+#include <string_view>
+
+#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 >= 20
+
+namespace __formatter {
+
+//
+// Generic
+//
+
+_LIBCPP_HIDE_FROM_ABI inline char* __insert_sign(char* __buf, bool __negative, __format_spec::__sign __sign) {
+  if (__negative)
+    *__buf++ = '-';
+  else
+    switch (__sign) {
+    case __format_spec::__sign::__default:
+    case __format_spec::__sign::__minus:
+      // No sign added.
+      break;
+    case __format_spec::__sign::__plus:
+      *__buf++ = '+';
+      break;
+    case __format_spec::__sign::__space:
+      *__buf++ = ' ';
+      break;
+    }
+
+  return __buf;
+}
+
+/**
+ * Determines the required grouping based on the size of the input.
+ *
+ * The grouping's last element will be repeated. For simplicity this repeating
+ * is unwrapped based on the length of the input. (When the input is short some
+ * groups are not processed.)
+ *
+ * @returns The size of the groups to write. This means the number of
+ * separator characters written is size() - 1.
+ *
+ * @note Since zero-sized groups cause issues they are silently ignored.
+ *
+ * @note The grouping field of the locale is always a @c std::string,
+ * regardless whether the @c std::numpunct's type is @c char or @c wchar_t.
+ */
+_LIBCPP_HIDE_FROM_ABI inline string __determine_grouping(ptrdiff_t __size, const string& __grouping) {
+  _LIBCPP_ASSERT(!__grouping.empty() && __size > __grouping[0],
+                 "The slow grouping formatting is used while there will be no "
+                 "separators written");
+  string __r;
+  auto __end = __grouping.end() - 1;
+  auto __ptr = __grouping.begin();
+
+  while (true) {
+    __size -= *__ptr;
+    if (__size > 0)
+      __r.push_back(*__ptr);
+    else {
+      // __size <= 0 so the value pushed will be <= *__ptr.
+      __r.push_back(*__ptr + __size);
+      return __r;
+    }
+
+    // Proceed to the next group.
+    if (__ptr != __end) {
+      do {
+        ++__ptr;
+        // Skip grouping with a width of 0.
+      } while (*__ptr == 0 && __ptr != __end);
+    }
+  }
+
+  __libcpp_unreachable();
+}
+
+//
+// Char
+//
+
+template <__fmt_char_type _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __format_char(
+    integral auto __value,
+    output_iterator<const _CharT&> auto __out_it,
+    __format_spec::__parsed_specifications<_CharT> __specs) -> decltype(__out_it) {
+  using _Tp = decltype(__value);
+  if constexpr (!same_as<_CharT, _Tp>) {
+    // cmp_less and cmp_greater can't be used for character types.
+    if constexpr (signed_integral<_CharT> == signed_integral<_Tp>) {
+      if (__value < numeric_limits<_CharT>::min() || __value > numeric_limits<_CharT>::max())
+        std::__throw_format_error("Integral value outside the range of the char type");
+    } else if constexpr (signed_integral<_CharT>) {
+      // _CharT is signed _Tp is unsigned
+      if (__value > static_cast<make_unsigned_t<_CharT>>(numeric_limits<_CharT>::max()))
+        std::__throw_format_error("Integral value outside the range of the char type");
+    } else {
+      // _CharT is unsigned _Tp is signed
+      if (__value < 0 || static_cast<make_unsigned_t<_Tp>>(__value) > numeric_limits<_CharT>::max())
+        std::__throw_format_error("Integral value outside the range of the char type");
+    }
+  }
+
+  const auto __c = static_cast<_CharT>(__value);
+  return __formatter::__write(_VSTD::addressof(__c), _VSTD::addressof(__c) + 1, _VSTD::move(__out_it), __specs);
+}
+
+//
+// Integer
+//
+
+/** Wrapper around @ref to_chars, returning the output pointer. */
+template <integral _Tp>
+_LIBCPP_HIDE_FROM_ABI char* __to_buffer(char* __first, char* __last, _Tp __value, int __base) {
+  // TODO FMT Evaluate code overhead due to not calling the internal function
+  // directly. (Should be zero overhead.)
+  to_chars_result __r = _VSTD::to_chars(__first, __last, __value, __base);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  return __r.ptr;
+}
+
+/**
+ * Helper to determine the buffer size to output a integer in Base @em x.
+ *
+ * There are several overloads for the supported bases. The function uses the
+ * base as template argument so it can be used in a constant expression.
+ */
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 2)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+       + 2                           // Reserve space for the '0[Bb]' prefix.
+       + 1;                          // Reserve space for the sign.
+}
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 8)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+           / 3                       // Adjust to octal.
+       + 1                           // Turn floor to ceil.
+       + 1                           // Reserve space for the '0' prefix.
+       + 1;                          // Reserve space for the sign.
+}
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 10)
+{
+  return numeric_limits<_Tp>::digits10 // The floored value.
+       + 1                             // Turn floor to ceil.
+       + 1;                            // Reserve space for the sign.
+}
+
+template <unsigned_integral _Tp, size_t _Base>
+consteval size_t __buffer_size() noexcept
+  requires(_Base == 16)
+{
+  return numeric_limits<_Tp>::digits // The number of binary digits.
+           / 4                       // Adjust to hexadecimal.
+       + 2                           // Reserve space for the '0[Xx]' prefix.
+       + 1;                          // Reserve space for the sign.
+}
+
+template <unsigned_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator __format_integer(
+    _Tp __value,
+    _FormatContext& __ctx,
+    __format_spec::__parsed_specifications<_CharT> __specs,
+    bool __negative,
+    char* __begin,
+    char* __end,
+    const char* __prefix,
+    int __base) {
+  char* __first = __formatter::__insert_sign(__begin, __negative, __specs.__std_.__sign_);
+  if (__specs.__std_.__alternate_form_ && __prefix)
+    while (*__prefix)
+      *__first++ = *__prefix++;
+
+  char* __last = __formatter::__to_buffer(__first, __end, __value, __base);
+
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  if (__specs.__std_.__locale_specific_form_) {
+    const auto& __np  = std::use_facet<numpunct<_CharT>>(__ctx.locale());
+    string __grouping = __np.grouping();
+    ptrdiff_t __size  = __last - __first;
+    // Writing the grouped form has more overhead than the normal output
+    // routines. If there will be no separators written the locale-specific
+    // form is identical to the normal routine. Test whether to grouped form
+    // is required.
+    if (!__grouping.empty() && __size > __grouping[0])
+      return __formatter::__write_using_decimal_separators(
+          __ctx.out(),
+          __begin,
+          __first,
+          __last,
+          __formatter::__determine_grouping(__size, __grouping),
+          __np.thousands_sep(),
+          __specs);
+  }
+#  endif
+  auto __out_it = __ctx.out();
+  if (__specs.__alignment_ != __format_spec::__alignment::__zero_padding)
+    __first = __begin;
+  else {
+    // __buf contains [sign][prefix]data
+    //                              ^ location of __first
+    // The zero padding is done like:
+    // - Write [sign][prefix]
+    // - Write data right aligned with '0' as fill character.
+    __out_it             = __formatter::__copy(__begin, __first, _VSTD::move(__out_it));
+    __specs.__alignment_ = __format_spec::__alignment::__right;
+    __specs.__fill_.__data[0] = _CharT('0');
+    int32_t __size       = __first - __begin;
+
+    __specs.__width_ -= _VSTD::min(__size, __specs.__width_);
+  }
+
+  if (__specs.__std_.__type_ != __format_spec::__type::__hexadecimal_upper_case) [[likely]]
+    return __formatter::__write(__first, __last, __ctx.out(), __specs);
+
+  return __formatter::__write_transformed(__first, __last, __ctx.out(), __specs, __formatter::__hex_to_upper);
+}
+
+template <unsigned_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_integer(_Tp __value,
+                 _FormatContext& __ctx,
+                 __format_spec::__parsed_specifications<_CharT> __specs,
+                 bool __negative = false) {
+  switch (__specs.__std_.__type_) {
+  case __format_spec::__type::__binary_lower_case: {
+    array<char, __formatter::__buffer_size<decltype(__value), 2>()> __array;
+    return __formatter::__format_integer(__value, __ctx, __specs, __negative, __array.begin(), __array.end(), "0b", 2);
+  }
+  case __format_spec::__type::__binary_upper_case: {
+    array<char, __formatter::__buffer_size<decltype(__value), 2>()> __array;
+    return __formatter::__format_integer(__value, __ctx, __specs, __negative, __array.begin(), __array.end(), "0B", 2);
+  }
+  case __format_spec::__type::__octal: {
+    // Octal is special; if __value == 0 there's no prefix.
+    array<char, __formatter::__buffer_size<decltype(__value), 8>()> __array;
+    return __formatter::__format_integer(
+        __value, __ctx, __specs, __negative, __array.begin(), __array.end(), __value != 0 ? "0" : nullptr, 8);
+  }
+  case __format_spec::__type::__default:
+  case __format_spec::__type::__decimal: {
+    array<char, __formatter::__buffer_size<decltype(__value), 10>()> __array;
+    return __formatter::__format_integer(
+        __value, __ctx, __specs, __negative, __array.begin(), __array.end(), nullptr, 10);
+  }
+  case __format_spec::__type::__hexadecimal_lower_case: {
+    array<char, __formatter::__buffer_size<decltype(__value), 16>()> __array;
+    return __formatter::__format_integer(__value, __ctx, __specs, __negative, __array.begin(), __array.end(), "0x", 16);
+  }
+  case __format_spec::__type::__hexadecimal_upper_case: {
+    array<char, __formatter::__buffer_size<decltype(__value), 16>()> __array;
+    return __formatter::__format_integer(__value, __ctx, __specs, __negative, __array.begin(), __array.end(), "0X", 16);
+  }
+  default:
+    _LIBCPP_ASSERT(false, "The parse function should have validated the type");
+    __libcpp_unreachable();
+  }
+}
+
+template <signed_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_integer(_Tp __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
+  // Depending on the std-format-spec string the sign and the value
+  // might not be outputted together:
+  // - alternate form may insert a prefix string.
+  // - zero-padding may insert additional '0' characters.
+  // Therefore the value is processed as a positive unsigned value.
+  // The function @ref __insert_sign will a '-' when the value was negative.
+  auto __r        = std::__to_unsigned_like(__value);
+  bool __negative = __value < 0;
+  if (__negative)
+    __r = std::__complement(__r);
+
+  return __formatter::__format_integer(__r, __ctx, __specs, __negative);
+}
+
+//
+// Formatter arithmetic (bool)
+//
+
+template <class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __bool_strings;
+
+template <>
+struct _LIBCPP_TEMPLATE_VIS __bool_strings<char> {
+  static constexpr string_view __true{"true"};
+  static constexpr string_view __false{"false"};
+};
+
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <>
+struct _LIBCPP_TEMPLATE_VIS __bool_strings<wchar_t> {
+  static constexpr wstring_view __true{L"true"};
+  static constexpr wstring_view __false{L"false"};
+};
+#  endif
+
+template <class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_bool(bool __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
+#  ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  if (__specs.__std_.__locale_specific_form_) {
+    const auto& __np           = std::use_facet<numpunct<_CharT>>(__ctx.locale());
+    basic_string<_CharT> __str = __value ? __np.truename() : __np.falsename();
+    return __formatter::__write_string_no_precision(basic_string_view<_CharT>{__str}, __ctx.out(), __specs);
+  }
+#  endif
+  basic_string_view<_CharT> __str =
+      __value ? __formatter::__bool_strings<_CharT>::__true : __formatter::__bool_strings<_CharT>::__false;
+  return __formatter::__write(__str.begin(), __str.end(), __ctx.out(), __specs);
+}
+
+} // namespace __formatter
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___FORMAT_FORMATTER_INTEGRAL_H

third_party/libcxx/__format/formatter_output.h

@@ -0,0 +1,597 @@
+// -*- 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_FORMATTER_OUTPUT_H
+#define _LIBCPP___FORMAT_FORMATTER_OUTPUT_H
+
+#include <__algorithm/ranges_copy.h>
+#include <__algorithm/ranges_fill_n.h>
+#include <__algorithm/ranges_for_each.h>
+#include <__algorithm/ranges_transform.h>
+#include <__bit/countl.h>
+#include <__charconv/to_chars_integral.h>
+#include <__charconv/to_chars_result.h>
+#include <__chrono/statically_widen.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/buffer.h>
+#include <__format/concepts.h>
+#include <__format/escaped_output_table.h>
+#include <__format/formatter.h>
+#include <__format/parser_std_format_spec.h>
+#include <__format/unicode.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__iterator/concepts.h>
+#include <__iterator/readable_traits.h> // iter_value_t
+#include <__system_error/errc.h>
+#include <__type_traits/make_unsigned.h>
+#include <__utility/move.h>
+#include <__utility/unreachable.h>
+#include <cstddef>
+#include <string>
+#include <string_view>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __formatter {
+
+_LIBCPP_HIDE_FROM_ABI constexpr char __hex_to_upper(char __c) {
+  switch (__c) {
+  case 'a':
+    return 'A';
+  case 'b':
+    return 'B';
+  case 'c':
+    return 'C';
+  case 'd':
+    return 'D';
+  case 'e':
+    return 'E';
+  case 'f':
+    return 'F';
+  }
+  return __c;
+}
+
+struct _LIBCPP_TYPE_VIS __padding_size_result {
+  size_t __before_;
+  size_t __after_;
+};
+
+_LIBCPP_HIDE_FROM_ABI constexpr __padding_size_result
+__padding_size(size_t __size, size_t __width, __format_spec::__alignment __align) {
+  _LIBCPP_ASSERT(__width > __size, "don't call this function when no padding is required");
+  _LIBCPP_ASSERT(
+      __align != __format_spec::__alignment::__zero_padding, "the caller should have handled the zero-padding");
+
+  size_t __fill = __width - __size;
+  switch (__align) {
+  case __format_spec::__alignment::__zero_padding:
+    __libcpp_unreachable();
+
+  case __format_spec::__alignment::__left:
+    return {0, __fill};
+
+  case __format_spec::__alignment::__center: {
+    // The extra padding is divided per [format.string.std]/3
+    // __before = floor(__fill, 2);
+    // __after = ceil(__fill, 2);
+    size_t __before = __fill / 2;
+    size_t __after  = __fill - __before;
+    return {__before, __after};
+  }
+  case __format_spec::__alignment::__default:
+  case __format_spec::__alignment::__right:
+    return {__fill, 0};
+  }
+  __libcpp_unreachable();
+}
+
+/// Copy wrapper.
+///
+/// This uses a "mass output function" of __format::__output_buffer when possible.
+template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __copy(basic_string_view<_CharT> __str, output_iterator<const _OutCharT&> auto __out_it)
+    -> decltype(__out_it) {
+  if constexpr (_VSTD::same_as<decltype(__out_it), _VSTD::back_insert_iterator<__format::__output_buffer<_OutCharT>>>) {
+    __out_it.__get_container()->__copy(__str);
+    return __out_it;
+  } else if constexpr (_VSTD::same_as<decltype(__out_it),
+                                      typename __format::__retarget_buffer<_OutCharT>::__iterator>) {
+    __out_it.__buffer_->__copy(__str);
+    return __out_it;
+  } else {
+    return std::ranges::copy(__str, _VSTD::move(__out_it)).out;
+  }
+}
+
+template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__copy(const _CharT* __first, const _CharT* __last, output_iterator<const _OutCharT&> auto __out_it)
+    -> decltype(__out_it) {
+  return __formatter::__copy(basic_string_view{__first, __last}, _VSTD::move(__out_it));
+}
+
+template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __copy(const _CharT* __first, size_t __n, output_iterator<const _OutCharT&> auto __out_it)
+    -> decltype(__out_it) {
+  return __formatter::__copy(basic_string_view{__first, __n}, _VSTD::move(__out_it));
+}
+
+/// Transform wrapper.
+///
+/// This uses a "mass output function" of __format::__output_buffer when possible.
+template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT, class _UnaryOperation>
+_LIBCPP_HIDE_FROM_ABI auto
+__transform(const _CharT* __first,
+            const _CharT* __last,
+            output_iterator<const _OutCharT&> auto __out_it,
+            _UnaryOperation __operation) -> decltype(__out_it) {
+  if constexpr (_VSTD::same_as<decltype(__out_it), _VSTD::back_insert_iterator<__format::__output_buffer<_OutCharT>>>) {
+    __out_it.__get_container()->__transform(__first, __last, _VSTD::move(__operation));
+    return __out_it;
+  } else if constexpr (_VSTD::same_as<decltype(__out_it),
+                                      typename __format::__retarget_buffer<_OutCharT>::__iterator>) {
+    __out_it.__buffer_->__transform(__first, __last, _VSTD::move(__operation));
+    return __out_it;
+  } else {
+    return std::ranges::transform(__first, __last, _VSTD::move(__out_it), __operation).out;
+  }
+}
+
+/// Fill wrapper.
+///
+/// This uses a "mass output function" of __format::__output_buffer when possible.
+template <__fmt_char_type _CharT, output_iterator<const _CharT&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _OutIt __fill(_OutIt __out_it, size_t __n, _CharT __value) {
+  if constexpr (_VSTD::same_as<decltype(__out_it), _VSTD::back_insert_iterator<__format::__output_buffer<_CharT>>>) {
+    __out_it.__get_container()->__fill(__n, __value);
+    return __out_it;
+  } else if constexpr (_VSTD::same_as<decltype(__out_it), typename __format::__retarget_buffer<_CharT>::__iterator>) {
+    __out_it.__buffer_->__fill(__n, __value);
+    return __out_it;
+  } else {
+    return std::ranges::fill_n(_VSTD::move(__out_it), __n, __value);
+  }
+}
+
+#  ifndef _LIBCPP_HAS_NO_UNICODE
+template <__fmt_char_type _CharT, output_iterator<const _CharT&> _OutIt>
+  requires(same_as<_CharT, char>)
+_LIBCPP_HIDE_FROM_ABI _OutIt __fill(_OutIt __out_it, size_t __n, __format_spec::__code_point<_CharT> __value) {
+  std::size_t __bytes = std::countl_one(static_cast<unsigned char>(__value.__data[0]));
+  if (__bytes == 0)
+    return __formatter::__fill(std::move(__out_it), __n, __value.__data[0]);
+
+  for (size_t __i = 0; __i < __n; ++__i)
+    __out_it = __formatter::__copy(
+        std::addressof(__value.__data[0]), std::addressof(__value.__data[0]) + __bytes, std::move(__out_it));
+  return __out_it;
+}
+
+#    ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <__fmt_char_type _CharT, output_iterator<const _CharT&> _OutIt>
+  requires(same_as<_CharT, wchar_t> && sizeof(wchar_t) == 2)
+_LIBCPP_HIDE_FROM_ABI _OutIt __fill(_OutIt __out_it, size_t __n, __format_spec::__code_point<_CharT> __value) {
+  if (!__unicode::__is_high_surrogate(__value.__data[0]))
+    return __formatter::__fill(std::move(__out_it), __n, __value.__data[0]);
+
+  for (size_t __i = 0; __i < __n; ++__i)
+    __out_it = __formatter::__copy(
+        std::addressof(__value.__data[0]), std::addressof(__value.__data[0]) + 2, std::move(__out_it));
+  return __out_it;
+}
+
+template <__fmt_char_type _CharT, output_iterator<const _CharT&> _OutIt>
+  requires(same_as<_CharT, wchar_t> && sizeof(wchar_t) == 4)
+_LIBCPP_HIDE_FROM_ABI _OutIt __fill(_OutIt __out_it, size_t __n, __format_spec::__code_point<_CharT> __value) {
+  return __formatter::__fill(std::move(__out_it), __n, __value.__data[0]);
+}
+#    endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+#  else    // _LIBCPP_HAS_NO_UNICODE
+template <__fmt_char_type _CharT, output_iterator<const _CharT&> _OutIt>
+_LIBCPP_HIDE_FROM_ABI _OutIt __fill(_OutIt __out_it, size_t __n, __format_spec::__code_point<_CharT> __value) {
+  return __formatter::__fill(std::move(__out_it), __n, __value.__data[0]);
+}
+#  endif   // _LIBCPP_HAS_NO_UNICODE
+
+template <class _OutIt, class _CharT>
+_LIBCPP_HIDE_FROM_ABI _OutIt __write_using_decimal_separators(_OutIt __out_it, const char* __begin, const char* __first,
+                                                              const char* __last, string&& __grouping, _CharT __sep,
+                                                              __format_spec::__parsed_specifications<_CharT> __specs) {
+  int __size = (__first - __begin) +    // [sign][prefix]
+               (__last - __first) +     // data
+               (__grouping.size() - 1); // number of separator characters
+
+  __padding_size_result __padding = {0, 0};
+  if (__specs.__alignment_ == __format_spec::__alignment::__zero_padding) {
+    // Write [sign][prefix].
+    __out_it = __formatter::__copy(__begin, __first, _VSTD::move(__out_it));
+
+    if (__specs.__width_ > __size) {
+      // Write zero padding.
+      __padding.__before_ = __specs.__width_ - __size;
+      __out_it            = __formatter::__fill(_VSTD::move(__out_it), __specs.__width_ - __size, _CharT('0'));
+    }
+  } else {
+    if (__specs.__width_ > __size) {
+      // Determine padding and write padding.
+      __padding = __formatter::__padding_size(__size, __specs.__width_, __specs.__alignment_);
+
+      __out_it = __formatter::__fill(_VSTD::move(__out_it), __padding.__before_, __specs.__fill_);
+    }
+    // Write [sign][prefix].
+    __out_it = __formatter::__copy(__begin, __first, _VSTD::move(__out_it));
+  }
+
+  auto __r = __grouping.rbegin();
+  auto __e = __grouping.rend() - 1;
+  _LIBCPP_ASSERT(__r != __e, "The slow grouping formatting is used while "
+                             "there will be no separators written.");
+  // The output is divided in small groups of numbers to write:
+  // - A group before the first separator.
+  // - A separator and a group, repeated for the number of separators.
+  // - A group after the last separator.
+  // This loop achieves that process by testing the termination condition
+  // midway in the loop.
+  //
+  // TODO FMT This loop evaluates the loop invariant `__parser.__type !=
+  // _Flags::_Type::__hexadecimal_upper_case` for every iteration. (This test
+  // happens in the __write call.) Benchmark whether making two loops and
+  // hoisting the invariant is worth the effort.
+  while (true) {
+    if (__specs.__std_.__type_ == __format_spec::__type::__hexadecimal_upper_case) {
+      __last = __first + *__r;
+      __out_it = __formatter::__transform(__first, __last, _VSTD::move(__out_it), __hex_to_upper);
+      __first = __last;
+    } else {
+      __out_it = __formatter::__copy(__first, *__r, _VSTD::move(__out_it));
+      __first += *__r;
+    }
+
+    if (__r == __e)
+      break;
+
+    ++__r;
+    *__out_it++ = __sep;
+  }
+
+  return __formatter::__fill(_VSTD::move(__out_it), __padding.__after_, __specs.__fill_);
+}
+
+/// Writes the input to the output with the required padding.
+///
+/// Since the output column width is specified the function can be used for
+/// ASCII and Unicode output.
+///
+/// \pre \a __size <= \a __width. Using this function when this pre-condition
+///      doesn't hold incurs an unwanted overhead.
+///
+/// \param __str       The string to write.
+/// \param __out_it    The output iterator to write to.
+/// \param __specs     The parsed formatting specifications.
+/// \param __size      The (estimated) output column width. When the elements
+///                    to be written are ASCII the following condition holds
+///                    \a __size == \a __last - \a __first.
+///
+/// \returns           An iterator pointing beyond the last element written.
+///
+/// \note The type of the elements in range [\a __first, \a __last) can differ
+/// from the type of \a __specs. Integer output uses \c std::to_chars for its
+/// conversion, which means the [\a __first, \a __last) always contains elements
+/// of the type \c char.
+template <class _CharT, class _ParserCharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__write(basic_string_view<_CharT> __str,
+        output_iterator<const _CharT&> auto __out_it,
+        __format_spec::__parsed_specifications<_ParserCharT> __specs,
+        ptrdiff_t __size) -> decltype(__out_it) {
+  if (__size >= __specs.__width_)
+    return __formatter::__copy(__str, _VSTD::move(__out_it));
+
+  __padding_size_result __padding = __formatter::__padding_size(__size, __specs.__width_, __specs.__std_.__alignment_);
+  __out_it                        = __formatter::__fill(_VSTD::move(__out_it), __padding.__before_, __specs.__fill_);
+  __out_it                        = __formatter::__copy(__str, _VSTD::move(__out_it));
+  return __formatter::__fill(_VSTD::move(__out_it), __padding.__after_, __specs.__fill_);
+}
+
+template <contiguous_iterator _Iterator, class _ParserCharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__write(_Iterator __first,
+        _Iterator __last,
+        output_iterator<const iter_value_t<_Iterator>&> auto __out_it,
+        __format_spec::__parsed_specifications<_ParserCharT> __specs,
+        ptrdiff_t __size) -> decltype(__out_it) {
+  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
+  return __formatter::__write(basic_string_view{__first, __last}, _VSTD::move(__out_it), __specs, __size);
+}
+
+/// \overload
+///
+/// Calls the function above where \a __size = \a __last - \a __first.
+template <contiguous_iterator _Iterator, class _ParserCharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__write(_Iterator __first,
+        _Iterator __last,
+        output_iterator<const iter_value_t<_Iterator>&> auto __out_it,
+        __format_spec::__parsed_specifications<_ParserCharT> __specs) -> decltype(__out_it) {
+  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
+  return __formatter::__write(__first, __last, _VSTD::move(__out_it), __specs, __last - __first);
+}
+
+template <class _CharT, class _ParserCharT, class _UnaryOperation>
+_LIBCPP_HIDE_FROM_ABI auto __write_transformed(const _CharT* __first, const _CharT* __last,
+                                               output_iterator<const _CharT&> auto __out_it,
+                                               __format_spec::__parsed_specifications<_ParserCharT> __specs,
+                                               _UnaryOperation __op) -> decltype(__out_it) {
+  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
+
+  ptrdiff_t __size = __last - __first;
+  if (__size >= __specs.__width_)
+    return __formatter::__transform(__first, __last, _VSTD::move(__out_it), __op);
+
+  __padding_size_result __padding = __formatter::__padding_size(__size, __specs.__width_, __specs.__alignment_);
+  __out_it                        = __formatter::__fill(_VSTD::move(__out_it), __padding.__before_, __specs.__fill_);
+  __out_it                        = __formatter::__transform(__first, __last, _VSTD::move(__out_it), __op);
+  return __formatter::__fill(_VSTD::move(__out_it), __padding.__after_, __specs.__fill_);
+}
+
+/// Writes additional zero's for the precision before the exponent.
+/// This is used when the precision requested in the format string is larger
+/// than the maximum precision of the floating-point type. These precision
+/// digits are always 0.
+///
+/// \param __exponent           The location of the exponent character.
+/// \param __num_trailing_zeros The number of 0's to write before the exponent
+///                             character.
+template <class _CharT, class _ParserCharT>
+_LIBCPP_HIDE_FROM_ABI auto __write_using_trailing_zeros(
+    const _CharT* __first,
+    const _CharT* __last,
+    output_iterator<const _CharT&> auto __out_it,
+    __format_spec::__parsed_specifications<_ParserCharT> __specs,
+    size_t __size,
+    const _CharT* __exponent,
+    size_t __num_trailing_zeros) -> decltype(__out_it) {
+  _LIBCPP_ASSERT(__first <= __last, "Not a valid range");
+  _LIBCPP_ASSERT(__num_trailing_zeros > 0, "The overload not writing trailing zeros should have been used");
+
+  __padding_size_result __padding =
+      __formatter::__padding_size(__size + __num_trailing_zeros, __specs.__width_, __specs.__alignment_);
+  __out_it = __formatter::__fill(_VSTD::move(__out_it), __padding.__before_, __specs.__fill_);
+  __out_it = __formatter::__copy(__first, __exponent, _VSTD::move(__out_it));
+  __out_it = __formatter::__fill(_VSTD::move(__out_it), __num_trailing_zeros, _CharT('0'));
+  __out_it = __formatter::__copy(__exponent, __last, _VSTD::move(__out_it));
+  return __formatter::__fill(_VSTD::move(__out_it), __padding.__after_, __specs.__fill_);
+}
+
+/// Writes a string using format's width estimation algorithm.
+///
+/// \pre !__specs.__has_precision()
+///
+/// \note When \c _LIBCPP_HAS_NO_UNICODE is defined the function assumes the
+/// input is ASCII.
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __write_string_no_precision(
+    basic_string_view<_CharT> __str,
+    output_iterator<const _CharT&> auto __out_it,
+    __format_spec::__parsed_specifications<_CharT> __specs) -> decltype(__out_it) {
+  _LIBCPP_ASSERT(!__specs.__has_precision(), "use __write_string");
+
+  // No padding -> copy the string
+  if (!__specs.__has_width())
+    return __formatter::__copy(__str, _VSTD::move(__out_it));
+
+  // Note when the estimated width is larger than size there's no padding. So
+  // there's no reason to get the real size when the estimate is larger than or
+  // equal to the minimum field width.
+  size_t __size =
+      __format_spec::__estimate_column_width(__str, __specs.__width_, __format_spec::__column_width_rounding::__up)
+          .__width_;
+  return __formatter::__write(__str, _VSTD::move(__out_it), __specs, __size);
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI int __truncate(basic_string_view<_CharT>& __str, int __precision) {
+  __format_spec::__column_width_result __result =
+      __format_spec::__estimate_column_width(__str, __precision, __format_spec::__column_width_rounding::__down);
+  __str = basic_string_view<_CharT>{__str.begin(), __result.__last_};
+  return __result.__width_;
+}
+
+/// Writes a string using format's width estimation algorithm.
+///
+/// \note When \c _LIBCPP_HAS_NO_UNICODE is defined the function assumes the
+/// input is ASCII.
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __write_string(
+    basic_string_view<_CharT> __str,
+    output_iterator<const _CharT&> auto __out_it,
+    __format_spec::__parsed_specifications<_CharT> __specs) -> decltype(__out_it) {
+  if (!__specs.__has_precision())
+    return __formatter::__write_string_no_precision(__str, _VSTD::move(__out_it), __specs);
+
+  int __size = __formatter::__truncate(__str, __specs.__precision_);
+
+  return __formatter::__write(__str.begin(), __str.end(), _VSTD::move(__out_it), __specs, __size);
+}
+
+#  if _LIBCPP_STD_VER >= 23
+
+struct __nul_terminator {};
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI bool operator==(const _CharT* __cstr, __nul_terminator) {
+  return *__cstr == _CharT('\0');
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void
+__write_escaped_code_unit(basic_string<_CharT>& __str, char32_t __value, const _CharT* __prefix) {
+  back_insert_iterator __out_it{__str};
+  std::ranges::copy(__prefix, __nul_terminator{}, __out_it);
+
+  char __buffer[8];
+  to_chars_result __r = std::to_chars(std::begin(__buffer), std::end(__buffer), __value, 16);
+  _LIBCPP_ASSERT(__r.ec == errc(0), "Internal buffer too small");
+  std::ranges::copy(std::begin(__buffer), __r.ptr, __out_it);
+
+  __str += _CharT('}');
+}
+
+// [format.string.escaped]/2.2.1.2
+// ...
+// then the sequence \u{hex-digit-sequence} is appended to E, where
+// hex-digit-sequence is the shortest hexadecimal representation of C using
+// lower-case hexadecimal digits.
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void __write_well_formed_escaped_code_unit(basic_string<_CharT>& __str, char32_t __value) {
+  __formatter::__write_escaped_code_unit(__str, __value, _LIBCPP_STATICALLY_WIDEN(_CharT, "\\u{"));
+}
+
+// [format.string.escaped]/2.2.3
+// Otherwise (X is a sequence of ill-formed code units), each code unit U is
+// appended to E in order as the sequence \x{hex-digit-sequence}, where
+// hex-digit-sequence is the shortest hexadecimal representation of U using
+// lower-case hexadecimal digits.
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void __write_escape_ill_formed_code_unit(basic_string<_CharT>& __str, char32_t __value) {
+  __formatter::__write_escaped_code_unit(__str, __value, _LIBCPP_STATICALLY_WIDEN(_CharT, "\\x{"));
+}
+
+template <class _CharT>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool __is_escaped_sequence_written(basic_string<_CharT>& __str, char32_t __value) {
+#    ifdef _LIBCPP_HAS_NO_UNICODE
+  // For ASCII assume everything above 127 is printable.
+  if (__value > 127)
+    return false;
+#    endif
+
+  if (!__escaped_output_table::__needs_escape(__value))
+    return false;
+
+  __formatter::__write_well_formed_escaped_code_unit(__str, __value);
+  return true;
+}
+
+template <class _CharT>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr char32_t __to_char32(_CharT __value) {
+  return static_cast<make_unsigned_t<_CharT>>(__value);
+}
+
+enum class _LIBCPP_ENUM_VIS __escape_quotation_mark { __apostrophe, __double_quote };
+
+// [format.string.escaped]/2
+template <class _CharT>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
+__is_escaped_sequence_written(basic_string<_CharT>& __str, char32_t __value, __escape_quotation_mark __mark) {
+  // 2.2.1.1 - Mapped character in [tab:format.escape.sequences]
+  switch (__value) {
+  case _CharT('\t'):
+    __str += _LIBCPP_STATICALLY_WIDEN(_CharT, "\\t");
+    return true;
+  case _CharT('\n'):
+    __str += _LIBCPP_STATICALLY_WIDEN(_CharT, "\\n");
+    return true;
+  case _CharT('\r'):
+    __str += _LIBCPP_STATICALLY_WIDEN(_CharT, "\\r");
+    return true;
+  case _CharT('\''):
+    if (__mark == __escape_quotation_mark::__apostrophe)
+      __str += _LIBCPP_STATICALLY_WIDEN(_CharT, R"(\')");
+    else
+      __str += __value;
+    return true;
+  case _CharT('"'):
+    if (__mark == __escape_quotation_mark::__double_quote)
+      __str += _LIBCPP_STATICALLY_WIDEN(_CharT, R"(\")");
+    else
+      __str += __value;
+    return true;
+  case _CharT('\\'):
+    __str += _LIBCPP_STATICALLY_WIDEN(_CharT, R"(\\)");
+    return true;
+
+  // 2.2.1.2 - Space
+  case _CharT(' '):
+    __str += __value;
+    return true;
+  }
+
+  // 2.2.2
+  //   Otherwise, if X is a shift sequence, the effect on E and further
+  //   decoding of S is unspecified.
+  // For now shift sequences are ignored and treated as Unicode. Other parts
+  // of the format library do the same. It's unknown how ostream treats them.
+  // TODO FMT determine what to do with shift sequences.
+
+  // 2.2.1.2.1 and 2.2.1.2.2 - Escape
+  return __formatter::__is_escaped_sequence_written(__str, __formatter::__to_char32(__value));
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void
+__escape(basic_string<_CharT>& __str, basic_string_view<_CharT> __values, __escape_quotation_mark __mark) {
+  __unicode::__code_point_view<_CharT> __view{__values.begin(), __values.end()};
+
+  while (!__view.__at_end()) {
+    auto __first                                  = __view.__position();
+    typename __unicode::__consume_result __result = __view.__consume();
+    if (__result.__status == __unicode::__consume_result::__ok) {
+      if (!__formatter::__is_escaped_sequence_written(__str, __result.__code_point, __mark))
+        // 2.2.1.3 - Add the character
+        ranges::copy(__first, __view.__position(), std::back_insert_iterator(__str));
+    } else {
+      // 2.2.3 sequence of ill-formed code units
+      ranges::for_each(__first, __view.__position(), [&](_CharT __value) {
+        __formatter::__write_escape_ill_formed_code_unit(__str, __formatter::__to_char32(__value));
+      });
+    }
+  }
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__format_escaped_char(_CharT __value,
+                      output_iterator<const _CharT&> auto __out_it,
+                      __format_spec::__parsed_specifications<_CharT> __specs) -> decltype(__out_it) {
+  basic_string<_CharT> __str;
+  __str += _CharT('\'');
+  __formatter::__escape(__str, basic_string_view{std::addressof(__value), 1}, __escape_quotation_mark::__apostrophe);
+  __str += _CharT('\'');
+  return __formatter::__write(__str.data(), __str.data() + __str.size(), _VSTD::move(__out_it), __specs, __str.size());
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI auto
+__format_escaped_string(basic_string_view<_CharT> __values,
+                        output_iterator<const _CharT&> auto __out_it,
+                        __format_spec::__parsed_specifications<_CharT> __specs) -> decltype(__out_it) {
+  basic_string<_CharT> __str;
+  __str += _CharT('"');
+  __formatter::__escape(__str, __values, __escape_quotation_mark::__double_quote);
+  __str += _CharT('"');
+  return __formatter::__write_string(basic_string_view{__str}, _VSTD::move(__out_it), __specs);
+}
+
+#  endif // _LIBCPP_STD_VER >= 23
+
+} // namespace __formatter
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_OUTPUT_H

third_party/libcxx/__format/formatter_pointer.h

@@ -0,0 +1,72 @@
+// -*- 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_FORMATTER_POINTER_H
+#define _LIBCPP___FORMAT_FORMATTER_POINTER_H
+
+#include <__availability>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <cstddef>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_pointer {
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_pointer);
+    __format_spec::__process_display_type_pointer(__parser_.__type_);
+    return __result;
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const void* __ptr, _FormatContext& __ctx) const {
+    __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
+    __specs.__std_.__alternate_form_                       = true;
+    __specs.__std_.__type_                                 = __format_spec::__type::__hexadecimal_lower_case;
+    return __formatter::__format_integer(reinterpret_cast<uintptr_t>(__ptr), __ctx, __specs);
+  }
+
+  __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__right};
+};
+
+// [format.formatter.spec]/2.4
+// For each charT, the pointer type specializations template<>
+// - struct formatter<nullptr_t, charT>;
+// - template<> struct formatter<void*, charT>;
+// - template<> struct formatter<const void*, charT>;
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<nullptr_t, _CharT>
+    : public __formatter_pointer<_CharT> {};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<void*, _CharT> : public __formatter_pointer<_CharT> {
+};
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<const void*, _CharT>
+    : public __formatter_pointer<_CharT> {};
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_POINTER_H

third_party/libcxx/__format/formatter_string.h

@@ -0,0 +1,155 @@
+// -*- 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_FORMATTER_STRING_H
+#define _LIBCPP___FORMAT_FORMATTER_STRING_H
+
+#include <__availability>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__utility/move.h>
+#include <string>
+#include <string_view>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS __formatter_string {
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_string);
+    __format_spec::__process_display_type_string(__parser_.__type_);
+    return __result;
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(basic_string_view<_CharT> __str, _FormatContext& __ctx) const {
+#  if _LIBCPP_STD_VER >= 23
+    if (__parser_.__type_ == __format_spec::__type::__debug)
+      return __formatter::__format_escaped_string(__str, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
+#  endif
+
+    return __formatter::__write_string(__str, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
+  }
+
+#  if _LIBCPP_STD_VER >= 23
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_debug_format() { __parser_.__type_ = __format_spec::__type::__debug; }
+#  endif
+
+  __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__left};
+};
+
+// Formatter const char*.
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<const _CharT*, _CharT>
+    : public __formatter_string<_CharT> {
+  using _Base = __formatter_string<_CharT>;
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const _CharT* __str, _FormatContext& __ctx) const {
+    _LIBCPP_ASSERT(__str, "The basic_format_arg constructor should have "
+                          "prevented an invalid pointer.");
+
+    __format_spec::__parsed_specifications<_CharT> __specs = _Base::__parser_.__get_parsed_std_specifications(__ctx);
+#  if _LIBCPP_STD_VER >= 23
+    if (_Base::__parser_.__type_ == __format_spec::__type::__debug)
+      return __formatter::__format_escaped_string(basic_string_view<_CharT>{__str}, __ctx.out(), __specs);
+#  endif
+
+    // When using a center or right alignment and the width option the length
+    // of __str must be known to add the padding upfront. This case is handled
+    // by the base class by converting the argument to a basic_string_view.
+    //
+    // When using left alignment and the width option the padding is added
+    // after outputting __str so the length can be determined while outputting
+    // __str. The same holds true for the precision, during outputting __str it
+    // can be validated whether the precision threshold has been reached. For
+    // now these optimizations aren't implemented. Instead the base class
+    // handles these options.
+    // TODO FMT Implement these improvements.
+    if (__specs.__has_width() || __specs.__has_precision())
+      return __formatter::__write_string(basic_string_view<_CharT>{__str}, __ctx.out(), __specs);
+
+    // No formatting required, copy the string to the output.
+    auto __out_it = __ctx.out();
+    while (*__str)
+      *__out_it++ = *__str++;
+    return __out_it;
+  }
+};
+
+// Formatter char*.
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<_CharT*, _CharT>
+    : public formatter<const _CharT*, _CharT> {
+  using _Base = formatter<const _CharT*, _CharT>;
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT* __str, _FormatContext& __ctx) const {
+    return _Base::format(__str, __ctx);
+  }
+};
+
+// Formatter char[].
+template <__fmt_char_type _CharT, size_t _Size>
+struct _LIBCPP_TEMPLATE_VIS formatter<_CharT[_Size], _CharT>
+    : public __formatter_string<_CharT> {
+  using _Base = __formatter_string<_CharT>;
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT __str[_Size], _FormatContext& __ctx) const {
+    return _Base::format(basic_string_view<_CharT>(__str, _Size), __ctx);
+  }
+};
+
+// Formatter std::string.
+template <__fmt_char_type _CharT, class _Traits, class _Allocator>
+struct _LIBCPP_TEMPLATE_VIS formatter<basic_string<_CharT, _Traits, _Allocator>, _CharT>
+    : public __formatter_string<_CharT> {
+  using _Base = __formatter_string<_CharT>;
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(const basic_string<_CharT, _Traits, _Allocator>& __str, _FormatContext& __ctx) const {
+    // Drop _Traits and _Allocator to have one std::basic_string formatter.
+    return _Base::format(basic_string_view<_CharT>(__str.data(), __str.size()), __ctx);
+  }
+};
+
+// Formatter std::string_view.
+template <__fmt_char_type _CharT, class _Traits>
+struct _LIBCPP_TEMPLATE_VIS formatter<basic_string_view<_CharT, _Traits>, _CharT>
+    : public __formatter_string<_CharT> {
+  using _Base = __formatter_string<_CharT>;
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(basic_string_view<_CharT, _Traits> __str, _FormatContext& __ctx) const {
+    // Drop _Traits to have one std::basic_string_view formatter.
+    return _Base::format(basic_string_view<_CharT>(__str.data(), __str.size()), __ctx);
+  }
+};
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_STRING_H

third_party/libcxx/__format/formatter_tuple.h

@@ -0,0 +1,155 @@
+// -*- 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_FORMATTER_TUPLE_H
+#define _LIBCPP___FORMAT_FORMATTER_TUPLE_H
+
+#include <__algorithm/ranges_copy.h>
+#include <__availability>
+#include <__chrono/statically_widen.h>
+#include <__config>
+#include <__format/buffer.h>
+#include <__format/concepts.h>
+#include <__format/format_args.h>
+#include <__format/format_context.h>
+#include <__format/format_error.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/integer_sequence.h>
+#include <__utility/pair.h>
+#include <string_view>
+#include <tuple>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <__fmt_char_type _CharT, class _Tuple, formattable<_CharT>... _Args>
+struct _LIBCPP_TEMPLATE_VIS __formatter_tuple {
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_separator(basic_string_view<_CharT> __separator) noexcept {
+    __separator_ = __separator;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void
+  set_brackets(basic_string_view<_CharT> __opening_bracket, basic_string_view<_CharT> __closing_bracket) noexcept {
+    __opening_bracket_ = __opening_bracket;
+    __closing_bracket_ = __closing_bracket;
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_tuple);
+
+    auto __end = __ctx.end();
+    if (__begin != __end) {
+      if (*__begin == _CharT('m')) {
+        if constexpr (sizeof...(_Args) == 2) {
+          set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ": "));
+          set_brackets({}, {});
+          ++__begin;
+        } else
+          std::__throw_format_error("The format specifier m requires a pair or a two-element tuple");
+      } else if (*__begin == _CharT('n')) {
+        set_brackets({}, {});
+        ++__begin;
+      }
+    }
+
+    if (__begin != __end && *__begin != _CharT('}'))
+      std::__throw_format_error("The format-spec should consume the input or end with a '}'");
+
+    __ctx.advance_to(__begin);
+
+    // [format.tuple]/7
+    //   ... For each element e in underlying_, if e.set_debug_format()
+    //   is a valid expression, calls e.set_debug_format().
+    std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
+      auto& __formatter = std::get<_Index>(__underlying_);
+      __formatter.parse(__ctx);
+      // Unlike the range_formatter we don't guard against evil parsers. Since
+      // this format-spec never has a format-spec for the underlying type
+      // adding the test would give additional overhead.
+      std::__set_debug_format(__formatter);
+    });
+
+    return __begin;
+  }
+
+  template <class _FormatContext>
+  typename _FormatContext::iterator _LIBCPP_HIDE_FROM_ABI
+  format(conditional_t<(formattable<const _Args, _CharT> && ...), const _Tuple&, _Tuple&> __tuple,
+         _FormatContext& __ctx) const {
+    __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
+
+    if (!__specs.__has_width())
+      return __format_tuple(__tuple, __ctx);
+
+    // The size of the buffer needed is:
+    // - open bracket characters
+    // - close bracket character
+    // - n elements where every element may have a different size
+    // - (n -1) separators
+    // The size of the element is hard to predict, knowing the type helps but
+    // it depends on the format-spec. As an initial estimate we guess 6
+    // characters.
+    // Typically both brackets are 1 character and the separator is 2
+    // characters. Which means there will be
+    //   (n - 1) * 2 + 1 + 1 = n * 2 character
+    // So estimate 8 times the range size as buffer.
+    __format::__retarget_buffer<_CharT> __buffer{8 * tuple_size_v<_Tuple>};
+    basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> __c{
+        __buffer.__make_output_iterator(), __ctx};
+
+    __format_tuple(__tuple, __c);
+
+    return __formatter::__write_string_no_precision(basic_string_view{__buffer.__view()}, __ctx.out(), __specs);
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator __format_tuple(auto&& __tuple, _FormatContext& __ctx) const {
+    __ctx.advance_to(std::ranges::copy(__opening_bracket_, __ctx.out()).out);
+
+    std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
+      if constexpr (_Index)
+        __ctx.advance_to(std::ranges::copy(__separator_, __ctx.out()).out);
+      __ctx.advance_to(std::get<_Index>(__underlying_).format(std::get<_Index>(__tuple), __ctx));
+    });
+
+    return std::ranges::copy(__closing_bracket_, __ctx.out()).out;
+  }
+
+  __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__left};
+
+private:
+  tuple<formatter<remove_cvref_t<_Args>, _CharT>...> __underlying_;
+  basic_string_view<_CharT> __separator_       = _LIBCPP_STATICALLY_WIDEN(_CharT, ", ");
+  basic_string_view<_CharT> __opening_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, "(");
+  basic_string_view<_CharT> __closing_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, ")");
+};
+
+template <__fmt_char_type _CharT, formattable<_CharT>... _Args>
+struct _LIBCPP_TEMPLATE_VIS formatter<pair<_Args...>, _CharT>
+    : public __formatter_tuple<_CharT, pair<_Args...>, _Args...> {};
+
+template <__fmt_char_type _CharT, formattable<_CharT>... _Args>
+struct _LIBCPP_TEMPLATE_VIS formatter<tuple<_Args...>, _CharT>
+    : public __formatter_tuple<_CharT, tuple<_Args...>, _Args...> {};
+
+#endif //_LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_TUPLE_H

third_party/libcxx/__format/range_default_formatter.h

@@ -0,0 +1,216 @@
+// -*- 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_RANGE_DEFAULT_FORMATTER_H
+#define _LIBCPP___FORMAT_RANGE_DEFAULT_FORMATTER_H
+
+#include <__algorithm/ranges_copy.h>
+#include <__availability>
+#include <__chrono/statically_widen.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/concepts.h>
+#include <__format/formatter.h>
+#include <__format/range_formatter.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__ranges/concepts.h>
+#include <__ranges/data.h>
+#include <__ranges/size.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/pair.h>
+#include <string_view>
+#include <tuple>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <class _Rp, class _CharT>
+concept __const_formattable_range =
+    ranges::input_range<const _Rp> && formattable<ranges::range_reference_t<const _Rp>, _CharT>;
+
+template <class _Rp, class _CharT>
+using __fmt_maybe_const = conditional_t<__const_formattable_range<_Rp, _CharT>, const _Rp, _Rp>;
+
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wshadow")
+_LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wshadow")
+// This shadows map, set, and string.
+enum class range_format { disabled, map, set, sequence, string, debug_string };
+_LIBCPP_DIAGNOSTIC_POP
+
+// There is no definition of this struct, it's purely intended to be used to
+// generate diagnostics.
+template <class _Rp>
+struct _LIBCPP_TEMPLATE_VIS __instantiated_the_primary_template_of_format_kind;
+
+template <class _Rp>
+constexpr range_format format_kind = [] {
+  // [format.range.fmtkind]/1
+  // A program that instantiates the primary template of format_kind is ill-formed.
+  static_assert(sizeof(_Rp) != sizeof(_Rp), "create a template specialization of format_kind for your type");
+  return range_format::disabled;
+}();
+
+template <ranges::input_range _Rp>
+  requires same_as<_Rp, remove_cvref_t<_Rp>>
+inline constexpr range_format format_kind<_Rp> = [] {
+  // [format.range.fmtkind]/2
+
+  // 2.1 If same_as<remove_cvref_t<ranges::range_reference_t<R>>, R> is true,
+  // Otherwise format_kind<R> is range_format::disabled.
+  if constexpr (same_as<remove_cvref_t<ranges::range_reference_t<_Rp>>, _Rp>)
+    return range_format::disabled;
+  // 2.2 Otherwise, if the qualified-id R::key_type is valid and denotes a type:
+  else if constexpr (requires { typename _Rp::key_type; }) {
+    // 2.2.1 If the qualified-id R::mapped_type is valid and denotes a type ...
+    if constexpr (requires { typename _Rp::mapped_type; } &&
+                  // 2.2.1 ... If either U is a specialization of pair or U is a specialization
+                  // of tuple and tuple_size_v<U> == 2
+                  __fmt_pair_like<remove_cvref_t<ranges::range_reference_t<_Rp>>>)
+      return range_format::map;
+    else
+      // 2.2.2 Otherwise format_kind<R> is range_format::set.
+      return range_format::set;
+  } else
+    // 2.3 Otherwise, format_kind<R> is range_format::sequence.
+    return range_format::sequence;
+}();
+
+template <range_format _Kp, ranges::input_range _Rp, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __range_default_formatter;
+
+// Required specializations
+
+template <ranges::input_range _Rp, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __range_default_formatter<range_format::sequence, _Rp, _CharT> {
+private:
+  using __maybe_const_r = __fmt_maybe_const<_Rp, _CharT>;
+  range_formatter<remove_cvref_t<ranges::range_reference_t<__maybe_const_r>>, _CharT> __underlying_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_separator(basic_string_view<_CharT> __separator) noexcept {
+    __underlying_.set_separator(__separator);
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void
+  set_brackets(basic_string_view<_CharT> __opening_bracket, basic_string_view<_CharT> __closing_bracket) noexcept {
+    __underlying_.set_brackets(__opening_bracket, __closing_bracket);
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return __underlying_.parse(__ctx);
+  }
+
+  template <class FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename FormatContext::iterator format(__maybe_const_r& __range, FormatContext& __ctx) const {
+    return __underlying_.format(__range, __ctx);
+  }
+};
+
+template <ranges::input_range _Rp, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __range_default_formatter<range_format::map, _Rp, _CharT> {
+private:
+  using __maybe_const_map = __fmt_maybe_const<_Rp, _CharT>;
+  using __element_type    = remove_cvref_t<ranges::range_reference_t<__maybe_const_map>>;
+  range_formatter<__element_type, _CharT> __underlying_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr __range_default_formatter()
+    requires(__fmt_pair_like<__element_type>)
+  {
+    __underlying_.set_brackets(_LIBCPP_STATICALLY_WIDEN(_CharT, "{"), _LIBCPP_STATICALLY_WIDEN(_CharT, "}"));
+    __underlying_.underlying().set_brackets({}, {});
+    __underlying_.underlying().set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ": "));
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return __underlying_.parse(__ctx);
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(__maybe_const_map& __range, _FormatContext& __ctx) const {
+    return __underlying_.format(__range, __ctx);
+  }
+};
+
+template <ranges::input_range _Rp, class _CharT>
+struct _LIBCPP_TEMPLATE_VIS __range_default_formatter<range_format::set, _Rp, _CharT> {
+private:
+  using __maybe_const_set = __fmt_maybe_const<_Rp, _CharT>;
+  using __element_type    = remove_cvref_t<ranges::range_reference_t<__maybe_const_set>>;
+  range_formatter<__element_type, _CharT> __underlying_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr __range_default_formatter() {
+    __underlying_.set_brackets(_LIBCPP_STATICALLY_WIDEN(_CharT, "{"), _LIBCPP_STATICALLY_WIDEN(_CharT, "}"));
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return __underlying_.parse(__ctx);
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(__maybe_const_set& __range, _FormatContext& __ctx) const {
+    return __underlying_.format(__range, __ctx);
+  }
+};
+
+template <range_format _Kp, ranges::input_range _Rp, class _CharT>
+  requires(_Kp == range_format::string || _Kp == range_format::debug_string)
+struct _LIBCPP_TEMPLATE_VIS __range_default_formatter<_Kp, _Rp, _CharT> {
+private:
+  // This deviates from the Standard, there the exposition only type is
+  //   formatter<basic_string<charT>, charT> underlying_;
+  // Using a string_view allows the format function to avoid a copy of the
+  // input range when it is a contigious range.
+  formatter<basic_string_view<_CharT>, _CharT> __underlying_;
+
+public:
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __i = __underlying_.parse(__ctx);
+    if constexpr (_Kp == range_format::debug_string)
+      __underlying_.set_debug_format();
+    return __i;
+  }
+
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(conditional_t<ranges::input_range<const _Rp>, const _Rp&, _Rp&> __range, _FormatContext& __ctx) const {
+    // When the range is contiguous use a basic_string_view instead to avoid a
+    // copy of the underlying data. The basic_string_view formatter
+    // specialization is the "basic" string formatter in libc++.
+    if constexpr (ranges::contiguous_range<_Rp> && std::ranges::sized_range<_Rp>)
+      return __underlying_.format(basic_string_view<_CharT>{ranges::data(__range), ranges::size(__range)}, __ctx);
+    else {
+      // P2106's from_range has not been implemented yet. Instead use a simple
+      // copy operation.
+      // TODO FMT use basic_string's "from_range" constructor.
+      // return __underlying_.format(basic_string<_CharT>{from_range, __range}, __ctx);
+      basic_string<_CharT> __str;
+      std::ranges::copy(__range, back_insert_iterator{__str});
+      return __underlying_.format(static_cast<basic_string_view<_CharT>>(__str), __ctx);
+    }
+  }
+};
+
+template <ranges::input_range _Rp, class _CharT>
+  requires(format_kind<_Rp> != range_format::disabled && formattable<ranges::range_reference_t<_Rp>, _CharT>)
+struct _LIBCPP_TEMPLATE_VIS formatter<_Rp, _CharT> : __range_default_formatter<format_kind<_Rp>, _Rp, _CharT> {};
+
+#endif //_LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_RANGE_DEFAULT_FORMATTER_H

third_party/libcxx/__format/range_formatter.h

@@ -0,0 +1,277 @@
+// -*- 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_RANGE_FORMATTER_H
+#define _LIBCPP___FORMAT_RANGE_FORMATTER_H
+
+#include <__algorithm/ranges_copy.h>
+#include <__availability>
+#include <__chrono/statically_widen.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/buffer.h>
+#include <__format/concepts.h>
+#include <__format/format_args.h>
+#include <__format/format_context.h>
+#include <__format/format_error.h>
+#include <__format/formatter.h>
+#include <__format/formatter_output.h>
+#include <__format/parser_std_format_spec.h>
+#include <__iterator/back_insert_iterator.h>
+#include <__ranges/concepts.h>
+#include <__ranges/data.h>
+#include <__ranges/size.h>
+#include <__type_traits/remove_cvref.h>
+#include <string_view>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <class _Tp, class _CharT = char>
+  requires same_as<remove_cvref_t<_Tp>, _Tp> && formattable<_Tp, _CharT>
+struct _LIBCPP_TEMPLATE_VIS range_formatter {
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_separator(basic_string_view<_CharT> __separator) noexcept {
+    __separator_ = __separator;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void
+  set_brackets(basic_string_view<_CharT> __opening_bracket, basic_string_view<_CharT> __closing_bracket) noexcept {
+    __opening_bracket_ = __opening_bracket;
+    __closing_bracket_ = __closing_bracket;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr formatter<_Tp, _CharT>& underlying() noexcept { return __underlying_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr const formatter<_Tp, _CharT>& underlying() const noexcept { return __underlying_; }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_range);
+    auto __end   = __ctx.end();
+    // Note the cases where __begin == __end in this code only happens when the
+    // replacement-field has no terminating }, or when the parse is manually
+    // called with a format-spec. The former is an error and the latter means
+    // using a formatter without the format functions or print.
+    if (__begin == __end) [[unlikely]]
+      return __parse_empty_range_underlying_spec(__ctx, __begin);
+
+    // The n field overrides a possible m type, therefore delay applying the
+    // effect of n until the type has been procesed.
+    bool __clear_brackets = (*__begin == _CharT('n'));
+    if (__clear_brackets) {
+      ++__begin;
+      if (__begin == __end) [[unlikely]] {
+        // Since there is no more data, clear the brackets before returning.
+        set_brackets({}, {});
+        return __parse_empty_range_underlying_spec(__ctx, __begin);
+      }
+    }
+
+    __parse_type(__begin, __end);
+    if (__clear_brackets)
+      set_brackets({}, {});
+    if (__begin == __end) [[unlikely]]
+      return __parse_empty_range_underlying_spec(__ctx, __begin);
+
+    bool __has_range_underlying_spec = *__begin == _CharT(':');
+    if (__has_range_underlying_spec) {
+      // range-underlying-spec:
+      //   :  format-spec
+      ++__begin;
+    } else if (__begin != __end && *__begin != _CharT('}'))
+      // When there is no underlaying range the current parse should have
+      // consumed the format-spec. If not, the not consumed input will be
+      // processed by the underlying. For example {:-} for a range in invalid,
+      // the sign field is not present. Without this check the underlying_ will
+      // get -} as input which my be valid.
+      std::__throw_format_error("The format-spec should consume the input or end with a '}'");
+
+    __ctx.advance_to(__begin);
+    __begin = __underlying_.parse(__ctx);
+
+    // This test should not be required if __has_range_underlying_spec is false.
+    // However this test makes sure the underlying formatter left the parser in
+    // a valid state. (Note this is not a full protection against evil parsers.
+    // For example
+    //   } this is test for the next argument {}
+    //   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
+    // could consume more than it should.
+    if (__begin != __end && *__begin != _CharT('}'))
+      std::__throw_format_error("The format-spec should consume the input or end with a '}'");
+
+    if (__parser_.__type_ != __format_spec::__type::__default) {
+      // [format.range.formatter]/6
+      //   If the range-type is s or ?s, then there shall be no n option and no
+      //   range-underlying-spec.
+      if (__clear_brackets) {
+        if (__parser_.__type_ == __format_spec::__type::__string)
+          std::__throw_format_error("The n option and type s can't be used together");
+        std::__throw_format_error("The n option and type ?s can't be used together");
+      }
+      if (__has_range_underlying_spec) {
+        if (__parser_.__type_ == __format_spec::__type::__string)
+          std::__throw_format_error("Type s and an underlying format specification can't be used together");
+        std::__throw_format_error("Type ?s and an underlying format specification can't be used together");
+      }
+    } else if (!__has_range_underlying_spec)
+      std::__set_debug_format(__underlying_);
+
+    return __begin;
+  }
+
+  template <ranges::input_range _Rp, class _FormatContext>
+    requires formattable<ranges::range_reference_t<_Rp>, _CharT> &&
+             same_as<remove_cvref_t<ranges::range_reference_t<_Rp>>, _Tp>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_Rp&& __range, _FormatContext& __ctx) const {
+    __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
+
+    if (!__specs.__has_width())
+      return __format_range(__range, __ctx, __specs);
+
+    // The size of the buffer needed is:
+    // - open bracket characters
+    // - close bracket character
+    // - n elements where every element may have a different size
+    // - (n -1) separators
+    // The size of the element is hard to predict, knowing the type helps but
+    // it depends on the format-spec. As an initial estimate we guess 6
+    // characters.
+    // Typically both brackets are 1 character and the separator is 2
+    // characters. Which means there will be
+    //   (n - 1) * 2 + 1 + 1 = n * 2 character
+    // So estimate 8 times the range size as buffer.
+    std::size_t __capacity_hint = 0;
+    if constexpr (std::ranges::sized_range<_Rp>)
+      __capacity_hint = 8 * ranges::size(__range);
+    __format::__retarget_buffer<_CharT> __buffer{__capacity_hint};
+    basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> __c{
+        __buffer.__make_output_iterator(), __ctx};
+
+    __format_range(__range, __c, __specs);
+
+    return __formatter::__write_string_no_precision(__buffer.__view(), __ctx.out(), __specs);
+  }
+
+  template <ranges::input_range _Rp, class _FormatContext>
+  typename _FormatContext::iterator _LIBCPP_HIDE_FROM_ABI
+  __format_range(_Rp&& __range, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) const {
+    if constexpr (same_as<_Tp, _CharT>) {
+      switch (__specs.__std_.__type_) {
+      case __format_spec::__type::__string:
+      case __format_spec::__type::__debug:
+        return __format_as_string(__range, __ctx, __specs.__std_.__type_ == __format_spec::__type::__debug);
+      default:
+        return __format_as_sequence(__range, __ctx);
+      }
+    } else
+      return __format_as_sequence(__range, __ctx);
+  }
+
+  template <ranges::input_range _Rp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  __format_as_string(_Rp&& __range, _FormatContext& __ctx, bool __debug_format) const {
+    // When the range is contiguous use a basic_string_view instead to avoid a
+    // copy of the underlying data. The basic_string_view formatter
+    // specialization is the "basic" string formatter in libc++.
+    if constexpr (ranges::contiguous_range<_Rp> && std::ranges::sized_range<_Rp>) {
+      std::formatter<basic_string_view<_CharT>, _CharT> __formatter;
+      if (__debug_format)
+        __formatter.set_debug_format();
+      return __formatter.format(
+          basic_string_view<_CharT>{
+              ranges::data(__range),
+              ranges::size(__range),
+          },
+          __ctx);
+    } else {
+      std::formatter<basic_string<_CharT>, _CharT> __formatter;
+      if (__debug_format)
+        __formatter.set_debug_format();
+      // P2106's from_range has not been implemented yet. Instead use a simple
+      // copy operation.
+      // TODO FMT use basic_string's "from_range" constructor.
+      // return std::formatter<basic_string<_CharT>, _CharT>{}.format(basic_string<_CharT>{from_range, __range}, __ctx);
+      basic_string<_CharT> __str;
+      ranges::copy(__range, back_insert_iterator{__str});
+      return __formatter.format(__str, __ctx);
+    }
+  }
+
+  template <ranges::input_range _Rp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  __format_as_sequence(_Rp&& __range, _FormatContext& __ctx) const {
+    __ctx.advance_to(ranges::copy(__opening_bracket_, __ctx.out()).out);
+    bool __use_separator = false;
+    for (auto&& __e : __range) {
+      if (__use_separator)
+        __ctx.advance_to(ranges::copy(__separator_, __ctx.out()).out);
+      else
+        __use_separator = true;
+
+      __ctx.advance_to(__underlying_.format(__e, __ctx));
+    }
+
+    return ranges::copy(__closing_bracket_, __ctx.out()).out;
+  }
+
+  __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__left};
+
+private:
+  template <contiguous_iterator _Iterator>
+  _LIBCPP_HIDE_FROM_ABI constexpr void __parse_type(_Iterator& __begin, _Iterator __end) {
+    switch (*__begin) {
+    case _CharT('m'):
+      if constexpr (__fmt_pair_like<_Tp>) {
+        set_brackets(_LIBCPP_STATICALLY_WIDEN(_CharT, "{"), _LIBCPP_STATICALLY_WIDEN(_CharT, "}"));
+        set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ", "));
+        ++__begin;
+      } else
+        std::__throw_format_error("The range-format-spec type m requires two elements for a pair or tuple");
+      break;
+
+    case _CharT('s'):
+      if constexpr (same_as<_Tp, _CharT>) {
+        __parser_.__type_ = __format_spec::__type::__string;
+        ++__begin;
+      } else
+        std::__throw_format_error("The range-format-spec type s requires formatting a character type");
+      break;
+
+    case _CharT('?'):
+      ++__begin;
+      if (__begin == __end || *__begin != _CharT('s'))
+        std::__throw_format_error("The format-spec should consume the input or end with a '}'");
+      if constexpr (same_as<_Tp, _CharT>) {
+        __parser_.__type_ = __format_spec::__type::__debug;
+        ++__begin;
+      } else
+        std::__throw_format_error("The range-format-spec type ?s requires formatting a character type");
+    }
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator
+  __parse_empty_range_underlying_spec(_ParseContext& __ctx, typename _ParseContext::iterator __begin) {
+    __ctx.advance_to(__begin);
+    [[maybe_unused]] typename _ParseContext::iterator __result = __underlying_.parse(__ctx);
+    _LIBCPP_ASSERT(__result == __begin,
+                   "the underlying's parse function should not advance the input beyond the end of the input");
+    return __begin;
+  }
+
+  formatter<_Tp, _CharT> __underlying_;
+  basic_string_view<_CharT> __separator_       = _LIBCPP_STATICALLY_WIDEN(_CharT, ", ");
+  basic_string_view<_CharT> __opening_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, "[");
+  basic_string_view<_CharT> __closing_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, "]");
+};
+
+#endif //_LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_RANGE_FORMATTER_H

third_party/libcxx/__format/unicode.h

@@ -0,0 +1,483 @@
+// -*- 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_UNICODE_H
+#define _LIBCPP___FORMAT_UNICODE_H
+
+#include <__assert>
+#include <__bit/countl.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__format/extended_grapheme_cluster_table.h>
+#include <__iterator/concepts.h>
+#include <__iterator/readable_traits.h> // iter_value_t
+#include <__type_traits/make_unsigned.h>
+#include <__utility/unreachable.h>
+#include <string_view>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __unicode {
+
+// Helper struct for the result of a consume operation.
+//
+// The status value for a correct code point is 0. This allows a valid value to
+// be used without masking.
+// When the decoding fails it know the number of code units affected. For the
+// current use-cases that value is not needed, therefore it is not stored.
+// The escape routine needs the number of code units for both a valid and
+// invalid character and keeps track of it itself. Doing it in this result
+// unconditionally would give some overhead when the value is unneeded.
+struct __consume_result {
+  // When __status == __ok it contains the decoded code point.
+  // Else it contains the replacement character U+FFFD
+  char32_t __code_point : 31;
+
+  enum : char32_t {
+    // Consumed a well-formed code point.
+    __ok = 0,
+    // Encountered invalid UTF-8
+    __error = 1
+  } __status : 1 {__ok};
+};
+static_assert(sizeof(__consume_result) == sizeof(char32_t));
+
+#  ifndef _LIBCPP_HAS_NO_UNICODE
+
+/// Implements the grapheme cluster boundary rules
+///
+/// These rules are used to implement format's width estimation as stated in
+/// [format.string.std]/11
+///
+/// The Standard refers to UAX \#29 for Unicode 12.0.0
+/// https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundary_Rules
+///
+/// The data tables used are
+/// https://www.unicode.org/Public/UCD/latest/ucd/auxiliary/GraphemeBreakProperty.txt
+/// https://www.unicode.org/Public/UCD/latest/ucd/emoji/emoji-data.txt
+/// https://www.unicode.org/Public/UCD/latest/ucd/auxiliary/GraphemeBreakTest.txt (for testing only)
+
+inline constexpr char32_t __replacement_character = U'\ufffd';
+
+// The error of a consume operation.
+//
+// This sets the code point to the replacement character. This code point does
+// not participate in the grapheme clustering, so grapheme clustering code can
+// ignore the error status and always use the code point.
+inline constexpr __consume_result __consume_result_error{__replacement_character, __consume_result::__error};
+
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool __is_high_surrogate(char32_t __value) {
+  return __value >= 0xd800 && __value <= 0xdbff;
+}
+
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool __is_low_surrogate(char32_t __value) {
+  return __value >= 0xdc00 && __value <= 0xdfff;
+}
+
+// https://www.unicode.org/glossary/#surrogate_code_point
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_surrogate(char32_t __value) {
+  return __value >= 0xd800 && __value <= 0xdfff;
+}
+
+// https://www.unicode.org/glossary/#code_point
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_code_point(char32_t __value) {
+  return __value <= 0x10ffff;
+}
+
+// https://www.unicode.org/glossary/#unicode_scalar_value
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_scalar_value(char32_t __value) {
+  return __unicode::__is_code_point(__value) && !__unicode::__is_surrogate(__value);
+}
+
+template <contiguous_iterator _Iterator>
+  requires same_as<iter_value_t<_Iterator>, char>
+_LIBCPP_HIDE_FROM_ABI constexpr bool __is_continuation(_Iterator __char, int __count) {
+  do {
+    if ((*__char & 0b1000'0000) != 0b1000'0000)
+      return false;
+    --__count;
+    ++__char;
+  } while (__count);
+  return true;
+}
+
+/// Helper class to extract a code unit from a Unicode character range.
+///
+/// The stored range is a view. There are multiple specialization for different
+/// character types.
+template <class _CharT>
+class __code_point_view;
+
+/// UTF-8 specialization.
+template <>
+class __code_point_view<char> {
+  using _Iterator = basic_string_view<char>::const_iterator;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
+      : __first_(__first), __last_(__last) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
+
+  // https://www.unicode.org/versions/latest/ch03.pdf#G7404
+  // Based on Table 3-7, Well-Formed UTF-8 Byte Sequences
+  //
+  // Code Points        First Byte Second Byte Third Byte Fourth Byte  Remarks
+  // U+0000..U+007F     00..7F                                         U+0000..U+007F 1 code unit range
+  //                    C0..C1     80..BF                              invalid overlong encoding
+  // U+0080..U+07FF     C2..DF     80..BF                              U+0080..U+07FF 2 code unit range
+  //                    E0         80..9F      80..BF                  invalid overlong encoding
+  // U+0800..U+0FFF     E0         A0..BF      80..BF                  U+0800..U+FFFF 3 code unit range
+  // U+1000..U+CFFF     E1..EC     80..BF      80..BF
+  // U+D000..U+D7FF     ED         80..9F      80..BF
+  // U+D800..U+DFFF     ED         A0..BF      80..BF                  invalid encoding of surrogate code point
+  // U+E000..U+FFFF     EE..EF     80..BF      80..BF
+  //                    F0         80..8F      80..BF     80..BF       invalid overlong encoding
+  // U+10000..U+3FFFF   F0         90..BF      80..BF     80..BF       U+10000..U+10FFFF 4 code unit range
+  // U+40000..U+FFFFF   F1..F3     80..BF      80..BF     80..BF
+  // U+100000..U+10FFFF F4         80..8F      80..BF     80..BF
+  //                    F4         90..BF      80..BF     80..BF       U+110000.. invalid code point range
+  //
+  // Unlike other parsers, these invalid entries are tested after decoding.
+  // - The parser always needs to consume these code units
+  // - The code is optimized for well-formed UTF-8
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
+    _LIBCPP_ASSERT(__first_ != __last_, "can't move beyond the end of input");
+
+    // Based on the number of leading 1 bits the number of code units in the
+    // code point can be determined. See
+    // https://en.wikipedia.org/wiki/UTF-8#Encoding
+    switch (std::countl_one(static_cast<unsigned char>(*__first_))) {
+    case 0:
+      return {static_cast<unsigned char>(*__first_++)};
+
+    case 2: {
+      if (__last_ - __first_ < 2 || !__unicode::__is_continuation(__first_ + 1, 1)) [[unlikely]]
+        break;
+
+      char32_t __value = static_cast<unsigned char>(*__first_++) & 0x1f;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+
+      // These values should be encoded in 1 UTF-8 code unit.
+      if (__value < 0x0080) [[unlikely]]
+        return __consume_result_error;
+
+      return {__value};
+    }
+
+    case 3: {
+      if (__last_ - __first_ < 3 || !__unicode::__is_continuation(__first_ + 1, 2)) [[unlikely]]
+        break;
+
+      char32_t __value = static_cast<unsigned char>(*__first_++) & 0x0f;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+
+      // These values should be encoded in 1 or 2 UTF-8 code units.
+      if (__value < 0x0800) [[unlikely]]
+        return __consume_result_error;
+
+      // A surrogate value is always encoded in 3 UTF-8 code units.
+      if (__unicode::__is_surrogate(__value)) [[unlikely]]
+        return __consume_result_error;
+
+      return {__value};
+    }
+
+    case 4: {
+      if (__last_ - __first_ < 4 || !__unicode::__is_continuation(__first_ + 1, 3)) [[unlikely]]
+        break;
+
+      char32_t __value = static_cast<unsigned char>(*__first_++) & 0x07;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+      __value <<= 6;
+      __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
+
+      // These values should be encoded in 1, 2, or 3 UTF-8 code units.
+      if (__value < 0x10000) [[unlikely]]
+        return __consume_result_error;
+
+      // A value too large is always encoded in 4 UTF-8 code units.
+      if (!__unicode::__is_code_point(__value)) [[unlikely]]
+        return __consume_result_error;
+
+      return {__value};
+    }
+    }
+    // An invalid number of leading ones can be garbage or a code unit in the
+    // middle of a code point. By consuming one code unit the parser may get
+    // "in sync" after a few code units.
+    ++__first_;
+    return __consume_result_error;
+  }
+
+private:
+  _Iterator __first_;
+  _Iterator __last_;
+};
+
+#    ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+_LIBCPP_HIDE_FROM_ABI constexpr bool __is_surrogate_pair_high(wchar_t __value) {
+  return __value >= 0xd800 && __value <= 0xdbff;
+}
+
+_LIBCPP_HIDE_FROM_ABI constexpr bool __is_surrogate_pair_low(wchar_t __value) {
+  return __value >= 0xdc00 && __value <= 0xdfff;
+}
+
+/// This specialization depends on the size of wchar_t
+/// - 2 UTF-16 (for example Windows and AIX)
+/// - 4 UTF-32 (for example Linux)
+template <>
+class __code_point_view<wchar_t> {
+  using _Iterator = typename basic_string_view<wchar_t>::const_iterator;
+
+public:
+  static_assert(sizeof(wchar_t) == 2 || sizeof(wchar_t) == 4, "sizeof(wchar_t) has a not implemented value");
+
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
+      : __first_(__first), __last_(__last) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
+    _LIBCPP_ASSERT(__first_ != __last_, "can't move beyond the end of input");
+
+    char32_t __value = static_cast<char32_t>(*__first_++);
+    if constexpr (sizeof(wchar_t) == 2) {
+      if (__unicode::__is_low_surrogate(__value)) [[unlikely]]
+        return __consume_result_error;
+
+      if (__unicode::__is_high_surrogate(__value)) {
+        if (__first_ == __last_ || !__unicode::__is_low_surrogate(static_cast<char32_t>(*__first_))) [[unlikely]]
+          return __consume_result_error;
+
+        __value -= 0xd800;
+        __value <<= 10;
+        __value += static_cast<char32_t>(*__first_++) - 0xdc00;
+        __value += 0x10000;
+
+        if (!__unicode::__is_code_point(__value)) [[unlikely]]
+          return __consume_result_error;
+      }
+    } else {
+      if (!__unicode::__is_scalar_value(__value)) [[unlikely]]
+        return __consume_result_error;
+    }
+
+    return {__value};
+  }
+
+private:
+  _Iterator __first_;
+  _Iterator __last_;
+};
+#    endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+
+_LIBCPP_HIDE_FROM_ABI constexpr bool __at_extended_grapheme_cluster_break(
+    bool& __ri_break_allowed,
+    bool __has_extened_pictographic,
+    __extended_grapheme_custer_property_boundary::__property __prev,
+    __extended_grapheme_custer_property_boundary::__property __next) {
+  using __extended_grapheme_custer_property_boundary::__property;
+
+  __has_extened_pictographic |= __prev == __property::__Extended_Pictographic;
+
+  // https://www.unicode.org/reports/tr29/tr29-39.html#Grapheme_Cluster_Boundary_Rules
+
+  // *** Break at the start and end of text, unless the text is empty. ***
+
+  _LIBCPP_ASSERT(__prev != __property::__sot, "should be handled in the constructor"); // GB1
+  _LIBCPP_ASSERT(__prev != __property::__eot, "should be handled by our caller");      // GB2
+
+  // *** Do not break between a CR and LF. Otherwise, break before and after controls. ***
+  if (__prev == __property::__CR && __next == __property::__LF) // GB3
+    return false;
+
+  if (__prev == __property::__Control || __prev == __property::__CR || __prev == __property::__LF) // GB4
+    return true;
+
+  if (__next == __property::__Control || __next == __property::__CR || __next == __property::__LF) // GB5
+    return true;
+
+  // *** Do not break Hangul syllable sequences. ***
+  if (__prev == __property::__L &&
+      (__next == __property::__L || __next == __property::__V || __next == __property::__LV ||
+       __next == __property::__LVT)) // GB6
+    return false;
+
+  if ((__prev == __property::__LV || __prev == __property::__V) &&
+      (__next == __property::__V || __next == __property::__T)) // GB7
+    return false;
+
+  if ((__prev == __property::__LVT || __prev == __property::__T) && __next == __property::__T) // GB8
+    return false;
+
+  // *** Do not break before extending characters or ZWJ. ***
+  if (__next == __property::__Extend || __next == __property::__ZWJ)
+    return false; // GB9
+
+  // *** Do not break before SpacingMarks, or after Prepend characters. ***
+  if (__next == __property::__SpacingMark) // GB9a
+    return false;
+
+  if (__prev == __property::__Prepend) // GB9b
+    return false;
+
+  // *** Do not break within emoji modifier sequences or emoji zwj sequences. ***
+
+  // GB11 \p{Extended_Pictographic} Extend* ZWJ x \p{Extended_Pictographic}
+  //
+  // Note that several parts of this rule are matched by GB9: Any x (Extend | ZWJ)
+  // - \p{Extended_Pictographic} x Extend
+  // - Extend x Extend
+  // - \p{Extended_Pictographic} x ZWJ
+  // - Extend x ZWJ
+  //
+  // So the only case left to test is
+  // - \p{Extended_Pictographic}' x ZWJ x \p{Extended_Pictographic}
+  //   where  \p{Extended_Pictographic}' is stored in __has_extened_pictographic
+  if (__has_extened_pictographic && __prev == __property::__ZWJ && __next == __property::__Extended_Pictographic)
+    return false;
+
+  // *** Do not break within emoji flag sequences ***
+
+  // That is, do not break between regional indicator (RI) symbols if there
+  // is an odd number of RI characters before the break point.
+
+  if (__prev == __property::__Regional_Indicator && __next == __property::__Regional_Indicator) { // GB12 + GB13
+    __ri_break_allowed = !__ri_break_allowed;
+    return __ri_break_allowed;
+  }
+
+  // *** Otherwise, break everywhere. ***
+  return true; // GB999
+}
+
+/// Helper class to extract an extended grapheme cluster from a Unicode character range.
+///
+/// This function is used to determine the column width of an extended grapheme
+/// cluster. In order to do that only the first code point is evaluated.
+/// Therefore only this code point is extracted.
+template <class _CharT>
+class __extended_grapheme_cluster_view {
+  using _Iterator = typename basic_string_view<_CharT>::const_iterator;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __extended_grapheme_cluster_view(_Iterator __first, _Iterator __last)
+      : __code_point_view_(__first, __last),
+        __next_code_point_(__code_point_view_.__consume().__code_point),
+        __next_prop_(__extended_grapheme_custer_property_boundary::__get_property(__next_code_point_)) {}
+
+  struct __cluster {
+    /// The first code point of the extended grapheme cluster.
+    ///
+    /// The first code point is used to estimate the width of the extended
+    /// grapheme cluster.
+    char32_t __code_point_;
+
+    /// Points one beyond the last code unit in the extended grapheme cluster.
+    ///
+    /// It's expected the caller has the start position and thus can determine
+    /// the code unit range of the extended grapheme cluster.
+    _Iterator __last_;
+  };
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __cluster __consume() {
+    _LIBCPP_ASSERT(
+        __next_prop_ != __extended_grapheme_custer_property_boundary::__property::__eot,
+        "can't move beyond the end of input");
+
+    char32_t __code_point = __next_code_point_;
+    if (!__code_point_view_.__at_end())
+      return {__code_point, __get_break()};
+
+    __next_prop_ = __extended_grapheme_custer_property_boundary::__property::__eot;
+    return {__code_point, __code_point_view_.__position()};
+  }
+
+private:
+  __code_point_view<_CharT> __code_point_view_;
+
+  char32_t __next_code_point_;
+  __extended_grapheme_custer_property_boundary::__property __next_prop_;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __get_break() {
+    bool __ri_break_allowed         = true;
+    bool __has_extened_pictographic = false;
+    while (true) {
+      _Iterator __result                                              = __code_point_view_.__position();
+      __extended_grapheme_custer_property_boundary::__property __prev = __next_prop_;
+      if (__code_point_view_.__at_end()) {
+        __next_prop_ = __extended_grapheme_custer_property_boundary::__property::__eot;
+        return __result;
+      }
+      __next_code_point_ = __code_point_view_.__consume().__code_point;
+      __next_prop_       = __extended_grapheme_custer_property_boundary::__get_property(__next_code_point_);
+
+      __has_extened_pictographic |=
+          __prev == __extended_grapheme_custer_property_boundary::__property::__Extended_Pictographic;
+
+      if (__at_extended_grapheme_cluster_break(__ri_break_allowed, __has_extened_pictographic, __prev, __next_prop_))
+        return __result;
+    }
+  }
+};
+
+template <contiguous_iterator _Iterator>
+__extended_grapheme_cluster_view(_Iterator, _Iterator) -> __extended_grapheme_cluster_view<iter_value_t<_Iterator>>;
+
+#  else //  _LIBCPP_HAS_NO_UNICODE
+
+// For ASCII every character is a "code point".
+// This makes it easier to write code agnostic of the _LIBCPP_HAS_NO_UNICODE define.
+template <class _CharT>
+class __code_point_view {
+  using _Iterator = typename basic_string_view<_CharT>::const_iterator;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
+      : __first_(__first), __last_(__last) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
+    _LIBCPP_ASSERT(__first_ != __last_, "can't move beyond the end of input");
+    return {static_cast<char32_t>(*__first_++)};
+  }
+
+private:
+  _Iterator __first_;
+  _Iterator __last_;
+};
+
+#  endif //  _LIBCPP_HAS_NO_UNICODE
+
+} // namespace __unicode
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_UNICODE_H

third_party/libcxx/__format/width_estimation_table.h

@@ -0,0 +1,271 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// WARNING, this entire header is generated by
+// utils/generate_width_estimation_table.py
+// DO NOT MODIFY!
+
+// UNICODE, INC. LICENSE AGREEMENT - DATA FILES AND SOFTWARE
+//
+// See Terms of Use <https://www.unicode.org/copyright.html>
+// for definitions of Unicode Inc.'s Data Files and Software.
+//
+// NOTICE TO USER: Carefully read the following legal agreement.
+// BY DOWNLOADING, INSTALLING, COPYING OR OTHERWISE USING UNICODE INC.'S
+// DATA FILES ("DATA FILES"), AND/OR SOFTWARE ("SOFTWARE"),
+// YOU UNEQUIVOCALLY ACCEPT, AND AGREE TO BE BOUND BY, ALL OF THE
+// TERMS AND CONDITIONS OF THIS AGREEMENT.
+// IF YOU DO NOT AGREE, DO NOT DOWNLOAD, INSTALL, COPY, DISTRIBUTE OR USE
+// THE DATA FILES OR SOFTWARE.
+//
+// COPYRIGHT AND PERMISSION NOTICE
+//
+// Copyright (c) 1991-2022 Unicode, Inc. All rights reserved.
+// Distributed under the Terms of Use in https://www.unicode.org/copyright.html.
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of the Unicode data files and any associated documentation
+// (the "Data Files") or Unicode software and any associated documentation
+// (the "Software") to deal in the Data Files or Software
+// without restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, and/or sell copies of
+// the Data Files or Software, and to permit persons to whom the Data Files
+// or Software are furnished to do so, provided that either
+// (a) this copyright and permission notice appear with all copies
+// of the Data Files or Software, or
+// (b) this copyright and permission notice appear in associated
+// Documentation.
+//
+// THE DATA FILES AND SOFTWARE ARE PROVIDED "AS IS", WITHOUT WARRANTY OF
+// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+// WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT OF THIRD PARTY RIGHTS.
+// IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS INCLUDED IN THIS
+// NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL
+// DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+// DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THE DATA FILES OR SOFTWARE.
+//
+// Except as contained in this notice, the name of a copyright holder
+// shall not be used in advertising or otherwise to promote the sale,
+// use or other dealings in these Data Files or Software without prior
+// written authorization of the copyright holder.
+
+#ifndef _LIBCPP___FORMAT_WIDTH_ESTIMATION_TABLE_H
+#define _LIBCPP___FORMAT_WIDTH_ESTIMATION_TABLE_H
+
+#include <__algorithm/ranges_upper_bound.h>
+#include <__config>
+#include <cstddef>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __width_estimation_table {
+
+/// The entries of the characters with an estimated width of 2.
+///
+/// Contains the entries for [format.string.std]/12
+///  -  Any code point with the East_Asian_Width="W" or East_Asian_Width="F"
+///     Derived Extracted Property as described by UAX #44
+/// - U+4DC0 - U+4DFF (Yijing Hexagram Symbols)
+/// - U+1F300 - U+1F5FF (Miscellaneous Symbols and Pictographs)
+/// - U+1F900 - U+1F9FF (Supplemental Symbols and Pictographs)
+///
+/// The data is generated from
+/// - https://www.unicode.org/Public/UCD/latest/ucd/EastAsianWidth.txt
+/// - The "overrides" in [format.string.std]/12
+///
+/// The format of EastAsianWidth.txt is two fields separated by a semicolon.
+/// Field 0: Unicode code point value or range of code point values
+/// Field 1: East_Asian_Width property, consisting of one of the following values:
+///         "A", "F", "H", "N", "Na", "W"
+///  - All code points, assigned or unassigned, that are not listed
+///      explicitly are given the value "N".
+///  - The unassigned code points in the following blocks default to "W":
+///         CJK Unified Ideographs Extension A: U+3400..U+4DBF
+///         CJK Unified Ideographs:             U+4E00..U+9FFF
+///         CJK Compatibility Ideographs:       U+F900..U+FAFF
+///  - All undesignated code points in Planes 2 and 3, whether inside or
+///      outside of allocated blocks, default to "W":
+///         Plane 2:                            U+20000..U+2FFFD
+///         Plane 3:                            U+30000..U+3FFFD
+///
+/// The table is similar to the table
+///  __extended_grapheme_custer_property_boundary::__entries
+/// which explains the details of these classes. The only difference is this
+/// table lacks a property, thus having more bits available for the size.
+///
+/// The maximum code point that has an estimated width of 2 is U+3FFFD. This
+/// value can be encoded in 18 bits. Thus the upper 3 bits of the code point
+/// are always 0. These 3 bits are used to enlarge the offset range. This
+/// optimization reduces the table in Unicode 15 from 184 to 104 entries,
+/// saving 320 bytes.
+///
+/// The data has 2 values:
+/// - bits [0, 13] The size of the range, allowing 16384 elements.
+/// - bits [14, 31] The lower bound code point of the range. The upper bound of
+///   the range is lower bound + size.
+inline constexpr uint32_t __entries[108] = {
+    0x0440005f /* 00001100 - 0000115f [   96] */, //
+    0x08c68001 /* 0000231a - 0000231b [    2] */, //
+    0x08ca4001 /* 00002329 - 0000232a [    2] */, //
+    0x08fa4003 /* 000023e9 - 000023ec [    4] */, //
+    0x08fc0000 /* 000023f0 - 000023f0 [    1] */, //
+    0x08fcc000 /* 000023f3 - 000023f3 [    1] */, //
+    0x097f4001 /* 000025fd - 000025fe [    2] */, //
+    0x09850001 /* 00002614 - 00002615 [    2] */, //
+    0x0992000b /* 00002648 - 00002653 [   12] */, //
+    0x099fc000 /* 0000267f - 0000267f [    1] */, //
+    0x09a4c000 /* 00002693 - 00002693 [    1] */, //
+    0x09a84000 /* 000026a1 - 000026a1 [    1] */, //
+    0x09aa8001 /* 000026aa - 000026ab [    2] */, //
+    0x09af4001 /* 000026bd - 000026be [    2] */, //
+    0x09b10001 /* 000026c4 - 000026c5 [    2] */, //
+    0x09b38000 /* 000026ce - 000026ce [    1] */, //
+    0x09b50000 /* 000026d4 - 000026d4 [    1] */, //
+    0x09ba8000 /* 000026ea - 000026ea [    1] */, //
+    0x09bc8001 /* 000026f2 - 000026f3 [    2] */, //
+    0x09bd4000 /* 000026f5 - 000026f5 [    1] */, //
+    0x09be8000 /* 000026fa - 000026fa [    1] */, //
+    0x09bf4000 /* 000026fd - 000026fd [    1] */, //
+    0x09c14000 /* 00002705 - 00002705 [    1] */, //
+    0x09c28001 /* 0000270a - 0000270b [    2] */, //
+    0x09ca0000 /* 00002728 - 00002728 [    1] */, //
+    0x09d30000 /* 0000274c - 0000274c [    1] */, //
+    0x09d38000 /* 0000274e - 0000274e [    1] */, //
+    0x09d4c002 /* 00002753 - 00002755 [    3] */, //
+    0x09d5c000 /* 00002757 - 00002757 [    1] */, //
+    0x09e54002 /* 00002795 - 00002797 [    3] */, //
+    0x09ec0000 /* 000027b0 - 000027b0 [    1] */, //
+    0x09efc000 /* 000027bf - 000027bf [    1] */, //
+    0x0ac6c001 /* 00002b1b - 00002b1c [    2] */, //
+    0x0ad40000 /* 00002b50 - 00002b50 [    1] */, //
+    0x0ad54000 /* 00002b55 - 00002b55 [    1] */, //
+    0x0ba00019 /* 00002e80 - 00002e99 [   26] */, //
+    0x0ba6c058 /* 00002e9b - 00002ef3 [   89] */, //
+    0x0bc000d5 /* 00002f00 - 00002fd5 [  214] */, //
+    0x0bfc000b /* 00002ff0 - 00002ffb [   12] */, //
+    0x0c00003e /* 00003000 - 0000303e [   63] */, //
+    0x0c104055 /* 00003041 - 00003096 [   86] */, //
+    0x0c264066 /* 00003099 - 000030ff [  103] */, //
+    0x0c41402a /* 00003105 - 0000312f [   43] */, //
+    0x0c4c405d /* 00003131 - 0000318e [   94] */, //
+    0x0c640053 /* 00003190 - 000031e3 [   84] */, //
+    0x0c7c002e /* 000031f0 - 0000321e [   47] */, //
+    0x0c880027 /* 00003220 - 00003247 [   40] */, //
+    0x0c943fff /* 00003250 - 0000724f [16384] */, //
+    0x1c94323c /* 00007250 - 0000a48c [12861] */, //
+    0x29240036 /* 0000a490 - 0000a4c6 [   55] */, //
+    0x2a58001c /* 0000a960 - 0000a97c [   29] */, //
+    0x2b002ba3 /* 0000ac00 - 0000d7a3 [11172] */, //
+    0x3e4001ff /* 0000f900 - 0000faff [  512] */, //
+    0x3f840009 /* 0000fe10 - 0000fe19 [   10] */, //
+    0x3f8c0022 /* 0000fe30 - 0000fe52 [   35] */, //
+    0x3f950012 /* 0000fe54 - 0000fe66 [   19] */, //
+    0x3f9a0003 /* 0000fe68 - 0000fe6b [    4] */, //
+    0x3fc0405f /* 0000ff01 - 0000ff60 [   96] */, //
+    0x3ff80006 /* 0000ffe0 - 0000ffe6 [    7] */, //
+    0x5bf80004 /* 00016fe0 - 00016fe4 [    5] */, //
+    0x5bfc0001 /* 00016ff0 - 00016ff1 [    2] */, //
+    0x5c0017f7 /* 00017000 - 000187f7 [ 6136] */, //
+    0x620004d5 /* 00018800 - 00018cd5 [ 1238] */, //
+    0x63400008 /* 00018d00 - 00018d08 [    9] */, //
+    0x6bfc0003 /* 0001aff0 - 0001aff3 [    4] */, //
+    0x6bfd4006 /* 0001aff5 - 0001affb [    7] */, //
+    0x6bff4001 /* 0001affd - 0001affe [    2] */, //
+    0x6c000122 /* 0001b000 - 0001b122 [  291] */, //
+    0x6c4c8000 /* 0001b132 - 0001b132 [    1] */, //
+    0x6c540002 /* 0001b150 - 0001b152 [    3] */, //
+    0x6c554000 /* 0001b155 - 0001b155 [    1] */, //
+    0x6c590003 /* 0001b164 - 0001b167 [    4] */, //
+    0x6c5c018b /* 0001b170 - 0001b2fb [  396] */, //
+    0x7c010000 /* 0001f004 - 0001f004 [    1] */, //
+    0x7c33c000 /* 0001f0cf - 0001f0cf [    1] */, //
+    0x7c638000 /* 0001f18e - 0001f18e [    1] */, //
+    0x7c644009 /* 0001f191 - 0001f19a [   10] */, //
+    0x7c800002 /* 0001f200 - 0001f202 [    3] */, //
+    0x7c84002b /* 0001f210 - 0001f23b [   44] */, //
+    0x7c900008 /* 0001f240 - 0001f248 [    9] */, //
+    0x7c940001 /* 0001f250 - 0001f251 [    2] */, //
+    0x7c980005 /* 0001f260 - 0001f265 [    6] */, //
+    0x7cc0034f /* 0001f300 - 0001f64f [  848] */, //
+    0x7da00045 /* 0001f680 - 0001f6c5 [   70] */, //
+    0x7db30000 /* 0001f6cc - 0001f6cc [    1] */, //
+    0x7db40002 /* 0001f6d0 - 0001f6d2 [    3] */, //
+    0x7db54002 /* 0001f6d5 - 0001f6d7 [    3] */, //
+    0x7db70003 /* 0001f6dc - 0001f6df [    4] */, //
+    0x7dbac001 /* 0001f6eb - 0001f6ec [    2] */, //
+    0x7dbd0008 /* 0001f6f4 - 0001f6fc [    9] */, //
+    0x7df8000b /* 0001f7e0 - 0001f7eb [   12] */, //
+    0x7dfc0000 /* 0001f7f0 - 0001f7f0 [    1] */, //
+    0x7e4000ff /* 0001f900 - 0001f9ff [  256] */, //
+    0x7e9c000c /* 0001fa70 - 0001fa7c [   13] */, //
+    0x7ea00008 /* 0001fa80 - 0001fa88 [    9] */, //
+    0x7ea4002d /* 0001fa90 - 0001fabd [   46] */, //
+    0x7eafc006 /* 0001fabf - 0001fac5 [    7] */, //
+    0x7eb3800d /* 0001face - 0001fadb [   14] */, //
+    0x7eb80008 /* 0001fae0 - 0001fae8 [    9] */, //
+    0x7ebc0008 /* 0001faf0 - 0001faf8 [    9] */, //
+    0x80003fff /* 00020000 - 00023fff [16384] */, //
+    0x90003fff /* 00024000 - 00027fff [16384] */, //
+    0xa0003fff /* 00028000 - 0002bfff [16384] */, //
+    0xb0003ffd /* 0002c000 - 0002fffd [16382] */, //
+    0xc0003fff /* 00030000 - 00033fff [16384] */, //
+    0xd0003fff /* 00034000 - 00037fff [16384] */, //
+    0xe0003fff /* 00038000 - 0003bfff [16384] */, //
+    0xf0003ffd /* 0003c000 - 0003fffd [16382] */};
+
+/// The upper bound entry of EastAsianWidth.txt.
+///
+/// Values greater than this value may have more than 18 significant bits.
+/// They always have a width of 1. This property makes it possible to store
+/// the table in its compact form.
+inline constexpr uint32_t __table_upper_bound = 0x0003fffd;
+
+/// Returns the estimated width of a Unicode code point.
+///
+/// \pre The code point is a valid Unicode code point.
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int __estimated_width(const char32_t __code_point) noexcept {
+  // Since __table_upper_bound contains the unshifted range do the
+  // comparison without shifting.
+  if (__code_point > __table_upper_bound) [[unlikely]]
+    return 1;
+
+  // When the code-point is less than the first element in the table
+  // the lookup is quite expensive. Since quite some scripts are in
+  // that range, it makes sense to validate that first.
+  // The std_format_spec_string_unicode benchmark gives a measurable
+  // improvement.
+  if (__code_point < (__entries[0] >> 14))
+    return 1;
+
+  ptrdiff_t __i = std::ranges::upper_bound(__entries, (__code_point << 14) | 0x3fffu) - __entries;
+  if (__i == 0)
+    return 1;
+
+  --__i;
+  uint32_t __upper_bound = (__entries[__i] >> 14) + (__entries[__i] & 0x3fffu);
+  return 1 + (__code_point <= __upper_bound);
+}
+
+} // namespace __width_estimation_table
+
+#endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_WIDTH_ESTIMATION_TABLE_H