1 files changed, 178 insertions, 0 deletions
diff --git a/libcxx/include/__format/formatter_tuple.h b/libcxx/include/__format/formatter_tuple.h
new file mode 100644
index 000000000000..82f5ada6e012
--- /dev/null
+++ b/libcxx/include/__format/formatter_tuple.h
@@ -0,0 +1,178 @@
+// -*- 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/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 > 20
+
+template <__fmt_char_type _CharT, class _Tuple, formattable<_CharT>... _Args>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __formatter_tuple {
+  _LIBCPP_HIDE_FROM_ABI constexpr void set_separator(basic_string_view<_CharT> __separator) {
+    __separator_ = __separator;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr void
+  set_brackets(basic_string_view<_CharT> __opening_bracket, basic_string_view<_CharT> __closing_bracket) {
+    __opening_bracket_ = __opening_bracket;
+    __closing_bracket_ = __closing_bracket;
+  }
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __parse_ctx) {
+    const _CharT* __begin = __parser_.__parse(__parse_ctx, __format_spec::__fields_tuple);
+
+    // [format.tuple]/7
+    //   ... For each element e in underlying_, if e.set_debug_format()
+    //   is a valid expression, calls e.set_debug_format().
+    // TODO FMT this can be removed when P2733 is accepted.
+    std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
+      std::__set_debug_format(std::get<_Index>(__underlying_));
+    });
+
+    const _CharT* __end = __parse_ctx.end();
+    if (__begin == __end)
+      return __begin;
+
+    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 '}'");
+
+    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);
+
+    basic_string<_CharT> __str;
+
+    // Since the output is written to a different iterator a new context is
+    // created. Since the underlying formatter uses the default formatting it
+    // doesn't need a locale or the formatting arguments. So creating a new
+    // context works.
+    //
+    // This solution works for this formatter, but it will not work for the
+    // range_formatter. In that patch a generic solution is work in progress.
+    // Once that is finished it can be used here. (The range_formatter will use
+    // these features so it's easier to add it there and then port it.)
+    //
+    // TODO FMT Use formatting wrapping used in the range_formatter.
+    basic_format_context __c = std::__format_context_create(
+        back_insert_iterator{__str},
+        basic_format_args<basic_format_context<back_insert_iterator<basic_string<_CharT>>, _CharT>>{});
+
+    __format_tuple(__tuple, __c);
+
+    return __formatter::__write_string_no_precision(basic_string_view{__str}, __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);
+
+        // During review Victor suggested to make the exposition only
+        // __underlying_ member a local variable. Currently the Standard
+        // requires nested debug-enabled formatter specializations not to
+        // output escaped output. P2733 fixes that bug, once accepted the
+        // code below can be used.
+        // (Note when a paper allows parsing a tuple-underlying-spec the
+        // exposition only member needs to be a class member. Earlier
+        // revisions of P2286 proposed that, but this was not pursued,
+        // due to time constrains and complexity of the matter.)
+        // TODO FMT This can be updated after P2733 is accepted.
+#  if 0
+      // P2286 uses an exposition only member in the formatter
+      //   tuple<formatter<remove_cvref_t<_Args>, _CharT>...> __underlying_;
+      // This was used in earlier versions of the paper since
+      // __underlying_.parse(...) was called. This is no longer the case
+      // so we can reduce the scope of the formatter.
+      //
+      // It does require the underlying's parse effect to be moved here too.
+      using _Arg = tuple_element<_Index, decltype(__tuple)>;
+      formatter<remove_cvref_t<_Args>, _CharT> __underlying;
+
+      // [format.tuple]/7
+      //   ... For each element e in underlying_, if e.set_debug_format()
+      //   is a valid expression, calls e.set_debug_format().
+      std::__set_debug_format(__underlying);
+#  else
+      __ctx.advance_to(std::get<_Index>(__underlying_).format(std::get<_Index>(__tuple), __ctx));
+#  endif
+    });
+
+    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 _LIBCPP_AVAILABILITY_FORMAT formatter<pair<_Args...>, _CharT>
+    : public __formatter_tuple<_CharT, pair<_Args...>, _Args...> {};
+
+template <__fmt_char_type _CharT, formattable<_CharT>... _Args>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<tuple<_Args...>, _CharT>
+    : public __formatter_tuple<_CharT, tuple<_Args...>, _Args...> {};
+
+#endif //_LIBCPP_STD_VER > 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMATTER_TUPLE_H