Function parse_format_specs

extlibs/fmt/include/fmt/format.h:2497–2543

// components to handler.
template <typename Char, typename SpecHandler>
FMT_CONSTEXPR const Char* parse_format_specs(const Char* begin, const Char* end,
                                             SpecHandler&& handler) {
  if (begin == end || *begin == '}') return begin;

  begin = parse_align(begin, end, handler);
  if (begin == end) return begin;

  // Parse sign.
  switch (static_cast<char>(*begin)) {
  case '+':
    handler.on_plus();
    ++begin;
    break;
  case '-':
    handler.on_minus();
    ++begin;
    break;
  case ' ':
    handler.on_space();
    ++begin;
    break;
  }
  if (begin == end) return begin;

  if (*begin == '#') {
    handler.on_hash();
    if (++begin == end) return begin;
  }

  // Parse zero flag.
  if (*begin == '0') {
    handler.on_zero();
    if (++begin == end) return begin;
  }

  begin = parse_width(begin, end, handler);
  if (begin == end) return begin;

  // Parse precision.
  if (*begin == '.') {
    begin = parse_precision(begin, end, handler);
  }

  // Parse type.
  if (begin != end && *begin != '}') handler.on_type(*begin++);
  return begin;
}

// Return the result via the out param to workaround gcc bug 77539.
template <bool IS_CONSTEXPR, typename T, typename Ptr = const T*>