Method parse

external/fmt/include/fmt/format.h:3960–3974

  constexpr nested_formatter() : width_(0) {}

  FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
    auto it = ctx.begin(), end = ctx.end();
    if (it == end) return it;
    auto specs = format_specs();
    it = detail::parse_align(it, end, specs);
    specs_ = specs;
    Char c = *it;
    auto width_ref = detail::arg_ref<Char>();
    if ((c >= '0' && c <= '9') || c == '{') {
      it = detail::parse_width(it, end, specs, width_ref, ctx);
      width_ = specs.width;
    }
    ctx.advance_to(it);
    return formatter_.parse(ctx);
  }

  template <typename FormatContext, typename F>
  auto write_padded(FormatContext& ctx, F write) const -> decltype(ctx.out()) {