Method on_format_specs

include/fmt/format.h:3808–3826

  }

  auto on_format_specs(int id, const Char* begin, const Char* end)
      -> const Char* {
    auto arg = ctx.arg(id);
    if (!arg) report_error("argument not found");
    // Not using a visitor for custom types gives better codegen.
    if (arg.format_custom(begin, parse_ctx, ctx)) return parse_ctx.begin();

    auto specs = dynamic_format_specs<Char>();
    begin = parse_format_specs(begin, end, specs, parse_ctx, arg.type());
    if (specs.dynamic()) {
      handle_dynamic_spec(specs.dynamic_width(), specs.width, specs.width_ref,
                          ctx);
      handle_dynamic_spec(specs.dynamic_precision(), specs.precision,
                          specs.precision_ref, ctx);
    }

    arg.visit(arg_formatter<Char>{ctx.out(), specs, ctx.locale()});
    return begin;
  }

  FMT_NORETURN void on_error(const char* message) { report_error(message); }
};