add_default_name_and_id

# File actionpack/lib/action_view/helpers/form_helper.rb, line 1054
        def add_default_name_and_id(options)
          if options.has_key?("index")
            options["name"] ||= tag_name_with_index(options["index"])
            options["id"] = options.fetch("id"){ tag_id_with_index(options["index"]) }
            options.delete("index")
          elsif defined?(@auto_index)
            options["name"] ||= tag_name_with_index(@auto_index)
            options["id"] = options.fetch("id"){ tag_id_with_index(@auto_index) }
          else
            options["name"] ||= tag_name + (options.has_key?('multiple') ? '[]' : '')
            options["id"] = options.fetch("id"){ tag_id }
          end
        end