なかなか賢い。

Controller.respond_to :json すると積み上がるのね確認

module ClassMethods
     def respond_to(*mimes)
       options = mimes.extract_options!
       only_actions   = Array(options.delete(:only))
       except_actions = Array(options.delete(:except))
       new = mimes_for_respond_to.dup
       mimes.each do |mime|
         mime = mime.to_sym
         new[mime]          = {}
         new[mime][:only]   = only_actions   unless only_actions.empty?
         new[mime][:except] = except_actions unless except_actions.empty?
       end
       self.mimes_for_respond_to = new.freeze
     end
     def clear_respond_to
       self.mimes_for_respond_to = ActiveSupport::OrderedHash.new.freeze
     end