Rails 3中Rake任务的源代码在哪里？

find / -name "rakefile"

require 'rake/tasklib'

module Rake
  class Task
    attr_accessor :name, :source, :description, :comments

    def initialize(name, source = nil, &block)
      @name, @source, @description, @comments = name, source, block && block.description, (source || File.basename($0))
    end

    def execute
      if @comments
        @comments.each { |comment| puts comment }
      end

      if @source
        puts "Running task: #{@source}"
        Kernel.load(@source)
      else
        puts "Task definition is empty."
      end
    end

    def self.define(name, &block)
      task = new(name, nil, &block)
      task.source = File.join(Rake.application.original_dir, task.name)
      Rake.application[task.name] = task
    end
  end
end