我用 rails new command 建了一个新的项目，在 config\application.rb 里有一段这样的代码

require File.expand_path('../boot', __FILE__)

require 'rails/all'

if defined?(Bundler)
  # If you precompile assets before deploying to production, use this line
  Bundler.require(*Rails.groups(:assets => %w(development test)))
  # If you want your assets lazily compiled in production, use this line
  # Bundler.require(:default, :assets, Rails.env)
end

里面require 'rails/all' 这是指的哪里的文件，我在哪里可以找到？谢谢