lib/rack/unreloader.rb
def record_dependency(dependency, *files)
      if @reloader
        files = Unreloader.expand_paths(files)
        Unreloader.expand_paths(dependency).each do |path|
          @reloader.record_dependency(path, files)
        end
      end
    end
def record_dependency(dependency, *files)
      if @reloader
        files = Unreloader.expand_paths(files)
        Unreloader.expand_paths(dependency).each do |path|
          @reloader.record_dependency(path, files)
        end
      end
    end
Records that each path in +files+ depends on +dependency+.  If there
 is a modification to +dependency+, all related files will be reloaded
 after +dependency+ is reloaded.  Both +dependency+ and each entry in +files+
 can be an array of path globs.