directories_to_watch

# File activesupport/lib/active_support/evented_file_update_checker.rb, line 125
      def directories_to_watch
        dtw = (@files + @dirs.keys).map { |f| @ph.existing_parent(f) }
        dtw.compact!
        dtw.uniq!

        normalized_gem_paths = Gem.path.map { |path| File.join path, "" }
        dtw = dtw.reject do |path|
          normalized_gem_paths.any? { |gem_path| path.to_s.start_with?(gem_path) }
        end

        @ph.filter_out_descendants(dtw)
      end