def find_upwards(basename, path, root = nil)
      path_parents(path, root).each do |dir|
        filename = File.join(dir, basename)
        return filename if file?(filename)
      end
      nil
    end
def find_upwards(basename, path, root = nil)
      path_parents(path, root).each do |dir|
        filename = File.join(dir, basename)
        return filename if file?(filename)
      end
      nil
    end
Internal: Find target basename checking upwards from path.

 basename - String filename: ".sprocketsrc"
 path     - String path to start search: "app/assets/javascripts/app.js"
 root     - String path to stop at (default: system root)

 Returns String filename or nil.