class Sprockets::DirectiveProcessor

def expand_relative_dirname(directive, path)
  if @environment.relative_path?(path)
    path = File.expand_path(path, @dirname)
    stat = @environment.stat(path)
    if stat && stat.directory?
      path
    else
      raise ArgumentError, "#{directive} argument must be a directory"
    end
  else
    # The path must be relative and start with a `./`.
    raise ArgumentError, "#{directive} argument must be a relative path"
  end
end