class Sass::Importers::Filesystem

def public_url(name, sourcemap_directory)
  file_pathname = Sass::Util.cleanpath(Sass::Util.absolute_path(name, @root))
  return Sass::Util.file_uri_from_path(file_pathname) if sourcemap_directory.nil?
  sourcemap_pathname = Sass::Util.cleanpath(sourcemap_directory)
  begin
    Sass::Util.file_uri_from_path(
      Sass::Util.relative_path_from(file_pathname, sourcemap_pathname))
  rescue ArgumentError # when a relative path cannot be constructed
    Sass::Util.file_uri_from_path(file_pathname)
  end
end