class Sass::Importers::Filesystem

def warn_about_public_url(uri)
  @warnings_issued ||= Set.new
  unless @warnings_issued.include?(uri)
    Sass::Util.sass_warn <<WARNING
G: Couldn't determine public URL for "#{uri}" while generating sourcemap.
out a public URL, there's nothing for the source map to link to.
G
    @warnings_issued << uri
  end
  nil
end