class Sass::Tree::WarnNode

def _perform(environment)
  environment.push_frame(:filename => filename, :line => line)
  res = @expr.perform(environment)
  res = res.value if res.is_a?(Sass::Script::String)
  msg = "WARNING: #{res}\n"
  environment.stack.reverse.each_with_index do |entry, i|
    msg << "        #{i == 0 ? "on" : "from"} line #{entry[:line]}" <<
      " of #{entry[:filename] || "an unknown file"}"
    msg << ", in `#{entry[:mixin]}'" if entry[:mixin]
    msg << "\n"
  end
  Haml::Util.haml_warn msg
  []
ensure
  environment.pop_frame
end