# File lib/sass/tree/visitors/perform.rb, line 483
  def visit_warn(node)
    res = node.expr.perform(@environment)
    res = res.value if res.is_a?(Sass::Script::Value::String)
    msg = "WARNING: #{res}\n         "
    msg << @environment.stack.to_s.gsub("\n", "\n         ") << "\n"
    Sass::Util.sass_warn msg
    []
  end