# File lib/sass/tree/visitors/perform.rb, line 333
  def visit_warn(node)
    @stack.push(:filename => node.filename, :line => node.line)
    res = node.expr.perform(@environment)
    res = res.value if res.is_a?(Sass::Script::String)
    msg = "WARNING: #{res}\n         "
    msg << stack_trace.join("\n         ") << "\n"
    Sass::Util.sass_warn msg
    []
  ensure
    @stack.pop
  end