# File lib/sass/tree/visitors/perform.rb, line 464
  def visit_variable(node)
    env = @environment
    env = env.global_env if node.global
    if node.guarded
      var = env.var(node.name)
      return [] if var && !var.null?
    end

    val = node.expr.perform(@environment)
    if node.expr.source_range
      val.source_range = node.expr.source_range
    else
      val.source_range = node.source_range
    end
    env.set_var(node.name, val)
    []
  end