class Sass::Tree::Visitors::Perform

def visit_debug(node)
  res = node.expr.perform(@environment)
  if res.is_a?(Sass::Script::Value::String)
    res = res.value
  else
    res = res.to_sass
  end
  if node.filename
    Sass::Util.sass_warn "#{node.filename}:#{node.line} DEBUG: #{res}"
  else
    Sass::Util.sass_warn "Line #{node.line} DEBUG: #{res}"
  end
  []
end