class Sass::Tree::MixinNode

def _cssize(extends, parent)
  children.map do |c|
    parent.check_child! c
    c.cssize(extends, parent)
  end.flatten
rescue Sass::SyntaxError => e
  e.modify_backtrace(:mixin => @name, :filename => filename, :line => line)
  e.add_backtrace(:filename => filename, :line => line)
  raise e
end