class Sass::Tree::Visitors::Perform

def handle_import_loop!(node)
  msg = "An @import loop has been found:"
  files = @environment.stack.frames.select {|f| f.is_import?}.map {|f| f.filename}.compact
  if node.filename == node.imported_file.options[:filename]
    raise Sass::SyntaxError.new("#{msg} #{node.filename} imports itself")
  end
  files << node.filename << node.imported_file.options[:filename]
  msg << "\n" << files.each_cons(2).map do |m1, m2|
    "    #{m1} imports #{m2}"
  end.join("\n")
  raise Sass::SyntaxError.new(msg)
end