class Sass::Tree::Visitors::Perform

def visit_import(node)
  if (path = node.css_import?)
    resolved_node = Sass::Tree::CssImportNode.resolved("url(#{path})")
    resolved_node.options = node.options
    resolved_node.source_range = node.source_range
    return resolved_node
  end
  file = node.imported_file
  if @environment.stack.frames.any? {|f| f.is_import? && f.filename == file.options[:filename]}
    handle_import_loop!(node)
  end
  begin
    @environment.stack.with_import(node.filename, node.line) do
      root = file.to_tree
      Sass::Tree::Visitors::CheckNesting.visit(root)
      node.children = root.children.map {|c| visit(c)}.flatten
      node
    end
  rescue Sass::SyntaxError => e
    e.modify_backtrace(:filename => node.imported_file.options[:filename])
    e.add_backtrace(:filename => node.filename, :line => node.line)
    raise e
  end
end