Drupal中每个模块都可以传值到twig模板中，负责这一工作的是钩子hook_template_preprocess_default_variables_alter()
比如user模块中提供了user对象，is_admin变量，logged_in变量

/**
 * Implements hook_template_preprocess_default_variables_alter().
 *
 * @see user_user_login()
 * @see user_user_logout()
 */
function user_template_preprocess_default_variables_alter(&$variables) {
  $user = \Drupal::currentUser();

  $variables['user'] = clone $user;
  // Remove password and session IDs, since themes should not need nor see them.
  unset($variables['user']->pass, $variables['user']->sid, $variables['user']->ssid);

  $variables['is_admin'] = $user->hasPermission('access administration pages');
  $variables['logged_in'] = $user->isAuthenticated();
}