如何检查Idis_single() 插件中的外部循环？

当我尝试时，总是会遇到致命错误代码

 add_action(\'transition_post_status\', \'pmc_update_notification\',10,3);

function pmc_update_notification($new_status, $old_status, $post) {
 if ( $old_status == \'publish\' && $new_status == \'publish\' ) {
 $post_id = get_the_ID($post);
  if (is_single($post_id)){
 $post_title = get_the_title($post);
 $post_url = get_permalink($post);
 $message = __(\'Post updated\',\'pmc\').":\\n";
 $message .= $post_title . ": " . $post_url;

   // Send notification
   pmc_send($message);
     }
    }
   }