我必须在 web/app.php 和 web/app_dev.php 中添加以下行:

I had to add the following line to web/app.php and web/app_dev.php:

$loader = require __DIR__.'/../app/autoload.php';

同时更新应用程序/控制台.

And also update app/console.

通过将我的文件与全新安装的 Symfony 2.8 进行比较发现

Found this by comparing my files with a fresh install of Symfony 2.8