首先，我已经看到了这个问题。
当我尝试将 Symfony 3.3 更新到 3.4 时，我得到了以下弃用：
User Deprecated: The "assetic.filter_manager" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop using the container directly and use dependency injection instead.
User Deprecated: The "assetic.filter.cssrewrite" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop …