When running debug:container --show-private, it doesn't show private aliases. A scenario where this happens is when a private alias is used for a private service to optimize them away and prevent Container->get() usage.

My company has code that automates generating services for repositories, this follows a specific setup: order.repository.clients_order_line where clients is the entity manager (connection) name. This would result in a private alias: order.repository.order_line pointing at order.repository.clients_order_line. This code works perfect with one downside, private alias cannot be found back.

The naming follows a convention so we can always find it back one way or another, but we cannot find it using the debug:container command nor can an IDE such as PHPStorm find it as it's optimized away. I've been digging in the code and in TextDescriptor::describeContainerServices() this is not available.

My guess is that private aliases are optimized away if they are not used before hitting this code and is therefore a bug. If I wanted to find all un-used private services/alias, I would be unable to do so with the current setup.