There are 2 usability problems with the cache that I think it's important to solve:

1. Though there is a TagAwareAdapter class, to use cache tagging, you need to setup your own service via decoration ([FrameworkBundle] Is TagAwareAdapter declared as a service? #20764). That's too much complex work and makes cache tagging out-of-reach for most users.

2. The interface names for autowiring are quite bad: CacheItemPoolInterface or AdapterInterface. A TaggableCacheInterface would be much better ... and it would extend TagAwareAdapterInterface. It's a bit silly... as this would exist just for better autowiring, but it is important. In 4.1, this would give us autowiring with CacheInterface (for simple PSR-16 style) or TaggableCacheInterface(in addition to the 2 uglier [sorry] interface names I listed first).

Question: Is there a downside to always using TagAwareAdapter? My guess is that there's some performance impact. If so, we could "opt-in" to wrapping cache.app in TagAwareAdapter with config. Or have a separate, wrapped service always exist, but only autowire when the TaggableCacheInterface is used.