Most code using the container builder are wrongly type-hinted

Drupal 8 most code using the container builder are type-hinting using Drupal\Core\DependencyInjection\ContainerBuilder which makes the container builder non-replaceable.

Believe it or not, but in a specific project I'm switching back the base kernel implementation and container builder implemetation to Symfony's native ones (and yes, it works) but I have found a few problems, wrong type hinting is one of them.

The Drupal ContainerBuilder is a sub-class of Symfony's Symfony\Component\DependencyInjection\ContainerBuilder, is API compatible, and does not add additional methods, so all Drupal code using it should type hint with Symfony class instead, making it replaceable.

It's flexibility at a free cost, I think this should be seriously considered.

Writing the patch right now.