Services that do not specify their visibility are private by default in Symfony 3.4.

Such services that use dynamic settings injection result in a deprecation message "User Deprecated: Checking for the initialization of the "xyz" private service is deprecated since Symfony 3.4 and won't be supported anymore in Symfony 4.0."

eZ kernel should be able to support dynamic settings injection for private services, or document a way to implement custom services that do not trigger a deprecation message.