so the templating service always is of the right interface if it exists, after all?

Yes, as long as we do not composer require symfony/templating, which is kind of derpecated and configure it in framework configuration. the last is done on older apps, but not with the new component.

I really had trouble yesterday to get it working. as interface_exists() seems to require the interface and sends an warning.

you can now create a symfony skeleton app composer create-project "symfony/skeleton:^3.3", require cli (the comandline and cache calls won't work) composer req cli and call our reciepe then: SYMFONY_ENDPOINT=https://symfony.sh/r/github.com/symfony/recipes-contrib/91 composer remove symfony-cmf/routing-bundle and it should go green. In sandbox we have the former configuration with the old framework-bundle and that works fine too.

great job, thanks a lot max!