Invokable controllers are coming! In routing config they're already addressable using a FQCN e.g. in a routing YAML:

home:
    path: /home
    defaults: { _controller: AppBundle\Controller\HomeController::__invoke }

And when #22330 is merged we can drop the __invoke:

defaults: { _controller: AppBundle\Controller\HomeController }

When defining routes it would be good to to also support invokable controllers using the shorter colon-based syntax. Currently the ControllerResolver / ControllerNameParser can't handle these two cases:

defaults: { _controller: AppBundle:Home:__invoke }

fails as it resolves to AppBundle\Controller\HomeController::__invokeAction which doesn't work for obvious reasons. Fixing this would be a case of not transforming __invoke into __invokeAction in the ControllerNameParser.

defaults: { _controller: AppBundle:Home }

Fails as this format doesn't get passed into the ControllerNameParser to be parsed in the ControllerResolver so thus results in a ServiceNotFoundException.

Expected Behaviour

Both AppBundle:Home and AppBundle:Home:__invoke should resolve to invoking AppBundle\Controller\HomeController.

(This ticket was spun out from comments on #22202).