Description
When in routing the controller is defined with starting back slash and the corresponding service is declared without a starting back slash, the service cannot found because the name of the service does not match exactly with the name of the controller.

If the controller does not have a custom constructor, it still works, because the service is not found the controller is instantiated without DI.

IMO, a notice should be raised to inform the user that using a starting back slash should be avoided.

Example
routing.yaml

test:
    path: /test
    controller: \MyBundle\Controller\Test::index

services.yaml

services:
  _defaults:
    autowire: true
    autoconfigure: true
    public: false

  MyBundle\Controller\Test:
    arguments:
      - '%kernel.environment%'
    tags:
      - controller.service_arguments