Symfony 3.4 inject service inside another fail - symfony

Question

I am doing a service in Symfony and I need to inject my mail service. The mail service depends on a parameter:
app.email:
class: AppBundle\Services\EmailNotificationService
autowire: false
public: true
arguments:
- '#doctrine.orm.entity_manager'
- '#swiftmailer.mailer'
- '#templating.engine.twig'
- '%mailer_user%'
- '#logger'
It works to inject it into one service:
app.booking:
class: AppBundle\Services\BookingService
autowire: false
public: true
arguments:
- '#doctrine'
- '#pay.pay'
- '#app.calendar'
- '#app.email'
- '#app.push'
but when I include it in another:
services:
app.servicios_extras:
class: AppBundle\Services\ServiciosExtrasService
autowire: false
public: true
arguments:
- '#app.email'
...
class ServiciosExtrasService
{
private $mailer;
public function __construct(EmailNotificationService $mailer)
{
$this->mailer = $mailer;
}
it gives me the error:
Cannot autowire service "AppBundle\Services\EmailNotificationService": argument "$mailerUser" of method "__construct()" has no type-hint, you should configure its value explicitly.
I'm missing something?
UPDATE
app/config/services.yml:
_defaults:
# automatically injects dependencies in your services
autowire: true
# automatically registers your services as commands, event subscribers, etc.
autoconfigure: true
# this means you cannot fetch services directly from the container via $container->get()
# if you need to do this, you can override this setting on individual services
public: false

Answer 1

I don't normally answer these sorts of questions because there are a number of similar questions with the same answer. But I could not find one that could be considered to be a duplicate.
The short answer is to add the Services directory to the list of excluded directories:
#app/config/services.yml
AppBundle\:
resource: '../../src/AppBundle/*'
exclude: '../../src/AppBundle/{Entity,Repository,Tests,Services}'
Doing so prevents autowire from trying to create a service with an id of AppBundle\Services\EmailNotificationService and then failing because $emailUser is a string.
The Symfony container has moved away from explicitly naming services with things like app.email. Instead, the class name (AppBundle\Services\EmailNotificationService) is preferred. So autowire finds all classes under src, looks in container to see if a service has been defined with the same class name and, if none is found, creates a new service. Autowire does not link app.email with your email class. Unless you are supporting a legacy project then it might be best to do away with app.* service names.
And, as a bonus, by going with class names you can eliminate all the service configuration except for a bind under the _default section. But it looks like you do have a legacy project in which case you should probably turn off autowire under _default just to preserve your own sanity.