Can't use non-fqcn service id when using ServiceSubscriberInterface. Why?

[javaDeveloperKid]

When using ServiceSubscriberInterface I can't use the non-fqcn service id. Why? What's the limitation?

The following:

    public static function getSubscribedServices()
    {
        return [
            'app.service.my_service'
        ];
    }

throws:
"App\MyController::getSubscribedServices()" must return valid PHP types for service "App\MyController" key "0", "app.service.my_service" returned.

[MatTheCat]

From the interface you mention:

Returns an array of service types

app.service.my_service is a service name, not type.

You’ll have to tag your subscriber yourself: https://symfony.com/doc/current/service_container/service_subscribers_locators.html#aliased-services