[EventDispatcher][DX] Autoconfigure event listeners

[jderusse]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	NA
License	MIT
Doc PR	symfony/symfony-docs/pull/11252

Now that event's FQDN could be used a eventName, this PR adds an alternative to EventSubscriberInterface that uses method's typehint to guess the event to subscribe.

usage for developers:

class MyListener implements EventListenerInterface {
  public function __invoke(MyEvent $e) {
  }
}

That's is. No more services to configure nor getSubscribedEvents to implement.

This PR contains 2 parts:

• extends the tag kernel.event_listener to automatically register available methods when the tag does not contains the required name attribute.
• add a new EventListenerInterface (which is empty) that's just use to trigger the registerForAutoconfiguration.

Few questionable choices made on that PR.

• reuse the tag kernel.event_listener instead of creating a new one
• priority is not configurable: EventSubscriberInterface is here for that

Fixed 2 issues:

• tag container.hot_path was harcoded in subscriber logic (instead of using the injected variable)
• dynamic registration of onMyEventName when event name is a FQDN className

[nicolas-grekas]

nice move :)

[nicolas-grekas]

with minor comment + small rebase needed

[nicolas-grekas]

Oh! When a class implements both EventListenerInterface and EventSubscriberInterface, I think we should ignore the EventListenerInterface part and consider EventSubscriberInterface knows better here, isn't it?

[fabpot]

I agree @nicolas-grekas

[fabpot]

Re-reading this PR, I think I'm 👎 adding it. It looks a solution to a problem that does not exist. Also, I'm not a big fan of using reflection in the Container. We are slowly adding more of this and I'm not comfortable with it.

[nicolas-grekas]

I'm on the same side as @fabpot - let's be light on reflection-enabled magic, the compiler should be able to do as little reflection as possible.

[fabpot]

Two more issues that make me think that this is not something we want in core: the priority is not configurable and it adds a new way to declare Listeners.