[Symfony 5] Update EventDispatcher::dispatch() to make it forward-compatible with Symfony 5

CR could be polished to explain that dispatch() is not so strict

+++ b/core/core.api.php
@@ -2509,7 +2509,7 @@ function hook_validation_constraint_alter(array &$definitions) {
- * \Symfony\Component\EventDispatcher\Event object; normally you will need to
+ * \Drupal\Component\EventDispatcher\Event object; normally you will need to

+++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
@@ -6,6 +6,8 @@
 use Symfony\Component\EventDispatcher\Event;
...
+use Symfony\Contracts\EventDispatcher\Event as ContractsEvent;

@@ -86,9 +88,38 @@ public function __construct(ContainerInterface $container, array $listeners = []
+      $deprecation_message = 'Symfony\Component\EventDispatcher\Event is deprecated in drupal:9.1.0 and will be replaced by Symfony\Contracts\EventDispatcher\Event in drupal:10.0.0. A new Drupal\Component\EventDispatcher\Event class is available to bridge the two versions of the class.';

+++ b/core/lib/Drupal/Component/EventDispatcher/Event.php
@@ -0,0 +1,15 @@
+use Symfony\Component\EventDispatcher\Event as SymfonyEvent;
...
+class Event extends SymfonyEvent {}

As I see line 7 still using SF Event class?!

Needs reroll following #3055198: [Symfony 5] Symfony/Component/EventDispatcher/Event is deprecated in Symfony 4.3 use Symfony/Contracts/EventDispatcher/Event instead

The new deprecation (both versions) are not yet committed, I had to manually reconstruct this as patch thinks these hunks are already committed but really it was only the first few lines of each hunk.

Can we add a “see” to the CR in the deprecation message?

Nice. RTBC+1

Better to prevent to compare strings twice if not needed

Ignore

1. Combine code that triggers the same deprecation message.

// Trigger a deprecation error if the deprecated Event class is used directly.
// Also try to trigger deprecation errors when classes are in the Drupal
// namespace and inherit directly from the deprecated class. If a class is
// in the Symfony namespace or a different one, we have to assume those will
// be updated by the dependency itself. Exclude the Drupal Event bridge
// class as a special case, otherwise it's pointless.
if ($class_name === 'Symfony\Component\EventDispatcher\Event')
  || strpos($class_name, 'Drupal') !== FALSE && $class_name !== 'Drupal\Component\EventDispatcher\Event' && get_parent_class($event) === 'Symfony\Component\EventDispatcher\Event') {
  $deprecation_message = 'Symfony\Component\EventDispatcher\Event is deprecated in drupal:9.1.0 and will be replaced by Symfony\Contracts\EventDispatcher\Event in drupal:10.0.0. A new Drupal\Component\EventDispatcher\Event class is available to bridge the two versions of the class. See https://www.drupal.org/node/3159012';
  @trigger_error($deprecation_message, E_USER_DEPRECATED);
}

2. Trigger "Symfony\Component\EventDispatcher\Event is deprecated..." regardless of the argument order.

$event_dispatcher->dispatch($event_name, $event);
$event_dispatcher->dispatch($event, $event_name);

FWIW I think the combined if statement is much harder to read, I don't think it's necessary to combine here.

@longwave Thanks for review. What about #26.2?

1. Trigger "Symfony\Component\EventDispatcher\Event is deprecated..." regardless of the argument order.

$event_dispatcher->dispatch($event_name, $event);
$event_dispatcher->dispatch($event, $event_name);

Fix coding standards.

Ignore my previous patches (redundant changes).
#23 looks good. Reuploaded patch #23.

1. +++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
   @@ -92,6 +92,25 @@ public function dispatch($event/*, string $event_name = NULL*/) {
          $event_name = $event_name ?? \get_class($event);
   +
   +      $class_name = get_class($event);
   

   We just had an issue that removed calls to get_class... See #2619482: Convert all get_called_class()/get_class() to static::... looks like we introduced one above already. Whoops.

   Also if we going to get the events class let's do this once.

   So I think we can do

   $class_name = $event::class;
   $event_name = $event_name ?? $class_name;
   

2. +++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
   @@ -92,6 +92,25 @@ public function dispatch($event/*, string $event_name = NULL*/) {
   +      $deprecation_message = 'Symfony\Component\EventDispatcher\Event is deprecated in drupal:9.1.0 and will be replaced by Symfony\Contracts\EventDispatcher\Event in drupal:10.0.0. A new Drupal\Component\EventDispatcher\Event class is available to bridge the two versions of the class. See https://www.drupal.org/node/3159012';
   

   I'm umming and ahhing about this. I know that there is an effort to use PHPCS to standardise our deprecation messages so sticking them in variables doesn't help. I guess we can move this if that happens.

3. +++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
   @@ -92,6 +92,25 @@ public function dispatch($event/*, string $event_name = NULL*/) {
   +      // Trigger a deprecation error if the deprecated Event class is used
   +      // directly.
   +      if ($class_name === 'Symfony\Component\EventDispatcher\Event') {
   +        @trigger_error($deprecation_message, E_USER_DEPRECATED);
   +      }
   +      // Also try to trigger deprecation errors when classes are in the Drupal
   +      // namespace and inherit directly from the deprecated class. If a class is
   +      // in the Symfony namespace or a different one, we have to assume those
   +      // will be updated by the dependency itself. Exclude the Drupal Event
   +      // bridge class as a special case, otherwise it's pointless.
   +      elseif ($class_name !== 'Drupal\Component\EventDispatcher\Event' && strpos($class_name, 'Drupal') !== FALSE) {
   +        if (get_parent_class($event) === 'Symfony\Component\EventDispatcher\Event') {
   +          @trigger_error($deprecation_message, E_USER_DEPRECATED);
   +        }
   +      }
   

   Can this be

         // Trigger a deprecation error if the deprecated Event class is used
         // directly.
         if ($event instanceof Event && !($event instanceof DrupalEvent)) {
           @trigger_error($deprecation_message, E_USER_DEPRECATED);
         }
   

   If we add use Drupal\Component\EventDispatcher\Event as DrupalEvent;.

   As far as I can see any Symfony events will be using the new Contracts event class. If I change the code to this the test still passes.

Hello everyone!
In Drupal\Component\EventDispatcher, Symfony\Component\EventDispatcher\Event should be replaced?

@catch thanks for working through #34 and adding the extra test.

+++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
@@ -92,6 +92,25 @@ public function dispatch($event/*, string $event_name = NULL*/) {
       $event_name = $event_name ?? \get_class($event);
+
+      $class_name = get_class($event);

This can optimised - given we're going to be calling get_class() no matter what.

Committed f3f320a and pushed to 9.1.x. Thanks!