feature #31429 [Messenger] add support for abstract handlers (timiTao)

This PR was submitted for the 4.4 branch but it was merged into the 5.1-dev branch instead.

Discussion
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[Messenger] add support for abstract handlers

| Q             | A
| ------------- | ---
| Branch?       | master <!-- see below -->
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #31417    <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Added handling abstract handler.

Commits
-------

22e59f31be [Messenger] fix support for abstract handlers

src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php

@@ -78,7 +78,7 @@ class MessengerPass implements CompilerPassInterface
                     throw new RuntimeException(sprintf('Invalid handler service "%s": bus "%s" specified on the tag "%s" does not exist (known ones are: %s).', $serviceId, $tag['bus'], $this->handlerTag, implode(', ', $busIds)));
                 }
 
-                $className = $container->getDefinition($serviceId)->getClass();
+                $className = $this->getServiceClass($container, $serviceId);
                 $r = $container->getReflectionClass($className);
 
                 if (null === $r) {
@@ -240,7 +240,7 @@ class MessengerPass implements CompilerPassInterface
         $receiverMapping = [];
 
         foreach ($container->findTaggedServiceIds($this->receiverTag) as $id => $tags) {
-            $receiverClass = $container->findDefinition($id)->getClass();
+            $receiverClass = $this->getServiceClass($container, $id);
             if (!is_subclass_of($receiverClass, ReceiverInterface::class)) {
                 throw new RuntimeException(sprintf('Invalid receiver "%s": class "%s" must implement interface "%s".', $id, $receiverClass, ReceiverInterface::class));
             }
@@ -336,4 +336,19 @@ class MessengerPass implements CompilerPassInterface
 
         $container->getDefinition($busId)->replaceArgument(0, new IteratorArgument($middlewareReferences));
     }
+
+    private function getServiceClass(ContainerBuilder $container, string $serviceId): string
+    {
+        while (true) {
+            $definition = $container->findDefinition($serviceId);
+
+            if (!$definition->getClass() && $definition instanceof ChildDefinition) {
+                $serviceId = $definition->getParent();
+
+                continue;
+            }
+
+            return $definition->getClass();
+        }
+    }
 }

src/Symfony/Component/Messenger/Tests/DependencyInjection/MessengerPassTest.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\Messenger\Tests\DependencyInjection;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\DependencyInjection\ChildDefinition;
 use Symfony\Component\DependencyInjection\Compiler\ResolveChildDefinitionsPass;
 use Symfony\Component\DependencyInjection\Compiler\ResolveClassPass;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
@@ -225,6 +226,34 @@ class MessengerPassTest extends TestCase
         $this->assertSame(PrioritizedHandler::class, $secondHandlerDefinition->getClass());
     }
 
+    public function testRegisterAbstractHandler()
+    {
+        $container = $this->getContainerBuilder($messageBusId = 'message_bus');
+        $container->register($messageBusId, MessageBusInterface::class)->addTag('messenger.bus')->setArgument(0, []);
+
+        $container
+            ->register(DummyHandler::class, DummyHandler::class)
+            ->setAbstract(true);
+
+        $container
+            ->setDefinition($abstractDirectChildId = 'direct_child', new ChildDefinition(DummyHandler::class))
+            ->setAbstract(true);
+
+        $container
+            ->setDefinition($abstractHandlerId = 'child', new ChildDefinition($abstractDirectChildId))
+            ->addTag('messenger.message_handler');
+
+        (new MessengerPass())->process($container);
+
+        $messageHandlerMapping = $container->getDefinition($messageBusId.'.messenger.handlers_locator')->getArgument(0);
+        $this->assertHandlerDescriptor(
+            $container,
+            $messageHandlerMapping,
+            DummyMessage::class,
+            [$abstractHandlerId]
+        );
+    }
+
     public function testThrowsExceptionIfTheHandlerClassDoesNotExist()
     {
         $this->expectException('Symfony\Component\DependencyInjection\Exception\RuntimeException');