👮 Prevent feed providers with duplicate source

The feed provider source should be unique for each class that extends
the FeedProvider interface.

In this commit we add a compiler pass who guards against violations of
this rule. The container won't compile if a developer picks a source
name that is already taken by another implementation of the
feed provider interface.

src/Feed/Infrastructure/Framework/CompilerPass/FeedProviderSourceShouldBeUniqueCompilerPass.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace App\Feed\Infrastructure\Framework\CompilerPass;
+
+use App\Feed\Application\Service\FeedProvider\FeedProvider;
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+final class FeedProviderSourceShouldBeUniqueCompilerPass implements CompilerPassInterface
+{
+    public function process(ContainerBuilder $container): void
+    {
+        $sources = [];
+
+        $services = $container->findTaggedServiceIds(FeedProvider::class);
+
+        foreach ($services as $service => $attributes) {
+            if (class_exists($service) === false) {
+                throw new \Exception(sprintf('Couldn\'t derive existing FQCN from service %s, the service is probably aliased', $service));
+            }
+
+            if (method_exists($service, 'getSource') === false) {
+                throw new \Exception('%s must implement static method `getSource`.');
+            }
+
+            $source = call_user_func([$service, 'getSource']);
+
+            if (in_array($source, $sources)) {
+                throw new \Exception(sprintf(
+                    'The \'source\' on a FeedProvider should be unique. Duplicate source found for %s.',
+                    $service,
+                ));
+            }
+
+            $sources[] = $source;
+        }
+    }
+}

src/Kernel.php

@@ -4,6 +4,7 @@
 
 use App\Common\Infrastructure\Messenger\CommandBus\AsCommandHandler;
 use App\Common\Infrastructure\Messenger\EventBus\AsEventSubscriber;
+use App\Feed\Infrastructure\Framework\CompilerPass\FeedProviderSourceShouldBeUniqueCompilerPass;
 use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
 use Symfony\Component\Console\Attribute\AsCommand;
 use Symfony\Component\DependencyInjection\ChildDefinition;
@@ -47,5 +48,8 @@ protected function build(ContainerBuilder $container): void
 
             $definition->addTag('messenger.message_handler', $tagAttributes);
         });
+
+        // @todo move to bundle
+        $container->addCompilerPass(new FeedProviderSourceShouldBeUniqueCompilerPass());
     }
 }