at the end of the day, it was inevitable

src/CacheBundle/DependencyInjection/Compiler/CollectFeedFetchersCompilerPass.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace CacheBundle\DependencyInjection\Compiler;
+
+use CacheBundle\Feed\Fetcher\Factory\LazyFeedFetcherFactory;
+use CacheBundle\Feed\Fetcher\FeedFetcherInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+
+/**
+ * Class CollectFeedFetchersCompilerPass
+ * @package CacheBundle\DependencyInjection\Compiler
+ */
+class CollectFeedFetchersCompilerPass implements CompilerPassInterface
+{
+
+    const LAZY_FACTORY_ID = 'cache.feed_fetcher_factory.lazy';
+
+    /**
+     * You can modify the container here before it is dumped to PHP code.
+     *
+     * @param ContainerBuilder $container A ContainerBuilder instance.
+     *
+     * @return void
+     */
+    public function process(ContainerBuilder $container)
+    {
+        if (! $container->has(self::LAZY_FACTORY_ID)) {
+            $this->throwException('Lazy factory not registered.');
+        }
+
+        $lazyFactory = $container->getDefinition(self::LAZY_FACTORY_ID);
+        if ($lazyFactory->getClass() !== LazyFeedFetcherFactory::class) {
+            $this->throwException(
+                'Invalid factory, expected '. LazyFeedFetcherFactory::class
+                .' but got '. $lazyFactory->getClass()
+            );
+        }
+
+        $fetchers = array_keys($container->findTaggedServiceIds('socialhose.feed_fetcher'));
+
+        $map = [];
+        foreach ($fetchers as $id) {
+            $class = $container->getDefinition($id)->getClass();
+            $reflection = new \ReflectionClass($class);
+            if (! $reflection->implementsInterface(FeedFetcherInterface::class)) {
+                $this->throwException('');
+            }
+
+            $map[$class::support()] = $id;
+        }
+
+        $lazyFactory->replaceArgument(1, $map);
+    }
+
+    /**
+     * @param string $message A additional exception message.
+     *
+     * @return void
+     */
+    private function throwException($message = '')
+    {
+        throw new \RuntimeException('Can\'t register feed fetchers in lazy factory. '. $message);
+    }
+}