harden the config when using workflow guards

This will forbid using the FrameworkBundle in 3.3 with previous releases
of the Workflow to avoid issues related to the GuardListener class not
being present. Additionally, it provides a useful exception in case the
guard option is used without the ExpressionLanguage component being
installed.

Author: xabbuh

DependencyInjection/FrameworkExtension.php

@@ -25,6 +25,7 @@
 use Symfony\Component\DependencyInjection\Exception\LogicException;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
+use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
 use Symfony\Component\Finder\Finder;
 use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 use Symfony\Component\Config\FileLocator;
@@ -508,6 +509,11 @@ private function registerWorkflowConfiguration(array $workflows, ContainerBuilde
                 if (!isset($config['guard'])) {
                     continue;
                 }
+
+                if (!class_exists(ExpressionLanguage::class)) {
+                    throw new LogicException('Cannot guard workflows as the ExpressionLanguage component is not installed.');
+                }
+
                 $eventName = sprintf('workflow.%s.guard.%s', $name, $transitionName);
                 $guard->addTag('kernel.event_listener', array('event' => $eventName, 'method' => 'onTransition'));
                 $configuration[$eventName] = $config['guard'];

composer.json

@@ -67,7 +67,8 @@
         "symfony/property-info": "<3.3",
         "symfony/serializer": "<3.3",
         "symfony/translations": "<3.2",
-        "symfony/validator": "<3.3"
+        "symfony/validator": "<3.3",
+        "symfony/workflow": "<3.3"
     },
     "suggest": {
         "ext-apcu": "For best performance of the system caches",