[FrameworkBundle] framework.annotations default should be true only if doctrine/annotations is installed

Author: ogizanagi

DependencyInjection/Configuration.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Bundle\FrameworkBundle\DependencyInjection;
 
+use Doctrine\Common\Annotations\Annotation;
 use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
@@ -602,7 +603,7 @@ private function addAnnotationsSection(ArrayNodeDefinition $rootNode)
             ->children()
                 ->arrayNode('annotations')
                     ->info('annotation configuration')
-                    ->canBeDisabled()
+                    ->{class_exists(Annotation::class) ? 'canBeDisabled' : 'canBeEnabled'}()
                     ->children()
                         ->scalarNode('cache')->defaultValue('php_array')->end()
                         ->scalarNode('file_cache_dir')->defaultValue('%kernel.cache_dir%/annotations')->end()