[FrameworkBundle] Simplified the MicroKernelTrait setup

Author: javiereguiluz

configuration/micro_kernel_trait.rst

@@ -40,13 +40,6 @@ Next, create an ``index.php`` file that defines the kernel class and runs it:
         {
             use MicroKernelTrait;
 
-            public function registerBundles(): array
-            {
-                return [
-                    new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
-                ];
-            }
-
             protected function configureContainer(ContainerConfigurator $container): void
             {
                 // PHP equivalent of config/packages/framework.yaml
@@ -86,13 +79,6 @@ Next, create an ``index.php`` file that defines the kernel class and runs it:
         {
             use MicroKernelTrait;
 
-            public function registerBundles(): array
-            {
-                return [
-                    new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
-                ];
-            }
-
             protected function configureContainer(ContainerConfigurator $container): void
             {
                 // PHP equivalent of config/packages/framework.yaml
@@ -120,12 +106,6 @@ Next, create an ``index.php`` file that defines the kernel class and runs it:
         $response->send();
         $kernel->terminate($request, $response);
 
-.. note::
-
-    In addition to the ``index.php`` file, you'll need to create a directory called
-    ``config/`` in your project (even if it's empty because you define the configuration
-    options inside the ``configureContainer()`` method).
-
 That's it! To test it, start the :doc:`Symfony Local Web Server
 </setup/symfony_server>`:
 
@@ -135,14 +115,50 @@ That's it! To test it, start the :doc:`Symfony Local Web Server
 
 Then see the JSON response in your browser: http://localhost:8000/random/10
 
+.. tip::
+
+    If your kernel only defines a single controller, you can use an invokable method::
+
+        class Kernel extends BaseKernel
+        {
+            use MicroKernelTrait;
+
+            // ...
+
+            #[Route('/random/{limit}', name: 'random_number')]
+            public function __invoke(int $limit): JsonResponse
+            {
+                // ...
+            }
+        }
+
 The Methods of a "Micro" Kernel
 -------------------------------
 
 When you use the ``MicroKernelTrait``, your kernel needs to have exactly three methods
 that define your bundles, your services and your routes:
 
 **registerBundles()**
-    This is the same ``registerBundles()`` that you see in a normal kernel.
+    This is the same ``registerBundles()`` that you see in a normal kernel. By
+    default, the micro kernel only registers the ``FrameworkBundle``. If you need
+    to register more bundles, override this method::
+
+        use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
+        use Symfony\Bundle\TwigBundle\TwigBundle;
+        // ...
+
+        class Kernel extends BaseKernel
+        {
+            use MicroKernelTrait;
+
+            // ...
+
+            public function registerBundles(): array
+            {
+                yield new FrameworkBundle();
+                yield new TwigBundle();
+            }
+        }
 
 **configureContainer(ContainerConfigurator $container)**
     This method builds and configures the container. In practice, you will use
@@ -151,9 +167,13 @@ that define your bundles, your services and your routes:
     services directly in PHP or load external configuration files (shown below).
 
 **configureRoutes(RoutingConfigurator $routes)**
-    Your job in this method is to add routes to the application. The
-    ``RoutingConfigurator`` has methods that make adding routes in PHP more
-    fun. You can also load external routing files (shown below).
+    In this method, you can use the ``RoutingConfigurator`` object to define routes
+    in your application and associate them to the controllers defined in this very
+    same file.
+
+    However, it's more convenient to define the controller routes using PHP attributes,
+    as shown above. That's why this method is commonly used only to load external
+    routing files (e.g. from bundles) as shown below.
 
 Adding Interfaces to "Micro" Kernel
 -----------------------------------
@@ -231,7 +251,10 @@ Now it looks like this::
     namespace App;
 
     use App\DependencyInjection\AppExtension;
+    use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
     use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
+    use Symfony\Bundle\TwigBundle\TwigBundle;
+    use Symfony\Bundle\WebProfilerBundle\WebProfilerBundle;
     use Symfony\Component\DependencyInjection\ContainerBuilder;
     use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
     use Symfony\Component\HttpKernel\Kernel as BaseKernel;
@@ -241,18 +264,14 @@ Now it looks like this::
     {
         use MicroKernelTrait;
 
-        public function registerBundles(): array
+        public function registerBundles(): iterable
         {
-            $bundles = [
-                new \Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
-                new \Symfony\Bundle\TwigBundle\TwigBundle(),
-            ];
+            yield FrameworkBundle();
+            yield TwigBundle();
 
             if ('dev' === $this->getEnvironment()) {
-                $bundles[] = new \Symfony\Bundle\WebProfilerBundle\WebProfilerBundle();
+                yield WebProfilerBundle();
             }
-
-            return $bundles;
         }
 
         protected function build(ContainerBuilder $containerBuilder): void