feature #15990 added a micro kernel (fabpot)

This PR was merged into the 2.8 branch.

Discussion
----------

added a micro kernel

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Related to #15948 and #15820

Commits
-------

eab0f0a added a micro kernel

src/Symfony/Bundle/FrameworkBundle/Kernel/MicroKernelTrait.php

@@ -0,0 +1,87 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\FrameworkBundle\Kernel;
+
+use Symfony\Component\Config\Loader\LoaderInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\Routing\RouteCollectionBuilder;
+
+/**
+ * A Kernel that provides configuration hooks.
+ *
+ * @author Ryan Weaver <ryan@knpuniversity.com>
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+trait MicroKernelTrait
+{
+    /**
+     * Add or import routes into your application.
+     *
+     *     $routes->import('config/routing.yml');
+     *     $routes->add('/admin', 'AppBundle:Admin:dashboard', 'admin_dashboard');
+     *
+     * @param RouteCollectionBuilder $routes
+     */
+    abstract protected function configureRoutes(RouteCollectionBuilder $routes);
+
+    /**
+     * Configures the container.
+     *
+     * You can register extensions:
+     *
+     * $c->loadFromExtension('framework', array(
+     *     'secret' => '%secret%'
+     * ));
+     *
+     * Or services:
+     *
+     * $c->register('halloween', 'FooBundle\HalloweenProvider');
+     *
+     * Or parameters:
+     *
+     * $c->setParameter('halloween', 'lot of fun');
+     *
+     * @param ContainerBuilder $c
+     * @param LoaderInterface  $loader
+     */
+    abstract protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader);
+
+    /**
+     * {@inheritdoc}
+     */
+    public function registerContainerConfiguration(LoaderInterface $loader)
+    {
+        $loader->load(function (ContainerBuilder $container) use ($loader) {
+            $container->loadFromExtension('framework', array(
+                'router' => array(
+                    'resource' => 'kernel:loadRoutes',
+                    'type' => 'service',
+                ),
+            ));
+
+            $this->configureContainer($container, $loader);
+
+            $container->addObjectResource($this);
+        });
+    }
+
+    /**
+     * @internal
+     */
+    public function loadRoutes(LoaderInterface $loader)
+    {
+        $routes = new RouteCollectionBuilder($loader);
+        $this->configureRoutes($routes);
+
+        return $routes->build();
+    }
+}

src/Symfony/Bundle/FrameworkBundle/Tests/Kernel/ConcreteMicroKernel.php

@@ -0,0 +1,71 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\FrameworkBundle\Tests\Kernel;
+
+use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
+use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
+use Symfony\Component\Config\Loader\LoaderInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\Filesystem\Filesystem;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Kernel;
+use Symfony\Component\Routing\RouteCollectionBuilder;
+
+class ConcreteMicroKernel extends Kernel
+{
+    use MicroKernelTrait;
+
+    private $cacheDir;
+
+    public function halloweenAction()
+    {
+        return new Response('halloween');
+    }
+
+    public function registerBundles()
+    {
+        return array(
+            new FrameworkBundle(),
+        );
+    }
+
+    public function getCacheDir()
+    {
+        return $this->cacheDir = sys_get_temp_dir().'/sf_micro_kernel';
+    }
+
+    public function getLogDir()
+    {
+        return $this->cacheDir;
+    }
+
+    public function __destruct()
+    {
+        $fs = new Filesystem();
+        $fs->remove($this->cacheDir);
+    }
+
+    protected function configureRoutes(RouteCollectionBuilder $routes)
+    {
+        $routes->add('/', 'kernel:halloweenAction');
+    }
+
+    protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader)
+    {
+        $c->loadFromExtension('framework', array(
+            'secret' => '$ecret',
+        ));
+
+        $c->setParameter('halloween', 'Have a great day!');
+        $c->register('halloween', 'stdClass');
+    }
+}

src/Symfony/Bundle/FrameworkBundle/Tests/Kernel/MicroKernelTraitTest.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\FrameworkBundle\Tests\Kernel;
+
+use Symfony\Component\HttpFoundation\Request;
+
+class MicroKernelTraitTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @requires PHP 5.4
+     */
+    public function test()
+    {
+        $kernel = new ConcreteMicroKernel('test', true);
+        $kernel->boot();
+
+        $request = Request::create('/');
+        $response = $kernel->handle($request);
+
+        $this->assertEquals('halloween', $response->getContent());
+        $this->assertEquals('Have a great day!', $kernel->getContainer()->getParameter('halloween'));
+        $this->assertInstanceOf('stdClass', $kernel->getContainer()->get('halloween'));
+    }
+}