feature #20121 Class existence resource (fabpot)

This PR was merged into the 3.2-dev branch.

Discussion
----------

Class existence resource

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | see #20094
| License       | MIT
| Doc PR        | n/a

Commits
-------

222b56d [TwigBundle] added support for ClassExistenceResource when relevant
d98eb7b [Config] added ClassExistenceResource

src/Symfony/Bundle/TwigBundle/DependencyInjection/Compiler/ExtensionPass.php

@@ -11,9 +11,13 @@
 
 namespace Symfony\Bundle\TwigBundle\DependencyInjection\Compiler;
 
+use Symfony\Component\Config\Resource\ClassExistenceResource;
 use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Reference;
+use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
+use Symfony\Component\Stopwatch\Stopwatch;
+use Symfony\Component\Yaml\Parser as YamlParser;
 
 /**
  * @author Jean-François Simon <jeanfrancois.simon@sensiolabs.com>
@@ -72,15 +76,18 @@ public function process(ContainerBuilder $container)
             $container->getDefinition('twig.extension.assets')->addTag('twig.extension');
         }
 
-        if (class_exists('Symfony\Component\Yaml\Parser')) {
+        $container->addResource(new ClassExistenceResource(YamlParser::class));
+        if (class_exists(YamlParser::class)) {
             $container->getDefinition('twig.extension.yaml')->addTag('twig.extension');
         }
 
-        if (class_exists('Symfony\Component\Stopwatch\Stopwatch')) {
+        $container->addResource(new ClassExistenceResource(Stopwatch::class));
+        if (class_exists(Stopwatch::class)) {
             $container->getDefinition('twig.extension.debug.stopwatch')->addTag('twig.extension');
         }
 
-        if (class_exists('Symfony\Component\ExpressionLanguage\ExpressionLanguage')) {
+        $container->addResource(new ClassExistenceResource(ExpressionLanguage::class));
+        if (class_exists(ExpressionLanguage::class)) {
             $container->getDefinition('twig.extension.expression')->addTag('twig.extension');
         }
     }

src/Symfony/Bundle/TwigBundle/composer.json

@@ -27,7 +27,7 @@
         "symfony/stopwatch": "~2.8|~3.0",
         "symfony/dependency-injection": "~2.8|~3.0",
         "symfony/expression-language": "~2.8|~3.0",
-        "symfony/config": "~2.8|~3.0",
+        "symfony/config": "~3.2",
         "symfony/finder": "~2.8|~3.0",
         "symfony/routing": "~2.8|~3.0",
         "symfony/templating": "~2.8|~3.0",

src/Symfony/Component/Config/Resource/ClassExistenceResource.php

@@ -0,0 +1,75 @@
+<?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\Component\Config\Resource;
+
+/**
+ * ClassExistenceResource represents a class existence.
+ * Freshness is only evaluated against resource existence.
+ *
+ * The resource must be a fully-qualified class name.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class ClassExistenceResource implements SelfCheckingResourceInterface, \Serializable
+{
+    private $resource;
+    private $exists;
+
+    /**
+     * @param string $resource The fully-qualified class name
+     */
+    public function __construct($resource)
+    {
+        $this->resource = $resource;
+        $this->exists = class_exists($resource);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __toString()
+    {
+        return $this->resource;
+    }
+
+    /**
+     * @return string The file path to the resource
+     */
+    public function getResource()
+    {
+        return $this->resource;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isFresh($timestamp)
+    {
+        return class_exists($this->resource) === $this->exists;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function serialize()
+    {
+        return serialize(array($this->resource, $this->exists));
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function unserialize($serialized)
+    {
+        list($this->resource, $this->exists) = unserialize($serialized);
+    }
+}

src/Symfony/Component/Config/Tests/Resource/ClassExistenceResourceTest.php

@@ -0,0 +1,54 @@
+<?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\Component\Config\Tests\Resource;
+
+use Symfony\Component\Config\Resource\ClassExistenceResource;
+
+class ClassExistenceResourceTest extends \PHPUnit_Framework_TestCase
+{
+    public function testToString()
+    {
+        $res = new ClassExistenceResource('BarClass');
+        $this->assertSame('BarClass', (string) $res);
+    }
+
+    public function testGetResource()
+    {
+        $res = new ClassExistenceResource('BarClass');
+        $this->assertSame('BarClass', $res->getResource());
+    }
+
+    public function testIsFreshWhenClassDoesNotExist()
+    {
+        $res = new ClassExistenceResource('Symfony\Component\Config\Tests\Fixtures\BarClass');
+
+        $this->assertTrue($res->isFresh(time()));
+
+        eval(<<<EOF
+namespace Symfony\Component\Config\Tests\Fixtures;
+
+class BarClass
+{
+}
+EOF
+        );
+
+        $this->assertFalse($res->isFresh(time()));
+    }
+
+    public function testIsFreshWhenClassExists()
+    {
+        $res = new ClassExistenceResource('Symfony\Component\Config\Tests\Resource\ClassExistenceResourceTest');
+
+        $this->assertTrue($res->isFresh(time()));
+    }
+}