minor #9994 [Twig] Fix Twig namespaces (Phenix789)

This PR was submitted for the master branch but it was merged into the 2.8 branch instead (closes #9994).

Discussion
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[Twig] Fix Twig namespaces

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Fix Twig namespaces used in documentation

Commits
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de8b1e7 Fix Twig namespaces and update doc for twig runtime extension

Author: javiereguiluz

components/form.rst

@@ -181,6 +181,9 @@ to bootstrap or access Twig and add the :class:`Symfony\\Bridge\\Twig\\Extension
     use Symfony\Bridge\Twig\Extension\FormExtension;
     use Symfony\Bridge\Twig\Form\TwigRenderer;
     use Symfony\Bridge\Twig\Form\TwigRendererEngine;
+    use Twig\Environment;
+    use Twig\Loader\FilesystemLoader;
+    use Twig\RuntimeLoader\FactoryRuntimeLoader;
 
     // the Twig file that holds all the default markup for rendering forms
     // this file comes with TwigBridge
@@ -194,7 +197,7 @@ to bootstrap or access Twig and add the :class:`Symfony\\Bridge\\Twig\\Extension
     // the path to your other templates
     $viewsDirectory = realpath(__DIR__.'/../views');
 
-    $twig = new Twig_Environment(new Twig_Loader_Filesystem(array(
+    $twig = new Environment(new FilesystemLoader(array(
         $viewsDirectory,
         $vendorTwigBridgeDirectory.'/Resources/views/Form',
     )));
@@ -251,7 +254,7 @@ installed:
     $ composer require symfony/translation symfony/config
 
 Next, add the :class:`Symfony\\Bridge\\Twig\\Extension\\TranslationExtension`
-to your ``Twig_Environment`` instance::
+to your ``Twig\\Environment`` instance::
 
     use Symfony\Component\Form\Forms;
     use Symfony\Component\Translation\Translator;

reference/configuration/twig.rst

@@ -84,7 +84,7 @@ called to determine the default escaping applied to the template.
 base_template_class
 ~~~~~~~~~~~~~~~~~~~
 
-**type**: ``string`` **default**: ``'Twig_Template'``
+**type**: ``string`` **default**: ``'Twig\\Template'``
 
 Twig templates are compiled into PHP classes before using them to render
 contents. This option defines the base class from which all the template classes

templating/twig_extension.rst

@@ -33,12 +33,15 @@ As an example you'll create a price filter to format a given number into price::
     // src/AppBundle/Twig/AppExtension.php
     namespace AppBundle\Twig;
 
-    class AppExtension extends \Twig_Extension
+    use Twig\Extension\AbstractExtension;
+    use Twig\TwigFilter;
+
+    class AppExtension extends AbstractExtension
     {
         public function getFilters()
         {
             return array(
-                new \Twig_SimpleFilter('price', array($this, 'priceFilter')),
+                new TwigFilter('price', array($this, 'priceFilter')),
             );
         }