drupal_render - twig integration

test.php

<?php

define('DRUPAL_ROOT', getcwd());

require_once DRUPAL_ROOT . '/Twig/lib/Twig/Autoloader.php';
Twig_Autoloader::register();

// Almost empty class, just swaps Twig_Node_Print objects to Drupal_Twig_Node_Print objects.
class Drupal_Twig_NodeVisitor implements Twig_NodeVisitorInterface {
  function enterNode(Twig_NodeInterface $node, Twig_Environment $env) {
    if ($node instanceof Twig_Node_Print) {
      return new Drupal_Twig_Node_Print($node->getNode('expr'), $node->getLine(), $node->getNodeTag());
    }
    return $node;
  }
  function leaveNode(Twig_NodeInterface $node, Twig_Environment $env) {
    return $node;
  }
  function getPriority() {
    return 0;
  }
}

// A copy of the class Twig_Node_Print with a minor change, see below.
class Drupal_Twig_Node_Print extends Twig_Node implements Twig_NodeOutputInterface {
    public function __construct(Twig_Node_Expression $expr, $lineno, $tag = null)
    {
        parent::__construct(array('expr' => $expr), array(), $lineno, $tag);
    }

    /**
     * Compiles the node to PHP.
     *
     * @param Twig_Compiler A Twig_Compiler instance
     */
    public function compile(Twig_Compiler $compiler)
    {
        $compiler
            ->addDebugInfo($this)
            // This was just ->write('echo') in Twig_Node_Print
            ->write('echo render(')
            ->subcompile($this->getNode('expr'))
            ->raw(");\n")
        ;
    }
}

require_once DRUPAL_ROOT . '/core/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

$loader = new Twig_Loader_Filesystem(DRUPAL_ROOT . '/templates');
$twig = new Twig_Environment($loader, array(
    'cache' => DRUPAL_ROOT . '/compilation_cache',
));
// This is where the magic ties in.
$twig->addNodeVisitor(new Drupal_Twig_NodeVisitor);
$template = $twig->loadTemplate('index.html');
$build = node_view(node_load(1));
echo $template->render(array('build' => $build));

index.html was just {{ build }}