How to Upgrade Twig from Underscored to Namespaces

This post was updated at November 2020

Switch from deprecated --set option to rector.php config.

Symfony recently announced a new version of Twig with namespaces as we know it. Before PHP 5.2 there was Underscored_Namespace - I remember because that was the first version I used.

Today I'll show you how to upgrade from _ to \\ in few minutes seconds.

This set would not be possible and as good as it is without you, open-source PHP community. I'd like to thank 👏:

Find and Replace?

So all we need to do is replace Twig_ with Twig\?


This would fail since Twig\Function class doesn't exist. Twig\TwigFunction does. There 150 more cases where find and replace fails.

2 Places

We need to replace both docblocks:

- * @throws \Twig_Error_Loader
+ * @throws \Twig\Error\LoaderError
 public function render(): void
-    /** @var \Twig_Environment $env */
+    /** @var \Twig\Environment $env */
     $env = $this->getTwigEnv();

     // ...

And the code:

-$safeTwigEnvironment = new \Twig_Environment(
+$safeTwigEnvironment = new \Twig\Environment(
-   new \Twig_Loader_Array([])
+   new \Twig\Loader\ArrayLoader([])

In a reaction to the Symfony blog post, I see many developers do upgrades manually. In case of 50 changes, it's ok, but private code bases will go 1000+ use cases.

Code Pattern Refactoring

For Rector it just 1 pattern to refactor. Just tell him to process your files src:

  1. Install Rector
composer require rector/rector --dev
  1. Update rector.php
use Rector\Core\Configuration\Option;
use Rector\Set\ValueObject\SetList;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return static function (ContainerConfigurator $containerConfigurator): void {
    $parameters = $containerConfigurator->parameters();

    $parameters->set(Option::SETS, [
  1. Run Rector
vendor/bin/rector process src

Happy coding!