Efficient Twig extensions using Lazy Extensions

Lazy Twig extensions were introduced in Twig 1.35 / 2.4.4, albeit there’re still see so many Symfony apps that don’t use them.

One has to be aware that to create the Twig environment, every extension has to be instantiated. Now multiply that by the number of extensions in your app, some of them with possibly large dependency tree.

For instance, take a look at Sylius – popular e-commerce platform based on Symfony and its CheckoutStepsExtension – it depends on a helper, which depends on two services, both depending on composite resolvers, which in turn load another set of their dependencies.

This extension has to be instantiated every single time Twig is used, even though it’s not needed.

So instead of:

final class CheckoutStepsExtension extends \Twig_Extension
{
    private $checkoutStepsHelper;

    public function __construct(CheckoutStepsHelper $checkoutStepsHelper)
    {
        $this->checkoutStepsHelper = $checkoutStepsHelper;
    }

    public function getFunctions(): array
    {
        return [
            new \Twig_Function('sylius_is_shipping_required', [$this->checkoutStepsHelper, 'isShippingRequired']),
            new \Twig_Function('sylius_is_payment_required', [$this->checkoutStepsHelper, 'isPaymentRequired']),
        ];
    }
}

we could move dependencies from the extension to a Twig Runtime:

final class CheckoutStepsExtension extends \Twig_Extension
{
    public function getFunctions(): array
    {
        return [
            new \Twig_Function('sylius_is_shipping_required', [CheckoutStepsHelperRuntime::class, 'isShippingRequired']),
            new \Twig_Function('sylius_is_payment_required', [CheckoutStepsHelperRuntime::class, 'isPaymentRequired']),
        ];
    }
}

and the Runtime proxy:

final class CheckoutStepsHelperRuntime implements RuntimeExtensionInterface
{
    private $checkoutStepsHelper;

    public function __construct(CheckoutStepsHelper $checkoutStepsHelper)
    {
        $this->checkoutStepsHelper = $checkoutStepsHelper;
    }
    
    public function isShippingRequired(OrderInterface $order): bool
    {
        return $this->checkoutStepsHelper->isShippingRequired($order);
    }

    public function isPaymentRequired(OrderInterface $order): bool
    {
        return $this->checkoutStepsHelper->isPaymentRequired($order);
    }
}

The RuntimeExtensionInterface interface is just for convenience. It enables Symfony DI’s autoconfiguration feature to tag the class with the twig.runtime tag.

Last, but not least I hope, remember to test your Twig extensions. In the next post I’ll show you how to do that properly.

Written on March 7, 2020