How to register a Twig Extension as a service without autowire in Symfony 4

If the autowire feature of your Symfony 4 project is enabled, twig extensions are automatically registered in your app if the extension extends the AbstractExtension class and they're stored on the app/src/Twig directory. However, in some project this feature may disabled for reasons that are not of our interest. If that's your case, you may need to know how to register such extension in Symfony 4.

In this tutorial, we'll explain you how to register a Twig extension in your project easily without the autowire feature.

1. Create extension

As first step, you will need to have a Twig extension created, you can either use your own extension or use an example extension. In this case, in our example extension we'll add a filter and a function to our proyect (just remove them of the class if you are using the following example). The class will use the App\Twig namespace and extends the AbstractExtension:

<?php

// app/src/Twig/AppExtension.php
namespace App\Twig;

use Twig\Extension\AbstractExtension;
use Twig\TwigFilter;
use Twig\TwigFunction;

class AppExtension extends AbstractExtension
{
    public function getFilters()
    {
        return [
            new TwigFilter('minifyVal', [$this, 'minifyVal']),
        ];
    }
    
    public function getFunctions()
    {
        return [
            new TwigFunction('is_mobile', [$this, 'is_mobile']),
        ];
    }
    
    /**
     * Verificar si el dispositivo es un mobil desde php
     * @return boolean
     */
    public function is_mobile(){
        $useragent = $_SERVER['HTTP_USER_AGENT'];
        if(preg_match('/(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i',$useragent)||preg_match('/1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i',substr($useragent,0,4))){
            return true;
        }
        
        return false;
    }

    /**
     * Allows you to determine the most readable format of a number of bytes.
     * 
     * @param type $n
     * @param type $precision
     * @return type
     */
    public function minifyVal($n, $precision = 1 ){
	if ($n < 900) {
            $n_format = number_format($n, $precision);
            $suffix = '';
	} else if ($n < 900000) {
            $n_format = number_format($n / 1000, $precision);
            $suffix = 'K';
	} else if ($n < 900000000) {
            $n_format = number_format($n / 1000000, $precision);
            $suffix = 'M';
	} else if ($n < 900000000000) {
            $n_format = number_format($n / 1000000000, $precision);
            $suffix = 'B';
	} else {
            $n_format = number_format($n / 1000000000000, $precision);
            $suffix = 'T';
	}
        
	if ( $precision > 0 ) {
            $dotzero = '.' . str_repeat( '0', $precision );
            $n_format = str_replace( $dotzero, '', $n_format );
	}
        
	return $n_format . $suffix;
    }
}

2. Register extension

Once the extension file is in the mentioned directory, proceed to register it in the services.yaml file of your project like this (under the services block):

# app/config/services.yaml
services:
    app.twig_extension:
        class: App\Twig\AppExtension
        public: false
        tags:
            - { name: twig.extension } 

If you are in the dev environment, once you reload your app, the extension will be loaded and immediately available (the minifiVal filter and is_mobile function).

Happy coding !