Twig: Creating a variable named "null" is valid

Created on 22 Apr 2016 · 7Comments · Source: twigphp/Twig

Hi,

I was making some experiments with Twig variables management and I found a weird edge case. Indeed you cannot create a Twig variable called true or false but it works if you create a variable called null.

Look at the following snippet:

{% set null = 'hello' %}
{{ 'BEGIN VARIABLE CALLED NULL' }}
{{ null }}
{% if null is not null %}
    NULL = {{ null }}
{% endif %}
{{ 'END VARIABLE CALLED NULL' }}

This template compiles without any issues and renders the following output when it's evaluated:

BEGIN VARIABLE CALLED NULL
END VARIABLE CALLED NULL

The compiled version is the following:

<?php

/* view.twig */
class __TwigTemplate_42e679c29ec1ae34fc295d195e08fffe178e7ef502d6464c900c66cc092f89ee extends Twig_Template
{
    public function __construct(Twig_Environment $env)
    {
        parent::__construct($env);

        $this->parent = false;

        $this->blocks = array(
        );
    }

    protected function doDisplay(array $context, array $blocks = array())
    {
        // line 1
        $context["null"] = "hello";
        // line 2
        echo "BEGIN VARIABLE CALLED NULL";
        echo "
";
        // line 3
        if ( !(null === null)) {
            // line 4
            echo "    NULL = ";
            echo null;
            echo "
";
        }
        // line 6
        echo "END VARIABLE CALLED NULL";
        echo "
";
    }

    public function getTemplateName()
    {
        return "view.twig";
    }

    public function isTraitable()
    {
        return false;
    }

    public function getDebugInfo()
    {
        return array (  33 => 6,  27 => 4,  25 => 3,  21 => 2,  19 => 1,);
    }
}
/* {% set null = 'hello' %}*/
/* {{ 'BEGIN VARIABLE CALLED NULL' }}*/
/* {% if null is not null %}*/
/*     NULL = {{ null }}*/
/* {% endif %}*/
/* {{ 'END VARIABLE CALLED NULL' }}*/
/* */

I know it sounds weird and its an edge case but I think we should forbit the null keyword as a structure name.

Source