{{ dump_array({'foo': 'bar'}) }}

dumpArray.php

<?php
class AcmeDemoExtension extends \Twig_Extension {

    public function getFunctions() {
        return [
            'dump_array' => new \Twig_Function_Method($this, 'dumpArray'),
        ];
    }
  
    public function dumpArray($arrayLikeObject, $indentLevel = 1) {
        $dump   = "[\n";
        $indentation = '    ';
        foreach ($arrayLikeObject as $key => $value) {
            if (is_scalar($value)) {
                $value = '\'' . addcslashes($value, '\\\'') . '\'';
            } else {
                $value = $this->dumpArray($value, $indentLevel + 1);
            }
            $dump .= str_repeat($indentation, $indentLevel) . "'$key' => $value,\n";
        }
        $dump .= str_repeat($indentation, $indentLevel - 1) . ']';
        return $dump;
    }

}