Sonata list route type

list_route_type.html.twig

{% extends admin.getTemplate('base_list_field') %}

{% block field %}
    {% set parameters = {} %}
    {% for name, value in field_description.options.parameters %}
        {% set parameters = parameters|merge({ (name): call_user_func(value, object) }) %}
    {% endfor %}

    <a {% for name, value in field_description.options.a.attributes %}{{ name }}="{{ value }}" {% endfor %}
        href="{{ path(call_user_func(field_description.options.name, object), parameters) }}" >
        {{ call_user_func(field_description.options.a.html, object)|raw }}
    </a>
{% endblock %}

PhpFunctionExtension.php

<?php

class PhpFunctionExtension extends \Twig_Extension
{
    /**
     * {@inheritdoc}
     */
    public function getFunctions()
    {
        return [
            new \Twig_SimpleFunction('call_user_func', 'call_user_func'),
            new \Twig_SimpleFunction('call_user_func_array', 'call_user_func_array'),
        ];
    }

    /**
     * {@inheritdoc}
     */
    public function getName()
    {
        return 'phpfunc';
    }
}

You can use this instead of the extension: https://github.com/umpirsky/twig-php-function

Usage

$listMapper
    ->add(
        'url',
        'route',
        [
            'name' => function (Content $content) {
                return 'route_name';
            },
            'parameters' => [
                'id' => function (Content $content) {
                    return $content->getId();
                },
                'slug' => function (Content $content) {
                    return $content->getSlug();
                }
            ],
            'a' => [
                'html' => function (Content $content) {
                    return $content->getTitle();
                },
                'attributes' => [
                    'target' => '_blank'
                ]
            ]
        ]
    )
;

Using Symfony 4.3, how can I tell Sonata to use the custom template? I only get an error that the (original) template doesn't understand this syntax ("Catchable Fatal Error: Object of class Closure could not be converted to string") and the list_url template is not listed here as overridable: https://symfony.com/doc/master/bundles/SonataAdminBundle/reference/templates.html#configuring-templates