[Bug-fix] Fix default form problem with _token field

[Zales0123]

Discussion

Q	A
Branch?	1.9
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets
License	MIT

After upgrade to Symfony 5, there is a problem with the default form for custom resources. Already rendered _token with form_widget(form) throws an exception when rendered again (previously it was just not rendered again).

Probably it would be nice to have some test for a custom resource with default templates 💃 Write now it can be easily reproduced by removing vars->all->templates->form from one of the resources (e.g. AdminUser).

[pamil]

Thanks, Mateusz! 🥇

[maximehuran]

Why do we have to keep the {{ form_row(form._token) }} when configuration.vars.templates.form is defined ?
I have an issue on one of our plugin because we customize the template form and I have the same error :

An exception has been thrown during the rendering of a template ("Field "_token" has already been rendered, save the result of previous render call to a variable and output that instead.").

I think the best way to manage it is to use :

{% if not form._token.isRendered %}
            {{ form_row(form._token) }}
        {% endif %}