Custom Form Field Type in Symfony to display plain text (or even html)

Question

Is it possible to add a new form field type in symfony that would simply render a configurable message? I tried to add a new AlertType which should render a given message as a bootstrap 4 alert component. It actually works, but the problem is, that if I am using this form field type in an actual form, then the data mapper is searching for a property in the assigned data class. But it makes no sense to have a property in the data class, because this form type is not really expecting any user input. Is it possible to disable data mapping for a form type? I guess it is, because the \Symfony\Component\Form\Extension\Core\Type\ButtonType does what I would like to achieve - but how?

Currently, my custom form field type is as follows:

<?php
// src/Form/Type/AlertType.php
namespace App\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\OptionsResolver\OptionsResolver;

class AlertType extends AbstractType
{
    /**
     * @inheritDoc
     */
    public function configureOptions(OptionsResolver $resolver): void
    {
        parent::configureOptions($resolver);

        $resolver->setDefaults(
            [
                'context' => 'danger',
                'message' => '',
            ]
        );
    }

    /**
     * @inheritDoc
     */
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        $view->vars['context'] = $options['context'];
        $view->vars['message'] = $options['message'];
    }
}

And the template is as follows:

{% block alert_row %}
    <div class="alert alert-{{ context|escape('html_attr') }}" role="alert">
        {{ message }}
    </div>
{% endblock %}

And the form type (which uses the form field type) is:

<?php
namespace App\Form\Type;

use App\Setup\SetupFormData;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\PasswordType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class SetupFormType extends AbstractType
{
    /**
     * @inheritDoc
     */
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add(
                'setupPassword',
                PasswordType::class
            )
            ->add(
                'warning',
                AlertType::class,
                ['message' => 'HELLO', 'context' => 'primary']
            )
            ->add(
                'save',
                SubmitType::class
            );
    }

    /**
     * @inheritDoc
     */
    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults(
            [
                'data_class' => SetupFormData::class,
            ]
        );
    }
}

As long as the SetupFormData has a property called $warning, everything is working as desired. But I don't like to add this property to the data class.

Answer 1

From Symfony 4+ you have help and help_html options in TextFormField and few extend form types.

Help Html. You can configure the help text as you want with additional html and css.

Answer 2

If you don't want that is mapped just add this 'mapped' => false,

$builder
            ->add(
                'setupPassword',
                PasswordType::class
            )
            ->add(
                'warning',
                AlertType::class,
                ['message' => 'HELLO', 'context' => 'primary'],
                'mapped' => false,
            )
            ->add(
                'save',
                SubmitType::class
            );