Dynamic form validation groups with callback in Symfony 2.8

MaterialQuantityDto.php

<?php

use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;

class MaterialQuantityDto
{
    /**
     * @var string
     * @Assert\NotNull(groups={"available_material"})
     * @Assert\Type(type="string")
     */
    public $materialId;

    /**
     * @var bool
     * @Assert\NotNull(groups={"available_material"})
     * @Assert\Type(type="bool")
     */
    public $isAvailable;

    /**
     * @var string[]
     */
    public $claddingMaterials;

    /**
     * @var int
     * @Assert\NotNull(groups={"available_material"})
     * @Assert\NotBlank(groups={"availableMaterial"})
     * @Assert\Type(type="float", groups={"available_material"})
     * @Assert\Range(min="0", groups={"available_material"})
     */
    public $quantity;

    /** @Assert\Callback(groups={"availableMaterial"}) */
    public function checkAvailability(ExecutionContextInterface $context)
    {
        dump($context->getGroup());
    }
}

MaterialQuantityType.php

<?php

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
use Symfony\Component\Form\Extension\Core\Type\HiddenType;
use Symfony\Component\Form\Extension\Core\Type\NumberType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

final class MaterialQuantityType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add(
                'isAvailable', CheckboxType::class, [
                'label' => false,
                'required' => false
            ])
            ->add(
                'quantity', NumberType::class, [
                'required' => true,
                'attr' => ['min' => 1]
            ])
            ->add(
                'claddingMaterials', WallCladdingMaterialType::class, [
                'required' => true,
                'choice_translation_domain' => 'cladding_material',
                'multiple' => true
            ]);

        $builder->addEventListener(
            FormEvents::PRE_SET_DATA,
            function (FormEvent $event) use ($options) {
                $data = $event->getData();
                $form = $event->getForm();

                // Skip empty data when collection is initialized
                if (null === $options['materialData']) {
                    return;
                }

                $this->addMaterialId($form, $options);
            }
        );
    }

    private function addMaterialId($form, array $options)
    {
        $form
            ->add('materialId', HiddenType::class, [
                'required' => true,
                'label' => $options['materialData']['name'],
                'data' => $options['materialData']['id']
            ]);
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => MaterialQuantityDto::class,
            'materialData' => null,
            'validation_groups' => function (FormInterface $form) {
                $data = $form->getData();
        
                if (false === $data->isAvailable) {
                    return ['unavailable_material'];
                }
        
                return ['availableMaterial'];
            },
            'cascade_validation' => true,
            'translation_domain' => 'dormer_construction_element'
        ]);
    }

    public function getBlockPrefix()
    {
        return 'dormer_construction_element_material_quantity';
    }
}

Came from:
https://twitter.com/webdevilopers/status/1200375985100730370

When dumping the $resolver it shows "validation_groups" => "Object(Closure)".
Dumping the $context->getGroup() always shows Default.

Maybe this is a problem with the closure in Symfony 2.8? Docs:
https://symfony.com/doc/2.8/form/data_based_validation.html

Here is my current workaround which I prefer since it does not require form manipulation at all - this command DTO would for instance also work with the Symfony Messenger and Validation middleware:

    /** @Assert\Callback() */
    public function checkAvailability(ExecutionContextInterface $context)
    {
        if (false !== $this->isAvailable) {
            $context->getValidator()
                ->inContext($context)
                ->atPath('claddingMaterials')
                ->validate(
                    $this->claddingMaterials,
                    new Assert\Count(["min" => 1])
                );

            $context->getValidator()
                ->inContext($context)
                ->atPath('quantity')
                ->validate(
                    $this->quantity,
                    new Assert\NotNull()
                );
        }