For choosing between a html select or checkboxes on your form, just toggle the “multiple” parameter on the ChoiceType class. Since the roles are an array, we need a data transformer.

Example:

<?php

namespace App\Form;

use App\Entity\User;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
use Symfony\Component\Form\CallbackTransformer;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('email')
            ->add('Roles', ChoiceType::class, [
                    'required' => true,
                    'multiple' => false,
                    'expanded' => false,
                    'choices'  => [
                      'User' => 'ROLE_USER',
                      'Partner' => 'ROLE_PARTNER',
                      'Admin' => 'ROLE_ADMIN',
                    ],
                ])

            ->add('password')
            ->add('groups')

        ;


        // Data transformer
        $builder->get('Roles')
            ->addModelTransformer(new CallbackTransformer(
                function ($rolesArray) {
                     // transform the array to a string
                     return count($rolesArray)? $rolesArray[0]: null;
                },
                function ($rolesString) {
                     // transform the string back to an array
                     return [$rolesString];
                }
        ));


    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => User::class,
        ]);
    }
}