// src/Form/UserType.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\EmailType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\Extension\Core\Type\RepeatedType;
use Symfony\Component\Form\Extension\Core\Type\PasswordType;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('email', EmailType::class)
            ->add('username', TextType::class)
            ->add('plainPassword', RepeatedType::class, array(
                'type' => PasswordType::class,
                'first_options'  => array('label' => 'Password'),
                'second_options' => array('label' => 'Repeat Password'),
            ))
        ;
    }

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

// src/Controller/RegistrationController.php
namespace App\Controller;

use App\Form\UserType;
use App\Entity\User;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Component\Security\Core\Encoder\UserPasswordEncoderInterface;

class RegistrationController extends AbstractController
{
    /**
     * @Route("/register", name="user_registration")
     */
    public function register(Request $request, UserPasswordEncoderInterface $passwordEncoder)
    {
        // 1) build the form
        $user = new User();
        $form = $this->createForm(UserType::class, $user);

        // 2) handle the submit (will only happen on POST)
        $form->handleRequest($request);
        if ($form->isSubmitted() && $form->isValid()) {

            // 3) Encode the password (you could also do this via Doctrine listener)
            $password = $passwordEncoder->encodePassword($user, $user->getPlainPassword());
            $user->setPassword($password);

            // 4) save the User!
            $entityManager = $this->getDoctrine()->getManager();
            $entityManager->persist($user);
            $entityManager->flush();

            // ... do any other work - like sending them an email, etc
            // maybe set a "flash" success message for the user

            return $this->redirectToRoute('replace_with_some_route');
        }

        return $this->render(
            'registration/register.html.twig',
            array('form' => $form->createView())
        );
    }
}

// src/Entity/User.php
// ...

class User implements UserInterface
{
    // ...

    public function getUsername()
    {
        return $this->email;
    }

    // ...
}

// src/Form/UserType.php
// ...
use Symfony\Component\Validator\Constraints\IsTrue;
use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
use Symfony\Component\Form\Extension\Core\Type\EmailType;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('email', EmailType::class);
            // ...
            ->add('termsAccepted', CheckboxType::class, array(
                'mapped' => false,
                'constraints' => new IsTrue(),
            ))
        );
    }
}