use Symfony\Component\Security\Core\Validator\Constraints\UserPassword;
use Symfony\Component\Form\Extension\Core\Type\PasswordType;

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('current_password', PasswordType::class, [
                'required' => true,
                'mapped' => false,
                'constraints' => [
                    new Assert\NotBlank(),
                    new UserPassword(),
                ],
            ])

<div class="ec-input{{ has_errors(form.current_password) ? ' error' }}">
        {{ form_widget(form.current_password, {
            'attr': { 'placeholder': '変更前のパスワードを入力してください'|trans },
            'type': 'password'
        }) }}
        {{ form_errors(form.current_password) }}
    </div>