UserMailRequiredValidator.php

<?php

namespace Drupal\user\Plugin\Validation\Constraint;

use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Constraint;

/**
 * Checks if the user's email address is provided if required.
 *
 * The user mail field is NOT required if account originally had no mail set
 * and the user performing the edit has 'administer users' permission.
 * This allows users without email address to be edited and deleted.
 */
class UserMailRequiredValidator extends ConstraintValidator {
    
    /**
     * {@inheritdoc}
     */
    public function validate($items, Constraint $constraint) : void {
        
        /** @var \Drupal\Core\Field\FieldItemListInterface $items */
        
        /** @var \Drupal\user\UserInterface $account */
        $account = $items->getEntity();
        if (!isset($account)) {
            return;
        }
        $existing_value = NULL;
        // Only validate for existing user.
        if (!$account->isNew()) {
            $account_unchanged = \Drupal::entityTypeManager()->getStorage('user')
                ->loadUnchanged($account->id());
            $existing_value = $account_unchanged->getEmail();
        }
        $required = !(!$existing_value && \Drupal::currentUser()->hasPermission('administer users'));
        if ($required && (!isset($items) || $items->isEmpty())) {
            $this->context
                ->addViolation($constraint->message, [
                '@name' => $account->getFieldDefinition('mail')
                    ->getLabel(),
            ]);
        }
    }

}