New EmailValidatorInterface interface for typehinting the email.validator service

In future if the email.validator service is injected into a class then the service should be typehinted to \Drupal\Component\Utility\EmailValidatorInterface. For example:

  /**
   * Constructs a new ContactFormEditForm.
   *
   * @param \Drupal\Component\Utility\EmailValidatorInterface $email_validator
   *   The email validator.
   * @param \Drupal\Core\Path\PathValidatorInterface $path_validator
   *   The path validator service.
   */
  public function __construct(EmailValidatorInterface $email_validator, PathValidatorInterface $path_validator) {
    $this->emailValidator = $email_validator;
    $this->pathValidator = $path_validator;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('email.validator'),
      $container->get('path.validator')
    );
  }

Basic email validation is unchanged:

$email_validator = \Drupal::service('email.validator');
assert($email_validator instanceof \Egulias\EmailValidator\EmailValidator);
$email_validator->isValid('info@example.com');

In order to change core's email validation you can swap out the existing email.validator with a service that implements \Drupal\Component\Utility\EmailValidatorInterface. See https://www.drupal.org/docs/8/api/services-and-dependency-injection/alte... for more. To stay compatible with existing Drupal 8 code, it is recommended that the new class extends from \Egulias\EmailValidator\EmailValidator.

If you have overridden the email.validator service there is a small chance that the overridden service will not implement EmailValidatorInterface::isValid() correctly. In such cases, PHP will error immediately and the solution is to fix your overridden implementation to comply with the interface.