class EntityUntranslatableFieldsConstraintValidator

class EntityUntranslatableFieldsConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    use EntityChangesDetectionTrait;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * Constructs an EntityUntranslatableFieldsConstraintValidator object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager) {
        $this->entityTypeManager = $entity_type_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($entity, Constraint $constraint) {
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
        
        /** @var \Drupal\Core\Entity\Plugin\Validation\Constraint\EntityUntranslatableFieldsConstraint $constraint */
        // Untranslatable field restrictions apply only to revisions of multilingual
        // entities.
        if ($entity->isNew() || !$entity->isTranslatable() || !$entity->getEntityType()
            ->isRevisionable()) {
            return;
        }
        if ($entity->isDefaultRevision() && !$entity->isDefaultTranslationAffectedOnly()) {
            return;
        }
        // To avoid unintentional reverts and data losses, we forbid changes to
        // untranslatable fields in pending revisions for multilingual entities. The
        // only case where changes in pending revisions are acceptable is when
        // untranslatable fields affect only the default translation, in which case
        // a pending revision contains only one affected translation. Even in this
        // case, multiple translations would be affected in a single revision, if we
        // allowed changes to untranslatable fields while editing non-default
        // translations, so that is forbidden too. For the same reason, when changes
        // to untranslatable fields affect all translations, we can only allow them
        // in default revisions.
        if ($this->hasUntranslatableFieldsChanges($entity)) {
            if ($entity->isDefaultTranslationAffectedOnly()) {
                foreach ($entity->getTranslationLanguages(FALSE) as $langcode => $language) {
                    if ($entity->getTranslation($langcode)
                        ->hasTranslationChanges()) {
                        $this->context
                            ->addViolation($constraint->defaultTranslationMessage);
                        break;
                    }
                }
            }
            else {
                $this->context
                    ->addViolation($constraint->defaultRevisionMessage);
            }
        }
    }
    
    /**
     * Checks whether an entity has untranslatable field changes.
     *
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   A content entity object.
     *
     * @return bool
     *   TRUE if untranslatable fields have changes, FALSE otherwise.
     */
    protected function hasUntranslatableFieldsChanges(ContentEntityInterface $entity) {
        $skip_fields = $this->getFieldsToSkipFromTranslationChangesCheck($entity);
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $original */
        if (isset($entity->original)) {
            $original = $entity->original;
        }
        else {
            $original = $this->entityTypeManager
                ->getStorage($entity->getEntityTypeId())
                ->loadRevision($entity->getLoadedRevisionId());
        }
        foreach ($entity->getFieldDefinitions() as $field_name => $definition) {
            if (in_array($field_name, $skip_fields, TRUE) || $definition->isTranslatable() || $definition->isComputed()) {
                continue;
            }
            $items = $entity->get($field_name)
                ->filterEmptyItems();
            $original_items = $original->get($field_name)
                ->filterEmptyItems();
            if ($items->hasAffectingChanges($original_items, $entity->getUntranslated()
                ->language()
                ->getId())) {
                return TRUE;
            }
        }
        return FALSE;
    }

}