/**
   * Check if a field on the entity type to update is a possible destination field.
   *
   * @todo Should this be on our FieldManager service?
   *
   * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $definition
   *  Field definition on entity type to update to check.
   * @param \Drupal\Core\Field\FieldDefinitionInterface $source_field
   *  Source field to check compatibility against. If none then check generally.
   *
   * @return bool
   */
  protected function isDestinationFieldCompatible(FieldStorageDefinitionInterface $definition, FieldDefinitionInterface $source_field = NULL) {
    // @todo Create field definition wrapper class to treat FieldDefinitionInterface and FieldStorageDefinitionInterface the same.
    if ($definition instanceof BaseFieldDefinition && $definition->isReadOnly()) {
      return FALSE;
    }
    // Don't allow updates on updates!
    if ($definition->getType() == 'entity_reference') {
      if ($definition->getSetting('target_type') == 'scheduled_update') {
        return FALSE;
      }
    }

    if ($source_field) {
      $matching_types = $this->getMatchingFieldTypes($source_field->getType());
      if (!in_array($definition->getType(), $matching_types)) {
        return FALSE;
      }
      // Check cardinality
      $destination_cardinality = $definition->getCardinality();
      $source_cardinality = $source_field->getFieldStorageDefinition()->getCardinality();
      // $destination_cardinality is unlimited. It doesn't matter what source is.
      if ($destination_cardinality != -1) {
        if ($source_cardinality == -1) {
          return FALSE;
        }
        if ($source_cardinality > $destination_cardinality) {
          return FALSE;
        }
      }


      switch($definition->getType()) {
        case 'entity_reference':
          // Entity reference field must match entity target types.
          if ($definition->getSetting('target_type') != $source_field->getSetting('target_type')) {
            return FALSE;
          }
          // @todo Check bundles
          break;
        // @todo Other type specific conditions?
      }

    }
    return TRUE;
  }
 /**
  * Creates a new field definition based upon a field storage definition.
  *
  * In cases where one needs a field storage definitions to act like full
  * field definitions, this creates a new field definition based upon the
  * (limited) information available. That way it is possible to use the field
  * definition in places where a full field definition is required; e.g., with
  * widgets or formatters.
  *
  * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $definition
  *   The field storage definition to base the new field definition upon.
  *
  * @return $this
  */
 public static function createFromFieldStorageDefinition(FieldStorageDefinitionInterface $definition)
 {
     return static::create($definition->getType())->setCardinality($definition->getCardinality())->setConstraints($definition->getConstraints())->setCustomStorage($definition->hasCustomStorage())->setDescription($definition->getDescription())->setLabel($definition->getLabel())->setName($definition->getName())->setProvider($definition->getProvider())->setQueryable($definition->isQueryable())->setRequired($definition->isRequired())->setRevisionable($definition->isRevisionable())->setSettings($definition->getSettings())->setTargetEntityTypeId($definition->getTargetEntityTypeId())->setTranslatable($definition->isTranslatable());
 }