6 files declare their use of ComplexDataInterface

EntityInterface.php in drupal/core/lib/Drupal/Core/Entity/EntityInterface.php
Definition of Drupal\Core\Entity\EntityInterface.
EntityTranslation.php in drupal/core/lib/Drupal/Core/Entity/Field/Type/EntityTranslation.php
Definition of Drupal\Core\Entity\Type\EntityTranslation.
EntityTranslationUITest.php in drupal/core/modules/translation_entity/lib/Drupal/translation_entity/Tests/EntityTranslationUITest.php
Definition of Drupal\entity\Tests\EntityTranslationUITest.
EntityWrapper.php in drupal/core/lib/Drupal/Core/Entity/Field/Type/EntityWrapper.php
Definition of Drupal\Core\Entity\Field\Type\EntityWrapper.
FieldItemBase.php in drupal/core/lib/Drupal/Core/Entity/Field/FieldItemBase.php
Definition of Drupal\Core\Entity\Field\FieldItemBase.
FieldItemInterface.php in drupal/core/lib/Drupal/Core/Entity/Field/FieldItemInterface.php
Definition of Drupal\Core\Entity\Field\FieldItemInterface.