15 files declare their use of ComplexDataInterface

AllowedValuesConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/AllowedValuesConstraintValidator.php
ArrayElement.php in core/lib/Drupal/Core/Config/Schema/ArrayElement.php
ComplexDataConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/ComplexDataConstraintValidator.php
ComplexDataNormalizer.php in core/modules/serialization/src/Normalizer/ComplexDataNormalizer.php
ComplexDataNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/ComplexDataNormalizerTest.php
ContentEntityNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/ContentEntityNormalizerTest.php
EntityAdapter.php in core/lib/Drupal/Core/Entity/Plugin/DataType/EntityAdapter.php
EntityFieldTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
FieldItemInterface.php in core/lib/Drupal/Core/Field/FieldItemInterface.php
IsNullConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/IsNullConstraintValidator.php
ItemList.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
Map.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
NotNullConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/NotNullConstraintValidator.php
RecursiveContextualValidator.php in core/lib/Drupal/Core/TypedData/Validation/RecursiveContextualValidator.php
TypedConfigTest.php in core/tests/Drupal/KernelTests/Config/TypedConfigTest.php

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