11 files declare their use of PrimitiveInterface in Drupal 8

AllowedValuesConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/AllowedValuesConstraintValidator.php

BinaryInterface.php in core/lib/Drupal/Core/TypedData/Type/BinaryInterface.php

BooleanInterface.php in core/lib/Drupal/Core/TypedData/Type/BooleanInterface.php

FloatInterface.php in core/lib/Drupal/Core/TypedData/Type/FloatInterface.php

IntegerInterface.php in core/lib/Drupal/Core/TypedData/Type/IntegerInterface.php

PrimitiveDataNormalizer.php in core/modules/serialization/src/Normalizer/PrimitiveDataNormalizer.php

PrimitiveTypeConstraintValidatorTest.php in core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php

SchemaCheckTrait.php in core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php

StorableConfigBase.php in core/lib/Drupal/Core/Config/StorableConfigBase.php

StringInterface.php in core/lib/Drupal/Core/TypedData/Type/StringInterface.php

UriInterface.php in core/lib/Drupal/Core/TypedData/Type/UriInterface.php