6 files declare their use of DeriverInterface

ContainerDeriverInterface.php in core/lib/Drupal/Core/Plugin/Discovery/ContainerDeriverInterface.php
MockLayoutBlockDeriver.php in core/modules/system/tests/modules/plugin_test/src/Plugin/plugin_test/mock_block/MockLayoutBlockDeriver.php
MockMenuBlockDeriver.php in core/modules/system/tests/modules/plugin_test/src/Plugin/plugin_test/mock_block/MockMenuBlockDeriver.php
TestDerivativeDiscovery.php in core/tests/Drupal/Tests/Core/Plugin/Discovery/TestDerivativeDiscovery.php
TestDerivativeDiscoveryWithObject.php in core/tests/Drupal/Tests/Core/Plugin/Discovery/TestDerivativeDiscoveryWithObject.php
TestHelpTopicDeriver.php in core/modules/help_topics/tests/modules/help_topics_test/src/Plugin/Deriver/TestHelpTopicDeriver.php

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