21 files declare their use of DiscoveryInterface

AnnotatedClassDiscovery.php in core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php
AnnotationBridgeDecorator.php in core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotationBridgeDecorator.php
AnnotationBridgeDecoratorTest.php in core/tests/Drupal/Tests/Component/Annotation/Plugin/Discovery/AnnotationBridgeDecoratorTest.php
BlockManagerTest.php in core/tests/Drupal/Tests/Core/Block/BlockManagerTest.php
ConfigSchemaDiscovery.php in core/lib/Drupal/Core/Config/Schema/ConfigSchemaDiscovery.php
DefaultFactory.php in core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php
ElementInfoManagerInterface.php in core/lib/Drupal/Core/Render/ElementInfoManagerInterface.php
EntityTypeManagerTest.php in core/tests/Drupal/Tests/Core/Entity/EntityTypeManagerTest.php
Contains \Drupal\Tests\Core\Entity\EntityTypeManagerTest.
FieldDefinitionIntegrityTest.php in core/modules/field/tests/src/Kernel/FieldDefinitionIntegrityTest.php
HelpTopicDiscovery.php in core/modules/help_topics/src/HelpTopicDiscovery.php
HookDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/HookDiscovery.php
InfoHookDecorator.php in core/lib/Drupal/Core/Plugin/Discovery/InfoHookDecorator.php
LocalActionManagerTest.php in core/tests/Drupal/Tests/Core/Menu/LocalActionManagerTest.php
Contains \Drupal\Tests\Core\Menu\LocalActionManagerTest.
MailManagerTest.php in core/tests/Drupal/Tests/Core/Mail/MailManagerTest.php
Contains \Drupal\Tests\Core\Mail\MailManagerTest.
NoSourcePluginDecorator.php in core/modules/migrate/src/Plugin/NoSourcePluginDecorator.php
PluginManagerInterface.php in core/lib/Drupal/Component/Plugin/PluginManagerInterface.php
ProviderFilterDecorator.php in core/modules/migrate/src/Plugin/Discovery/ProviderFilterDecorator.php
SectionStorageManagerInterface.php in core/modules/layout_builder/src/SectionStorage/SectionStorageManagerInterface.php
SectionStorageManagerTest.php in core/modules/layout_builder/tests/src/Unit/SectionStorageManagerTest.php
YamlDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/YamlDiscovery.php
YamlDiscoveryDecorator.php in core/lib/Drupal/Core/Plugin/Discovery/YamlDiscoveryDecorator.php

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