33 files declare their use of FlagInterface in Flag 8.4

AccessDenied.php in tests/modules/flag_test_plugins/src/Plugin/Flag/AccessDenied.php

AccessGranted.php in tests/modules/flag_test_plugins/src/Plugin/Flag/AccessGranted.php

ActionLinkController.php in src/Controller/ActionLinkController.php

ActionLinkNoJsController.php in src/Controller/ActionLinkNoJsController.php

ActionLinkTypeBase.php in src/ActionLink/ActionLinkTypeBase.php

ActionLinkTypePluginInterface.php in src/ActionLink/ActionLinkTypePluginInterface.php

AJAXactionLink.php in src/Plugin/ActionLink/AJAXactionLink.php

CommentFlagType.php in src/Plugin/Flag/CommentFlagType.php

ConfirmForm.php in src/Plugin/ActionLink/ConfirmForm.php

CountLink.php in modules/flag_count/src/Plugin/ActionLink/CountLink.php

EntityFlagType.php in src/Plugin/Flag/EntityFlagType.php

FieldEntry.php in src/Plugin/ActionLink/FieldEntry.php

FieldEntryFormController.php in src/Controller/FieldEntryFormController.php

flag.api.php in ./flag.api.php

Hooks provided by the Flag module.

flag.module in ./flag.module

The Flag module.

Flag.php in src/Entity/Flag.php

FlagAccessCheck.php in src/Access/FlagAccessCheck.php

FlagActionTest.php in tests/src/Unit/Plugin/Action/FlagActionTest.php

FlagConfirmFormBase.php in src/Form/FlagConfirmFormBase.php

FlagCount.php in src/TwigExtension/FlagCount.php

FlagDisableConfirmForm.php in src/Form/FlagDisableConfirmForm.php

FlagEventBase.php in src/Event/FlagEventBase.php

FlagKernelTestBase.php in tests/src/Kernel/FlagKernelTestBase.php

FlagListBuilder.php in src/Controller/FlagListBuilder.php

FlagPermissionsTrait.php in tests/src/Traits/FlagPermissionsTrait.php

FlagResetForm.php in src/Form/FlagResetForm.php

FlagTypeBase.php in src/FlagType/FlagTypeBase.php

FlagTypePluginInterface.php in src/FlagType/FlagTypePluginInterface.php

FormEntryTypeBase.php in src/Plugin/ActionLink/FormEntryTypeBase.php

LinkOutputLocationTest.php in tests/src/Functional/LinkOutputLocationTest.php

Reload.php in src/Plugin/ActionLink/Reload.php

UnFlagAccessCheck.php in src/Access/UnFlagAccessCheck.php

UserFlagType.php in src/Plugin/Flag/UserFlagType.php