16 files declare their use of AccessResultReasonInterface

AccessAwareRouter.php in core/lib/Drupal/Core/Routing/AccessAwareRouter.php
AccessResultTest.php in core/tests/Drupal/Tests/Core/Access/AccessResultTest.php
BlockContentAccessHandlerTest.php in core/modules/block_content/tests/src/Kernel/BlockContentAccessHandlerTest.php
ConfigTestRestHooks.php in core/modules/rest/tests/modules/config_test_rest/src/Hook/ConfigTestRestHooks.php
config_test_rest.module in core/modules/rest/tests/modules/config_test_rest/config_test_rest.module
EntityAccessChecker.php in core/modules/jsonapi/src/Access/EntityAccessChecker.php
EntityAccessDeniedHttpException.php in core/modules/jsonapi/src/Exception/EntityAccessDeniedHttpException.php
EntityCreateAnyAccessCheck.php in core/lib/Drupal/Core/Entity/EntityCreateAnyAccessCheck.php
EntityResource.php in core/modules/rest/src/Plugin/rest/resource/EntityResource.php
FieldResolver.php in core/modules/jsonapi/src/Context/FieldResolver.php
FileUpload.php in core/modules/jsonapi/src/Controller/FileUpload.php
MediaLibraryAccessTest.php in core/modules/media_library/tests/src/Kernel/MediaLibraryAccessTest.php
RelationshipRouteAccessCheck.php in core/modules/jsonapi/src/Access/RelationshipRouteAccessCheck.php
ResourceResponseTestTrait.php in core/modules/jsonapi/tests/src/Functional/ResourceResponseTestTrait.php
ResourceTestBase.php in core/modules/jsonapi/tests/src/Functional/ResourceTestBase.php
UserAccessControlHandler.php in core/modules/user/src/UserAccessControlHandler.php

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