8 files declare their use of SmartDateRule in Smart Date 3.3.x

Frequency.php in modules/smart_date_recur/src/Plugin/views/filter/Frequency.php

Instances.php in modules/smart_date_recur/src/Controller/Instances.php

RecurRuleUpdate.php in modules/smart_date_recur/src/Plugin/QueueWorker/RecurRuleUpdate.php

SmartDateDailyRangeFormatter.php in modules/smart_date_recur/src/Plugin/Field/FieldFormatter/SmartDateDailyRangeFormatter.php

SmartDateRecurrenceFormatter.php in modules/smart_date_recur/src/Plugin/Field/FieldFormatter/SmartDateRecurrenceFormatter.php

SmartDateRemoveInstanceForm.php in modules/smart_date_recur/src/Form/SmartDateRemoveInstanceForm.php

SmartDateWidgetBase.php in src/Plugin/Field/FieldWidget/SmartDateWidgetBase.php

smart_date_recur.module in modules/smart_date_recur/smart_date_recur.module

Field hooks for a field that stores a start and end date as timestamps.