[stable6.6] fix: recurrence rule truncation on nth occurrence save

src/store/calendarObjectInstance.js

@@ -1498,7 +1498,7 @@ export default defineStore('calendarObjectInstance', {
 					// we might be editing an instance or fork, not the base component itself. Both properties
 					// eventComponent already shared with the base component AND ones it didn't (e.g. a LOCATION
 					// added for the first time) need to end up on the base component.
-					const excludedPropertyNames = ['UID', 'RECURRENCE-ID', 'DTSTART', 'DTEND']
+					const excludedPropertyNames = ['UID', 'RECURRENCE-ID', 'DTSTART', 'DTEND', 'RRULE', 'RDATE', 'EXDATE']
 					for (const property of baseComponent.getPropertyIterator()) {
 						if (excludedPropertyNames.includes(property.name)) {
 							continue
@@ -1511,13 +1511,25 @@ export default defineStore('calendarObjectInstance', {
 						}
 						baseComponent.addProperty(property.clone())
 					}
-					// DTSTART and DTEND need to be cloned separately so that internal logic of ical.js
-					// can adjust all the recurrence rules and exceptions accordingly. Only do so when
-					// editing the base occurrence - otherwise we risk changing the date/time of the whole
-					// series when the user only intended to change a single occurrence.
+					// DTSTART, DTEND, and the recurrence-rule properties need to be handled separately, and
+					// only when editing the base occurrence - otherwise we risk changing the date/time or
+					// recurrence pattern of the whole series when the user only intended to change a single
+					// occurrence. DTSTART/DTEND need cloning separately so ical.js can adjust recurrence
+					// rules/exceptions accordingly; forkItem()'s COUNT adjustment above is a no-op for the
+					// primary occurrence itself, so its own RRULE/RDATE/EXDATE are safe to copy as-is here.
 					if (isPrimaryOccurrence) {
 						baseComponent.startDate = eventComponent.startDate.clone()
 						baseComponent.endDate = eventComponent.endDate.clone()
+
+						const recurrencePropertyNames = ['RRULE', 'RDATE', 'EXDATE']
+						for (const propertyName of recurrencePropertyNames) {
+							baseComponent.deleteAllProperties(propertyName)
+						}
+						for (const property of eventComponent.getPropertyIterator()) {
+							if (recurrencePropertyNames.includes(property.name)) {
+								baseComponent.addProperty(property.clone())
+							}
+						}
 					}
 					// Only VALARM is copied here because it's the only sub-component the
 					// editor currently lets users change; other sub-components (e.g.

tests/javascript/unit/store/calendarObjectInstance.test.ts

@@ -1059,6 +1059,66 @@ describe('store/calendarObjectInstance test suite', () => {
 			expect(calendarObjectsStore.createCalendarObjectFromFork).not.toHaveBeenCalled()
 			expect(calendarObjectsStore.updateCalendarObject).toHaveBeenCalledWith({ calendarObject })
 		})
+
+		it('preserves the original RRULE when saving series scope from a non-primary occurrence (real calendar-js)', async () => {
+			// Regression test for a real bug: forkItem() adjusts a forked occurrence's
+			// own RRULE COUNT down to "occurrences remaining from this point" (needed
+			// for the "this and future" truncate flow) - but the same fork is also
+			// used for ordinary editing. Saving with series scope from anything but
+			// the primary occurrence used to blindly copy that locally-adjusted RRULE
+			// onto the master, silently truncating the whole series - even when the
+			// user never touched the recurrence rule at all.
+			const ics = [
+				'BEGIN:VCALENDAR',
+				'VERSION:2.0',
+				'PRODID:-//Nextcloud//calendar-js tests//EN',
+				'BEGIN:VEVENT',
+				'UID:series-rrule-preserved-test',
+				'DTSTART:20260907T100000Z',
+				'DTEND:20260907T110000Z',
+				'DTSTAMP:20260901T000000Z',
+				'SUMMARY:Original title',
+				'RRULE:FREQ=DAILY;COUNT=5',
+				'END:VEVENT',
+				'END:VCALENDAR',
+			].join('\r\n')
+
+			const parser = getParserManager().getParserForFileType('text/calendar')
+			parser.parse(ics)
+			const calendarComponent = parser.getItemIterator().next().value
+
+			let masterComponent = null
+			for (const component of calendarComponent.getComponentIterator()) {
+				if (component.name === 'VEVENT' && !component.hasProperty('RECURRENCE-ID')) {
+					masterComponent = component
+				}
+			}
+			const rangeEnd = masterComponent.startDate.clone()
+			rangeEnd.year += 1
+			// The 3rd occurrence - not the primary
+			const thirdOccurrence = masterComponent.recurrenceManager.getAllOccurrencesBetween(masterComponent.startDate, rangeEnd)[2]
+
+			// The user only edits an unrelated property, never touching the recurrence rule
+			thirdOccurrence.updatePropertyWithValue('SUMMARY', 'Edited title')
+			thirdOccurrence.markDirty()
+
+			const calendarObject = { calendarId: 'personal', calendarComponent: markRaw(calendarComponent) }
+
+			const store = useCalendarObjectInstanceStore()
+			const calendarObjectsStore = useCalendarObjectsStore()
+			store.calendarObject = calendarObject
+			store.calendarObjectInstance = { eventComponent: markRaw(thirdOccurrence) }
+			mockedisBaseOccurrence.mockReturnValue(false)
+			vi.spyOn(calendarObjectsStore, 'updateCalendarObject').mockResolvedValue()
+
+			await store.saveCalendarObjectInstance({
+				scope: 'series',
+				calendarId: 'personal',
+			})
+
+			expect(masterComponent.getFirstPropertyFirstValue('SUMMARY')).toBe('Edited title')
+			expect(masterComponent.getFirstPropertyFirstValue('RRULE').count).toBe(5)
+		})
 	})
 
 	describe('deleteCalendarObjectInstance', () => {