fix: preserve VALUE=DATE in DTSTART for RRULE parsing (#432)

When parsing recurring events with VALUE=DATE (all-day events),
preserve the VALUE=DATE parameter in the DTSTART string passed to
rrule-temporal. This ensures that rrule-temporal can correctly
validate that UNTIL values have the same type as DTSTART.

Previously, date-only information was lost when building the RRULE
string, causing rrule-temporal to incorrectly assume DTSTART was
DATE-TIME and reject valid DATE-only UNTIL values with the error:
"UNTIL rule part MUST have the same value type as DTSTART"

The fix uses local date components (getFullYear, getMonth, getDate)
which is consistent with how dateOnly dates are created in the
dateParameter function using new Date(year, month, day).

Fixes issue reported in MagicMirrorOrg/MagicMirror#4016 where
Google Calendar birthday events with yearly RRULE and DATE-only
UNTIL in the past failed to parse.

Test coverage:
- Yearly recurring DATE events with UNTIL
- Monthly recurring DATE events with UNTIL
- DATE events with COUNT instead of UNTIL
- Edge case: VALUE=DATE with TZID (correctly ignores TZID)

Author: KristjanESPERANTO

ical.js

@@ -745,7 +745,17 @@ module.exports = {
               // BUT: UTC (Etc/UTC, UTC, Etc/GMT) should use ISO format with Z, not TZID
               const isUtc = tzUtil.isUtcTimezone(curr.start.tz);
 
-              if (curr.start.tz && !isUtc) {
+              // For date-only events (VALUE=DATE), we need to preserve that information
+              // so rrule-temporal can properly validate UNTIL values.
+              // Use local date components since dateOnly dates are created with local timezone
+              // (see dateParameter where new Date(year, month, day) is used without UTC)
+              if (curr.start.dateOnly) {
+                // Format: YYYYMMDD using local date components
+                const year = curr.start.getFullYear();
+                const month = String(curr.start.getMonth() + 1).padStart(2, '0');
+                const day = String(curr.start.getDate()).padStart(2, '0');
+                rule += `;DTSTART;VALUE=DATE:${year}${month}${day}`;
+              } else if (curr.start.tz && !isUtc) {
                 const tzInfo = tzUtil.resolveTZID(curr.start.tz);
                 const localStamp = tzUtil.formatDateForRrule(curr.start, tzInfo);
                 const tzidLabel = tzInfo.iana || tzInfo.etc || tzInfo.original;
@@ -777,7 +787,7 @@ module.exports = {
         if (curr.start) {
           // Extract RRULE segments while preserving everything except inline DTSTART
           let rruleOnly = rule.split(';')
-            .filter(segment => !segment.startsWith('DTSTART'))
+            .filter(segment => !segment.startsWith('DTSTART') && !segment.startsWith('VALUE='))
             .join(';');
 
           // Fix non-UTC UNTIL when DTSTART has a TZID

test/date-only-rrule-until.test.js

@@ -0,0 +1,111 @@
+/* eslint-env mocha */
+/* eslint-disable prefer-arrow-callback */
+
+const assert = require('node:assert/strict');
+const {describe, it} = require('mocha');
+const ical = require('../node-ical.js');
+
+describe('DATE-only RRULE with UNTIL (regression test for Google Calendar birthday events)', function () {
+  it('should parse DATE-only events with yearly RRULE and UNTIL in the past', function () {
+    // This is the exact format that Google Calendar uses for birthday events
+    // that caused the bug report in MagicMirror PR #4016
+    const icsData = `BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+DTSTART;VALUE=DATE:20160313
+DTEND;VALUE=DATE:20160314
+RRULE:FREQ=YEARLY;UNTIL=20190312;BYMONTHDAY=13;BYMONTH=3
+DTSTAMP:20260122T223427Z
+UID:test-birthday-event
+SUMMARY:Birthday Event
+TRANSP:OPAQUE
+END:VEVENT
+END:VCALENDAR`;
+
+    // Should parse without throwing "UNTIL rule part MUST have the same value type as DTSTART"
+    const parsed = ical.parseICS(icsData);
+    const event = Object.values(parsed).find(event_ => event_.type === 'VEVENT');
+
+    assert.ok(event, 'Event should be defined');
+    assert.strictEqual(event.summary, 'Birthday Event');
+    assert.strictEqual(event.start.dateOnly, true, 'Start should be date-only');
+    assert.ok(event.rrule, 'RRULE should be defined');
+
+    // Should not throw when accessing rrule
+    assert.doesNotThrow(() => event.rrule.toString());
+
+    // Generate recurrences
+    const recurrences = event.rrule.all();
+    assert.ok(recurrences.length > 0, 'Should have recurrences');
+
+    // Should have exactly 3 occurrences (2016, 2017, 2018)
+    // UNTIL=20190312 means up to and including 2018-03-13 (not 2019-03-13)
+    assert.strictEqual(recurrences.length, 3, 'Should have 3 occurrences');
+
+    // First occurrence should be on 2016-03-13
+    const firstDate = new Date(recurrences[0]);
+    assert.strictEqual(firstDate.getUTCFullYear(), 2016);
+    assert.strictEqual(firstDate.getUTCMonth(), 2); // March (0-indexed)
+    assert.strictEqual(firstDate.getUTCDate(), 13);
+
+    // Last occurrence should be on 2018-03-13
+    const lastDate = new Date(recurrences.at(-1));
+    assert.strictEqual(lastDate.getUTCFullYear(), 2018);
+    assert.strictEqual(lastDate.getUTCMonth(), 2);
+    assert.strictEqual(lastDate.getUTCDate(), 13);
+  });
+
+  it('should preserve VALUE=DATE in DTSTART when creating RRULE string', function () {
+    const icsData = `BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+DTSTART;VALUE=DATE:20200101
+DTEND;VALUE=DATE:20200102
+RRULE:FREQ=MONTHLY;UNTIL=20201231;BYMONTHDAY=1
+UID:test-monthly-event
+SUMMARY:Monthly Event
+END:VEVENT
+END:VCALENDAR`;
+
+    const parsed = ical.parseICS(icsData);
+    const event = Object.values(parsed).find(event_ => event_.type === 'VEVENT');
+
+    assert.ok(event, 'Event should be defined');
+    assert.strictEqual(event.start.dateOnly, true, 'Start should be date-only');
+    assert.ok(event.rrule, 'RRULE should be defined');
+
+    // The internal RRULE string should include VALUE=DATE
+    const rruleString = event.rrule.toString();
+    assert.ok(rruleString, 'RRULE string should be defined');
+
+    // Generate recurrences
+    const recurrences = event.rrule.all();
+    assert.strictEqual(recurrences.length, 12, 'Should have 12 monthly occurrences');
+  });
+
+  it('should handle DATE-only RRULE without UNTIL', function () {
+    const icsData = `BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+DTSTART;VALUE=DATE:20200101
+DTEND;VALUE=DATE:20200102
+RRULE:FREQ=YEARLY;COUNT=5;BYMONTH=1;BYMONTHDAY=1
+UID:test-yearly-event
+SUMMARY:New Year's Day
+END:VEVENT
+END:VCALENDAR`;
+
+    const parsed = ical.parseICS(icsData);
+    const event = Object.values(parsed).find(event_ => event_.type === 'VEVENT');
+
+    assert.ok(event, 'Event should be defined');
+    assert.strictEqual(event.start.dateOnly, true, 'Start should be date-only');
+    assert.ok(event.rrule, 'RRULE should be defined');
+
+    const recurrences = event.rrule.all();
+    assert.strictEqual(recurrences.length, 5, 'Should have 5 occurrences');
+  });
+});