fix: prevent double timezone conversion for CalDAV events from Zimbra (#27877)

[kiro-dev28]

What does this PR do?

Fixes CalDAV events synced from Zimbra showing a negative duration (end time before start time, e.g. start 10:00 AM, end 9:00 AM for a 15-minute slot).

Root Cause

When a CalDAV server sends an event with DTSTART;TZID=Europe/Berlin:20260105T090000, ical.js parses this into a zone-aware ICAL.Time that already correctly represents 09:00 local → 08:00 UTC.

The subsequent event.startDate.convertToZone(zone) call was being made unconditionally. convertToZone on a non-floating time re-interprets the local wall-clock value as UTC first, then applies the zone offset a second time:

convertToZone on 09:00 (already Europe/Berlin):
  step 1: treat 09:00 as UTC
  step 2: apply +01:00 offset → 10:00 local ← wrong (+1h drift)

For a 15-minute event this produces start=10:00, end=09:00 — a -1h duration.

Fix

1. Guard convertToZone with isFloating() — only convert times that ical.js left in floating (zone-less) form. Already-zoned times (isFloating() === false) are correctly resolved by ical.js and must not be converted again.

2. Improve VTIMEZONE lookup for vendor-prefixed TZIDs — Zimbra uses DTSTART;TZID=/zimbra.com/standard/Europe/Berlin but the VTIMEZONE component has TZID:Europe/Berlin. The exact-match lookup failed silently, causing a mismatched VTIMEZONE to be selected. Now falls back to extracting the IANA suffix after the last /.

Tests

Two new test cases added to CalendarService.test.ts:

• Standard VTIMEZONE: verifies start=08:00 UTC (09:00 Berlin−1h), end > start
• Zimbra vendor-prefixed TZID: verifies fallback lookup resolves correctly, end > start

Related

Fixes #27877

---

[CLAassistant]

All committers have signed the CLA.

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="packages/lib/CalendarService.ts">

<violation number="1" location="packages/lib/CalendarService.ts:515">
P2: TZID fallback only takes the last segment (e.g., “Berlin”), so it won’t match standard IANA TZIDs like “Europe/Berlin”. This makes the vendor-prefixed lookup fail and can still select the wrong VTIMEZONE when multiple exist.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: TZID fallback only takes the last segment (e.g., “Berlin”), so it won’t match standard IANA TZIDs like “Europe/Berlin”. This makes the vendor-prefixed lookup fail and can still select the wrong VTIMEZONE when multiple exist.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At packages/lib/CalendarService.ts, line 515:

<comment>TZID fallback only takes the last segment (e.g., “Berlin”), so it won’t match standard IANA TZIDs like “Europe/Berlin”. This makes the vendor-prefixed lookup fail and can still select the wrong VTIMEZONE when multiple exist.</comment>

<file context>
@@ -505,7 +505,18 @@ export default abstract class BaseCalendarService implements Calendar {
+          // "/zimbra.com/standard/Europe/Berlin" or "/mozilla.org/20070129_1/Europe/Berlin".
+          // Extract the IANA part after the last "/" and retry the lookup.
+          if (!vtimezone && tzid.includes("/")) {
+            const ianaCandidate = tzid.split("/").pop();
+            if (ianaCandidate) {
+              vtimezone = allVtimezones.find((vtz) => vtz.getFirstPropertyValue("tzid") === ianaCandidate);
</file context>

[285729101]

@zomars fixes double timezone conversion for Zimbra CalDAV events — was causing events to show at the wrong time.