DAVx5 reported a 500 Internal Server Error on a time-range REPORT
against a calendar containing a recurring event whose DTSTART/DTEND used
a Windows-style TZID (e.g. "W. Europe Standard Time", as commonly written
by Outlook/Exchange and some Thunderbird/Lightning setups) instead of an
IANA zone name.
go-ical resolves TZID via a plain time.LoadLocation call, which only
understands IANA names. A simple decode of such an event succeeds (RRULE
dates aren't parsed eagerly), but expanding its recurrence - which
go-webdav's caldav.Filter does for every time-range REPORT - calls
Component.RecurrenceSet, which does call time.LoadLocation(tzid) and
fails with "ical: error parsing start time: unknown time zone ...".
Add internal/icalfix, a small shared helper that rewrites recognized
Windows timezone identifiers (TZID parameters and VTIMEZONE TZID: lines)
to their IANA equivalent in raw ICS bytes before decoding. Wire it into
every ical.NewDecoder call site: internal/caldav/backend.go's
decodeObject (fixes the reported bug), internal/web/calendar.go's event
rendering/ICS import, and internal/icssub's remote feed fetching, so a
subscribed feed with the same issue doesn't hit it either.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
