All-day EXDATEs are not applied to recurring date/time events

[rfc2822]

Some calendar clients generate recurring events with date and time, plus all-day EXDATEs:

BEGIN:VEVENT
UID:527f3d37-ed76-4c6a-8aae-bf6d71a4ad09
DTSTART;TZID=Europe/Vienna:20240317T100000          ← DATE-TIME value
DTEND;TZID=Europe/Vienna:20240317T150000
STATUS:CONFIRMED
SUMMARY:Test Event
RRULE:FREQ=WEEKLY;BYDAY=SU;UNTIL=20240526T080000Z
EXDATE;VALUE=DATE:20240331           ← DATE value
EXDATE;VALUE=DATE:20240421
EXDATE;VALUE=DATE:20240505
EXDATE;VALUE=DATE:20240519
EXDATE;VALUE=DATE:20240324
END:VEVENT
END:VCALENDAR

As I understand it, this is not a RFC 5545-conforming way to specify EXDATEs for the given event at 10:00. However it's clear that the recurring event should not occur on those dates.

Currently, Nextcloud expands to the given EXDATEs, too. It would be more compatible to omit the recurring events on the dates given by the EXDATEs.

DAVx5 handles this by rewriting all RDATE/EXDATE entries to the value type of DTSTART:

• If DTSTART is a DATE and EXDATE a DATE-TIME, just drop the EXDATE time and make it all-day.
• If DTSTART is a DATE-TIME and EXDATE is a DATE, take the time (+ time zone) of DTSTART and the date of EXDATE to generate the new EXDATE.

[kesselb]

cc @ChristophWurst @miaulalala

[miaulalala]

Do you know which clients produce these?

[rfc2822]

In my case I have created the event with Gnome Evolution (but as I know there are others)