Adding an EXDATE with type date does not set the element's VALUE as DATE

[semiprime]

If you set an EXDATE with an argument of type datetime.date, iCalendar does not set the VALUE of the element as DATE.

This violates RFC5545 section 3.8.5.1, which states that:

Value Type: The default value type for this property is DATE-TIME.
The value type can be set to DATE.

and (in the format definition)

;Value MUST match value type

Minimal code to reproduce:

import icalendar
import datetime

# Create an event with necessary elements
ev = icalendar.Event()
ev.add('UID', 'ical-test-20220129')
ev.add('DTSTAMP', datetime.datetime.now(datetime.timezone.utc))
ev.add('SUMMARY', 'EXDATE test')

# Add a date as start date
date = datetime.date(year=2022, month=1, day=1)
ev.add('DTSTART', date)

# Add weekly repeat rule
ev.add('RRULE', {'FREQ':'WEEKLY'})

# Add a date as exception date
exdate = datetime.date(year=2022, month=1, day=8)
ev.add('EXDATE', exdate)

print(ev.to_ical().decode())

With Python 3.9.10, icalendar 4.0.9, this gives output:

BEGIN:VEVENT
SUMMARY:EXDATE test
DTSTART;VALUE=DATE:20220101
DTSTAMP;VALUE=DATE-TIME:20220129T154609Z
UID:ical-test-20220129
RRULE:FREQ=WEEKLY
EXDATE:20220108
END:VEVENT

The error is that the EXDATE line should read:

EXDATE;VALUE=DATE:20220108

Note that in the above code, setting the DTSTART and DTSTAMP elements correctly sets their VALUE parameter from the given argument.

Workaround: The add('EXDATE',...) call can be changed to explicitly set the VALUE:

ev.add('EXDATE', exdate, parameters={'VALUE':'DATE'})