Invalid iCal generated when DateTimeZone is UTC

[janpawellek]

Code to reproduce:

$startDate = new DateTime();
$startDate->setTimezone(new \DateTimeZone('UTC'));
$endDate = new DateTime();
$endDate->setTimezone(new \DateTimeZone('UTC'));
$start = new \Eluceo\iCal\Domain\ValueObject\DateTime($startDate, true);
$end = new \Eluceo\iCal\Domain\ValueObject\DateTime($endDate, true);
$occurence = new \Eluceo\iCal\Domain\ValueObject\TimeSpan($start, $end);
$vEvent->setOccurrence($occurence);

This generates iCal that contains properties like this:

DTSTART;TZID=UTC:20220812T090000
DTEND;TZID=UTC:20220812T103000

However TZID=UTC is not allowed according to the specs: The "TZID" property parameter MUST NOT be applied to DATE properties and DATE-TIME or TIME properties whose time values are specified in UTC.

When this iCal export is passed to an iCal Validatior, it will fail with validation errors.

If I create the DateTime instace with $applyTimeZone = false:

$start = new \Eluceo\iCal\Domain\ValueObject\DateTime($startDate, false);
$end = new \Eluceo\iCal\Domain\ValueObject\DateTime($endDate, false);

This will create iCal without the "Z" suffix for UTC timestamps:

DTSTART:20220812T090000
DTEND:20220812T103000

Which results in wrong start and end times when imported into a calendar application.

I think the correct format shold look like this:

DTSTART:20220812T090000Z
DTEND:20220812T103000Z

Is there any option to get iCal properties like this?

Thank you!