Expansion of Etc/GMT is affected by system timezone

[marcoancona]

Today I run into a strange behavior that seems like a bug to me. I assume the result of a recurrent rule expansion should not be affected by the system timezone. However it is, when the event timezone is "Etc/GMT" (and maybe some other?)

Steps to reproduce.
Save this node script:

const ICAL = require('ical.js');

const ics = `
BEGIN:VCALENDAR
VERSION:2.0
BEGIN:VEVENT
SUMMARY:New Event
TRANSP:OPAQUE
CLASS:PUBLIC
DTSTAMP:20191101T103936Z
DTSTART;TZID=Etc/GMT:20191109T110000
DTEND;TZID=Etc/GMT:20191109T120000
CREATED:20191101T095430Z
LAST-MODIFIED:20191101T103935Z
RRULE:FREQ=WEEKLY;INTERVAL=1;BYDAY=SA
SEQUENCE:0
END:VEVENT
END:VCALENDAR
`;

var jcalData = ICAL.parse(ics);
var vcalendar = new ICAL.Component(jcalData);
var vevent = vcalendar.getFirstSubcomponent('vevent');
var expand = new ICAL.RecurExpansion({
	component: vevent,
	dtstart: vevent.getFirstPropertyValue('dtstart')
});
console.log(expand.next().toJSDate());

Run twice

> TZ="UTC" node test.js 
2019-11-09T11:00:00.000Z  // < correct!

> TZ="Europe/Amsterdam" node test.js 
startDate: 2019-11-09T10:00:00.000Z  // < wrong!

Notice that, if the event timezone is different, the result of the expansion is independent of the system timezone (as it should since the output dates are UTC). So, for example, with

DTSTART;TZID=Europe/Athens:20191109T110000
DTEND;TZID=Europe/Athens:20191109T120000

the result is correct

> TZ="UTC" node test.js 
2019-11-09T09:00:00.000Z

> TZ="Europe/Amsterdam" node test.js 
2019-11-09T09:00:00.000Z

[kewisch]

I'm not able to reproduce this on node v21.7.2. Is this still an issue for you?

[github-actions]

It looks like we haven't heard back on this issue, therefore we are closing this issue. If this problem persists in the latest version of ical.js, please re-open this issue.