Interval.hasSame ignores timezones unless the interval is empty

[brentobi]

Interval.hasSame ignores timezones unless the interval is empty.

Baseline Interval.hasSame (expectedly) returns

• false for 12:15 UTC+2 and 11:30 UTC+1 (different unix timestamp, same UTC hours, different local hours)
• true for 12:15 UTC+2 and 12:30 UTC+2 (different unix timestamp, different UTC hours, same local hours)

because the local hours are matching.

That is because Interval.hasSame internally uses DateTime.hasSame which ignores timezones when comparing unit values. https://github.com/moment/luxon/blob/d30908f973359e8c4127535858e48599d7e0b7c0/src/datetime.js#L1950

Expected behaviour I would expect Interval.hasSame to return

• false for 12:15 UTC+2 and 11:15 UTC+1 (same unix timestamp, same UTC hours, different local hours)

because that should be the same case as the first example above.

Actual behaviour Instead Interval.hasSame always returns true if the interval isEmpty (-> same unix timestamps) even if different timezones would result in different local unit values.

Analysis This bug (?) seems to have been introduced in https://github.com/moment/luxon/issues/709 by returning true early in case the interval isEmpty. https://github.com/moment/luxon/blob/33f79577a16f56629ddf9c1f1034259da7222d9c/src/interval.js#L251-L253

Example code

(() => {
let s,e,i;

const log = (expect) => {
console.log(s.hour, s.toLocaleString(luxon.DateTime.DATETIME_FULL_WITH_SECONDS), s.toUTC().toISO());
console.log(e.hour, e.toLocaleString(luxon.DateTime.DATETIME_FULL_WITH_SECONDS), e.toUTC().toISO());
console.log('i.hasSame("hour")', i.hasSame("hour"), "expect", expect);
};

s = luxon.DateTime.fromISO("2023-01-01T10:15:00.000+00:00", {zone: 'UTC+2'});
e = luxon.DateTime.fromISO("2023-01-01T10:30:00.000+00:00", {zone: 'UTC+1'});
i = luxon.Interval.fromDateTimes(s, e);
log(false);

// 12 '1 January 2023 at 12:15:00 GMT+2' '2023-01-01T10:15:00.000Z'
// 11 '1 January 2023 at 11:30:00 GMT+1' '2023-01-01T10:30:00.000Z'
// i.hasSame("hour") false expect false

s = luxon.DateTime.fromISO("2023-01-01T10:15:00.000+00:00", {zone: 'UTC+2'});
e = luxon.DateTime.fromISO("2023-01-01T11:30:00.000+00:00", {zone: 'UTC+1'});
i = luxon.Interval.fromDateTimes(s, e);
log(true);

// 12 '1 January 2023 at 12:15:00 GMT+2' '2023-01-01T10:15:00.000Z'
// 12 '1 January 2023 at 12:30:00 GMT+1' '2023-01-01T11:30:00.000Z'
// i.hasSame("hour") true expect true

s = luxon.DateTime.fromISO("2023-01-01T10:15:00.000+00:00", {zone: 'UTC+2'});
e = luxon.DateTime.fromISO("2023-01-01T10:15:00.000+00:00", {zone: 'UTC+1'});
i = luxon.Interval.fromDateTimes(s, e);
log(false);

// 12 '1 January 2023 at 12:15:00 GMT+2' '2023-01-01T10:15:00.000Z'
// 11 '1 January 2023 at 11:15:00 GMT+1' '2023-01-01T10:15:00.000Z'
// i.hasSame("hour") true expect false
})();

P.S.: Thank's for providing this lib!