Time is adjusted incorrectly when using utc() during summer time

[tbaliukynas]

Describe the bug
Converting local date/time to UTC by calling utc() function sometimes provides incorrect results. This seems to be happening when the conversion is taking place during DST observation and the provided local date/time is a non-DST one (or vice versa).

For example, converting 2022-11-01T13:30:00+02:00 at the time of writing this issue results in 2022-11-01T12:30:00+00:00 where time is not being adjusted by a correct offset. Minimal reproducible example:

import dayjs from 'dayjs';
import utc from 'dayjs/plugin/utc';
import timezone from 'dayjs/plugin/timezone';
import localizedFormat from 'dayjs/plugin/localizedFormat';

dayjs.extend(utc);
dayjs.extend(timezone);
dayjs.extend(localizedFormat);

// Current time zone (summer time) and current local time for reference:
const tz = dayjs.tz.guess(); // Europe/Kiev
dayjs();                     // 2022-04-21T16:21:45+03:00

// UTC date/time converted to local:
const dateTimeDST = dayjs('2022-04-01T11:30:00Z').tz(tz); // 2022-04-01T14:30:00+03:00
const dateTime    = dayjs('2022-11-01T11:30:00Z').tz(tz); // 2022-11-01T13:30:00+02:00

// Local date/time converted to UTC:
dateTimeDST.utc(); // 2022-04-01T11:30:00+00:00
dateTime.utc();    // 2022-11-01T12:30:00+00:00 (time is shifted by only 1 hour)

Similar thing happens when trying to convert a DST date/time when the DST observation has ended:

import { useFakeTimers } from 'sinon';
useFakeTimers(new Date('2022-11-01T11:30:00Z').getTime());

const tz = dayjs.tz.guess();
const dateTimeDST = dayjs('2022-04-01T11:30:00Z').tz(tz); // 2022-04-01T14:30:00+03:00
dateTimeDST.utc();                                        // 2022-04-01T10:30:00+00:00 (time is shifted by 4 hours)

Expected behavior
Since UTC doesn't observe DST, I expect utc() to adjust hours by the same amount as it's shown in format(). In this case, 2022-11-01T13:30:00+02:00 should be converted to 2022-11-01T11:30:00+00:00 (minus 2 hours) during DST observation and 2022-04-01T14:30:00+03:00 should be converted to 2022-11-01T11:30:00+00:00 (minus 3 hours) when the DST observation ends.

I can work around this issue by adjusting the minutes manually:

const tz = dayjs.tz.guess();

const dateTimeDST = dayjs('2022-04-01T11:30:00Z').tz(tz);
const dateTime = dayjs('2022-11-01T11:30:00Z').tz(tz);

dateTimeDST.utc(true).add(-dayjs().utcOffset(), 'minute');
dateTime.utc(true).add(-dayjs().utcOffset(), 'minute');

Information

• Day.js Version: 1.11.1
• OS: Windows 10, version 20H2
• Browser: Mozilla Firefox 99.0.1 / Google Chrome 101.0.4951.41 / Node.js 14.18.2
• Time zone: Europe/Vilnius (UTC offset: +02:00; DST: +03:00)

[bhavin-a]

The same is happening to me as well. Any resolutions?

[tbaliukynas]

This was fixed by #1448. The examples shown above are not reproducible when using v1.11.2 of Day.js. Closing the issue.