[php-src] Issue #24735: DateTime::setTime() in the repeated hour of Europe/Dublin moves to the later occurrence (an hour ahead)

Issue: https://github.com/php/php-src/issues/24735 Author: zoispag ### Description On the day clocks go back, DateTime::setTime() on a time in the repeated hour in Europe/Dublin moves it to the *second* occurrence of the wall time, an hour later, even when the new time is only seconds away on the same wall clock. Europe/London, at the same instant and with the same UTC offsets, keeps the first occurrence. The following code: ```php <?php foreach (['Europe/Dublin', 'Europe/London', 'Europe/Amsterdam'] as $tz) { $d = (new DateTimeImmutable('2026-10-25 00:10:30 UTC'))->setTimezone(new DateTimeZone($tz)); $e = $d->setTime((int) $d->format('H'), 10, 59); printf("%-16s %s -> %s (%+ds)\n", $tz, $d->format('Y-m-d H:i:s T'), $e->format('H:i:s T'), $e->getTimestamp() - $d->getTimestamp()); } ``` Resulted in this output: ``` Europe/Dublin 2026-10-25 01:10:30 IST -> 01:10:59 GMT (+3629s) Europe/London 2026-10-25 01:10:30 BST -> 01:10:59 BST (+29s) Europe/Amsterdam 2026-10-25 02:10:30 CEST -> 02:10:59 CEST (+29s) ``` But I expected this output instead: ``` Europe/Dublin 2026-10-25 01:10:30 IST -> 01:10:59 IST (+29s) Europe/London 2026-10-25 01:10:30 BST -> 01:10:59 BST (+29s) Europe/Amsterdam 2026-10-25 02:10:30 CEST -> 02:10:59 CEST (+29s) ``` Dublin and London both switch from UTC+1 to UTC+0 at 01:00 UTC on 25 October 2026, so I'd expect them to behave the same. The difference seems to be that the tz database models Irish time with a negative DST offset: IST (UTC+1) is the standard time and GMT is flagged as DST. So keeping or choosing a DST state when resolving the ambiguous wall time gives the opposite result to every other zone. Anything that rounds a time with setTime(), modify('...') or date libraries built on them (e.g. Carbon's endOfMinute()) is affected. We hit it in production: Laravel's scheduler computed "end of the current minute" this way, so during that hour each run waited an hour instead of seconds. That bug is being fixed on the Laravel side (https://github.com/laravel/framework/pull/62197), but the root cause looks like it's here. ### PHP Version ``` PHP 8.5.12 (cli) (built: Oct 19 2026 17:02:46) (ZTS) timezone_version_get(): 2026.5 ``` ### Operating System macOS, and Debian GNU/Linux 13 (trixie) with PHP 8.5.12 NTS