Bug #81072 [Ver->Nab]: Incorrect behavior of DateTime->modify across DST changes

Edit report at https://bugs.php.net/bug.php?id=81072&edit=1 ID: 81072 Updated by: derick@php.net Reported by: ph-bugs at allenjb dot me dot uk Summary: Incorrect behavior of DateTime->modify across DST changes -Status: Verified +Status: Not a bug Type: Bug Package: Date/time related PHP Version: 8.0.6 Block user comment: N Private report: N New Comment: Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php The result is, although perhaps surprising, expected. Just like any other overflow that happens, PHP moves the wall time forwards to what is possible. It is the same effect as doing: echo (new \DateTime("2022-03-31"))->modify("-1 month")->format('Y-m-d H:i:s O T'), "\n"; which outputs: 2022-03-03 00:00:00 +0000 UTC There is no February 31st. The 31st day since February 0th, is March 3rd. The same happens in this case: new \DateTimeImmutable('2022-03-13 03:00:00', new \DateTimeZone('America/Los_Angeles'))->modify('-5 minutes'); This resolves first to 2022-03-13 02:55:00 (PST), which does not exist. 2h and 55 minutes after the start of the day (2022-03-13 00:00:00 PST) is 2022-03-13 03:55:00 PDT. Previous Comments: ------------------------------------------------------------------------ [2022-04-29 09:47:31] r dot aalderink at visymo dot com Ran into the same issue, I have a very simple oneliner to reproduce it: ----- echo (new \DateTime('2022-03-13 03:00:00', new \DateTimeZone('America/Los_Angeles')))->modify('-5 minutes')->format('Y-m-d H:i:s'); ----- This becomes: 2022-03-13 03:55:00 Expected: 2022-03-13 01:55:00 ------------------------------------------------------------------------ [2021-10-01 18:25:40] cmb@php.net > As you can see, when working backwards with ->modify("-1 hour") > DateTime fails to properly handle the DST change and keeps pushing > the time forward to 03:00:00 So this about <https://3v4l.org/XWdf2>, right? If so, yes, that doesn't look right. ------------------------------------------------------------------------ [2021-07-30 10:53:24] antonino dot spampinato86 at gmail dot com Sorry change $dtWithout_test1 = incrementWithoutSwitch($dtWithout, $invert); to $dtWithout = incrementWithoutSwitch($dtWithout, $invert); The bug is there, the expected result is not obtained. :-) ------------------------------------------------------------------------ [2021-07-30 10:43:46] antonino dot spampinato86 at gmail dot com This is the refined version proposed. DST transition bug for modify function exists. Bug 74224 mentions that from php 8.1 that diff function has been changed and supports time not conversion to UTC and this makes time or date calculations consistent with local time. Actually diff function also suffers from DST or ST problems, If you deem it necessary I will also show it to you. function incrementWithSwitch($date, $invert) { $timezone = $date->getTimezone(); $date = $date->setTimezone(new \DateTimeZone('UTC')); $date = $date->modify(($invert ? '-' : '+') . '1 hour'); $date = $date->setTimezone($timezone); //$date = $date->setTime((int)$date->format('H'), 0); return $date; } function incrementWithoutSwitch($date, $invert) { $date = $date->modify(($invert ? '-' : '+') . '1 hour'); return $date; } $tz = new \DateTimeZone('Europe/London'); $dtWith = \DateTimeImmutable::createFromFormat('!Y-m-d H:i:s', '2021-03-28 04:00:00', $tz); $dtWithout = $dtWith; $invert = true; $string = 'Start ' . $dtWith->format('Y-m-d H:i:s Z') . PHP_EOL; for ($i = 0; $i < 4; $i++) { $string .= "Round {$i}: "; $dtWith = incrementWithSwitch($dtWith, $invert); $dtWithout_test1 = incrementWithoutSwitch($dtWithout, $invert); $string .= 'With switch: ' . $dtWith->format('Y-m-d H:i:s Z'); $string .= ' :: Without switch: '. $dtWithout->format('Y-m-d H:i:s Z') . PHP_EOL; } $string .= '---' . PHP_EOL; $dtWith = \DateTimeImmutable::createFromFormat('!Y-m-d H:i:s', '2021-03-27 23:00:00', $tz); $dtWithout = $dtWith; $invert = false; $string .= 'Start ' . $dtWith->format('Y-m-d H:i:s Z') . PHP_EOL; for ($i = 0; $i < 4; $i++) { $string .= "Round {$i}: "; $dtWith = incrementWithSwitch($dtWith, $invert); $dtWithout = incrementWithoutSwitch($dtWithout, $invert); $string .= 'With switch: ' . $dtWith->format('Y-m-d H:i:s Z'); $string .= ' :: Without switch: ' . $dtWithout->format('Y-m-d H:i:s Z') . PHP_EOL; } print($string); Expected: Start 2021-03-28 04:00:00 3600 Round 0: With switch: 2021-03-28 03:00:00 3600 :: Without switch: 2021-03-28 03:00:00 3600 Round 1: With switch: 2021-03-28 02:00:00 3600 :: Without switch: 2021-03-28 02:00:00 3600 Round 2: With switch: 2021-03-28 00:00:00 0 :: Without switch: 2021-03-28 00:00:00 3600 Round 3: With switch: 2021-03-27 23:00:00 0 :: Without switch: 2021-03-27 23:00:00 3600 --- Start 2021-03-27 23:00:00 0 Round 0: With switch: 2021-03-28 00:00:00 0 :: Without switch: 2021-03-28 00:00:00 0 Round 1: With switch: 2021-03-28 02:00:00 3600 :: Without switch: 2021-03-28 02:00:00 3600 Round 2: With switch: 2021-03-28 03:00:00 3600 :: Without switch: 2021-03-28 03:00:00 3600 Round 3: With switch: 2021-03-28 04:00:00 3600 :: Without switch: 2021-03-28 04:00:00 3600 Actual: Start 2021-03-28 04:00:00 3600 Round 0: With switch: 2021-03-28 03:00:00 3600 :: Without switch: 2021-03-28 04:00:00 3600 Round 1: With switch: 2021-03-28 02:00:00 3600 :: Without switch: 2021-03-28 04:00:00 3600 Round 2: With switch: 2021-03-28 00:00:00 0 :: Without switch: 2021-03-28 04:00:00 3600 Round 3: With switch: 2021-03-27 23:00:00 0 :: Without switch: 2021-03-28 04:00:00 3600 --- Start 2021-03-27 23:00:00 0 Round 0: With switch: 2021-03-28 00:00:00 0 :: Without switch: 2021-03-28 00:00:00 0 Round 1: With switch: 2021-03-28 02:00:00 3600 :: Without switch: 2021-03-28 02:00:00 3600 Round 2: With switch: 2021-03-28 03:00:00 3600 :: Without switch: 2021-03-28 03:00:00 3600 Round 3: With switch: 2021-03-28 04:00:00 3600 :: Without switch: 2021-03-28 04:00:00 3600 ------------------------------------------------------------------------ [2021-05-30 04:22:13] php-bugs at lists dot php dot net No feedback was provided. The bug is being suspended because we assume that you are no longer experiencing the problem. If this is not the case and you are able to provide the information that was requested earlier, please do so and change the status of the bug back to "Re-Opened". Thank you. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=81072 -- Edit this bug report at https://bugs.php.net/bug.php?id=81072&edit=1