PHP 8.1: DateTimeZone::getTransitions() change

[autotutorial]

This is a follow-up to #49038.

PHP 8.1 getTransitions, The data format that the library uses has changed, and will now only contain a list of transitions up until the last time the *rules* changed.
​https://bugs.php.net/bug.php?id=80963

[Rarst]

From quick check we only use transition list in options for informational output about next upcoming transition for the chosen time zone.

So, assuming this lands in stable PHP release, we would need either alternate way to calculate next transition or drop this output.

[GaryJ]

According the PHP bug report, this was fixed in 8.1.0beta3 / 8.1.0RC1, so can this be closed?

[SergeyBiryukov]

Yes, it looks like this was ​fixed in PHP 8.1.0beta3 and no further actions are needed for WordPress core at this time.

[autotutorial]

<?php
$tz = new DateTimeZone('America/Chicago');
$start = 1320562800;
$end = 1357020000;
$transitions = $tz->getTransitions($start, $end);
var_dump($transitions);
/*array(4) {
  [0]=>
  array(5) {
    ["ts"]=>
    int(1320562800)
    ["time"]=>
    string(24) "2011-11-06T07:00:00+0000"
    ["offset"]=>
    int(-21600)
    ["isdst"]=>
    bool(false)
    ["abbr"]=>
    string(3) "CST"
  }
  [1]=>
  array(5) {
    ["ts"]=>
    int(1320562800)
    ["time"]=>
    string(24) "2011-11-06T07:00:00+0000"
    ["offset"]=>
    int(-21600)
    ["isdst"]=>
    bool(false)
    ["abbr"]=>
    string(3) "CST"
  }
  [2]=>
  array(5) {
    ["ts"]=>
    int(1331452800)
    ["time"]=>
    string(24) "2012-03-11T08:00:00+0000"
    ["offset"]=>
    int(-18000)
    ["isdst"]=>
    bool(true)
    ["abbr"]=>
    string(3) "CDT"
  }
  [3]=>
  array(5) {
    ["ts"]=>
    int(1352012400)
    ["time"]=>
    string(24) "2012-11-04T07:00:00+0000"
    ["offset"]=>
    int(-21600)
    ["isdst"]=>
    bool(false)
    ["abbr"]=>
    string(3) "CST"
  }
}

PHP 8.1.0 - 8.1.5
array(1) {
  [0]=>
  array(5) {
    ["ts"]=>
    int(1320562800)
    ["time"]=>
    string(24) "2011-11-06T07:00:00+0000"
    ["offset"]=>
    int(-18000)
    ["isdst"]=>
    bool(true)
    ["abbr"]=>
    string(3) "CDT"
  }
}
*/

​https://github.com/WordPress/WordPress/blob/master/wp-admin/options-general.php#L284

$transitions[1] ? :)

[Rarst]

#55861 was marked as a duplicate.

[Rarst]

As of right now this should be fixed, starting with PHP 8.1.6. See ​https://3v4l.org/dT94b

It does look like future transitions weren't reported for PHP 8.1.0 to 8.1.5 inclusive.

I am not sure if that's anything we can do something about. Generally we are at mercy of PHP language providing timezone data to use.

We could not report DST detection, for PHP versions we know do not give us the data, but I don't think there is much precedent in core for such logic.

[Rarst]

I've tried to see if we can fish DST info out of DateTimeZone::listAbbreviations(), but the inconsistencies between PHP versions are even worse (and that's just for two time zones I tried) ​https://3v4l.org/qupTB#veol

[autotutorial]

Actually you can check by creating a date with the DateTime class and php decides when DST or ST or other offset exists transition that does not use 3600 seconds, also we have (wordpress) never checked for coincidence if the timezone parameter is offset since the timezone is theoretically set to UTC by the WordPress core.
In this RFC change the preferred mode to php, but previously used a reverse default mode.

<?php

$tz = new DateTimeZone('Europe/Rome');
$date = new DateTime('now', $tz);
$dst = (bool) $date->format('I');
$transitions = $date->getTransitions($date->format('U'));
//$transitions is same transitions of $date?

​https://github.com/WordPress/WordPress/blob/master/wp-settings.php#L68 and rfc php force DST ​https://wiki.php.net/rfc/datetime_and_daylight_saving_time

Or example 2 for one arg transitions and array > 1: ​https://3v4l.org/NiY8q

[Rarst]

Replying to autotutorial:

Actually you can check by creating a date with the DateTime class and php decides when DST or ST or other offset exists

Checking if timezone is in DST right now doesn't help us to reimplement this. The current output is if time zone is changing to/from DST during a year, which is determined by checking for a future transition event.

Checking if time zone is or isn't in DST now doesn't tell that, because it might be permanent state of it. Some time zones don't have DST, some are permanently in DST. Or at least that's the real world situation, sans deep dive to check how PHP interprets that.

Maybe we should just drop the not having DST case altogether and rather not mention anything than risk incorrect and confusing info.