DateTime modify with tz pattern should not update linked timezone

[marc-mabe]

Description

The following code: https://3v4l.org/EMU1K

<?php

$dt = new DateTime('2015-01-01 00:00:00+00:00');
var_dump($dt->format('c'));
var_dump($dt->modify('+1 s')->format('c'));

$dt = new DateTimeImmutable('2015-01-01 00:00:00+00:00');
var_dump($dt->format('c'));
var_dump($dt->modify('+1 s')->format('c'));

Resulted in this output:

string(25) "2015-01-01T00:00:00+00:00"
string(25) "2015-01-01T00:00:00+01:00"
string(25) "2015-01-01T00:00:00+00:00"
string(25) "2015-01-01T00:00:00+01:00"

But I expected this output instead:

string(25) "2015-01-01T00:00:00+00:00"
string(25) "2015-01-01T00:00:00+00:00"
string(25) "2015-01-01T00:00:00+00:00"
string(25) "2015-01-01T00:00:00+00:00"

As you can see it's modifying the time zone offset from +00:00 to +01:00 instead of doing nothing as s is not a valid unit according to https://www.php.net/manual/en/datetime.formats.relative.php.
It's interesting here because s is a common mistake as abbr. of second & sec where also ms and µs would be valid (which is another topic) but there is also no documented way of modifying the time zone using modify and in this particular case it's effectively moving backward instead of forward.

PHP Version

PHP 8.1.15 / PHP 8.2.2

Operating System

Linux

[hormus]

PHP 8.1.15, 8.2.2 and later this fix change offset of modify function #9891 (comment)

If unknow format new DateTime('2015-01-01 00:00:00' . '+1 s') is timezone offset 01:00 from php all.
tzcorrection "GMT"? [+-] hh valid syntax https://www.php.net/manual/en/datetime.formats.time.php

[marc-mabe]

@hormus You are right that the invalid unit is still ignored. Just tried it without any unit ->modify('+1') and now it's effectively setting the time zone.

Since 8.1.5 the following sets the time zone to +12:34 no matter what was set before:

$dt = new DateTime('2015-01-01 00:00:00+01:00');
var_dump($dt->format('c'));
var_dump($dt->modify('+12:34')->format('c'));

No sure if this is intended.

[hormus]

hello @marc-mabe , if you read the previous fix for the modify function for php 8.1.15, 8.2.2 and later it is now possible to change timezone.

[marc-mabe]

Hi @hormus,

The fix you linked is for setting the unix timestamp using @\d+ format where it's defined to be UTC. SO yes this will now set the timezone to UTC but I'm failing how this implies supporting [+-]\d+ format to set the time zone.

Please don't understand me wrong. I don't want to say this is definitely a bug but it's for sure a behavior change that I don't see documented anywhere.

[hormus]

If you open the link of the fix written in C++ code in that thread you can see the change from immutable to mutable "tmp_time" for timezone
Yes, the documentation needs improvement

[derickr]

This doesn't look right indeed. modify isn't meant to be able to set the timezone like this. I'll have a good look.

[derickr]

This was introduced in the fix for #9891: d19a70c