Seems like this wasn't working too good.. https://3v4l.org/niJsq and in 8.2 this is only deprecation warning not an actual exception: https://3v4l.org/niJsq/rfc#vgit.master I wouldn't call this regression since it wasn't supported in the first place. https://3v4l.org/8aeug

https://3v4l.org/R5dN8 shows that the DateTime properties are only dynamically created by the constructor, but are not declared properties. That matches the documentation.

While I agree with @KapitanOczywisty that this is not a regression, but a mere deprecation, it still looks somewhat strange to me to get this error.

But before PHP 8.2 we had $d being a usable DateTime object

Nope, assigning to the "properties" never did anything, as is illustrated in https://3v4l.org/8aeug

PHP 8.2 now (merely) warns you of this, just like it does for normal user-land dynamic properties.

I don't think there is anything wrong here, and showing this warning is the expected result.

It's used for caching data via serialization and it worked before:

https://3v4l.org/DROXa

This the code above breaking in PHP 8.2:

https://3v4l.org/DROXa/rfc#vgit.master

I'm not personally impacted but opis/closure use this construction way for dates, so similar cache system will break.

It's used for caching data via serialization and it worked before:

Makes more sense now. This was already reported in: #8152 please especially read comment explaining background: #8152 (comment)

Following that issue __serialize/__unserialize methods were added, so starting from 8.2 code could look like this:

<?php
$d = (new ReflectionClass(DateTime::class))->newInstanceWithoutConstructor();

$d->__unserialize([
    'date' => '1990-01-17 10:28:07',
    'timezone_type' => 3,
    'timezone' => 'US/Pacific',
]);

var_dump($d, $d->format('c'));

https://3v4l.org/4poVG/rfc#vgit.master

Change requires checking the php version, but fixes issue once and for all. It could be worth noting this as breaking change just because it is apparently common pattern.

Yep, it would be possible. As in this case DateTime::class is actually a dynamic value that could be anything, it will just need to check method_exists($d, '__unserialize') and keep the previous method as fallback, but globally it would allow to port it for PHP 8.2.