DateTime and wrong ISO 8601 week numbers

[Nekuin]

Description

The following code:

<?php
        $dates = ["2024-12-28", "2024-12-29", "2024-12-30", "2024-12-31", "2025-01-01"];
        foreach ($dates as $date) {
            $d = new \DateTime($date);
            echo $date . " => " . $d->format("Y-W") . PHP_EOL;
        }

Resulted in this output:

2024-12-28 => 2024-52

2024-12-29 => 2024-52

2024-12-30 => 2024-01

2024-12-31 => 2024-01

2025-01-01 => 2025-01

But I expected this output instead:

2024-12-28 => 2024-52

2024-12-29 => 2024-52

2024-12-30 => 2025-01

2024-12-31 => 2025-01

2025-01-01 => 2025-01

2024-12-30 and 2024-12-31 week numbers seem to be wrong

PHP Version

PHP 8.3.13

Operating System

Ubuntu 22.04

[Nekuin]

ah I actually just figured out I'm supposed to use 'o' format here

https://www.php.net/manual/en/datetime.format.php ISO 8601 week-numbering year. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead.

closing this!