DateTimeInterface::format reset week(W) to 01 in last days of year

[RicardoSette]

Description

The following code:

<?php
date_default_timezone_set('UTC');
$time = 1735516799;//Unix timestamps in seconds from Sunday, 29 December 2024 23:59:59
echo json_encode([
    '$time' => $time,
    'date "Y-m-d H:i:s"' => date('Y-m-d H:i:s', $time),
    'date "Y-m (W)"' => date('Y-m (W)', $time),
    'date "o"' => date('o', $time),
], JSON_PRETTY_PRINT) . PHP_EOL;
$time++;//Unix timestamps in seconds from Monday, 30 December 2024 00:00:00
echo json_encode([
    '$time' => $time,
    'date "Y-m-d H:i:s"' => date('Y-m-d H:i:s', $time),
    'date "Y-m (W)"' => date('Y-m (W)', $time),
    'date "o"' => date('o', $time),
], JSON_PRETTY_PRINT) . PHP_EOL;

Resulted in this output:

{
    "$time": 1735516799,
    "date \"Y-m-d H:i:s\"": "2024-12-29 23:59:59",
    "date \"Y-m (W)\"": "2024-12 (52)",
    "date \"o\"": "2024"
}
{
    "$time": 1735516800,
    "date \"Y-m-d H:i:s\"": "2024-12-30 00:00:00",
    "date \"Y-m (W)\"": "2024-12 (01)",
    "date \"o\"": "2025"
}

But I expected this output instead:

{
    "$time": 1735516799,
    "date \"Y-m-d H:i:s\"": "2024-12-29 23:59:59",
    "date \"Y-m (W)\"": "2024-12 (52)",
    "date \"o\"": "2024"
}
{
    "$time": 1735516800,
    "date \"Y-m-d H:i:s\"": "2024-12-30 00:00:00",
    "date \"Y-m (W)\"": "2024-12 (52)",
    "date \"o\"": "2024"
}

For the Operating System the week remains 52.

% date +"So this is week: %U epoch: %s" && uname -a
So this is week: 52 epoch: 1735572050
FreeBSD php-test 14.1-RELEASE-p5 FreeBSD 14.1-RELEASE-p5 GENERIC amd64

% php -v
PHP 8.2.24 (cli) (built: Oct 31 2024 02:19:49) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.2.24, Copyright (c) Zend Technologies

The same error occurs in docker Linux (image: hyperf-skeleton):

# date +"So this is week: %U epoch: %s" && uname -a
So this is week: 52 epoch: 1735572065
Linux 379e835bc8d6 5.15.49-linuxkit-pr #1 SMP PREEMPT Thu May 25 07:27:39 UTC 2023 aarch64 Linux

# php -v
PHP 8.3.8 (cli) (built: Jun  6 2024 17:04:22) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.8, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.8, Copyright (c), by Zend Technologies

PHP Version

PHP 8.2.24 and 8.3.8

Operating System

FreeBSD 14.1-RELEASE-p5

[cmb69]

A week has seven days. If your OS thinks a week could be longer, it would be wrong (I guess that is timezone related though).

Anyhow, PHP is correct here: 2024-12-30 is the first day of week 1 of 2025.

[RicardoSette]

In the PHP documentation (https://www.php.net/manual/en/datetime.format.php) we have:

Character: W
Description: ISO 8601 week number of year, weeks starting on Monday
Example: 42 (the 42nd week in the year)

How is it possible on December 30, 2024 to indicate the week (W) as 01? The same for tomorrow, December 31, 2024 where it will indicate the week (W) as 01. It is still the date of 2024, it should indicate the week referring to 2024 and not to 2025. In both cases it should keep week (W) 52 or add week (W) 53, I believe this rule would be defined in some ISO 8601.

See the test on OSX:

% date +"So this is week: %U epoch: %s" && uname -a
So this is week: 52 epoch: 1735578346
Darwin xyz.local 23.5.0 Darwin Kernel Version 23.5.0: Wed May  1 20:19:05 PDT 2024; root:xnu-10063.121.3~5/RELEASE_ARM64_T8112 arm64

Is Apple's operating system wrong in saying that the week is 52 and the PHP library would be correct in saying that the week is 01?

If all OS thinks a week could be longer or egual the last week all OS wrong? 🤔

[damianwadley]

The key here is that W means the ISO 8601 week number. That is not the same as the human being week number.
https://en.wikipedia.org/wiki/ISO_week_date

[cmb69]

Also note that W always belongs to o, but not to Y.

[MorganLOCode]

Also note that Darwin's date command will give the same result if %V (ISO calendar week number) were used instead of %U (Western traditional calendar number); Darwin's analogue of PHP's o that @cmb69 mentions would be %G. So, for example:

% date +"So this is week: %V of year: %G epoch: %s" && uname -a
So this is week: 01 of year: 2025 epoch: 1735578346
% date +"So this is week: %U of year: %Y epoch: %s" && uname -a
So this is week: 52 of year: 2024 epoch: 1735578346