Different diff->days between php 8.0.28 and php 8.1

[szpakucjusz]

Description

Good morning,
Link with different php versions comparison: https://3v4l.org/mgOoE#v8.1.0
The following code returns the difference for DateInterval->days:

<?php 
$d = new DateTime('-1 day');
$diff = $d->diff(new DateTime('-6 days') );
echo "\n";
print_r($diff);
echo $diff->days;
echo "\n";

Resulted in this output for php 8.0.28:

DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 4
    [h] => 23
    [i] => 59
    [s] => 59
    [f] => 0.999994
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 1
    [days] => 5
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)

But In PHP 8.1.0:

DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 4
    [h] => 23
    [i] => 59
    [s] => 59
    [f] => 0.99999
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 1
    [days] => 4
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)

PHP Version

Change between PHP 8.0.28 and 8.1

Operating System

No response

[hormus]

@szpakucjusz The expected result between two dates that have equal microseconds is zero microseconds. The diff function from php 8.1 says 4 days, the correct result. Also the difference between two dates is useful when you have to do something, hardly if memorized it will have a good result if created by php 8.1 and reproduced in php <= 8.1

<?php
$now1 = new DateTime('now', new DateTimeZone('Europe/Berlin'));
$now2 = new DateTime('now', new DateTimeZone('Europe/Berlin'));
$from = new DateTime('-1 day ' . $now1->format('Y-m-d H:i:s.' . $now1->format('u')), new DateTimeZone('Europe/Berlin')); // $to > microsecond
$to = new DateTime('-6 day ' . $now2->format('Y-m-d H:i:s.' . $now2->format('u')), new DateTimeZone('Europe/Berlin')); // $from < microsecond
$diff = $to->diff($from);
echo "\n";
print_r($diff);
echo $diff->days;
echo "\n";
//var_dump($from, $to);
//var_dump($from->sub($diff)); // php 8.1 is 4 day or php 8.0 is 5 day expected result = $to

[szpakucjusz]

@hormus
Sir, I am afraid that I didn't understand Your response.
Same PHP code for different PHP versions gives me different results.
And Your code also which is tested here:
https://3v4l.org/qAdXo
Is there any possibility to keep the results same between updating PHP Version?

[hormus]

https://www.php.net/manual/en/class.dateinterval.php
More specifically, the information in an object of the DateInterval class is an instruction to get from one date/time to another date/time. This process is not always reversible.
if $to <= $from (between date positive)

$from->sub($diff); // expected result for all php version

Now $from === $to

[ranvis]

Clearer example for me from what title says: https://3v4l.org/O9u7D

<?php
$d = new DateTime('2023-03-10');
$diff = $d->diff(new DateTime('2023-03-10 -1 day +1 microsecond') );
echo $diff->days, "\n";

https://www.php.net/manual/en/class.dateinterval.php#dateinterval.props.days
days
If the DateInterval object was created by DateTimeImmutable::diff() or DateTime::diff(), then this is the total number of full days between the start and end dates. Otherwise, days will be false.

I recently had read other dev saying that the doc is not a spec, but I think 8.1 behavior is correct, and this is rather a fixed bug in 904933e or somewhere.

Yet, reading the diff, I found that with different timezones this still yields 1 as before:

<?php
$d = new DateTime('2023-03-10 +00:00');
$diff = $d->diff(new DateTime('2023-03-10 +01:00 + 1 hour -1 day +1 microsecond') );
echo $diff->days, "\n";
var_dump($diff);

[szpakucjusz]

Thank You for current responses.
@ranvis wrote and I think that You are right:

I recently had read other dev saying that the doc is not a spec, but I think 8.1 behavior is correct, and this is rather a fixed bug in 904933e or somewhere.

[derickr]

The PHP 8.1 and later result (4 days) is the correct one, so there is no bug here.

[finwe]

Shouldn't this then be documented as a BC breaking change, anyway?

[ranvis]

@derickr The calculation of days between different time zones doesn't take microseconds into consideration (tested on PHP 8.2.4):

<?php
$d = new DateTime('2023-03-10 +00:00');
$diff = $d->diff(new DateTime('2023-03-10 +01:00 + 1 hour -1 day +1 microsecond') );
echo $diff->days, "\n";
var_dump($diff);

1
object(DateInterval)#3 (10) {
  ["y"]=>
  int(0)
  ["m"]=>
  int(0)
  ["d"]=>
  int(0)
  ["h"]=>
  int(23)
  ["i"]=>
  int(59)
  ["s"]=>
  int(59)
  ["f"]=>
  float(0.999999)
  ["invert"]=>
  int(1)
  ["days"]=>
  int(1)
  ["from_string"]=>
  bool(false)
}