DateTime::diff miscalculation is same time zone of different type

[jabelli]

Description

Something appears amiss when DateTime::diff is used on two dates in the same time zone with different time zone types in DST
Possibly related to #81263
The following code:

<?php

$foo = new DateTime('2022-06-08 09:15:00', new DateTimeZone('-04:00'));
$bar = new DateTime('2022-06-08 09:15:00', new DateTimeZone('US/Eastern'));
var_dump($foo->diff($bar));

Resulted in this output:

  ["y"]=>
  int(-1)
  ["m"]=>
  int(11)
  ["d"]=>
  int(30)
  ["h"]=>
  int(23)
  ["i"]=>
  int(0)
  ["s"]=>
  int(0)
  ["f"]=>
  float(0)
  ["weekday"]=>
  int(0)
  ["weekday_behavior"]=>
  int(0)
  ["first_last_day_of"]=>
  int(0)
  ["invert"]=>
  int(0)
  ["days"]=>
  int(0)
  ["special_type"]=>
  int(0)
  ["special_amount"]=>
  int(0)
  ["have_weekday_relative"]=>
  int(0)
  ["have_special_relative"]=>
  int(0)
}

But I expected this output instead:

  ["y"]=>
  int(0)
  ["m"]=>
  int(0)
  ["d"]=>
  int(0)
  ["h"]=>
  int(0)
  ["i"]=>
  int(0)
  ["s"]=>
  int(0)
  ["f"]=>
  float(0)
  ["weekday"]=>
  int(0)
  ["weekday_behavior"]=>
  int(0)
  ["first_last_day_of"]=>
  int(0)
  ["invert"]=>
  int(0)
  ["days"]=>
  int(0)
  ["special_type"]=>
  int(0)
  ["special_amount"]=>
  int(0)
  ["have_weekday_relative"]=>
  int(0)
  ["have_special_relative"]=>
  int(0)
}

Linky

If you change the month to 01, you get the expected difference of 0.

PHP Version

PHP 8.1.6

Operating System

Windows 10

[hormus]

Since php 8.1.0 diff compares time zone type equality, in some circumstances although type 1 (numeric time zone) or type 3 (literal time zone) may produce a date with daylight saving time setting. (it means that although type 3 time zone converted to numerical sequence of seconds is exactly the same as type 1 time zone, as php decides whether to consider daylight saving time or not).

https://wiki.php.net/rfc/datetime_and_daylight_saving_time

It is difficult to document and too much information is confusing, certainly a good encoding is to use the same type timezone for the two date objects requested by diff.
This change https://bugs.php.net/bug.php?id=81458

$foo is big to $bar, inverter to $bar->diff($foo));

<?php

date_default_timezone_set('America/New_York');
$foo = new DateTime('2022-06-08 09:15:00', new DateTimeZone('-04:00'));
$bar = new DateTime('2022-06-08 09:15:00', new DateTimeZone('America/New_York'));
var_dump($foo->format('U'), $bar->format('U'), $bar->diff($foo));
/*string(10) "1654694100"
string(10) "1654694100"
object(DateInterval)#3 (16) {
  ["y"]=>
  int(0)
  ["m"]=>
  int(0)
  ["d"]=>
  int(0)
  ["h"]=>
  int(1)
  ["i"]=>
  int(0)
  ["s"]=>
  int(0)
  ["f"]=>
  float(0)
  ["weekday"]=>
  int(0)
  ["weekday_behavior"]=>
  int(0)
  ["first_last_day_of"]=>
  int(0)
  ["invert"]=>
  int(0)
  ["days"]=>
  int(0)
  ["special_type"]=>
  int(0)
  ["special_amount"]=>
  int(0)
  ["have_weekday_relative"]=>
  int(0)
  ["have_special_relative"]=>
  int(0)
}*/
?>

Note* US/Eastern https://www.php.net/manual/en/timezones.others.php

before php 8.1 the comparison was for the date represented by the conversion to UTC

<?php

date_default_timezone_set('America/New_York');
$foo = new DateTime('2022-06-08 09:15:00', new DateTimeZone('-04:00'));
$bar = new DateTime('2022-06-08 09:15:00', new DateTimeZone('America/New_York'));
var_dump($foo->format('U'), $bar->format('U'), $bar->diff($foo)); //Before php 8.1.0 2022-06-08 13:15:00 - 2022-06-08 13:15:00 = 0

$foo = new DateTime('2022-06-08 09:15:00', new DateTimeZone('America/New_York'));
$bar = new DateTime('2022-06-08 09:15:00', new DateTimeZone('America/New_York'));
var_dump($foo->format('U'), $bar->format('U'), $bar->diff($foo)); //from php 8.1.0 2022-06-08 9:15:00 - 2022-06-08 9:15:00 = 0

?>

[derickr]

Fixed in timelib: derickr/timelib#128, and the fix will make it into PHP once timelib gets merged again.

[ToshY]

@derickr Could you give an estimation on when this (timelib fix) actually gets merged?

[derickr]

Just now :-)

[jabelli]

Create new for 8.2 or reopen this one? I just tested 8.2β1:

object(DateInterval)#3 (10) {
  ["y"]=>
  int(-1)
  ["m"]=>
  int(11)
  ["d"]=>
  int(30)
  ["h"]=>
  int(23)
  ["i"]=>
  int(0)
  ["s"]=>
  int(0)
  ["f"]=>
  float(0)
  ["invert"]=>
  int(0)
  ["days"]=>
  int(0)
  ["from_string"]=>
  bool(false)
}