Wrong DateInterval when going from summer time to winter time

[Geekimo]

Description

The following code:

<?php

$timezone = new \DateTimeZone('Europe/Paris');

$periodStart = (new \DateTimeImmutable('2024-10-21'))->setTimezone($timezone)->setTime(00, 00, 00);
$periodEnd = (new \DateTimeImmutable('2024-10-27'))->setTimezone($timezone)->setTime(23, 59, 59);

var_dump($periodStart);
var_dump($periodEnd);

var_dump($timezone->getOffset($periodStart));
var_dump($timezone->getOffset($periodEnd));

var_dump($periodStart->diff($periodEnd)->format('%y years %m months %a days %H hours %I minutes %s seconds'));

Resulted in this output:

object(DateTimeImmutable)#2 (3) {
  ["date"]=>
  string(26) "2024-10-21 00:00:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
object(DateTimeImmutable)#3 (3) {
  ["date"]=>
  string(26) "2024-10-27 23:59:59.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
int(7200) // UTC+2
int(3600) // UTC+1
string(54) "0 years 0 months 6 days 23 hours 59 minutes 59 seconds"

But I expected this output instead:

object(DateTimeImmutable)#2 (3) {
  ["date"]=>
  string(26) "2024-10-21 00:00:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
object(DateTimeImmutable)#3 (3) {
  ["date"]=>
  string(26) "2024-10-27 23:59:59.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
int(7200)
int(3600)
string(54) "0 years 0 months 7 days 0 hours 59 minutes 59 seconds"

I did the same test using winter to summer time switch and the result is good.

<?php

$timezone = new \DateTimeZone('Europe/Paris');

$periodStart = (new \DateTimeImmutable('2024-03-25'))->setTimezone($timezone)->setTime(00, 00, 00);
$periodEnd = (new \DateTimeImmutable('2024-03-31'))->setTimezone($timezone)->setTime(23, 59, 59);

var_dump($periodStart);
var_dump($periodEnd);

var_dump($timezone->getOffset($periodStart));
var_dump($timezone->getOffset($periodEnd));

var_dump($periodStart->diff($periodEnd)->format('%y years %m months %a days %H hours %I minutes %s seconds'));

Output:

object(DateTimeImmutable)#2 (3) {
  ["date"]=>
  string(26) "2024-03-25 00:00:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
object(DateTimeImmutable)#3 (3) {
  ["date"]=>
  string(26) "2024-03-31 23:59:59.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}
int(3600)
int(7200)
string(54) "0 years 0 months 6 days 22 hours 59 minutes 59 seconds"

3v4l.org links:

• Winter time to summer time: https://3v4l.org/AbF3B#v8.2.21 (good interval)
• Summer time to winter time: https://3v4l.org/5dsek#v8.2.21 (bad interval)
• Without DST transition: https://3v4l.org/eCGdj#v8.2.21 (same interval as summer to winter)

PHP Version

PHP 8.2.21 and up

Operating System

No response

[hormus]

It's not a bug.
You can set manual convert to UTC (DST or ST Europe/Paris +2 or +1)

<?php

$timezone = new \DateTimeZone('UTC');

$periodStart = (new \DateTimeImmutable('2024-10-20 22:00:00', $timezone));
$periodEnd = (new \DateTimeImmutable('2024-10-27 22:59:59', $timezone));

$timezone = new \DateTimeZone('Europe/Paris');
$periodStart = $periodStart->setTimezone($timezone);
$periodEnd = $periodEnd->setTimezone($timezone);

var_dump($periodStart->diff($periodEnd)->format('%y years %m months %a days %H hours %I minutes %s seconds'), $periodEnd->setTimezone(new DateTimeZone('UTC')));
?>

From PHP >= 8.2.6 expected result:

string(54) "0 years 0 months 6 days 23 hours 59 minutes 59 seconds"
object(DateTimeImmutable)#5 (3) {
  ["date"]=>
  string(26) "2024-10-27 22:59:59.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}

Or from PHP < 8.2.6 expected result:

string(54) "0 years 0 months 6 days 24 hours 59 minutes 59 seconds"
object(DateTimeImmutable)#5 (3) {
  ["date"]=>
  string(26) "2024-10-27 22:59:59.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}

It's never 7 days.

[Geekimo]

@hormus I don't get your point.
With the same timezone.
If I set a period, which has between his bounds a transition from winter to summertime, calculation is correct.
If I do the same transition, but from summertime to winter time, calculation is incorrect.
How could this not be a bug ?
Europe/Paris is a type 3 timezone, which according to https://wiki.php.net/rfc/datetime_and_daylight_saving_time has proper calculation rules, which should be applied in the current case.

[hormus]

Hi @Geekimo, the interval from 00:00:00 to 23:59:59 is 23:59:59 if with UTC time zone. If with forward transition "start daylight saving time" 02:00:00 is 03:00:00 local time.

02:00:00 does not exist for "daylight saving time". So applying this formula from 00:00:00 to 23:59:59 "24:59:59 hours DST end" -01:00:00 is 23:59:59.

[Geekimo]

@hormus Ok, so you didn't get my point.
Let me reformulate, it may be clearer this way. 😅

I have a recurring task, each week, where I need to have the exact number of years, months, days, hours, minutes and seconds between monday 00:00:00 and sunday 23:59:59, because it matters to my task.

On traditional weeks, like the previous one, which has no DST transition, I have 0 years 0 months 6 days 23 hours 59 minutes 59 seconds, which is perfectly normal, and is the result that I await.
When, I have a DST transition, from winter time to summer time, the same exact code will return 0 years 0 months 6 days 22 hours 59 minutes 59 seconds. This is what I expect this code to do and it's perfectly normal, as we remove one hour in this particular week.

Then, when I have the opposite DST transitoin, from summer time to winter time, like this week, the same exact code will return 0 years 0 months 6 days 23 hours 59 minutes 59 seconds, like there was no transition. This is not what I expect this code to do, because we add one hour in this particular week. (At 3 o'clock on sunday morning, it's 2am again).

What should happen is that my code should return 0 years 0 months 7 days 0 hours 59 minutes 59 seconds.
If you look closely at the code I provided, I apply the timezone before changing time, and setting timezone as seconde parameter of \DateTimeImmutable::__construct(...) has no impact.

[cmb69]

Indeed, looks like a bug to me. Interestingly, PHP 8.2.0 - 8.2.5 behaved roughly correct (see https://3v4l.org/4Jh9u#v826). Relevant:

php-src/NEWS

Lines 1664 to 1665 in 94fa2a4

	. Fixed bug where the diff() method would not return the right result around
	DST changeover for date/times associated with a timezone identifier. (Derick)

I think the actual change was in timelib 2022.6.

[hormus]

@Geekimo 0 years 0 months 7 days 0 hours 59 minutes 59 seconds, it's not correct.
@Geekimo and @cmb69 0 years 0 months 6 days 23 hours 59 minutes 59 seconds, it's correct (from php >= 8.2.6).
Europe/Paris If with forward transition "start daylight saving time" 02:00:00 is 03:00:00 local time. (2024-03-31 03:00:00 DST).

Example with DST:

<?php

$timezone = new \DateTimeZone('Europe/Paris');

$periodStart = new \DateTimeImmutable('2024-03-25 00:00:00', $timezone);
$periodEnd = new \DateTimeImmutable('2024-03-31 23:59:59', $timezone);

var_dump($periodStart->diff($periodEnd)->format('%y years %m months %a days %H hours %I minutes %s seconds'));
?>

if UTC 2024-03-31 21:59:59 (Europe/Paris DST +02:00) - UTC 2024-03-24 23:00:00 (Europe/Paris ST +01:00) = "0 years 0 months 6 days 22 hours 59 minutes 59 seconds"

[Geekimo]

@hormus You're confusing examples.
Transition from winter to summer time is correct, but not from summer time to winter time.
The example you're showing here is perfectly working. But if you use the following code for for $periodStart and $periodEnd, result will be wrong (transition from ST to DST happens between these two dates, on the morning of the 27th) :

$periodStart = new \DateTimeImmutable('2024-10-21 00:00:00', $timezone);
$periodEnd = new \DateTimeImmutable('2024-10-27 23:59:59', $timezone);

[macwinnie]

Just to second that Bug the same problem in some other lines of code (now in Europe/Berlin Timezone):

<?php

$tz = new DateTimezone("Europe/Berlin");
$d1 = DateTime::createFromFormat("Y-m-d H:i", "2025-03-30 01:59", $tz);
$d2 = DateTime::createFromFormat("Y-m-d H:i", "2025-03-30 03:00", $tz);

# calculate next minute of $d1
$m1 = clone $d1;
$m1->modify('+1 minute');

# calculate previous minute of $d2
$m2 = clone $d2;
$m2->modify('-1 minute');

# complare the results
var_dump($m1 == $d2); // true
var_dump($m2 == $d1); // false even though true expected

echo "\$m1 results in: " .  $m1->format('Y-m-d H:i') . "\n";
echo "\$m2 results in: " .  $m2->format('Y-m-d H:i') . "\n";

Output:

bool(true)
bool(false)
$m1 results in: 2025-03-30 03:00
$m2 results in: 2025-03-30 03:59

Would appreciate a fix =)

[macwinnie]

Ah ... forgot to mention: there's a workaround, I'm currently using in my implementations ... that's a mess but it works: changing into UTC Timezone for modifications (and though for calculations probably aswell) ...

<?php

# lines 3 - 9 from above

# calculate previous minute of $d2
$utc = new DateTimezone("UTC");
$m2 = clone $d2;
$m2->setTimezone($utc); # convert $m2 into UTC timezone object
$m2->modify('-1 minute');
$m2->setTimezone($tz); # convert $m2 back to Europe/Berlin tz object

# lines 15 - 20 from above

Output will change to expected:

bool(true)
bool(true)
$m1 results in: 2025-03-30 03:00
$m2 results in: 2025-03-30 01:59