DateInterval issues with negative directions

Description

I am going to put a few connected issues I have noticed around DateInterval and DatePeriod into a single report:

1: DateInterval->invert is "readonly"

DateInterval:::__construct() only allows positive $duration e.g. P1D not P-1D (I appreciate this is the correct behaviour as it is based around the ISO8601 which has no concept of negative periods). However... the DateInterval->invert which allows the period to be reversed can only be changed by manually setting that property and the docs explicitly say:

The available properties listed below depend on PHP version, and should be considered as readonly.

It would be good to be able to change this property safely.

2: DateInterval::createFromDateString allows negative periods

DateInterval::createFromDateString('-1 day') is accepted but this sets DateInterval->d = -1 rather than using the ::invert property. This is inconsistent with the always-positive periods which __construct allows.

I would expect it to:

• Reject mixed positive and negative period values, what would +1 year -6 month even mean?
• Accept if only negative periods passed but then set ::invert = 1 and the properties of ::y..f as +ve

3: DateInterval::createFromDateString('-1 day') leads to infinite loop in DatePeriod

$datePeriod = new \DatePeriod(
    new \DateTimeImmutable('2000-01-01'),
    \DateInterval::createFromDateString('-1 day'),
    new \DateTimeImmutable('2000-01-05'),
);

echo iterator_count($datePeriod); // stuck in infinite loop

4: DateInterval::createFromDateString('-1 day') still doesn't work if start and end reversed in DatePeriod

$datePeriod = new \DatePeriod(
    new \DateTimeImmutable('2000-01-05'),
    \DateInterval::createFromDateString('-1 day'),
    new \DateTimeImmutable('2000-01-01'),
);

echo iterator_count($datePeriod); // 0 (but would expect 4)

5: DatePeriod doesn't respect DateInterval->invert

$dateInterval = new \DateInterval('P1D');
$dateInterval->invert = 1;

# will not go backwards from high to low dates
$datePeriod = new \DatePeriod(
    new \DateTimeImmutable('2000-01-05'),
    $dateInterval,
    new \DateTimeImmutable('2000-01-01'),
);

echo iterator_count($datePeriod); // 0 (but would expect 4)

# incorrectly goes forward from low to high dates
$datePeriod = new \DatePeriod(
    new \DateTimeImmutable('2000-01-01'),
    $dateInterval,
    new \DateTimeImmutable('2000-01-05'),
);

echo iterator_count($datePeriod); // 4 (but would expect 0)

PHP Version

8.3.114

Operating System

Rocky 8

Commencez par reproduire les exemples à l’aide des points d’entrée DateInterval et DatePeriod, y compris les intervalles négatifs, les dates inversées et la propriété invert. Examinez le comportement existant des périodes de dates et déterminez une sémantique cohérente pour les directions négatives, les signes mixtes et les intervalles inversés. Le travail est terminé lorsque les cas signalés ont un comportement défini, sans boucle, et une couverture de régression.