DatePeriod::getEndDate can be null

[Alban-io]

Bug report

Code snippet that reproduces the problem

https://phpstan.org/r/1f444637-6319-49d9-be32-fcabb3f7c84e

Expected output

17    Cannot call method format() on DateTimeInterface|null.

DatePeriod::getEndDate return DateTimeInterface when __construct has for 3rd argument a DateTimeInterface.

'DatePeriod::__construct' => ['void', 'start'=>'DateTimeInterface', 'interval'=>'DateInterval', 'recur'=>'int', 'options='=>'int'],
'DatePeriod::__construct\'1' => ['void', 'start'=>'DateTimeInterface', 'interval'=>'DateInterval', 'end'=>'DateTimeInterface', 'options='=>'int'],
'DatePeriod::__construct\'2' => ['void', 'iso'=>'string', 'options='=>'int'],

PHP doc : public DatePeriod::getEndDate(): ?DateTimeInterface
PHPStan : 'DatePeriod::getEndDate' => ['DateTimeInterface'],

<?php declare(strict_types=1);

$start = new DateTime('2012-07-01');
$interval = new DateInterval('P7D');
$end = new DateTime('2012-07-31');
$recurrences = 4;
$iso = 'R4/2012-07-01T00:00:00Z/P7D';

var_dump([
    (new DatePeriod($start, $interval, $recurrences))->getEndDate(), // null
    (new DatePeriod($start, $interval, $end))->getEndDate(),         // DateTime
    (new DatePeriod($iso))->getEndDate(),                            // null
]);

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[herndlm]

This looks like a perfect first contribution - do you want to fix it yourself? :)

[Alban-io]

do you want to fix it yourself? :)

It depends on the desired fix :

• make the return type nullable DatePeriod::getEndDate' => ['?DateTimeInterface']
• make the return type variable based on the constructor call

To implement the second I will need a similar case in the codebase 😉

[herndlm]

Right, I did overlook that this is a bit more complex. And I'm still lacking phpstan internal knowledge, but maybe @staabm knows which kind of extension this needs?

[staabm]

usually you would need a DynamicMethodReturnTypeExtension extension - find other examples in the phpstan-src codebase

I am not 100% sure, but I guess in the extension you may check with getRecurrences what was passed in as 3rd construct arg

[Alban-io]

Thank @staabm I will try to make the PR

[github-actions]

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