array_chunk return type should take into account the $preserve_keys argument

[gnutix]

Feature request

Hello there. While adding some types and types' tests for a wrapper function around array_chunk() in our codebase, I noticed that the return type was always array<array> (not very precise), and it does not account for the $preserve_keys argument.

Example: https://phpstan.org/r/ccba8215-391a-43bf-b0c3-1bd779a1c16c

I'm not sure if this should be fixed using conditional return types or with an extension.

Talking about extensions, I wonder if PHPStan could easily go one step further and be able to infer the specific values of the array (if it is static/known), like below ? (PS: I know it sometimes provides types that are that specific, that's why I think of this, but I don't know how easy it is to do it in this scenario)

$array = [
    'test1' => 'this is test 1',
    'test2' => 'this is test 2',
    'test3' => 'this is test 3',
    'test4' => 'this is test 4',
];
array_chunk($array, 2); // array{0: array{0: 'this is test 1', 1: 'this is test 2'}, 1: array{0: 'this is test 3', 1: 'this is test 4'}}
array_chunk($array, 2, true); // array{0: array{test1: 'this is test 1', test2: 'this is test 2'}, 1: array{test3: 'this is test 3', test4: 'this is test 4'}}

Not sure if it's "that useful" either. Anyway, it's just an idea. 😉

(I don't currently have the time to work on an implementation, but maybe someone will.)

Did PHPStan help you today? Did it make you happy in any way?

(I have a bunch of small issues to create, sorry if I don't come up with something new for each of them 🙏 )

[herndlm]

Currently no return type extension for array_chunk exists at all. I think this can be solved relatively easily by creating one and using mostly already existing features from ConstantArrayType. E.g. slice and reindex (for $preserve_keys).
I can take a look at this next.

[gnutix]

Thanks @herndlm for your work!

[github-actions]

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