Narrow explode return to constant arrays for small positive limits

[herndlm]

Related to phpstan/phpstan#12187

kept this simple and only handle a single constant limit on purpose for now

Needs #3709 first

[staabm]

to cover the initial request of the discussion, I think it would be useful to assert the result of
explode(',', $date, 2) + [1 => null] in the tests

[staabm]

I guess you saw it already yourself, but just in case: seems you found a case in which we miss to narrow a constant arrays optional offsets :-)

https://phpstan.org/r/6286a642-020a-4e53-b713-72994a0bbcad

[herndlm]

Yes, was creating a similar example in parallel (https://phpstan.org/r/d6b8098a-282b-47cd-be91-38e42401d1eb) :) let's fix that first..

[phpstan-bot]

This pull request has been marked as ready for review.

[herndlm]

currently: https://phpstan.org/r/a1181543-1503-4108-bcf4-ee8e13abda66

so most of it are things like

Expected type array{0: string, 1?: string}, actual: non-empty-list

not sure if this PR even adds much value..
some max limits at least I guess hmm, could still be useful potentially?

[herndlm]

oh interesting, the 3 failing tests show that the narrower type can cause new offsetAccess.notFound errors to appear:

• https://github.com/phpstan/phpstan-src/actions/runs/13833502116/job/38703310885?pr=3708
• https://github.com/phpstan/phpstan-src/actions/runs/13833502116/job/38703311456?pr=3708
• https://github.com/phpstan/phpstan-src/actions/runs/13833502116/job/38703311898?pr=3708 -> https://github.com/doctrine/collections/blob/2790cb57e6510e4404873bdca6688e447550d720/src/Expr/ClosureExpressionVisitor.php#L44

which I think is expected and fine.