Add support for strict arrays, fix type alias intersection, fix array_is_list assertion on non-lists

[danog]

This PR introduces new syntax to define list-like keyed arrays: list{} which replaces the previously undocumented (and frankly confusing) array{int, string}.
Also introducing syntax for callable-list{}.

Finally, introducing strict-*{} for sealed variants of array types.

[orklah]

right now, sealed arrays can only be created by explicitly creating an array in php. The sealed flag is used for several things (like being sure of how many elements there is in an array or checking if the array can be inferred to be empty, things like that).

If you want to be able to document a sealed-array, there are a few new rules that will need to be enforced. For example, a method expecting a sealead-array param now need to check that the provided array is sealed. Likewise, trying to fetch an undocumented key from a sealed array should return TNever (EDIT: this seems handled by InvalidArrayOffset already)

There will be a bunch of things like that to handle that were not previously implemented because the sealed flag couldn't be used directly by people.

[kkmuffme]

I think list{} is ultra confusing, since a list currently is a 0-monotonous index array.

[orklah]

there was (I think) no pre-existing support for that in psalm

We have a is_list property in TKeyedArray that will change a standard keyed array like array{0: int, 1: string} into an array{int, string}. The second one enforces the order. That only works with list-like keys though

[danog]

That only works with list-like keys though

Ah that makes sense, I suppose it would be nice to have an ordered-strict-array variant, but that's for a future PR ;)

This PR should be now good to merge, the phpcs comments can be removed once @ondrejmirtes merges phpstan/phpdoc-parser#161 and tags, which adds basic strict-array, strict-list and list syntax support to phpstan and phpcs, and @romm merges CuyZ/Valinor#246 so at least strict-array syntax is supported in valinor :)

[orklah]

Thanks a lot again!

[zmitic]

This is very useful feature. Can it be added to 4.x branch?

[danog]

Sorry, the 4.x is in feature freeze, no more PRs are accepted for it, but you can already upgrade to the latest rc1 of Psalm v5 right now, the release itself is imminent! :D

[zmitic]

@danog I tried, but it is the Symfony plugin that depends on V4.

Never mind, I will see what I can do. Thank you for this awesome feature anyway.

[orklah]

It makes sense that Symfony still depends on Psalm 4 given the release is yet to come! One of our task after releasing will be to make sure there are no big plugins left behind for too long :)