Psalm 5.4 upgrade

[drupol]

This PR:

• Fix issues introduced by Psalm 5.4
• Has static analysis tests (psalm, phpstan)
• Needs PSalm > 5.4.0 to work (use dev version in the meantime)

[what-the-diff]

• Added a new function to generate random letters

• Changed the type of collection from CollectionInterface<int, int> to CollectionInterface<int, string|null> in scanLeft_checkListStringWithNull()

• Added a new function squash_checkList2 and squash_checkStringList2.
  This is because the original functions were not able to handle collections with non-int keys.

  The reason for this was that we had an explicit typehint of int in our collection interface, which meant
  that psalm would only allow us to pass integers as keys.

[drupol]

This PR needs to be merged once the upcoming version of PSalm is out (5.4.1).

[AlexandruGG]

I think we need to be careful not to make things way too restrictive -> I see lots of changes needed in the static analysis checks - these are all potential changes users would need to make in their own codebases.

If some of changes are unavoidable simply due to Psalm 5.4 then we can perhaps use a baseline and introduce them more gradually? Would be easier if we would only do it for a set of operations at a time so we can carefully think about how the change affects their usage.

[AlexandruGG]

not too sure about this change -> it's not a given that the elements in the unwrapped collection will be all of the same type 🤔

Collection::fromIterable([['a'], [1], [true]])
    ->unwrap(); // ['a', 1, true]

unless static analysis is able to interpret the template T as the union string|int|bool in this case. I'm not sure but you could test this with a static analysis check

[AlexandruGG]

this is not good, and it shows that the new type hints have made unwrap too restrictive and incorrect in this case

Collection::fromIterable([[1], 2, 3])->unwrap() 
// will result in Collection(1, 2, 3) aka `Collection<int, int>`, but the type hints think the resulting types are the same 
// as were passed in the original collection

[AlexandruGG]

same issue here as with the unwrap

[drupol]

@AlexandruGG All good for you now?

[drupol]

@AlexandruGG Good for you?

[AlexandruGG]

Thanks, I know this took lots of work!

[drupol]

Thanks! Indeed it was painful !