POC: Use SimultaneousTypeTraverser in RuleLevelHelper::transformAcceptedType

[VincentLanglet]

Static analysis is failing because TypeTraverserInstanceofVisitor doesn't support SimultaneousTypeTraverser (not sure it should).

The only current test failing is

16: Function ReturnListNullables\doFoo() should return array<string>|null but returns list<string|null>.

but I feel like we could reproduce more errors because...

UnionType/Intersection types doesn't work well with the SimultaneousTypeTraverser because

• when it's called with A&B&C and A we're not traversing because second type is not an Intersection
• when it's called with A&B&C and A&C we're not traversing because types count are different

The main issue would be, when traversing A&B&C and A&C, to match types in order to

• traverse (A, A)
• traverse (B, Never)
• traverse (C, C)

[ondrejmirtes]

The output from issue-bot is yummy here! https://github.com/phpstan/phpstan-src/actions/runs/16773630245

Please add regression tests for those.

I feel like we could improve IntersectionType::traverseSimultaneously() for all the common pseudotypes like non-empty-string, list etc. represented with IntersectionType.

I feel that even when there's non-empty-string on left side and string on the right side and vice versa, the callback should still be invoked for them.

This needs extensive tests of course.

[ondrejmirtes]

Linking phpstan/phpstan#9096

[VincentLanglet]

The output from issue-bot is yummy here! phpstan/phpstan-src/actions/runs/16773630245

Please add regression tests for those.

Sure, but shouldn't we fix the actual tests first ?

I feel like we could improve IntersectionType::traverseSimultaneously() for all the common pseudotypes like non-empty-string, list etc. represented with IntersectionType.

I feel that even when there's non-empty-string on left side and string on the right side and vice versa, the callback should still be invoked for them.

Yeah, but I dunno how to improve the implementation of the existing traverseSimultaneously, it's not easy :/