Feat: Add support for horizontal orientation to GridList & ListBox

[nwidynski]

This PR adds support for horizontal orientations to ListLayout and affected components in preparation for a Carousel contribution.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[nwidynski]

@LFDanLu Would you be so kind to issue a build for this PR? I'm going insane because of a bug with virtualized dnd, which I can't seem to get rid of locally, even after reverting all changes and clearing caches. I would really like to know whether the issue exists on remote 😅

[nwidynski]

@majornista Should we set aria-orientation only if deviating from the implicit orientation as defined in each role spec? I adjusted useTabList as well to match, let me know what you think 🙏

[LFDanLu]

@nwidynski heya sorry about the delay, opened #8544 for your build

[nwidynski]

@LFDanLu Thanks! I will take a look tmrw, otherwise this is ready for review if the team finds time 👍

[LFDanLu]

sounds good, we are gearing up for a release very soon, but noted this one down (and #8523) for the team to checkout right after!

[LFDanLu]

Will be bring this up with the team tomorrow, but looks good to me at a glance, thanks!

[LFDanLu]

mainly wondering if some of the changes/refactors can be simplified since we already supported orientation for Listbox previously

[nwidynski]

@LFDanLu Maybe the PR title is misleading - The primary target of this is to add orientation to the Layout class and its derivates, e.g. ListLayout. While the Listbox did support orientation, it was only affecting keyboard movement and not visual layout for virtualization.

[nwidynski]

@LFDanLu I removed the fallback as requested, anything else blocking this? One question I had was whether we should tackle #837 (comment) as a result of getOrientation() becoming available now. Maybe in a follow up?

[LFDanLu]

Nothing blocking from my perspective, but the team is in a holding pattern for your coming RFC so we can see how it all fits together. Definitely sounds like the getOrientation stuff could help with that comment you linked, happy for that to be follow up

[nwidynski]

@LFDanLu Alright, then I will refer to #8699, since I really need input on this to wrap up the RFC design section. I'm basically asking whether I should design with tab* ARIA roles or something else.

[uncvrd]

Thank you for working on this PR! Am I correct in assuming this would help allow horizontal drag and drop using GridList? Currently, I have an issue where the Left Right placement of the DragIndicator changes based on the Y position you are dragging and not the X position. I would also really appreciate an orientation prop as I think this would provide? I haven't found a workaround otherwise...

Thank you!

Screen.Recording.2025-08-30.at.2.00.03.PM.mov

[nwidynski]

@LFDanLu I finally got around to finish the RFC, sorry it took this long.

[LFDanLu]

@nwidynski Awesome and no worries, thank you so much for making that! Just to share some timelines, the team is currently pushing quite heavily on work around our new docs site, so the next month or two will be a bit hectic on our end. We'll definitely try to carve out some time so we can start discussions early though!

[nwidynski]

@LFDanLu Is there anything I can do to get this over the finish line? Now that the RFC is out, I think the reasoning for this PR should be apparent.

[LFDanLu]

Heya, I just got back from vacation sorry about the delay, I'll bump the team on your RFC again and see if I can get another pair of eyes on it and then we can see about getting these related PRs in.

[nwidynski]

@LFDanLu Since Devon is heading into 2 weeks off now, do you mind taking a look at my latest reply to his questions and see whether that lines up with your idea of what this RFC tries to do? Just want to ensure Devon can wrap it up once he's back, so we can skip this back and forth dragging on for further weeks.

PS: Sorry for the rather long read once more 😅