Add support for visionOS targets

[conradev]

Proposal

Apple recently released the first version of the visionOS SDK for their Apple Vision Pro device. The device has standalone operating system and corresponding SDK called xrOS, much like the Apple Watch has watchOS or the Apple TV has tvOS.

Apple is using the platform names xros and xrsimulator for the Vision devices and Vision simulator, respectively. In this proposal, I want to add these new targets to Rust:

• aarch64-apple-xros
• aarch64-apple-xros-sim
• x86_64-apple-xros-sim

The corresponding LLVM targets are:

• arm64-apple-xros
• arm64-apple-xros-simulator
• x86_64-apple-xros-simulator

There is also arm64e-apple-xros, but afaik Rust doesn't support PAC yet on Apple OSes

Mentors or Reviewers

• conradev

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[Noratrieb]

you need to fill out all the questions for new targets

[thomcc]

Isn't that just needed for the impl PR?

[thomcc]

I can volunteer for the implementation or the review. I was planning on doing the implementation for these anyway, as just did tvOS, but don't mind if someone else does this.

However, as discussed in Zulip there are some issues that prevent working on this in the near term:

• We're blocked by Apple upstreaming LLVM support for these -- doing it based on the LLVM from the preview SDK (similar to how we used to need to use the LLVM from the watchOS SDKs for those targets) is very painful.
• It is likely that these will not be the final target names.

[workingjubilee]

Isn't that just needed for the impl PR?

An MCP is technically not required at all. Rather, what is actually important is the requirements of the target tier policy are addressed by the author and the compiler team reviews it. An MCP is simply a vessel for that review.

[coolbluewater]

Hi folks, what is the status of this?

@thomcc

It is likely that these will not be the final target names.

I'm sure many developers, including myself, are eagerly awaiting this support.
To unblock here are a couple of choices:

1. Adopt the proposed target names based on 'xros' in nightly and change them down the road if Apple changes them, or
2. Adopt the seemingly committed brand name of 'visionOS' (which is what appears in user-facing text e.g. in Xcode).

I for one prefer the second option - it makes sense even if Apple continues to use the 'xros` name internally. We already have the precedent of a divergent naming convention in Rust for macOS ('darwin'), where both macOS and darwin seem reasonable choices.

Either way, hope that this issue progresses quick. It's problematic for a major OS to be impeded in this way, especially for simple Tier 3 support.

Thanks a lot folks!

[thomcc]

The status is that as far as I can tell, these are not in upstream LLVM (rg -e '(xros|visionos)' has no hits in LLVM main) so we still are blocked on that. We can't land support for them based on just the compilers in SDKs (or even based on Apple's LLVM fork). Note that even if this happens, we probably need to wait for them to be present in a released version of LLVM, so optimistically it could be LLVM 18, but maybe 19 (and that's assuming apple upstreams this to LLVM -- if they don't do that, then the path to support is more difficult).

The names are not a blocker.

[coolbluewater]

Understood. You mentioned that the tvOS scenario parallels this one. What were the issues/PRs that caused the needed changes to land upstream for tvOS? Who initiated those?

Also, what would it take to get a private build of Rust working against visionOS? Two or three versions of LLVM is a long time! :)

Thanks!

[workingjubilee]

Also, what would it take to get a private build of Rust working against visionOS? Two or three versions of LLVM is a long time! :)

There is a dev guide chapter on how to build the compiler. The Rust build system's config.toml has keys for specifying what LLVM you are building against and how you want to link (llvm-config and link-shared, amongst others). I recommend asking on Zulip if you need additional help building the compiler.

Also you will need to explain to rustc what the new targets are in rustc_target and thread the support for the new OS through std. Hopefully it doesn't do anything interesting and you can just pretend it's like iOS, or hopefully they document the relevant differences (in full and complete detail). Neither are necessarily the case which is kind of why we're waiting for the code to hit the open source LLVM.