Tracking issue for release notes of #131080: Stabilize WebAssembly multivalue, reference-types, and tail-call target features

[rustbot]

This issue tracks the release notes text for #131080.

Steps

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text

The responsible team for the underlying change should edit this section to replace the automatically generated link with a succinct description of what changed, drawing upon text proposed by the author (either in discussion or through direct editing).

# Category (e.g. Language, Compiler, Libraries, Compatibility notes, ...)
- [Stabilize WebAssembly `multivalue`, `reference-types`, and `tail-call` target features](https://github.com/rust-lang/rust/pull/131080)

Tip

Use the previous releases categories to help choose which one(s) to use.
The category will be de-duplicated with all the other ones by the release team.

More than one section can be included if needed.

Release blog section

If the change is notable enough for inclusion in the blog post, the responsible team should add content to this section.
Otherwise leave it empty.

cc @alexcrichton, @petrochenkov -- origin issue/PR authors and assignees for starting to draft text

[alexcrichton]

I think the suggested text just from the PR title is probably reasonable here. For a bit of a longer-form callout if that's desired it could be something like:

The WebAssembly target features multivalue, reference-types, and tail-call are now stable. Both multivalue and reference-types are explained in a previous blog post and stable features can be used to, for example, provide a first-class compile_error! indicating that the features should not be enabled (e.g. when targetting an older wasm runtime).

The tail-call feature of WebAssembly corresponds to the tail-call proposal to WebAssembly which advanced to the stabilization stage of "phase 4" earlier this year. This feature provides instructions in WebAssembly that guarantee a tail call is performed at the callsite. Rust does not have guaranteed tail calls at the language yet but LLVM may optimize function calls to tail calls where possible. When the tail-call feature is enabled for WebAssembly the return_call instruction may be used instead of a normal call instruction if LLVM deduces that it's an applicable optimization.