Can't get multivalue wasm to work

help
1

Hi,

I'm on nightly and have this exact issue: WebAssembly multi-value return in today's Rust without wasm-bindgen | vmx - the blllog.
(ie. multivalue functions have weird argument count and no return value when returning a tuple).

Comment in wat:

 ;; features section: mutable-globals, bulk-memory, sign-ext, reference-types, multivalue

#[no_mangle]
pub fn flip(a: u32, b: u32) -> (u32, u32) {
    (b, a)
}

 (func $8 (param $0 i32) (param $1 i32) (param $2 i32)
  (i32.store offset=4
   (local.get $0)
   (local.get $1)
  )
  (i32.store
   (local.get $0)
   (local.get $2)
  )
 )

Reading this blog post from a couple of days ago I would think multivalue should work ootb? WebAssembly targets: change in default target-features | Rust Blog

rustc 1.83.0-nightly (fa724e5d8 2024-09-27)
binary: rustc
commit-hash: fa724e5d8cbbdfbd1e53c4c656121af01b694406
commit-date: 2024-09-27
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0

I tried wasm32-wasip1 and wasm32-unknown-unknown

2

The blog you link says it doesn't. ("out on the horizon")

It is announcing breaking change in Rust 1.82. And how to use nightly if you need a new compiler while still having support for MVP.

3

Right, but it used to work a year ago, see:

Of course this is all nightly, so regressions are to be expected? I'm just wondering if I'm doing it wrong and it works for you.

4

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