Import error for bindgen functions using Result without JsError

[kevin-cgc]

Describe the Bug

When using a Result return type in a wasm-bindgen function without constructing a JsError, the generated JavaScript includes an unexpected wasm-bindgen internal(?) import: import * as __wbg_star0 from '__wbindgen_externref_xform__';.

Steps to Reproduce

Build the following

use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn causes_error() -> Result<f64, JsError> {
    return Ok(1.0);
}

// uncomment to prevent import issue
// #[wasm_bindgen]
// pub fn fix() -> JsError {
//     return JsError::new("with this, no issue");
// }

with

cargo build --lib --target wasm32-unknown-unknown && wasm-bindgen.exe --target web --out-dir "pkg" ./target/wasm32-unknown-unknown/debug/test.wasm

or wasm-pack

Expected Behavior

JavaScript bindings for --target web should not contain such imports.

Actual Behavior

JavaScript binding starts with

import * as __wbg_star0 from '__wbindgen_externref_xform__';

Additional Context

Using wasm-bindgen 0.2.99, rustc 1.83.0.

This seems to mostly be just an annoying behavior in an unlikely case, but took me a while of checking other things (e.g. for some version mismatch) to come up with the MRE.

[CryZe]

This happens again with the nightly compiler on wasm-bindgen 0.2.100. I assume the update to LLVM 20 broke it.

Update: Yeah the SIMD intrinsics (in this case llvm.wasm.sub.sat.unsigned.v16i8) are broken, which causes this incorrect import.

Fixed by: rust-lang/stdarch#1719