Exporting struct causes TypeError: WebAssembly.instantiate() when module imported

[AlexEales]

Describe the Bug

It appears whenever I try to import from a WASm bundle which contains an exported struct a TypeError: WebAssembly.instantiate() is thrown. I simplified down the struct I was trying to export to just be:

#[wasm_bindgen]
pub struct SimpleStruct {
    value: i32,
}

#[wasm_bindgen]
impl {
    pub fn new(value: i32) -> SimpleStruct {
        SimpleStruct { value }
    } 
}

And I'm still getting the error? Could this be something to do with the WASM module not being generated correctly? It seemed pretty normal when I checked and compared it to the expected output of exporting a struct on this page.

I'm using Parcel bundler to create a simple website using WASM, I'm aware of the lack of compatibility between the two out of the box so I am simply recompiling my Rust package when I need to and then pointing the TS files at the generates JS file in the pkg directory.

Steps to Reproduce

1. Copy above code + some arbitrary function exported to WASM
2. Compile with wasm-pack build.
3. Import arbitrary function inJS.
4. Serve local JS and observe error.

If applicable, add a link to a test case (as a zip file or link to a repository we can clone).

Expected Behavior

Importing from the bundle should not error if it contains a struct being exported.

Actual Behavior

TypeError: WebAssembly.instantiate() is thrown regardless of structs' contents.

Additional Context

Full error message: Uncaught (in promise) TypeError: WebAssembly.instantiate(): Imports argument must be present and must be an object

[AlexEales]

My Cargo.toml:

[package]
name = "simple"
version = "0.1.0"
authors = ["Alex Eales"]
edition = "2018"

[dependencies]
rand = "0.7"

[dependencies.wasm-bindgen]
version = "0.2.55"

[lib]
crate-type = ["cdylib"]

[Pauan]

I'm not 100% sure, but this sounds like a bug with Parcel (which doesn't have great wasm support at the moment).

Do you still get the error if you use Webpack instead?

[AlexEales]

Thanks for the quick response @Pauan I do not get the error with webpack, I had a feeling it would be a Parcel issue. Do you have any idea what might be causing this so I could relay this to the Parcel team and try and get a fix for this going? :)

[AlexEales]

Have found a Parcel plugin which seems to solve the issue, will leave the link here incase anyone else goes down this rabbit hole!

https://github.com/rustwasm/rust-parcel-template

[Pauan]

@AlexEales Yup, that's covered here:

parcel-bundler/parcel#647

parcel-bundler/parcel#1325

parcel-bundler/parcel#3485