rust wasm-pack compatibility

[benmkw]

• Rollup Plugin Name: wasm
• Rollup Plugin Version: ^3.0.0
• Rollup Version: ^1.20.0
• Operating System (or Browser): Version 1.4.96 Chromium: 80.0.3987.132 (Official Build) (64-bit)
• Node Version: v13.11.0

How Do We Reproduce?

Expected Behavior

bundling wasm created using wasmpack https://rustwasm.github.io/wasm-pack/book/

Note:
I used the rollup config from the default svelte template as a starting point, this issue might also be an issue with svelte instead of rollup.

Actual Behavior

may be nearly working but some steps remain where I want to try to help figure out what they are

I created a repository with a minimal example where I tried to provide as much information as possible such that you don't necessarily need to install rust tooling in order to investigate the bug https://github.com/benmkw/svelte_rust_test . I can provide further information if needed.

short overview of the issue is the following:

rust_wasm.js:9 Uncaught TypeError: undefined is not a function
    at add (rust_wasm.js:9)
    at Object.create [as c] (App.svelte:8)
    at init (index.mjs:1410)
    at new App (App.svelte:3)
    at main.js:3
    at main.js:8
add @ rust_wasm.js:9
create @ App.svelte:8
init @ index.mjs:1410
App @ App.svelte:3
(anonymous) @ main.js:3
(anonymous) @ main.js:8

because in in bundle.js:

    function add(a, b) {
        var ret = undefined(a, b);
        return ret;
    }

rollup seems to optimize the call away

function rust_wasm_bg(imports){return _loadWasmModule(0, 'AGFzbQEAAAABBwFgAn9/AX8DAgEABQMBABEHEAIGbWVtb3J5AgADYWRkAAAKDQELACAAIAFqQf8BcQsLUgEAQaSIwAALSQEAAAAAAAAAAQAAAAIAAAADAAAABAAAAAUAAAAAAAAAAQAAAAIAAAADAAAABAAAAAYAAAAEAAAABAAAAAcAAAAIAAAACQAAAAoAgwEJcHJvZHVjZXJzAghsYW5ndWFnZQEEUnVzdAAMcHJvY2Vzc2VkLWJ5AwVydXN0YyUxLjQzLjAtbmlnaHRseSAoNTY0NzU4YzRjIDIwMjAtMDMtMDgpBndhbHJ1cwYwLjE0LjAMd2FzbS1iaW5kZ2VuEjAuMi41OSAoZGI4ZDNlNDQxKQ==', imports)}

var wasm = /*#__PURE__*/Object.freeze({
        __proto__: null,
        'default': rust_wasm_bg
    });

As far as I can see the wasm module gets embedded into the js file but _loadWasmModule is never actually called, so this might actually be very close to being in a working state.

[benmkw]

I removed svelte from the equation thus the bundle.js is now really small.
The missing piece seems to be support for import await foo from bar.
Unfortunately I have not yet figured out if import await is a thing thats standardized/ likely be supported by rollup thus not sure how to go from here.

As can be seen in https://github.com/webpack/webpack/tree/master/examples/wasm-simple this would make it possible to call functions from a wasm module without worrying about async things (added to webpack here webpack/webpack#6615 (comment)).

[benmkw]

as mentioned in rustwasm/wasm-pack#699 (comment) fixed by other wasm rollup plugin which is specifically designed for rust interop https://github.com/wasm-tool/rollup-plugin-rust

[shellscape]

Thanks. I've added that plugin to our awesome list: rollup/awesome@d5826ee