🐛 BUG: Uncaught ReferenceError: FinalizationRegistry is not defined

[kevi-sun]

What version of Wrangler are you using?

2.4.2

What operating system are you using?

Linux and Mac

Describe the Bug

We have javascript call the wasm code, with WASM_BINDGEN_WEAKREF defined to generate code to register to javascript garbage collector, please see https://rustwasm.github.io/wasm-bindgen/reference/weak-references.html for detail.

here is an example of code generated by wasm-bindgen:

export class StreamWrapper {
    static __wrap(ptr) {
        const obj = Object.create(StreamWrapper.prototype);
        obj.ptr = ptr;
        StreamWrapperFinalization.register(obj, obj.ptr, obj);
        return obj;
    }

    __destroy_into_raw() {
        const ptr = this.ptr;
        this.ptr = 0;
        StreamWrapperFinalization.unregister(this);
        return ptr;
    }

    free() {
        const ptr = this.__destroy_into_raw();
        wasm.__wbg_streamwrapper_free(ptr);
    }
}

it works well with running "wrangler dev --local", but the following error was report when publish to CloudFlare with wrangler2

✘ [ERROR] A request to the Cloudflare API (/accounts/00000000000000000000000/workers/scripts/worker_name) failed.

  Uncaught ReferenceError: FinalizationRegistry is not defined
    at worker.js:446:35
   [code: 10021]

  
  If you think this is a bug, please open an issue at:
  https://github.com/cloudflare/wrangler2/issues/new/choose

[shyim]

Does it make sense to add a warning here? The error message does say nothing

[kevi-sun]

@shyim thanks, it would be nice to support FinalizationRegistry which makes use of javascript GC, but I don't know whether it is supported in Cloudflare env and how to fix that.
I tested in miniflare, looks all good with WASM_BINDGEN_WEAKREF defined.

[mrbbot]

Hey! 👋 Thanks for raising this. I brought this up internally, and it seems like there are some technical restrictions why we can't implement FinalizationRegistry in the Workers runtime. We could do a better job at documenting this limitation, but for now, you'll need to build your code without WASM_BINDGEN_WEAKREF when targeting Workers. Miniflare should be updated to remove support for this.