Webpack compat error for wasm files imported in web workers

[nickbabcock]

What version of Next.js are you using?

10.0.7

What version of Node.js are you using?

v14.3.0

What browser are you using?

N/A

What operating system are you using?

Ubuntu 20.04

How are you deploying your application?

N/A

Describe the Bug

I took the with-webassembly example and moved the loading and execution of wasm into a web worker (to simulate offloading of expensive functions to wasm in another thread). Unfortunately I receive the following error for both next dev and next build

Failed to compile.

webpack/runtime/compat
The "path" argument must be of type string. Received undefined

Which I have been unable to debug.

The project is straightforward (no additional dependencies, just plain next.js) but I'll copy the relevant bits here for posterity:

worker.js

onmessage = async function (e) {
  const rustModule = await import("../add.wasm");
  console.log(rustModule.add_one(10));
};

index.js

import { useEffect, useRef } from "react";

const Page = () => {
  const workerRef = useRef();
  useEffect(() => {
    if (workerRef.current === undefined) {
      workerRef.current = new Worker(new URL("./worker.js", import.meta.url));
    }
  }, []);

  return (
    <button onClick={() => workerRef.current.postMessage([])}>Click</button>
  );
};

export default Page;

One very important bit is that this is a webpack 5 project as webpack 5 supports web workers and wasm natively (albeit experimentally) and I've been unable to get webpack 4 working with the appropriate plugins due to #21679 .

Wasm files outside of web workers work, and web workers without wasm work, the combination of them seems to give rise to the error. It doesn't matter where the wasm module is imported in the web worker or even if it is dynamically imported or not.

Expected Behavior

For the project to be built

To Reproduce

I've created a bug repro: https://github.com/nickbabcock/next.js-wasm-worker

clone, install, and build to repro the error.

[nickbabcock]

I have found a workaround by leveraging webpack asset modules to instruct webpack and next to only return the path of the digested wasm. The downside is that now one has to write the code to fetch, compile, and instantiate which is not too hard. This is how I achieved it:

next.config.js

module.exports = {
  future: {
    webpack5: true
  },
  webpack: (config) => {
    const experiments = config.experiments || {};
    config.experiments = {...experiments, asyncWebAssembly: true};
    config.output.assetModuleFilename = `static/[hash][ext]`;
    config.output.publicPath = `/_next/`;
    config.module.rules.push({
      test: /\.wasm/,
      type: 'asset/resource',
    })
    return config
  },
}

worker.js

import wasmPath from "../add.wasm";
onmessage = async function (e) {
  const fetchPromise = fetch(wasmPath);
  const { instance } = await WebAssembly.instantiateStreaming(fetchPromise);
  console.log(instance.exports.add_one(10));
};

Look ma, no 3rd party dependencies.

I still believe there is a bug between how next.js and webpack communicate wam modules referenced by web workers, but at least the workaround is tolerable.

[nickbabcock]

The use of webpack asset modules is a good enough workaround that I'm closing this issue

[tomlagier]

This workaround doesn't work for me, unfortunately. I'm using wasm-pack and I need the "glue" it produces, which includes the wasm module import.

I've tracked the error down to this line: https://github.com/vercel/next.js/blob/canary/packages/next/build/webpack/plugins/nextjs-ssr-import.ts#L14

chunk.name is undefined. I believe what's happening is that the dynamic import plugin is incorrectly parsing the import statement, that should be getting handled by webpack alone. I'll see if there's some configuration I can pass that will achieve this but I'm not terribly hopeful of finding a fix without Next team help.

Here's chunk:

EDIT:

Just skipping the body of NextSSRImportPlugin if there is no chunk.name fixes the issue. I'm not sure what the implications of this are but I'm happy to open a PR just for discussion's sake.

[tomlagier]

To patch yourself without using the above PR, you can do this:

next.config.js

const SSRPlugin = require("next/dist/build/webpack/plugins/nextjs-ssr-import")
  .default;
 const { dirname, relative, resolve, join } = require("path");


module.exports = {
  webpack(config) {
     const ssrPlugin = config.plugins.find(
      plugin => plugin instanceof SSRPlugin
    );

    if (ssrPlugin) {
      patchSsrPlugin(ssrPlugin);
    }
  }
}

// Unfortunately there isn't an easy way to override the replacement function body, so we 
// have to just replace the whole plugin `apply` body.
function patchSsrPlugin(plugin) {
  plugin.apply = function apply(compiler) {
    compiler.hooks.compilation.tap("NextJsSSRImport", compilation => {
      compilation.mainTemplate.hooks.requireEnsure.tap(
        "NextJsSSRImport",
        (code, chunk) => {
          // This is the block that fixes https://github.com/vercel/next.js/issues/22581
          if (!chunk.name) {
            return;
          }

          // Update to load chunks from our custom chunks directory
          const outputPath = resolve("/");
          const pagePath = join("/", dirname(chunk.name));
          const relativePathToBaseDir = relative(pagePath, outputPath);
          // Make sure even in windows, the path looks like in unix
          // Node.js require system will convert it accordingly
          const relativePathToBaseDirNormalized = relativePathToBaseDir.replace(
            /\\/g,
            "/"
          );
          return code
            .replace(
              'require("./"',
              `require("${relativePathToBaseDirNormalized}/"`
            )
            .replace(
              "readFile(join(__dirname",
              `readFile(join(__dirname, "${relativePathToBaseDirNormalized}"`
            );
        }
      );
    });
  };
}

This is importing Next internals & mucking with them so it's likely to break in the future. Hopefully we can get that patch upstreamed :)

[joshrathke]

We use the Worker interface provided by Webpack 5 and ran into this issue when attempting to update to NextJS 11. @tomlagier 's patch appears to have fixed it, but it would be great to not have to have that in our config file.

[stuartmemo]

Thanks for the fix @tomlagier!

Just for others - I had to add a return config to the above (in the webpack function) to avoid this error...
Error: Webpack config is undefined. You may have forgot to return properly from within the "webpack" method of your next.config.js..

[tom-sherman]

I have also received this error although not related to wasm

The error appears when I import a file from a worker that isn't a relative import. eg.

/pages/test.js:

new Worker(new URL("../worker.js", import.meta.url))

/worker.js:

// Non relative import
import * as Curry from "rescript/lib/es6/curry.js";

The config workaround above fixes the problem, as does the patch in #26372

[Cyral]

@tom-sherman I am also receiving this error due to the web worker issue you describe (after upgrading to next 11). The fix by @tomlagier and patch #26372 work for me as well.