Parallel loading server modules during SSR compile results in initialization error

[dadezzz]

Hi, building an app with SvelteKit I introduced a change related to a Batch class, that probably caused some circular imports in the code. Before this change the app used to build and work fine, but now I can't compile it.

This is the log of the build script:

root@855b9ca72830:/workspace/packages/website# bun run build
$ cp ../../.env.example .env && svelte-kit sync && vite build
vite v7.3.0 building ssr environment for production...
✔ [paraglide-js] Compilation complete (message-modules)                                                                                                                                 
✓ 2758 modules transformed.
46 |     }
47 |   }
48 |   let er;
49 |   if (args.length > 0)
50 |     er = args[0];
51 |     throw er;
                 ^
ReferenceError: Cannot access 'Batch' before initialization.
      at emitError (node:events:51:13)
      at #onError (node:worker_threads:222:14)
✗ Build failed in 12.86s
error during build:
[vite-plugin-sveltekit-compile] Failed with code 1
    at <anonymous> (/workspace/node_modules/.bun/@sveltejs+kit@2.49.2+226e7cd46330b62b/node_modules/@sveltejs/kit/src/utils/fork.js:65:17)
    at emit (node:events:95:22)
    at #onClose (node:worker_threads:212:44)
error: script "build" exited with code 1

It shows an error related to a failed initialization of one of my modules, specifically when loading it inside the analyse function of SvelteKit.

I tried to search for issues in my code but the changes that I introduced shouldn't have caused the error to appear now. So I tried to look at SvelteKit's code and found that slightly modifying the snippet that loads the modules from the server manifest makes the compilation complete succesfully.

The change that I introduced ensures that the loading is sequential, in a for loop, instead of parallel with Promise.all. I don't have extensive knowledge of the internals of SvelteKit so this might be completely unrelated to the real problem, but it solves mine.

In packages/kit/src/core/postbuild/analyse.js:

async function analyse({ /*...*/ }) {
  // ...

  // Sequential loading, works.
  async function load_nodes() {
    const result = []

    for (const loader of manifest._.nodes) {
      result.push((await loader()));
    }

    return result
  }

  // Current implementation, throws error.
  async function load_nodes_2() {
    return await Promise.all(manifest._.nodes.map(l=>l()))
  }

  const nodes = await load_nodes();
	
  // ...
}

Unfortunately I don't know how I could reproduce this error in a minimal way, if someone has ideas any ideas for debugging then I would be grateful.

[dadezzz]

I found out it's an open issue in Bun, so I hope they will solve it there.