Turbopack fails to load valid .mjs module with UTF-8 error

[DennisSmolek]

Link to the code that reproduces this issue

https://github.com/utsuboco/r3f-perf/blob/752adc19edbcabc43fc917519c5366718fa0b9d0/src/components/TextsHighHZ.tsx#L10

To Reproduce

Description

Turbopack is failing to load a valid .mjs module that exports a base64 string. The module is from r3f-perf package and contains a valid JavaScript file that exports a base64-encoded font string.

Error Message

Module not found: Can't resolve '../roboto.woff.mjs'
8 | import as THREE from "three";
9 | import { useEvent } from "@utsubo/events";
> 10 | import localFont from "../roboto.woff.mjs";
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11 | import { getPerf } from "../store.mjs";
failed to convert rope into string
Caused by:
invalid utf-8 sequence of 1 bytes from index 11

Current vs. Expected behavior

Expected Behavior

The file should load successfully as it's a valid ES module that simply exports a string:

javascript
// Content of roboto.woff.mjs
const localFont = "data:font/woff;base64,..."
export { localFont as default };

Actual Behavior

Turbopack appears to be attempting UTF-8 validation before module parsing, causing it to fail on what should be a valid JavaScript file. The same file loads correctly when using webpack.

Their package is Typescript and builds for CJS and ESM. I tried aliasing and it failed.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Home
  Available memory (MB): 40638
  Available CPU cores: 16
Binaries:
  Node: 20.9.0
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 14.2.23 // An outdated version detected (latest is 15.1.5), upgrade is highly recommended!
  eslint-config-next: 14.1.0
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.7.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Webpack, Turbopack, Developer Experience

Which stage(s) are affected? (Select all that apply)

next dev (local), next start (local)

Additional context

• This worked in Next.js 14.1 with Turbopack
• Still works with webpack in Next.js 14.2
• The file is a valid ES module exporting a base64 string
• Attempted to use resolveAlias in turbo config but it's ignored
• Package affected: r3f-perf

Link to issue in other library : utsuboco/r3f-perf#59

Impact

This prevents using Turbopack with packages that use this pattern for asset loading, requiring fallback to webpack development server.

[github-actions]

We cannot recreate the issue with the provided information. Please add a reproduction in order for us to be able to investigate.

Why was this issue marked with the please add a complete reproduction label?

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Useful Resources

• How to Contribute to Open Source (Next.js)
• How to create a Minimal, Complete, and Verifiable example
• Reporting a Next.js bug
• Next.js Triaging issues

[samcx]

@DennisSmolek We will need a reproduction that uses Next.js!