Turbopack Error: Item already exists

[MaenAbabneh]

Turbopack version: v16.0.0-beta.0
Next.js version: 0.0.0

Error message:

Item already exists

Debug info:
- Execution of hmr_update_with_issues_operation failed
- Execution of PlainIssue::from_issue failed
- Execution of PlainSource::from_source failed
- Execution of <WebpackLoadersProcessedAsset as Asset>::content failed
- Execution of WebpackLoadersProcessedAsset::process failed
- Execution of evaluate_webpack_loader failed
- Item already exists

[DanielSalazarLoaiza]

This error usually happens when Turbopack detects duplicate asset entries or overlapping module references during HMR updates.
It can be triggered by symlinked dependencies, multiple React instances, or loaders producing the same output filename.

Try clearing.nextand reinstalling dependencies (rm -rf .next node_modules && npm i). If the issue persists, check for duplicated packages (e.g., react, next, or custom loaders) in your dependency tree.

It might also be worth verifying if the error disappears with a clean incremental build, as Turbopack sometimes misdetects changes during HMR on Windows file systems.

[amannn]

loaders producing the same output filename

@DanielSalazarLoaiza Can you elaborate what this means exactly?

I'm working on a custom Turbopack loader and I run into the "Item already exists" error from time to time. I've added a bug report with a minimal reproduction here: #85833