Somehow randomly, at some point this error will be printed: As you can see in the repro, I've added the most basic loader I can imagine. This seems to cause the error somehow.

TL;DR

The issue can likely be mitigated by adjusting the save interval or implementing a debouncing mechanism when making rapid changes to files like app/page.tsx or app/Client.tsx during next dev.

Guidance

• Rapid Save Intervals: The error seems to occur when saving changes at very short intervals (~1-2 seconds). Try increasing the time between saves to see if the issue persists.
• Debouncing: Consider implementing a debouncing mechanism in your development workflow to limit the frequency of saves or updates to the files, potentially reducing the occurrence of the "Item already exists" error.
• Environment Variable: Running with the RUST_BACKTRACE=1 environment variable might provide more detailed backtrace information, helping to pinpoint the exact cause of the issue.
• Version Check: Although the latest available version of Next.js is being used, keep an eye on future updates, as this issue might be addressed in subsequent releases.

Example

No specific code example can be provided without altering the original codebase, but a simple debouncing function in JavaScript might look like this:

function debounce(func, wait) {
  let timeout;
  return function(...args) {
    const context = this;
    clearTimeout(timeout);
    timeout = setTimeout(() => func.apply(context, args), wait);
  };
}

This example is a basic illustration and would need adaptation to fit the specific use case.

Notes

The provided information suggests that the issue is related to the rapid saving of changes during development with next dev, possibly triggering a race condition or an issue with how Turbopack handles concurrent updates. The exact cause within the Turbopack codebase or Next.js integration is not specified and would require further investigation.

Recommendation

Apply a workaround, such as debouncing saves or increasing the save interval, as the issue seems closely related to the frequency of file updates rather than a straightforward version fix.