Triggering notFound in generateMetadata results in Error: NEXT_NOT_FOUND when the delayed notFound call is used (e.g. fetch)

[fax1ty]

Link to the code that reproduces this issue

https://github.com/fax1ty/next-generatemetadata-repro

To Reproduce

1. Start the application in dev mode (yarn dev)
2. Go to /en/test/id

Current vs. Expected behavior

Current: I get NEXT_NOT_FOUND in console
Desired: I see the 404 content

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro
  Available memory (MB): 16291
  Available CPU cores: 12
Binaries:
  Node: 21.2.0
  npm: 10.2.3
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 14.2.3 // Latest available version is detected (14.2.3).
  eslint-config-next: 14.0.4
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.4.5
Next.js Config:
  output: N/A

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

Metadata, Navigation

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

next dev (local), next start (local), Vercel (Deployed), Other (Deployed)

Additional context

May relate to #65013
If you remove the setTimeout, everything works as expected
P.S. I have created a copy of real-world project that demonstrates this problem. Perhaps the issue is something else entirely.

[ztanner]

Hi @fax1ty --

This doesn't appear to be related to where you call it -- ie, I see the same problem when I do the setTimeout + notFound() inside the Page component itself.

Can you clarify the real-world use-case a bit more? If you're trying to trigger notFound() after some async work, you should await that async work and call notFound() afterwards. For example:

const asyncWork = new Promise((resolve) => {
  setTimeout(() => {
    resolve();
  }, 500);
});

await asyncWork;
notFound();

When you call it inside of a setTimeout callback, Next.js won't be able to catch & handle the error, because it will happen asynchronously outside the main execution flow of your component. The notFound() function needs to be called within the lifecycle of a request in a way that Next.js can properly handle and render the appropriate error page.

In your original code, the notFound() function is being executed inside the setTimeout callback, which detaches it from the main request lifecycle. Next.js is designed to handle such errors synchronously within the request lifecycle. To fix this, ensure any asynchronous operations are properly awaited and errors like notFound() are called synchronously after those operations complete.

I'm going to close this as I don't think there's a bug, but please let me know if I'm misunderstanding a use-case that makes the above recommendation not possible.

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.