Cannot name a folder "index" inside the app directory.

[jazsouf]

Link to the code that reproduces this issue

https://github.com/jazsouf/redirects-test

To Reproduce

Try to build the application with a folder named index with a page.tsx inside the app directory.

Current vs. Expected behavior

Expected to build the page and navigate to the /index route.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:21 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T8103
  Available memory (MB): 8192
  Available CPU cores: 8
Binaries:
  Node: 22.4.1
  npm: 10.8.2
  Yarn: N/A
  pnpm: 9.5.0
Relevant Packages:
  next: 14.2.5 // Latest available version is detected (14.2.5).
  eslint-config-next: 14.2.5
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.5.4
Next.js Config:
  output: N/A

Which area(s) are affected?

Routing

Which stage(s) are affected?

next build (local) / vercel build

Additional context

I had an issue with redirecting the home page to the "/index" page. I wanted to reproduce this issue, but actually found what I believe is the root cause: You cannot name a folder "index" inside your app router.
The build error in question:

`Error occurred prerendering page "/index". Read more: https://nextjs.org/docs/messages/prerender-error

TypeError: Cannot read properties of undefined (reading 'clientModules')`

[AbhiShake1]

I was looking into this and i observed a few things that could be useful for anyone debugging this:

• this issue does not occur with turbopack (in the reproduction, it was working in dev mode due to --turbo flag)

[jazsouf]

Yeah, it doesn't work in regular Webpack dev mode.

This issue must be with Webpack thinking that the '/index' route belongs to the pages router.

Maybe there is a isAppRouter condition somewhere not properly set?

[AbhiShake1]

@jazsouf if you actually mv .next/server/app/index/index/* .next/server/app/index it will work

[jazsouf]

Yes just saw the pr from @simonri . Will close this when merged.