Inconsistent results between app directory and pages directory when typechecking

[aranlucas]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

https://github.com/contentlayerdev/contentlayer/issues/506#issuecomment-1654798145

This piece of code https://github.com/vercel/next.js/blob/aed332b2f69772bb2abc8df2fbae1e4ad869a7fc/packages/next/src/build/index.ts#L411C1-L414C78 causes inconsistent results when using contentlayer. Contentlayer relies on the same behavior to check types AFTER webpack compile.

When using only a pages NextJS application, you can "fix" the behavior by adding an empty app folder or skipping typechecking in next.config

Is there any reason typechecking isn't always done after compile?

Which area(s) of Next.js are affected? (leave empty if unsure)

TypeScript (plugin, built-in types)

Link to the code that reproduces this issue or a replay of the bug

https://stackblitz.com/edit/github-38v7yj-w6w7em?file=next.config.mjs

To Reproduce

1. Create a new pages only NextJS app (No app folder!)
2. Follow contentlayer instructions for setup https://www.contentlayer.dev/docs/reference/next-contentlayer-e6e7eb3a
3. npm run build

./src/pages/[...slug].tsx:1:25
Type error: Cannot find module 'contentlayer/generated' or its corresponding type declarations.

  > 1 | import { allDocs } from "contentlayer/generated"
    |                         ^
  2 | import { GetStaticPaths, InferGetStaticPropsType } from "next"
  3 | import { useMDXComponent } from "next-contentlayer/hooks"
  4 | import Layout from "@/components/layout"

Describe the Bug

Typescript checking is done before webpack compile. Anyone relying on prebuild hook will not have generated their types.

This might be a Windows only bug as I could not reproduce on the stackblitz

Expected Behavior

Either a new hook is created for "pre-build" or typechecking should

Which browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

[balazsorban44]

Based on contentlayerdev/contentlayer#506 (comment), this is not a problem at least in later versions, make sure you upgrade (please test next@canary as well).

Keep in mind that withContentlayer is tapping into the Next.js Webpack configuration, which does not follow semver as mentioned in the docs:

https://nextjs.org/docs/app/api-reference/next-config-js/webpack

[github-actions]

Please verify that your issue can be recreated with next@canary.

Why was this issue marked with the please verify canary label?

We noticed the provided reproduction was using an older version of Next.js, instead of canary.

The canary version of Next.js ships daily and includes all features and fixes that have not been released to the stable version yet. You can think of canary as a public beta. Some issues may already be fixed in the canary version, so please verify that your issue reproduces by running npm install next@canary and test it in your project, using your reproduction steps.

If the issue does not reproduce with the canary version, then it has already been fixed and this issue can be closed.

How can I quickly verify if my issue has been fixed in canary?

The safest way is to install next@canary in your project and test it, but you can also search through closed Next.js issues for duplicates or check the Next.js releases. You can also use the GitHub templates (preferred) for pages and App Router, or the CodeSandbox: pages or CodeSandbox: App Router templates to create a reproduction with canary from scratch.

My issue has been open for a long time, why do I need to verify canary now?

Next.js does not backport bug fixes to older versions of Next.js. Instead, we are trying to introduce only a minimal amount of breaking changes between major releases.

What happens if I don't verify against the canary version of Next.js?

An issue with the please verify canary that receives no meaningful activity (e.g. new comments that acknowledge verification against canary) will be automatically closed and locked after 30 days.

If your issue has not been resolved in that time and it has been closed/locked, please open a new issue, with the required reproduction, using next@canary.

I did not open this issue, but it is relevant to me, what can I do to help?

Anyone experiencing the same issue is welcome to provide a minimal reproduction following the above steps. Furthermore, you can upvote the issue using the 👍 reaction on the topmost comment (please do not comment "I have the same issue" without reproduction steps). Then, we can sort issues by votes to prioritize.

I think my reproduction is good enough, why aren't you looking into it quicker?

We look into every Next.js issue and constantly monitor open issues for new comments.

However, sometimes we might miss one or two due to the popularity/high traffic of the repository. We apologize, and kindly ask you to refrain from tagging core maintainers, as that will usually not result in increased priority.

Upvoting issues to show your interest will help us prioritize and address them as quickly as possible. That said, every issue is important to us, and if an issue gets closed by accident, we encourage you to open a new one linking to the old issue and we will look into it.

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

[balazsorban44]

This issue has been automatically closed because it wasn't verified against next@canary. If you think it was closed by accident, please leave a comment. If you are running into a similar issue, please open a new issue with a reproduction. Thank you.

[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.