Error when building: Unexpected token u in JSON at position 0

[rijk]

Verify canary release

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

Provide environment information

npx next info

    Operating System:
      Platform: darwin
      Arch: arm64
      Version: Darwin Kernel Version 22.2.0: Fri Nov 11 02:06:26 PST 2022; root:xnu-8792.61.2~4/RELEASE_ARM64_T8112
    Binaries:
      Node: 16.18.1
      npm: 8.19.2
      Yarn: N/A
      pnpm: 7.26.3
    Relevant packages:
      next: 13.1.7-canary.2
      eslint-config-next: 13.1.1
      react: 18.2.0
      react-dom: 18.2.0

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

App directory (appDir: true)

Link to the code that reproduces this issue

https://github.com/rijk/repro-rsc-issue/tree/repro

To Reproduce

Run pnpm run build

Describe the Bug

I was tracking down another issue with Vercel support (requesting a certain page with RSC header returned an error 500). After updating my reproduction to Next canary it no longer wanted to build at all:

[==  ] info  - Generating static pages (4/13)SyntaxError: Unexpected token u in JSON at position 0
    at JSON.parse (<anonymous>)

Support engineer asked me to create an issue for it.

Expected Behavior

No error.

Which browser are you using? (if relevant)

Not relevant

How are you deploying your application? (if relevant)

Vercel

[rijk]

All right, I've discovered this is caused by a conditional return in several head components. Adding return null to the end fixed the build issue.

As an aside (and why I'll leave this open although the original issue is fixed), while debugging I found that if a page does not have a generateStaticParams() (or returns [] from it), it is called with params like this:

{
  organization: '%5Borganization%5D',
  path: '%5Bpath%5D',
  lesson: '%5Blesson%5D'
}

Is this intentional? It strikes me as odd.

[ijjk]

Hi, this is currently expected yes as we currently attempt prerendering the page with default params to test if it is static or not similar to the generation of fallback pages. We are investigating this behavior still though.

[github-actions]

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