[Next 14] Partial Pre-Rendering (`ppr`) causes duplicate fetch calls on page revalidation

[better-salmon]

Link to the code that reproduces this issue

https://github.com/better-salmon/next14-ppr-double-revalidation-bug

To Reproduce

1. Run backend server with npm run backend.
2. In the separate terminal build and start the app with npm run build && npm run start.
3. Open http://localhost:3000/count in the browser.
4. Wait for the Cache state field to change to stale.
5. Reload the page twice to see the revalidated page with Cache state: fresh.
6. Optionally, open the terminal with the backend and see that in logs /count route was triggered twice.

Current vs. Expected behavior

Expected behavior:

When ppr option is enabled or disabled, the value should be greater than before by 1 after each revalidation.

Actual behavior:

When ppr option is enabled, the value is greater than before by 2 after each revalidation, meaning that the fetch was triggered twice.

Verify canary release

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

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.1.0: Mon Oct  9 21:28:31 PDT 2023; root:xnu-10002.41.9~6/RELEASE_ARM64_T8112
Binaries:
  Node: 20.9.0
  npm: 10.1.0
  Yarn: N/A
  pnpm: 8.10.0
Relevant Packages:
  next: 14.0.2-canary.13
  eslint-config-next: N/A
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.1.3
Next.js Config:
  output: N/A

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

App Router

Additional context

No response

[nextjs-bot]

This issue has been automatically marked as stale due to two years of inactivity. It will be closed in 7 days unless there’s further input. If you believe this issue is still relevant, please leave a comment or provide updated details. Thank you.

[nextjs-bot]

This issue has been automatically closed due to two years of inactivity. If you’re still experiencing a similar problem or have additional details to share, please open a new issue following our current issue template. Your updated report helps us investigate and address concerns more efficiently. Thank you for your understanding!