CSS not loaded correctly in next@15 when using assetPrefix and next/dynamic

[noreiller]

Link to the code that reproduces this issue

https://github.com/noreiller/next-15-unfound-asset-with-next-dynamic-and-asset-prefix

To Reproduce

1. Start the asset proxy web server (to mimic a CDN)
2. Start the main app using the asset proxy
3. Go to http://localhost:3000/
4. See that the texts are not coloured and the CSS are loaded from http://localhost:3000/ instead of http://localhost:4000 while the pathname is ok.

Current vs. Expected behavior

Following the steps from the previous section, I expected the CSS are loaded from the host used in the assetPrefix config and the texts are coloured.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #47-Ubuntu SMP PREEMPT_DYNAMIC Fri Sep 27 21:40:26 UTC 2024
  Available memory (MB): 15642
  Available CPU cores: 8
Binaries:
  Node: 18.18.2
  npm: 9.8.1
  Yarn: N/A
  pnpm: 8.2.0
Relevant Packages:
  next: 15.0.3 // Latest available version is detected (15.0.3).
  eslint-config-next: N/A
  react: 19.0.0-rc-66855b96-20241106
  react-dom: 19.0.0-rc-66855b96-20241106
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

Webpack

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

next dev (local), next start (local)

Additional context

I initially proposed a PR (#72095) with the following fix, I'll reopen it. (I closed it since I thought it was fixed.)

The CSS files are loaded on the page only with the pathname instead of using the full URL of the asset.

https://github.com/vercel/next.js/blob/canary/packages/next/src/build/webpack/config/blocks/css/index.ts#L622

- _N_E_STYLE_LOAD(new URL(href).pathname).then(
+ _N_E_STYLE_LOAD(new URL(href).toString()).then(

[yiminghe]

bug in 15.1.2

[noreiller]

bug in 15.1.2

Yes, the fix has not yet been part of a stable release.