"Astro.request.headers was used" warning when rewriting root path

[si-fab]

Astro Info

Astro                    v5.1.3
Node                     v22.9.0
System                   macOS (arm64)
Package Manager          npm
Output                   static
Adapter                  none
Integrations             none

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

When rewriting from the / path to a subpath, Astro prints a warning about request headers being accessed.

14:49:27 [WARN] `Astro.request.headers` was used when rendering the route `src/pages/index.astro'`. `Astro.request.headers` is not available on prerendered pages. If you need access to request headers, make sure that the page is server-rendered using `export const prerender = false;` or by setting `output` to `"server"` in your Astro config to make all your pages server-rendered by default.

You can reproduce the issue with the attached repository by running npm run dev and then navigating the browser to localhost:4321.

The reproduction is the basic Astro template. The only changes I have made is moving index.astro to a /en subfolder and creating a top level index.astro that executes `Astro.rewrite("/en").

What's the expected result?

I expect no warning. I'm not accessing the request headers.

Link to Minimal Reproducible Example

https://github.com/si-fab/reproduce-header-warning

Participation

• I am willing to submit a pull request for this issue.

[matthewp]

The warning seems valid to me. index.astro is a prerendered page, it will be rendered to HTML at build time. So it cannot do a rewrite at runtime. You need to make it be not prerendered. Let me know if I'm missing something.

[ematipico]

I believe the issue is valid. In the reproduction, Astro.rewrite should work and shouldn't raise any warnings 🤔

[si-fab]

I also believe it is valid 😋. The rewrite is done during build time and not during runtime. Why should rewriting during build time need access to request headers?