fix(routing): emit error for forbidden rewrite

[ematipico]

Changes

Closes PLT-2607
Closes #12336

Even though the issue was reported for Astro v4, unfortunately, we can't fix it because the prerender field doesn't change there, and we fixed that issue in v5.

This PR forbids to rewrite a SSR route with a SSG route, when using the server output. That's because when the SSG routes are built, they aren't part of the server output, and they are emitted as static files. Static files are served by the host, and the Astro runtime can't retrieve them at runtime during the rewriting process. This results in a runtime error at the moment.

Because of that, I decided to simulate a similar behaviour and throw an error, with some information.

Testing

I added a new test case

Docs

I will probably send a PR to explain this limitation.

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[sarah11918]

Question: does this happen only with 'server' configured, or for any on-demand page that tries to rewrite with a prerendered page?

With the new 'static' mode, someone could still add an adapter and have an on-demand route that attempts a rewrite to a (default) prerendered page. Is that also a problem?

[lilnasy]

Couldn't it just be supported instead of being forbidden?
For example, Cloudflare provides a simple function to retrieve static assets.: https://developers.cloudflare.com/workers/static-assets/binding/. Similarly for node, it's a matter of reading from disk.

[ematipico]

Couldn't it just be supported instead of being forbidden? For example, Cloudflare provides a simple function to retrieve static assets.: developers.cloudflare.com/workers/static-assets/binding. Similarly for node, it's a matter of reading from disk.

Not at this time, because as you said it's the adapter that helps with that (Cloudflare and Node.js), but the rewrite code is runtime agnostic, so we can't easily implement this as bugfix without providing an adapter feature for this use case.

We can definitely support this via adapters, with some architectural changes, but that's definitely a feature, and it requires adapters to have a role in this.

[ematipico]

Question: does this happen only with 'server' configured, or for any on-demand page that tries to rewrite with a prerendered page?

With the new 'static' mode, someone could still add an adapter and have an on-demand route that attempts a rewrite to a (default) prerendered page. Is that also a problem?

@sarah11918 I am not really sure to be honest, I need to investigate

[sarah11918]

Just a note that I'll want to look over docs after we know whether we need to specifically say 'server' mode, or whether this is the case for any on-demand rendered route, even in the new 'static' mode!

[ematipico]

@sarah11918 I looked at it, and this change affects only server adapters.

[sarah11918]

Thanks @ematipico ! Had just wanted to make sure we needed the extra bit of wording (and that everything is fine in static mode) to know exactly what we needed to say! 🙌

Just fixed some tiny typos and had a thought about the error name for your consideration!

[sarah11918]

Just noting that there may eventually be other kinds of "forbidden" rewrites, so not sure whether you want to add more context like ForbiddenRewriteToStatic or something like that?

[ematipico]

I'd prefer not. The kind of error would be the same, but we can customise the message based on the situation.

[florian-lefebvre]

Is there a way we could avoid the duplication across all the pipelines?

[ematipico]

It really depends on how you want to avoid the duplication. We can put the check in one single function, but I think the error should be thrown where we consume the check. What do you have in mind?