Deprecates exporting prerender with dynamic values

[bluwy]

Changes

This PR deprecates exporting dynamic values from the prerender export.

Motivation

1. So we can properly split out Astro with two SSR builds, one for prerendered routes, the other for on-demand routes.
2. Two SSR builds allow us to easily strip out JS chunks that're only used for prerendering, so the on-demand chunks are better optimized
3. Two SSR builds allow us to build for different environments (resolve behaviour etc). For example:
   • We prerender pages in Node.js, so we build the prerendered routes for Node.js (uses library node condition)
   • We render on-demand on Cloudflare Workers, so we build the on-demand routes for Cloudflare (uses library worker condition)

Migration

There's a new integration hook called astro:route:setup, which is passed the route options with a prerender property that can be changed. (See changesets for example)

What I'd like from you 🫵

1. What do you think of the integration API? Due to the lifecycle of reading the prerender export, it can happen anytime, e.g. in dev when a request comes in, or build where you can do it upfront before building. As such, it requires a hook/acllback form in the integration and adds a astro:route:setup hook.
2. Is this too much churn for users?
3. Let me know if the motivation is still hard to grasp. Maybe it's better to open an RFC describing in detail.

Testing

Updated prerendering test to make sure the integration API works.

Docs

withastro/docs#9064

[changeset-bot]

🦋 Changeset detected

Latest commit: 16069fb

The changes in this PR will be included in the next version bump.

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[github-actions]

This PR is blocked because it contains a minor changeset. A reviewer will merge this at the next release if approved.

[Princesseuh]

This is personally completely fine with me, don't see any big issues. It's annoying for the users who used this ability, but it seems niche enough that they will hopefully understand the benefits this bring.

[bluwy]

I've refactored to add a new astro:route:setup instead as it feels right and better than forcing a callback API. Will start working on the docs.

[ematipico]

Thank you Bjorn! Awesome work

[sarah11918]

Looks great @bluwy ! Assuming I understand this correctly, I left a suggestion below for you to see if you can make work that I think would be helpful!

[matthewp]

lgtm!

[sarah11918]

Looks fantastic, @bluwy ! Thanks for the help!

[bluwy]

I just pushed a commit earlier that fixes a glaring mistake where the hook only runs if you had an explicit export const prerender code in the file. I moved it so the hook will always run as expected whenever the module is transformed (or per request)

merge day