[breaking] add builder.generateFallback(fallback) API

[Rich-Harris]

closes #7899. This changes the behaviour around fallback 200.html/404.html pages so that they are only generated when needed (which, in practice, means only in adapter-static).

As a result, no rendering takes place during the build unless prerender.entries is populated.

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🦋 Changeset detected

Latest commit: ccb7853

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

This PR includes changesets to release 2 packages

Name	Type
@sveltejs/adapter-static	Patch
@sveltejs/kit	Patch

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[JordanShurmer]

Did something change in recent releases around this behavior?

Specifically, is this claim still true: "no rendering takes place during the build unless prerender.entries is populated."?

When upgrading from 1.0.0 to 1.2.10 our build fails with "Prerendering failed with code 1", and an error saying fetch can't be found within one of our server files. Adding prerender: { entries: [] } does not fix it.

[dummdidumm]

What error message specifically? Is this #8536 by any chance?

[JordanShurmer]

No, it doesn't seem like that error. Here's what I am getting:

file:///stuff/.svelte-kit/output/server/chunks/landingPage.js:15
    fetch,
    ^

ReferenceError: fetch is not defined
    at ourClient (file:///stuff/.svelte-kit/output/server/chunks/landingPage.js:15:5)
    at file:///stuff/.svelte-kit/output/server/chunks/landingPage.js:44:16
    at ModuleJob.run (node:internal/modules/esm/module_job:198:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:385:24)
    at async Promise.all (index 1)
    at async file:///stuff/node_modules/.pnpm/@sveltejs+kit@1.2.10_svelte@3.55.1+vite@4.0.4/node_modules/@sveltejs/kit/src/core/postbuild/index.js:61:17
[vite-plugin-sveltekit-compile] Prerendering failed with code 1
error during build:
Error: Prerendering failed with code 1
    at ChildProcess.<anonymous> (file:///stuff/node_modules/.pnpm/@sveltejs+kit@1.2.10_svelte@3.55.1+vite@4.0.4/node_modules/@sveltejs/kit/src/exports/vite/index.js:629:15)
    at ChildProcess.emit (node:events:527:28)
    at Process.ChildProcess._handle.onexit (node:internal/child_process:291:12)
 ELIFECYCLE  Command failed with exit code 1.

[JordanShurmer]

Following up on my question about whether this behavior has changed. For our build, we start seeing the error above when we move from 1.0.12 to 1.0.13

https://github.com/sveltejs/kit/releases/tag/%40sveltejs%2Fkit%401.0.13

I'll check out what changes were included in this release.

[dummdidumm]

Might be #8655 then

[JordanShurmer]

Yes, I just found that issue as well. It does seem to be the same. Things provided by node are no longer available during the pre-render?

I still question why it is even pre-rendering at all though. Any ideas on that @dummdidumm ?

[dummdidumm]

It's not really prerendering, it's loading the code to analyse it