adapter-static does not create the fallback file when prerender.enabled = false

[dimfeld]

Describe the bug

With config like this, the fallback file is not created:

 import adapter from '@sveltejs/adapter-static';

export default {
 adapter: adapter({
   fallback: 'index.html'
 }),
 prerender: {
   enabled: false,
 },
}

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-hhb1ve?file=package.json

Run npm run build and notice that build/index.html does not exist. I suspect this changed with the recent "prerender during build" PR. It was working with kit version 288 and adapter-static 28.

Logs

No response

System Info

kit 303, adapter-static 29

Severity

blocking an upgrade

Additional Information

No response

[dimfeld]

Looks like

kit/packages/kit/src/core/build/prerender/prerender.js

Lines 58 to 60 in eebe928

	if (!config.kit.prerender.enabled) {
	return prerendered;
	}

checked if fallback was set before #4192 but now it doesn't.

[dimfeld]

I tried making a change to move the fallback creation from the bottom of the function to just after where server is created, and then moved the prerender.enabled check to just after that.

This appears to work fine in my testing. Any thoughts on this?

 const server = new Server(manifest);

 const rendered = await server.respond(new Request('http://sveltekit-prerender/[fallback]'), {
         getClientAddress,
         prerender: {
                 fallback: true,
                 default: false,
                 dependencies: new Map()
         }
 });

 const file = `${config.kit.outDir}/output/prerendered/fallback.html`;
 mkdirp(dirname(file));
 writeFileSync(file, await rendered.text());


 if (!config.kit.prerender.enabled) {
         return prerendered;
 }