I don't think this makes sense. How do you have multiple SPA fallbacks with static files?

I don't, there is just one fallback(index.html), but other routes get outputed if there is no dynamic parts/slugs in them, so we can output the appropriate link preloads in them so the loading happens quicker.

What link preloads are we talking about?

<link rel=modulepreload>

Right, but which modules are we preloading? We can't know which modules a given page depends on without server-rendering them, but the whole reason to use SPA+fallback is that you can't server-render those pages.

Yeah, but I'm not specifically talking about fallback page(200.html for ex.) but other routes that are not server rendered({ssr:false}) but create their own html files(books.html in my case is one of them) needs resources /_app/pages/__layout.svelte-xxxxxxxx.js (every page including fallback should include Layout preload) and /_app/pages/books/index.svelte-xxxxxxxx.js and we know those things in advance so we should include them when prerendering because it delays rendering(slightly) to have to parse start.js to find what resources it needs to render the current page.

This is related to issue #4157 I also created where I'm requesting to prerender even the parameterized routes when {ssr:false} and adapter-static is being used so I can manually create rewrite file for my specific hosting service for routes, essentially my request in that issue is if there is a route for /users/[user_id].svelte and ssr is false to prerender/output it as /users/_slug_id_.html or something similar, and in that case we do link preloads for them too, and that would make fallback file(at least for my case, and I believe for some others too) unnecessary.

Does that makes sense?

@Rich-Harris I could maybe try to do PR for this, but I don't know much about Svelte/Vite compilation

Note to self: an SSRNode looks like this:

import * as module from '../entries/pages/about.svelte.js';

export { module };
export const entry = 'pages/about.svelte-d3051e16.js';
export const js = ["pages/about.svelte-d3051e16.js","chunks/index-2e6eec55.js"];
export const css = ["assets/pages/about.svelte-bf4528fa.css"];

If it didn't eagerly import the module, or if the entry/js/css exports lived somewhere other than the SSRNode, we could create modulepreload/stylesheet links for non-SSR'd pages (though we'd be making an assumption that no error will occur when the page hydrates; if it did, we wouldn't have preloaded the error chunks, which is probably fine).

So this is possible, albeit not a top priority