Non-SSR'd pages should be prerendered by default

[Rich-Harris]

Describe the problem

While we recommend that people use SSR as widely as possible, some apps don't. In these cases, there's no obvious reason not to prerender the shell page.

Describe the proposed solution

If a page is rendered with ssr: false, don't bail out during prerendering here, unless export const prerender is explicitly false (to provide an escape hatch when the app is doing something funky in handle):

kit/packages/kit/src/runtime/server/page/respond.js

Lines 70 to 76 in b5cf676

	if (!leaf.prerender && state.prerender && !state.prerender.all) {
	// if the page has `export const prerender = true`, continue,
	// otherwise bail out at this point
	return new Response(undefined, {
	status: 204
	});
	}

Alternatives considered

The alternative is to continue dynamically server-rendering empty pages. Totally fine, since rendering an empty page is cheap, but wasteful nonetheless.

Importance

nice to have

Additional Information

No response

[Rich-Harris]

occurs to me that this is technically a breaking change, so added to 1.0

[Tal500]

Though this feature sounds awesome, this amplifies the problems with removing the option of disabling prerendering, as I said:

Today, you can disable that with config.kit.prerender.enabled = false. But if we're leaning more in this direction, we would probably need to get rid of that option.

For my testing, I like to build some projects locally with prerendering disabled (for debugging prerendering issues and also for faster build time). Therefore, removing the options to (temporary) disable prerendering is not preferable for me, and I believe also for other people.

I do agree that this configuration in svelte.config.js is problematic. As a compromise, maybe except some environment variable to disable prerendering or such?

Originally posted by @Tal500 in #7716 (comment)

Though this problem was amplified, the solution seems to be more clear now - perhaps add a configuration of prerendering, to be one of these three states:

1. 'disabled': No prerendering, ignoring each page settings.
2. 'strict': Prerender each page if and only if in the page settings prerender === true.
3. 'lax': Prerender each page if and only if in the condition you mentioned in this issue is happening(can be changed in the future to be even more laxed).

Obvious note: This issue suggests to make the third option the default, while currently the second one is the default.

[Rich-Harris]

I'm not totally sure I see the problem — you could prevent the prerendering from happening just by passing entries: [] (which you're probably already doing if you can't run handle inside build) or adding prerender = false alongside ssr = false.

[Tal500]

I'm not totally sure I see the problem — you could prevent the prerendering from happening just by passing entries: [] (which you're probably already doing if you can't run handle inside build) or adding prerender = false alongside ssr = false.

OK, missed that option. Tnx