Async page options

[CapitaineToinon]

Hey there!

I was wondering if there was any plan to add the posibility to have async page options. Basically having the possibility to export a function instead of a simple boolean. The use case I'm personally thinking of would by conditionnal client side rendering.

Imagine your frontpage has interactive content but requires you to be logged in for those interactive bits to work. Right now, you have no choice but enable CSR for the page even if anonymous won't need any javascript. For example this simple page:

<script>
    export let data;

    let count = 0;
</script>

<h1>Homepage</h1>

{#if data.user}
    <button on:click={() => count += 1}>{count}</button>
{/if}

Would break for logged in users if CSR is turned off. My idea would be to allow CSR to accept a function, similar to a load function.

export let csr = async ({ locals }) => {
	return locals.user !== null
}

Looking a bit at the code, it seems like the render function that actually gets the page options also have access to the current event and could therefore be passed down to the nodes instead through a function.

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

Lines 303 to 318 in b915dfe

	return await render_response({
	event,
	options,
	manifest,
	state,
	resolve_opts,
	page_config: {
	csr: get_option(nodes, 'csr') ?? true,
	ssr: true
	},
	status,
	error: null,
	branch: compact(branch),
	action_result,
	fetched
	});

Any thoughts on this?