semi public types

[Rich-Harris]

Deploy preview: https://kit-svelte-dev-git-semi-public-types-svelte.vercel.app/docs/types#additional-types

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I tried to do this in #4021 but the merge was too gnarly. Easier to start fresh.

The basic thinking here is that we have public types in index.d.ts and ambient.d.ts, and private-but-documented types in private.d.ts. Changes to these types should be made carefully to avoid breakage.

internal.d.ts is for things that aren't referenced by public types, and can be changed freely.

So far I haven't actually moved most of the types, I've just set up the logic for extracting/rendering/linking them.

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[Rich-Harris]

Ok I think this is ready for review. There's some further tweaks I'd like to make to the types (particularly EndpointOutput) but they probably warrant a separate PR.

The big change here, other than that private types are now documented, is that a bunch of formerly public types are now in private.d.ts. I've been quite liberal in moving things over, on the basis that we can easily move things from private.d.ts to index.d.ts, but we can't go the other way without breaking changes. The test for whether something goes in index.d.ts was 'is a user likely to need to import this type?'

[benmccann]

this looks great!

[benmccann]

maybe remove this TODO now that it's no longer public?

[tv42]

By unexporting LoadInput/LoadOutput, this change made using Typescript harder. Previously, I could say

  export async function load({ fetch }: LoadInput): Promise<LoadOutput> {

Now it seems I have to use this form

  export const load: Load = ({ fetch }) => {

I know this is a style thing, and a lot of people seem to write arrow expressions everywhere, but I'm more inclined to agree with https://deno.land/manual/contributing/style_guide#top-level-functions-should-not-use-arrow-syntax

[benmccann]

I'm not disagreeing about whether we should export LoadInput and LoadOutput, but I would think if you want to avoid arrow expressions you could write it as:

  export const load: Load = function({ fetch }) {

[tv42]

Sure, that avoids the arrow expression, but still uses an unnecessary const where just export function should suffice.