New Rule: svelte/kit-parent-function-at-bottom rule

[baseballyama]

Motivation

I would like to recognize performance overhead regarding parent.

/** @type {import('./$types').PageLoad} */
export async function load({ params, parent }) {
  const parentData = await parent();
  //                       ^ `parent` function can execute later to avoid a waterfall
  const data = await getData(params);

  return {
    ...data
    meta: { ...parentData.meta, ...data.meta }
  };
}

Description

SvelteKit has parent function. And according to the document, parent should use at the bottom of load function as much as possible in terms of performance.

https://kit.svelte.dev/docs/load#using-parent-data

But it's too difficult to recognize by human code review, so I would like to recognize this automatically.

Examples

/** @type {import('./$types').PageLoad} */
export async function load({ params, parent }) {
  // NG
  const parentData = await parent();
  const data = await getData(params);
  // OK
  const parentData = await parent();
  // OK (Because `doSomething` needs to use the return value of `parent`.)
  const foo = await doSomething(parentData);

  return {
    ...data
    meta: { ...parentData.meta, ...data.meta }
  };
}

Additional comments

I need to think about better rule name.😅

[ota-meshi]

New rule sound good to me!
We need a better rule name, as you say, but I don't have any ideas 😓

[devunt]

How about svelte/avoid-waterfall-in-kit-loads?

[ota-meshi]

Hmm. I'm not familiar with English, so I'm not sure what "waterfall" means. So I'm not sure if that naming of the rule makes sense 😓. I would like someone's opinion on that name.

[baseballyama]

waterfall is used in the kit doc. So this word itself is natural.

[baseballyama]

But to protect waterfall, possibly we need to take care something more in the future, so I'd like to use a name that has a specific check purpose.
I mean "This is is just check the place of parent function. Not check everything regarding avoiding waterfall"