Accumulate data

[Rich-Harris]

Closes #5994.

Today, if you have a page with a load...

// src/routes/foo/+page.js
export function load() {
  return {
    pagedata: 'hello from page load'
  };
}

...then the corresponding data prop will contain pagedata and nothing else. If you have some data from a layout load function that you need in the page, you need to call await parent() in the page's load:

// src/routes/foo/+page.js
-export function load() {
+export async function load({ parent }) {
+  const { layoutdata } = await parent();
  return {
+    layoutdata,
    pagedata: 'hello from page load'
  };
}

As of this PR, that's no longer the case — layout data will automatically be inherited (with correct types!) so that you can reference data.layoutdata (or, more realistically, data.user.name) throughout your app without boilerplate.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. All changesets should be patch until SvelteKit 1.0

[changeset-bot]

🦋 Changeset detected

Latest commit: b64a449

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[dummdidumm]

Looks good! I left three things that probably need a change, also the docs should probably mention this

[tsukhu]

Thank you for this update. I have deleted 3 +page.ts files now :-)

[rohanrajpal]

Love this!