+layout.server.js not correctly passing data down during client-side hydration

Describe the bug

After client side navigation, calling await parent() from within a +page.server.js exported load function returns {"data":null} instead of the value returned from the +layout.server.js exported load function

Reproduction

• Load https://stackblitz.com/edit/sveltejs-kit-template-default-8az3ew?file=src/routes/+page.server.js
• Note that layout data, and page data are correct initially
• Click on ‘Another page’ link, to do a client side navigation to a new page
• Note that layout data is now incorrect (as is the layout data that was merged into page data)

Logs

No response

System Info

stackblitz default template fork

Severity

serious, but I can work around it

Additional Information

No response

[rmunn]

On first navigation, the load function in +layout.server.js is run, because the server is hit. The second navigation is a client-side-only nagivation, so the server isn’t hit, and therefore +layout.server.js isn’t run and the values it returns aren’t preserved. And instead, await parent() gets { data: null }, which indeed doesn’t seem right.

In https://github.com/sveltejs/kit/discussions/5883#discussioncomment-3393943, Rich Harris wrote that load results are re-used; the question I don’t yet know the answer to is whether load results from server load functions are intended to be preserved after client-side navigations. I suspect the answer is yes, in which case the issue title should probably be changed to “load() results from server discarded after client-side nagivation” to better reflect what the actual bug is.

[robertadamsonsmith]

I agree - I don’t know if changing the title of the issue would confuse somebody that has already seen it once though. Unless the issue extends beyond the +layout.server.js though, perhaps the title should be: “load() results from +layout.server.js discarded after client-side navigation”

I’ve reduced the reproduction to one which shows the problem in a more minimal way (i.e. without a +page.server.js and await parent()): https://stackblitz.com/edit/sveltejs-kit-template-default-euznnp?file=src/routes/+layout.svelte