breaking: render the root error page for handle and endpoint errors when the request expects HTML

[Nic-Polumeyv]

Fixes #13646

Fatal errors from handle and +server.js now go through respond_with_error, which renders the root +error.svelte, when the request is a top-level document request that accepts HTML. Data, route-resolution, remote, sub-request, prerender and subresource requests keep the previous behavior, reusing the Sec-Fetch-Dest set from #16463.

This was already safe for handle errors: if the root layout load fails because the hook died before setting up locals, respond_with_error's existing catch falls back to error.html.

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

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 6db644f:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/6db644f7a8e593924ea44b9f1c4b53b1ec9509d2

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16488

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6db644f

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

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@sveltejs/kit	Major

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[theetrain]

Thanks for handling this. A couple of thoughts:

• This may need to be marked as a breaking change since previous behaviour no longer matches this new behaviour.
• Does only the root +error.svelte get rendered when a deep-nested route throws, or will the nearest +error.svelte render?

[Nic-Polumeyv]

Root only, same as 404s. The nearest boundary would need the route's load chain, which already failed for handle and does not exist for +server.js.

[Nic-Polumeyv]

Closing per https://github.com/owner/repo/issues/123#issuecomment-5065696448