Error Page load function doesn't respect redirect during SSR

[moatra]

Describe the bug

If an error page's load function returns a result with the redirect property set, the redirect is honored during client side navigation, but not during SSR.

Reproduction

git clone git@github.com:moatra/svelte_error_redirect.git
cd svelte_error_redirect
npm install
npm run dev

Working: Client side navigation

Load http://localhost:5173 in a browser, and click on the the "dashboard" link. The client will eventually land on /login?from=/dashboard due to the dashboard endpoint returning a 401 and the error page redirecting to the login page.

Not working: Server side rendering

Load http://localhost:5173/dashboard in a new browser tab. The browser will get the Error Page html response instead of being redirected to /login?from=/dashboard

Logs

Logging the error that the `__error.svelte` load function receives:

Error: Failed to load data
    at load_shadow_data (file:///home/thomas/Projects/svelte_repros/error_redirect/.svelte-kit/runtime/server/index.js:2705:18)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async load_node (file:///home/thomas/Projects/svelte_repros/error_redirect/.svelte-kit/runtime/server/index.js:2279:5)
    at async respond$1 (file:///home/thomas/Projects/svelte_repros/error_redirect/.svelte-kit/runtime/server/index.js:2980:15)
    at async resolve (file:///home/thomas/Projects/svelte_repros/error_redirect/.svelte-kit/runtime/server/index.js:3442:11)
    at async respond (file:///home/thomas/Projects/svelte_repros/error_redirect/.svelte-kit/runtime/server/index.js:3386:20)
    at async file:///home/thomas/Projects/svelte_repros/error_redirect/node_modules/@sveltejs/kit/dist/vite.js:2377:22

I believe that's expected due to `dasbhoard.js` always returning a 401 status.

System Info

error_redirect on  main [!] is 📦 v0.0.1 via  v18.6.0 took 4m41s 
❯ npx envinfo --system --binaries --browsers --npmPackages "{svelte,@sveltejs/*,vite}"

  System:
    OS: Linux 5.17 Pop!_OS 22.04 LTS
    CPU: (16) x64 AMD Ryzen 7 3700X 8-Core Processor
    Memory: 22.27 GB / 31.24 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 18.6.0 - ~/.nvm/versions/node/v18.6.0/bin/node
    npm: 8.13.2 - ~/.nvm/versions/node/v18.6.0/bin/npm
  Browsers:
    Firefox: 102.0
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.63 
    @sveltejs/kit: next => 1.0.0-next.390 
    svelte: ^3.44.0 => 3.49.0 
    vite: ^3.0.0 => 3.0.2

Severity

blocking an upgrade

Additional Information

No response

[Rich-Harris]

Closing as outdated since #5748 — +error.svelte files can no longer load data, which means redirect logic must be implemented elsewhere