__layout `Load` function generated type params are typed as an empty object.

[f-elix]

Describe the bug

As the title describes, the Load function type generated by Sveltekit casts the params as an empty object, since the file is at the root of the routes folder.

The problem with that is that since this load function runs on all routes, it does have access to dynamic params when they are present.

I'm not sure what should be done here, but there is definitely a mismatch between the types and what actually happens at runtime.

Reproduction

https://github.com/f-elix/sveltekit-generated-types-error

From this repo, you can run the app locally and go the any url that has two params (ie, '/en/about'). The lang param will be available inside the __layout load function, but the types will show an error if we try to access it.

Logs

No response

System Info

System:
    OS: Windows 10 10.0.22000
    CPU: (8) x64 Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz
    Memory: 25.93 GB / 39.76 GB
  Binaries:
    Node: 16.14.2 - C:\Program Files\nodejs\node.EXE
    npm: 8.5.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.22000.120.0), Chromium (98.0.1108.43)
    Internet Explorer: 11.0.22000.120
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.33
    @sveltejs/kit: next => 1.0.0-next.301
    svelte: ^3.44.0 => 3.46.4

Severity

serious, but I can work around it

Additional Information

No response

[Rich-Harris]

Ah, interesting. We probably do want to discourage people from accessing child dynamic parameters, but the current types are definitely buggy. Options:

1. the generated types for a given __layout include all the dynamic parameters for the entire subtree (which, for the root __layout, means all dynamic parameters in the entire app)
2. we use { known: string, [unknown: string]: string } — simpler, less type safety

The first seems preferable to me, though it's definitely a lot finickier to implement

[dummdidumm]

This was fixed recently, the param type should have optional params now for all possible children