config.kit.paths.assets does not support absolute URLs without a scheme

[freb]

Describe the bug

The documentation for paths.assets says it requires and "absolute path", but any value not specifying a scheme (e.g. https://, http://) will be rejected with the following error:

config.kit.paths.assets option must be an absolute path, if specified. See https://kit.svelte.dev/docs/configuration#paths

Any path starting with a / is a valid absolute path, so either the documentation needs updating or the validation check needs to be reworked, here:

kit/packages/kit/src/core/config/options.js

Line 169 in f766a54

if (!/^[a-z]+:\/\//.test(input)) {

My guess is the reason for implementing this feature was to host assets from a CDN which lead to the current validation. However, there are equally valid uses for this setting that would benefit from not having to specify the domain.

In my case, I'm using the static adapter (SPA) with the pages and assets settings defined. I want to serve all static assets from /static/* but the only way to get this to work with the %svelte.assets% variable is to hard code the domain. To avoid this I at least need to hard code the /static value for any of my own static content referenced in app.html. I haven't confirmed this, but I suppose this hard coding approach would not even work with with the built js files which also need access to the assets prefix.

Reproduction

termina

Logs

❯ npm run build
$ svelte-kit build
> config.kit.paths.assets option must be an absolute path, if specified. See https://kit.svelte.dev/docs/configuration#paths
    at eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:632:14)
    at eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:798:43)
    at eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:784:18)
    at eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:784:18)
    at eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:784:18)
    at validate_config (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:968:9)
    at load_config (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:945:20)
    at async eval (file:///home/projects/sveltejs-kit-template-default-7pbyt8/node_modules/@sveltejs/kit/dist/cli.js:1080:19)

System Info

System:
    OS: Linux 5.16 Arch Linux
    CPU: (24) x64 AMD Ryzen Threadripper 1920X 12-Core Processor
    Memory: 43.97 GB / 62.71 GB
    Container: Yes
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 17.4.0 - /usr/bin/node
    npm: 8.5.0 - /usr/bin/npm
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.17
    @sveltejs/adapter-static: ^1.0.0-next.28 => 1.0.0-next.28
    @sveltejs/kit: next => 1.0.0-next.278
    svelte: ^3.44.0 => 3.46.4

Severity

annoyance

Additional Information

No response

[Rich-Harris]

Paths beginning / (but not //) are root-relative, not absolute, and the current behaviour is intentional — as you say, it's for cases where assets are hosted on an external CDN. It sounds like the easiest solution here would be to put your static assets inside static/static and change appDir to static/_app or similar.

[freb]

I can confirm that using appDir in combination with subdirectories under src/static/. achieves what I was looking for in some respects. However, there are a couple of limitations due to the generated static paths being relative (e.g. ./favicon.png):

1. If you need to set kit.paths.base, the static asset paths will no longer be relative, but the static assets are then required to live under the path specified in kit.paths.base. I see no way around this except with the use of kit.paths.assets. Of course this is sort of always the case, even when serving the app from root, but it feels like more of a constraint when they must live under a specific URL path.
2. With a true SPA application, it is desirable to always serve the same index.html file whenever an application request is made to the server, regardless of the URL being requested. With relative static asset paths, this is not possible without manually changing the path in the generated index.html file. Attempting to serve the pages as generated also has some issues.

To clarify a bit on (2) above, the structure of pages that Svelte generates is something like this:

pages
├── index.html
├── nested1
│   └── nested2.html
└── nested1.html

As far as I know, most web servers don't automatically request nested1.html when the path /nested1 is requested. This would require a rewrite rule. So if I wanted to not serve index.html for all requests and instead try to serve the page they actually requested (so that the relative static asset paths would be correct), the generated page structure doesn't support this out of the box either. The page structure would need to look more like this:

pages
├── index.html
├── nested1
│   └── index.html
│   └── nested2.html

Note that I am NOT proposing you change the structure of generated pages, that was just to clarify the paragraph above.

As it stands, kit.paths.assets is a way to just declare the location from which you want to server your static assets, which is fantastic. If this setting permitted static paths it would solve the two limitations I mention above.

One last bit of feedback on the docs for paths.assets and paths.base:

Paths beginning / (but not //) are root-relative, not absolute...

I still don't think is quite right after looking at the HTML spec. Whether or not it is confusing to users is a separate question of course. But I still think it would be clearer if you used URL here instead of path. Unless, of course, you relax the constraint on paths.assets :)

[terwer]

I do not thank abs url is well.please support relative url,thanks