[Feature request] Push some validation to compiletime

[richard-uk1]

The following snippet will fail at runtime:

html!(
  <link href="sub/path.css" rel="stylesheet"/>
)

The reason for this is that "sub/path.css" is not a valid URI. If you do the following

html!(
  <link href={"sub/path.css"} rel="stylesheet"/>
)

you will get a failure at compile-time, because here the contents of href must be a Uri (the first version using str.parse::<Uri>().unwrap()).

It would be good if the proc macro tries this Uri conversion at compile-time, and rejects the program if the string isn't a valid Uri.

---

Unrelated, but TIL that './relative/path' is not a valid URI, at least according to hyper/http.

[bodil]

Problem is it's really hard to do, because the macro doesn't even know that the attribute takes a Uri, it just generates the code for the type checker to validate later (the only checking it does is whether it's a string literal so it'll generate .parse() instead of .into()). I feel like there must be some way to do it, but I haven't found it yet.

[richard-uk1]

Aah ok I see, the parser would need more context information.

EDIT

The big caveat for this: currently, the macro is not able to validate the string at compile time, and the conversion will panic at runtime if the string is invalid.

Apologies I should have seen this.

[bodil]

No worries, it's good to have an explicit issue for it, because I really want to find a good solution for it even if it turns out there isn't one.