Can't use uri! with routes that have optional query params

[anna-is-cute]

1. The version of Rocket you're using. Ensure it's the latest, if possible: 0.4.0-rc.1

2. The operating system (distribution and version) where the issue occurs: macOS 10.14.1

3. A brief description of the bug: It is not possible to use uri! for a route that has optional query params (Option<T>).

4. How you uncovered the bug. Short, reproducible tests are especially useful.

#[get("/?<a>")]
fn get(a: Option<u64>) -> String {
  format!("{:?}", a);
}

fn whatever() {
  let _uri = uri!(get: Some(1));
  let _uri = uri!(get: None);
}

the trait rocket::http::uri::FromUriParam<_> is not implemented for std::option::Option<u64>

[cazgp]

I don't think the linked commit resolves the issue, as I'm having the same problem and the provided code snippet continues to fail:

let _uri = uri!(get: None);
   |                          ^^^^ the trait `rocket::http::uri::FromUriParam<rocket::http::uri::Query, std::option::Option<_>>` is not implemented for `u64`

My use-case is that several parameters are optional for an endpoint. They are then passed through to a pagination template which generates "next" and "page number" links, keeping the values of the optional parameters so that the user's filters and searches persist.

However this is currently not possible using the uri! macro and the uri needs to be constructed manually. So instead of something simple like:

let link = uri!(
    actv::activities::all::all_get:
        date = filters.search_date,
        locations = &filters.locations_chosen,
        page = page_number,
        types = &filters.types_chosen,
);

you get:

let mut uri = vec![];
if filters.search_date.is_some() {
    uri.push(format!("date={}", filters.search_date.unwrap());
}
if filters.locations { ... }
...

Obviously this is not ideal.

[jebrosen]

@cazgp How did you define the route in question?

[cazgp]

Similarly to the OP's code snippet, which doesn't compile. Optional URL query params.

[jebrosen]

It turns out that what was implemented does not allow exactly what was originally posted for this issue. You can either provide a value (without Some) or omit it (by specifying _). There is a deficiency in this: it's not possible to insert a parameter if you already have an Option<T>. Unfortunately supporting both methods turns out to be tricky, so it will need some thought.

[cazgp]

Can we re-open this issue then please? It appears to be either a feature request or a bug. If there's a route with multiple optional parameters, a separate function which manually builds the URL is needed, because otherwise it ends up with a combinatorial explosion of the uri! macro (checking every combination for whether or not it should be value or _).