Support @mel.unwrap with uncurry

[tatchi]

I was trying to create bindings for the following Js code:

let navigate = useNavigate();

// Then later on in e.g an event handler:
navigate("/path") // or navigate(-1)

I tried the following reason code

[@mel.module "react-router-dom"]
external useNavigate:
  (unit, [@mel.unwrap] [ | `Str(string) | `Int(int)]) => unit =
  "useNavigate";

let navigate = useNavigate();

navigate(`Int(-1))

But it doesn't compile to what I need (related to #1022)

import * as ReactRouterDom from "react-router-dom";

function navigate(param) {
  ReactRouterDom.useNavigate(param.VAL);
}

ReactRouterDom.useNavigate(-1);

export {
  navigate ,
}

I thought I would use an uncurried version but it doesn't work with @mel.unwrap

[@mel.module "react-router-dom"]
external useNavigate:
  unit => (. ([@mel.unwrap] [ | `Str(string) | `Int(int)])) => unit =
  "useNavigate";

let navigate = useNavigate();
navigate(. `Str("hello"));

It gives the following alert:

Line 3, 16:
Alert: unused Unused attribute [@mel.unwrap]
This means such annotation is not annotated properly.
For example, some annotations are only meaningful in externals

The uncurried version without @mel.unwrap compiles to what I'd need (except that the argument is not unwrapped ofc)

[@mel.module "react-router-dom"]
external useNavigate: unit => (. [ | `Str(string) | `Int(int)]) => unit =
  "useNavigate";

let navigate = useNavigate();
navigate(. `Str("/path"));

import * as ReactRouterDom from "react-router-dom";

var navigate = ReactRouterDom.useNavigate();

navigate({
      NAME: "Str",
      VAL: "/path"
    });

export {
  navigate ,
}

Should we support @mel.unwrap with uncurry?

[anmonteiro]

In the meantime you can try Js.undefined instead of unit if you really need the undefined argument.

[tatchi]

Also note that in rescript 11, we can use unboxed with multiple constructors, so the following code compiles to what I need:

@unboxed
type stringOrInt = Str(string) | Int(int)

@module("react-router-dom")
external useNavigate: unit => stringOrInt => unit = "useNavigate"

let navigate = useNavigate()

navigate(Str("/path"))

Would supporting unboxed for multiple constructors be an option in melange?

[tatchi]

In the meantime you can try Js.undefined instead of unit if you really need the undefined argument.

Thanks, I tried with

[@mel.module "react-router-dom"]
external useNavigate:
  (Js.undefined(unit), [@mel.unwrap] [ | `Str(string) | `Int(int)]) => unit =
  "useNavigate";

let navigate = useNavigate(Js.undefined);

navigate(`Int(-1));

But it stills doesn't compile to what I need:

import * as ReactRouterDom from "react-router-dom";

function navigate(param) {
  ReactRouterDom.useNavigate(undefined, param.VAL);
}

ReactRouterDom.useNavigate(undefined, -1);

export {
  navigate ,
}

Is it what you had in mind ?

[anmonteiro]

This exposes a wider issue that we don't support these attributes inside uncurried externals, e.g.:

external x: (. ([@mel.as "hello"] _)) => unit = "asd";

[anmonteiro]

fixed in #1140