Bug in handling the JSON unboxed type when switching on it

[jfrolich]

Repro here

[zth]

cc @cristianoc

[cristianoc]

Smaller self contained repro:

type obj = {name:string}

@unboxed
type t =
  | Boolean(bool)
  | Object(obj)
  | Array(array<int>)

switch Object({name: "hello"}) {
| Object(v) => Console.log(v)
| Array(v) => Console.log(v)
| _ => Console.log("Not an object or array1")
}

produces:

var v = {
  name: "hello"
};

if (Array.isArray(v)) {
  console.log(v);
} else {
  switch (typeof v) {
    case "boolean" :
        console.log("Not an object or array1");
        break;
    case "object" :
    
  }
}

It seems the code for case "object" is not emitted.

[cristianoc]

The issue happens when 2 cases, here Object and Array, have identical body (here Console.log(v)).
The switch-generation code, which was not designed with untagged unions in mind, merges the two cases into one (and makes one of the two empty).

However, for Object and Array, what's generated is not a straight switch, but a mix of if-then-else and switch. This means that the Object and Array cases are apart in the generated code, and merging them (making one empty) is wrong.