Persistent comments in `@as` attribute payload

[cometkim]

In the compiler v10, since the variant outputs were an integer and were not able to customized, we added the original name as a comment as a hint. e.g.

type t =
 | A
 | B
 | Unknown

let test = (t) => switch t {
  | "A" => A
  | "B" => B
  | _ => Unknown
}

generated

function test(t) {
  switch (t) {
    case "A" :
        return /* A */0;
    case "B" :
        return /* B */1;
    default:
      return /* Unknown */2;
  }
}

I liked those little comments when debugging the output directly. But starting from v11 we no longer print comments on there.

Sometimes, I still make some integer variants for (size and perf) optimization, but the presence or absence of comments greatly affects my debugging experience.

So I suggest that any comments explicitly entered by the user are copied as-is to the output, so:

type t =
 | @as(/* leading comment and some space between */ 0) A
 | @as(1/*also trailing comment*/) B
 | Unknown

will produce:

function test(t) {
  switch (t) {
    case "A" :
        return /* leading comment and some space between */ 0;
    case "B" :
        return 1/*leading comment and some space between*/;
    default:
      return "Unknown";
  }
}

That means it can be truly "customizable" output

[cometkim]

real-world usecases by myself

[cometkim]

Let's do support sourcemaps then this would be not needed much