Missing discriminator field when using TypeScriptTaggedUnion

[joprice]

Description

When creating an enum value from a TypeScriptTaggedUnion, the type field doesn't get added if a case has a single argument.

Repro code

open Fable.Core

[<TypeScriptTaggedUnion("type")>]
type AuthState =
| Zero
| One of string
| Two of string * string

let zero = AuthState.Zero
let one = AuthState.One "a"
let two = AuthState.Two ("a", "b")

let check = function 
  | Zero -> "zero"
  | One _ -> "one"
  | Two _ -> "two"

https://fable.io/repl/#?code=PYBwpgdgBAYghgIwDZgHQGFgCcwFgBQBA2gDwAqAnuAMoDGWAliAC5lwDm7YAJgKoQNgEABQAiZlTCiAlAD4AugQngoAQQCuzABbVmcZmCgBeAgB8oALTBZgZqAHkIh4ADMoAZ2aMI7O2QDuwFCuHl4MPlAAVKHevoT4KMxQAF7WQUZqmjp6BqhWNgSJwU7Gmdq6+miOhqJwooVgScyBpRrlOWgBQWJ1ADRQoggyBA1JtFpgtADWpS7qELTMgtAEUFDm+UEAtLIDqTb1+Gvm1VAA+lA7A0JSq+tQXeeXu+KBokA&html=Q&css=Q

Expected and actual results

The One case gets compiled to the raw value, without the discriminator field "type", while the pattern match is checking for a field that will never be present:

export const one = "a";
....
export function check(_arg) {
    switch (_arg.type) {
        case "one":
....

I would expect it to look similar to Two:

export const one = {
    type: "one",
    Item1: "a"
};

Related information

• Fable version: 4.18.0

[joprice]

Just checked some other examples and found that adding a label to the One case definition (| One of value:string) fixes the generated code.

Fable/src/Fable.Transforms/FSharp2Fable.fs

Lines 77 to 85 in e2285d6

	| [ argExpr ] when not (FsUnionCase.HasNamedFields unionCase) -> argExpr
	| _ ->
	let isCompiledValue, tagExpr =
	match FsUnionCase.CompiledValue unionCase with
	| None -> false, transformStringEnum rule unionCase
	| Some(CompiledValue.Integer i) -> false, makeIntConst i
	| Some(CompiledValue.Float f) -> false, makeFloatConst f
	| Some(CompiledValue.Boolean b) -> false, makeBoolConst b

I also notice now that the labels on Two of Item1 and Item2 are the field names of the tuple. Perhaps this attribute should enforce labels when passed at least single arguments and maybe tuples as well?