Better output for Tagged Variants with non-inline record

Issue には再帰的な tagged-variant の例と、現在の JavaScript 出力および望ましい JavaScript 出力が示されています。まずその例を再現し、tagged-variant レコードを出力するコンパイラーパスを追跡してください。適用される tag/フィールド名と単一レコードの制約を明らかにし、そのうえで、その例が _0 ラッパーなしのフラット化されたフィールドを生成することを確認してください。

Inline records in Variant provide good JS output, which is especially useful for bindings. When combined with tagged variants, they also provide a better DX.

However, it’s not always possible to inline records (or spread them in the case of recursive types), so I’m wondering if it would be possible to improve the JS output in the case of tagged variants.

One possible constraint would be to verify that the tag does not conflict with any of the record fields. We could also keep the same constraint as inline records: only one record.

@tag("nodeType")
type rec node =
  | @as(1) Element(element)
  | @as(3) Text(text)
  | @as(9) Document(document)
and element = {
  childNodes: array<node>,
  ownerDocument: null<document>,
}
and text = {
  nextElementSibling: null<element>,
}
and document = {
  children: array<element>,
}

let anElement = Element({
  childNodes: [Text({nextElementSibling: Null.null})],
  ownerDocument: Null.null,
})

Current output:

let anElement = {
  nodeType: 1,
  _0: {
    childNodes: [{
        nodeType: 3,
        _0: {
          nextElementSibling: null
        }
      }],
    ownerDocument: null
  }
};

Wanted output:

let anElement = {
  nodeType: 1,
  childNodes: [{
    nodeType: 3,
    nextElementSibling: null
  }],
  ownerDocument: null
};