Make JSON encoding of DAML-LF variants easier to pattern match on

Currently, values of DAML-LF variant types like

variant Foo =
  | Bar Int
  | Baz Foo.Baz
record Foo.Baz = {baz : Text}

get encoded to JSON values like

{ "Bar": 5 }
{ "Baz": {"baz": "text"} }

“Pattern matching” on this representation in JavaScript/TypeScript is a bit inconvenient since you have to build a chain of if-statements and add a final unreachable else branch.

I suggest we rather follow the approach described in the TypeScript handbook, i.e., represent the same values as

{ "type": "Bar", "data": "Int" }
{ "type": "Baz", "data": {"baz": "text"} }

I’m also open to inlining the record in the second case, i.e.

{ "type": "Baz", "baz": "text" }

but I don’t care too much.

[leo-da]

The following DAML

data Qux =  Quux | Quuz

gets compiled into DAML LF Enum:

JsonEncodingTest:Qux -> Normal(DefDataType(ImmArray.ImmArraySeq(),Enum(ImmArray.ImmArraySeq(Quux, Quuz)))),

We currently encode Enums as JsStrings. I am changing it, to keep it consistent with Variants. So, it will be encoded as:

{"tag": "Quux"}

[hurryabit]

@leo-da Please keep enums as strings. That seems to be idiomatic JavaScript/TypeScript. There’s no problem with enums and variants being different. That was pretty much why we introduced enums in the first place.