Given an unboxed variant like this, Primary has the same runtime representation as Color("primary")

@unboxed
type color =
  | @as("primary") Primary
  | @as("secondary") Secondary
  | Color(string)

This means that a function like

let f = x =>
  switch x {
  | Color(x) => x
  | _ => "not Color"
  }

somewhat surprisingly produces "not Color" when called on Color("primary").

However, the optimizer treats this like a regular variant and so constant folding f(Color("primary")) produces "primary", which differs from the result of the generated JS.

Full playground example