type Opaque* {.incompleteStruct.} = object

type Normal* {.union.} = object
  x: int32
  y: float32

type NormalWithZST* {.union.} = object
  x: int32
  y: float32

proc root*(a: ptr Opaque, b: Normal, c: NormalWithZST) {.importc: "root".}