Aliases to Hard Unions don't reduce

[bishabosha]

Minimized code

When we make an alias to a union type, it is not reduced compared to a raw union type, i.e. in the following Lifted[Int] is not the same as Err | Int, despite being an alias

class Err                                                                                                        

type Lifted[A] = Err | A

def point[O](o: O): Lifted[O] = o
extension [O, U](o: Lifted[O]) def map(f: O => U): Lifted[U] = ???

val error: Err = Err()

def ok: Int | Err =
  point("a").map(_ => if true then 1 else error)

def fail: Lifted[Int] =
  point("a").map(_ => if true then 1 else error) // error

Output

14 |  point("a").map(_ => if true then 1 else error) // error
   |                                          ^^^^^
   |                                          Found:    (error : Err)
   |                                          Required: Int

Expectation

both ok and fail should compile