Enum case can't be defined in terms of itself

Compiler version

3.0.0-M3

Minimized code

enum Opt[T] {
  case Nn extends Opt[Nothing] with Comparable[Nn.type]

  def compareTo(nn: Nn.type) = 0
}

Output

2 |  case Nn extends Opt[Nothing] with Comparable[Nn.type]
  |                                               ^
  |                                             Recursive value Nn needs type

Expectation

I expected it to work much like the Scala 2 equivalent:

sealed trait Opt[T]
case object Nn extends Opt[Nothing] with Comparable[Nn.type] {
  def compareTo(nn: Nn.type) = 0
}

Btw, this error was also mentioned in #11249 but the original issue there is about vals.

[LPTK]

Weird, I would have sworn that this worked in Scala 2… 🤔

A workaround that works in both Scala 2 and Scala 3 (!):

abstract class Module {
  type Nn >: Nn.type <: Nn.type
  sealed trait Opt[T]
  object Nn extends Opt[Nn] with Comparable[Nn] {
    def compareTo(nn: Nn) = 0
  }
}
object Module extends Module {
  type Nn = Nn.type
}

In fact, in Scala 3 we can simplify it to just:

object Module {
  type Nn >: Nn.type <: Nn.type
  sealed trait Opt[T]
  object Nn extends Opt[Nn] with Comparable[Nn] {
    def compareTo(nn: Nn) = 0
  }
}

[bishabosha]

@yuriy-yarosh your example is a duplicate of #9177 which was closed 😕