newtype extending newtype when underlying values extend eachother?

Given:

trait Foo
trait Bar extends Foo

why wouldn’t

@newtype class NFoo(val internal: Foo)
@newtype class NBar(override val internal: Bar) extends NFoo(internal)

be valid?

[s5bug]

Here’s how it might be expanded:

type NFoo = NFoo.Type
object NFoo {
  type Repr = Foo
  type Base = Any { type NFoo$newtype }
  trait Tag extends Any
  type Type <: Base with Tag
  implicit final class Ops$newtype(val $this$: Type) extends AnyVal {
    def internal: Foo = $this$.asInstanceOf[Foo]
  }
}

type NBar = NBar.Type
object NBar {
  type Repr = Bar
  type Base = Any { type NBar$newtype }
  trait Tag extends Any
  type Type <: NFoo.Type with Base with Tag
  implicit final class Ops$newtype(val $this$: Type) extends AnyVal {
    def internal: Bar = $this$.asInstanceOf[Bar]
  }
}

My only worry is the internals conflicting; depending on how implicit priority works, NBar.Ops$newtype should take priority over NFoo.Ops$newtype.

[carymrobbins]

I think so; try adding the <: Foo bound on my previous example -

@newtype case class N[+A <: Foo](internal: T forSome { type T <: A })