existentials in structural type signatures

[scabug]

This works:

scala> var x: AnyVal { def *(other: Int): Int } = _
x: AnyVal{def *(other: Int): Int} = null

scala> x = 5
x: AnyVal{def *(other: Int): Int} = 5

This doesn't, nor obviously does any more useful attempt to apply existentials (more useful than the Int identity that is.)

scala> var x: AnyVal { def *(other: T forSome { type T >: Int <: Int }): Int } = _
x: AnyVal{def *(other: T forSome { type T >: Int <: Int }): Int} = null

scala> x = 5
<console>:8: error: type mismatch;
 found   : Int(5)
 required: AnyVal{def *(other: T forSome { type T >: Int <: Int }): Int}
       x = 5
           ^

Putting the shoe back on the other foot, this works:

scala> type SomeT[Bound] = T forSome { type T >: Bound <: Bound }
defined type alias SomeT

scala> var x: AnyVal { def *(other: SomeT[Int]): Int } = _
x: AnyVal{def *(other: SomeT[Int]): Int} = null

scala> x = 5
x: AnyVal{def *(other: SomeT[Int]): Int} = 5

So there are a lot of interesting questions here, but there is little doubt that at the least, it is a bug that it works with an alias but not by skipping the alias and using the identical expansion.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-4867?orig=1
Reporter: @paulp