Dotty does not erase intersection types like scalac

[smarter]

Given:

trait X
trait Y

trait Test {
  def foo[A <: X with Y, B <: Y with A](a: A, b: B): Unit
}

Scala 2 erases it as:

def foo(a: X, b: X): Unit

But Dotty erases it as:

 def foo(a: X, b: Y): Unit

This is problematic since it can affect which overloads are valid or not.
The Scala 2 implementation is at https://github.com/scala/scala/blob/a9275b50e425d29c0b7fd45c10317953d5bf7804/src/reflect/scala/reflect/internal/transform/Erasure.scala#L333-L366
The Dotty implementation is at https://github.com/lampepfl/dotty/blob/868d1995b0f10bacf13d365e12eb2b31061a1928/compiler/src/dotty/tools/dotc/core/TypeErasure.scala#L290-L315

[Blaisorblade]

Does this also affect erasure in calls to Scala2-defined methods? That would make the issue even more important.

[smarter]

Yes, I think so.

[Jasper-M]

Related ticket: #2920