// covariant linked list
abstract class M {
  self: M =>

  type T
  final type selfType = M {type T <: self.T}
  type actualSelfType >: self.type <: selfType

  def next: selfType

  // I don't understand why this doesn't compile, but that's a separate matter
  // Error: method all2 cannot be accessed in M.this.selfType
  // because its instance type => Stream[M{type T <: M.this.selfType#T}]
  // contains a malformed type: M.this.selfType#T
  def all2: Stream[M {type T <: self.T}] = Stream.cons(self: actualSelfType, next.all2)

  // compiles successfully
  def all3: Stream[M {type T <: self.T}] = all3Impl(self: actualSelfType)
  private def all3Impl(first: M {type T <: self.T}): Stream[M {type T <: self.T}] = Stream.cons(first, all3Impl(first.next))

  def all4: Stream[M {type T <: self.T}] = Unrelated.all4Impl[T](self: actualSelfType)
}

// TODO!!! fix this bug for real, it compiles successfully, but weird types are inferred
object Unrelated {
  // compiles successfully
  def all4Impl[U](first: M {type T <: U}): Stream[M {type T <: U}] = Stream.cons(first, all4Impl[U](first.next))

  // should compile successfully without the [U], but:
  // def all4ImplFail[U](first: M {type T <: U}): Stream[M {type T <: U}] = Stream.cons(first, all4ImplFail(first.next))
  //
  // test/files/pos/t1279a.scala:31: error: type mismatch;
  //  found   : first.selfType
  //     (which expands to)  M{type T <: first.T}
  //  required: M{type T <: Nothing}
  //   def all4ImplFail[U](first: M {type T <: U}): Stream[M {type T <: U}] = Stream.cons(first, all4ImplFail(first.next))
  //                                                                                                                ^
  // one error found
}