Orphan PolyParam

[propensive]

The following causes the compiler to crash when trying to pickle some trees.

class Contra[-D](task: AnyRef)
object Test {
  def narrow(task: AnyRef): Contra[task.type] = new Contra(task)
  def ident[Before](elems: Contra[Before]): Contra[Before] = elems
  val foo = null
  ident(narrow(foo))
}

The output from the compiler is here.

[DarkDimius]

Exception in thread "main" java.lang.AssertionError: assertion failed: orphan poly parameter: PolyParam($param$1)

That's an actual error, unrelated to pickling. Likely from typer.