Spurious unreachable/only null warning

[allanrenucci]

import scala.concurrent.duration.{Duration, FiniteDuration}

class Test {
  def test(d: Duration) = d match {
    case finite: FiniteDuration =>
    case d =>
  }
}

-- [E120] Only null matched Warning: tests/allan/Test.scala:7:9 ----------------
7 |    case d =>
  |         ^
  |         Only null is matched. Consider using `case null =>` instead.
one warning found

[allanrenucci]

This only happen when Duration comes from Scala2:

First compile with scalac:

sealed abstract class Duration
object Duration {
  final class FiniteDuration extends Duration
  sealed abstract class Infinite extends Duration
  val Undefined: Infinite = new Infinite {}
  val Inf: Infinite = new Infinite  {}
}

Then from Dotty with Duration on the classpath

import Duration._

class Test {

  def test(d: Duration) = d match {
    case finite: FiniteDuration =>
    case d =>
  }
}

[liufengyun]

In Scalac, it registers anonymous classes as children, in Dotty currently we don't. Let's discuss this in next meeting.