Pattern matching on a case object is affected by whether the outer trait is parameterised or not

scalacbug.scala

trait A {
  sealed trait Foo
  case object Bar extends Foo
  case class Baz() extends Foo

  def isBar(f: Foo) = f match {
    case Bar => true
    case Baz() => false
  }
}

trait B[V] {
  sealed trait Foo
  case object Bar extends Foo
  case class Baz() extends Foo

  def isBar(f: Foo) = f match {
    case Bar => true
    case Baz() => false
  }
}

// [warn] /…/test/src/main/scala/scalacbug.scala:17: match may not be exhaustive.
// [warn] It would fail on the following input: Bar
// [warn]   def isBar(f: Foo) = f match {
// [warn]                       ^
// [warn] one warning found

https://issues.scala-lang.org/browse/SI-8546

Weird.

Thanks for the issue reference, I couldn't find it. And I'm glad this is now fixed :-).