Match on inner type generates no compiler warning but fails at runtime

[scabug]

The attached sample code compiles fine in Scala 2.11.7 and Scala 2.10.3 (Scala 2.9.3 warns that "TestMain.scala:9: error: scrutinee is incompatible with pattern type") - even with -unchecked -deprecation -feature -Xfuture -Xfatal-warnings -Xlint compiler options - but prints "ChildA#InnerOne: b.InnerOne" when run, i.e. the match at TestMain:8 matches ChildA#InnerOne although x is ChildB#InnerOne (and thus I'd expect it to print "ChildB#InnerOne: b.InnerOne".
While I think the match should be possible (by type-checking the reference to the outer object) the compiler should at least generate a warning (like it does for matching things like case e:Seq[String]=> ???.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9484?orig=1
Reporter: Bernhard Messerer (messi)
Affected Versions: 2.11.7
See #2, #6583
Attachments:

• TestMain.scala (created on Sep 23, 2015 9:54:01 AM UTC, 608 bytes)

[scabug]

@som-snytt said:
Similar search terms might lead one to #2.

[som-snytt]

At 2.13.8, still no outer checking, but compiler overcompensates by warning:

t9484.scala:9: warning: match may not be exhaustive.
It would fail on the following input: (x: Parent#InnerOne forSome x not in (ChildA#InnerOne, ChildB#InnerOne))
    x match {
    ^

The attached test

object TestMain {
  def main(args:Array[String]): Unit = {
    val b=new ChildB
    val x:Parent#InnerOne=new b.InnerOne("b.InnerOne")
    matchInnerOne(x)
  }
  def matchInnerOne(x:Parent#InnerOne):Unit={
    x match {
      case ao:ChildA#InnerOne⇒ println("ChildA#InnerOne: "+ao.name)
      case bo:ChildB#InnerOne⇒ println("ChildB#InnerOne: "+bo.name)
    }
  }
}

sealed trait Parent {
  sealed trait Inner {
    def name:String
  }
  final class InnerOne(val name:String) extends Inner
  final class InnerTwo(val name:String) extends Inner
}
class ChildA extends Parent
class ChildB extends Parent

Oh wait, ChildX are not final. OK, same result if final.

[SethTisue]

anyone digging into this will probably also want to read #4440

[SethTisue]

Scala 3 (3.3.1-RC1-bin-20230323-ee2bfdb-NIGHTLY) doesn't even warn