crash on compilable code: assertion failed: symbol (method companion$module) entered the scope of non-class owner type B

[helloqirun]

scalac compiles but dotc crashes.

$ cat abc.scala

class GBTree[B] {
  class Tree[A, B]; class Node[A, B](value: Node[A, B]) extends Tree[A, B]
  case class B[A, B]() extends Tree[A, B]
}

$ dotc abc.scala

-- Error: abc.scala ------------------------------------------------------------
3 |  case class B[A, B]() extends Tree[A, B]
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  B is already defined as type B

exception occurred while typechecking abc.scala

exception occurred while compiling abc.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: symbol (method companion$module) entered the scope of non-class owner type B
	at scala.Predef$.assert(Predef.scala:165)
	at dotty.tools.dotc.core.Symbols$Symbol.entered(Symbols.scala:429)
	at dotty.tools.dotc.typer.Namer.dotty$tools$dotc$typer$Namer$$createLinks$1(Namer.scala:518)
	at dotty.tools.dotc.typer.Namer$$anonfun$createCompanionLinks$1$2.apply(Namer.scala:525)
	at dotty.tools.dotc.typer.Namer$$anonfun$createCompanionLinks$1$2.apply(Namer.scala:522)
	at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:778)
	at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(HashMap.scala:108)
	at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(HashMap.scala:108)
<snipped>

[odersky]

I think this one is as intended, but we need to spec it. It's clearly very dubious code to have a parameter of a class with the same name as a type member.

But of course there should be no crash.