Cannot override a val from the parent class

[LPTK]

This works in Scalac, but not in Dotty:

class A[T](val x:T)
class B[T](override val x:T) extends A[T](x)

Dotty complains:

Welcome to Scala.next (pre-alpha, git-hash: 06d3f7a)  (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_65).
Type in expressions to have them evaluated.
Type :help for more information.
scala> class A[T](val x:T)
defined class A
scala> class B[T](override val x:T) extends A[T](x)
-- Error: <console> ------------------------------------------------------------
5 |class B[T](override val x:T) extends A[T](x)
  |                        ^
  |                        overriding value x in class A of type T;
  |                         method x of type => T has incompatible type

Removing the override val keywords in B makes it compile, but it's not always possible (e.g. for case classes).

[DarkDimius]

Refchecks is to blame. should be easy to fix.