Refine same-kind criterion

 - Need to take of AnyKind
 - need to also copmare results

Author: odersky

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -524,17 +524,21 @@ trait ConstraintHandling[AbstractContext] {
           pruneLambdaParams(bound)
       }
 
-      def sameKind(tp1: Type, tp2: Type): Boolean =
-        tp1.typeParams.corresponds(tp2.typeParams)((p1, p2) =>
-          sameKind(p1.paramInfo, p2.paramInfo))
+      def kindCompatible(tp1: Type, tp2: Type): Boolean =
+        val tparams1 = tp1.typeParams
+        val tparams2 = tp2.typeParams
+        tparams1.corresponds(tparams2)((p1, p2) => kindCompatible(p1.paramInfo, p2.paramInfo))
+        && (tparams1.isEmpty || kindCompatible(tp1.hkResult, tp2.hkResult))
+        || tp1.hasAnyKind
+        || tp2.hasAnyKind
 
       try bound match {
         case bound: TypeParamRef if constraint contains bound =>
           addParamBound(bound)
         case _ =>
           val pbound = prune(bound)
           pbound.exists
-          && sameKind(param, pbound)
+          && kindCompatible(param, pbound)
           && (if fromBelow then addLowerBound(param, pbound) else addUpperBound(param, pbound))
       }
       finally addConstraintInvocations -= 1