Better fix

`superType` should never return a `TypeBounds` in the first place.
This commit makes sure it doesn't.

Author: odersky

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

@@ -239,7 +239,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
         case tp1: RecType =>
           tp1.rebind(approximateOr(tp1.parent, tp2))
         case tp1: TypeProxy if !isClassRef(tp1) =>
-          orDominator(tp1.superType.bounds.hi | tp2)
+          orDominator(tp1.superType | tp2)
         case _ =>
           tp2 match {
             case tp2: RecType =>

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

@@ -1276,7 +1276,10 @@ object Types {
      *  except for TypeRefs where the upper bound is returned, and HKApplys,
      *  where the upper bound of the constructor is re-applied to the arguments.
      */
-    def superType(implicit ctx: Context): Type = underlying
+    def superType(implicit ctx: Context): Type = underlying match {
+      case TypeBounds(_, hi) => hi
+      case st => st
+    }
   }
 
   // Every type has to inherit one of the following four abstract type classes.,
@@ -1762,11 +1765,6 @@ object Types {
     type ThisType = TypeRef
 
     override def underlying(implicit ctx: Context): Type = info
-
-    override def superType(implicit ctx: Context): Type = info match {
-      case TypeBounds(_, hi) => hi
-      case _ => info
-    }
   }
 
   final class TermRefWithSignature(prefix: Type, name: TermName, override val sig: Signature) extends TermRef(prefix, name) {