Fix findMember of SuperType

It used to return the joint denotation, but the correct
answer is the denotation of the symbol in the joint denotation
as seen from the super prefix.

Author: odersky

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

@@ -384,7 +384,7 @@ object Types {
 
     /** The base classes of this type as determined by ClassDenotation
      *  in linearization order, with the class itself as first element.
-     *  For AndTypes/OrTypes, the union/intersection of the operands' baseclasses.
+     *  For AndTypes/OrTypes, the merge/intersection of the operands' baseclasses.
      *  Inherited by all type proxies. `Nil` for all other types.
      */
     final def baseClasses(implicit ctx: Context): List[ClassSymbol] = track("baseClasses") {
@@ -475,22 +475,24 @@ object Types {
      */
     final def findMember(name: Name, pre: Type, excluded: FlagSet)(implicit ctx: Context): Denotation = {
       @tailrec def go(tp: Type): Denotation = tp match {
-        case tp: RefinedType =>
-          if (name eq tp.refinedName) goRefined(tp) else go(tp.parent)
-        case tp: ThisType =>
-          goThis(tp)
-        case tp: TypeRef =>
-          tp.denot.findMember(name, pre, excluded)
         case tp: TermRef =>
           go (tp.underlying match {
             case mt: MethodType
             if mt.paramInfos.isEmpty && (tp.symbol is Stable) => mt.resultType
             case tp1 => tp1
           })
-        case tp: TypeParamRef =>
-          goParam(tp)
+        case tp: TypeRef =>
+          tp.denot.findMember(name, pre, excluded)
+        case tp: ThisType =>
+          goThis(tp)
+        case tp: RefinedType =>
+          if (name eq tp.refinedName) goRefined(tp) else go(tp.parent)
         case tp: RecType =>
           goRec(tp)
+        case tp: TypeParamRef =>
+          goParam(tp)
+        case tp: SuperType =>
+          goSuper(tp)
         case tp: HKApply =>
           goApply(tp)
         case tp: TypeProxy =>
@@ -614,6 +616,12 @@ object Types {
             go(next)
         }
       }
+      def goSuper(tp: SuperType) = go(tp.underlying) match {
+        case d: JointRefDenotation =>
+          typr.println(i"redirecting super.$name from $tp to ${d.symbol.showLocated}")
+          new UniqueRefDenotation(d.symbol, tp.memberInfo(d.symbol), d.validFor)
+        case d => d
+      }
       def goAnd(l: Type, r: Type) = {
         go(l) & (go(r), pre, safeIntersection = ctx.pendingMemberSearches.contains(name))
       }