Replace TypeBound arguments by wildcards in wildApprox

Author: odersky

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -603,9 +603,14 @@ object ProtoTypes {
       else if (tp.symbol.isStatic || (tp.prefix `eq` NoPrefix)) tp
       else tp.derivedSelect(wildApprox(tp.prefix, theMap, seen))
     case tp @ AppliedType(tycon, args) =>
+      def dropBounds(tp: Type) = tp match {
+        case tp: TypeBounds if false => WildcardType(tp)
+        case tp => tp
+      }
       wildApprox(tycon, theMap, seen) match {
         case _: WildcardType => WildcardType // this ensures we get a * type
-        case tycon1 => tp.derivedAppliedType(tycon1, args.mapConserve(wildApprox(_, theMap, seen)))
+        case tycon1 => tp.derivedAppliedType(tycon1,
+          args.mapConserve(arg => dropBounds(wildApprox(arg, theMap, seen))))
       }
     case tp: RefinedType => // default case, inlined for speed
       tp.derivedRefinedType(