Closes #4603. Review by extempore.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Types.scala b/src/compiler/scala/tools/nsc/symtab/Types.scala
index a490e0272a..90ba03e2eb 100644
--- a/src/compiler/scala/tools/nsc/symtab/Types.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Types.scala
@@ -3361,6 +3361,7 @@ A type's typeSymbol should never be inspected directly.
    */
   object rawToExistential extends TypeMap {
     private var expanded = immutable.Set[Symbol]()
+    private var generated = immutable.Set[Type]()
     def apply(tp: Type): Type = tp match {
       case TypeRef(pre, sym, List()) if isRawIfWithoutArgs(sym) =>
         if (expanded contains sym) AnyRefClass.tpe
@@ -3371,8 +3372,10 @@ A type's typeSymbol should never be inspected directly.
         } finally {
           expanded -= sym
         }
-      case ExistentialType(_, _) => // stop to avoid infinite expansions
-        tp
+      case ExistentialType(_, _) if !(generated contains tp) => // to avoid infinite expansions. todo: not sure whether this is needed
+        val result = mapOver(tp)
+        generated += result
+        result
       case _ =>
         mapOver(tp)
     }