Fix for scala#4342

Author: gsps

compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala

@@ -336,12 +336,23 @@ object ExplicitOuter {
   class OuterOps(val ictx: Context) extends AnyVal {
     private implicit def ctx: Context = ictx
 
+    private def outerType(cls: ClassSymbol): Type = {
+      val encl = cls.owner.enclosingClass
+      if (cls.is(Scala2x))
+        encl.asClass.classInfo.selfInfo match {
+          case tp: TypeRef => tp.classSymbol.typeRef
+          case self: Symbol => self.typeRef
+          case _ => encl.typeRef
+        }
+      else encl.typeRef
+    }
+
     /** If `cls` has an outer parameter add one to the method type `tp`. */
     def addParam(cls: ClassSymbol, tp: Type): Type =
       if (hasOuterParam(cls)) {
         val mt @ MethodTpe(pnames, ptypes, restpe) = tp
         mt.derivedLambdaType(
-          nme.OUTER :: pnames, cls.owner.enclosingClass.typeRef :: ptypes, restpe)
+          nme.OUTER :: pnames, outerType(cls) :: ptypes, restpe)
       } else tp
 
     /** If function in an apply node is a constructor that needs to be passed an