Fix mapOuter to be type-preserving

Only outer references that point to the same class as the outer parameter should be
mapped. Other outer references should be left alone. Such references can appear
after the initial supercall of a constructor.

Author: odersky

src/dotty/tools/dotc/transform/Constructors.scala

@@ -159,7 +159,11 @@ class Constructors extends MiniPhaseTransform with SymTransformer { thisTransfor
     /** Map outer getters $outer and outer accessors $A$B$$$outer to the given outer parameter. */
     def mapOuter(outerParam: Symbol) = new TreeMap {
       override def transform(tree: Tree)(implicit ctx: Context) = tree match {
-        case Apply(fn, Nil) if fn.symbol.is(OuterAccessor) || fn.symbol.isGetter && fn.symbol.name == nme.OUTER =>
+        case Apply(fn, Nil)
+          if (fn.symbol.is(OuterAccessor)
+             || fn.symbol.isGetter && fn.symbol.name == nme.OUTER
+             ) &&
+             fn.symbol.info.resultType.classSymbol == outerParam.info.classSymbol =>
           ref(outerParam)
         case _ =>
           super.transform(tree)