Ref copier that works for Idents and Selects

The Ref copier copies Idents and Selects, changing the name
of either.

Author: odersky

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -890,6 +890,11 @@ object Trees {
         case tree: Select if (qualifier eq tree.qualifier) && (name == tree.name) => tree
         case _ => finalize(tree, untpd.Select(qualifier, name))
       }
+      /** Copy Ident or Select trees */
+      def Ref(tree: RefTree)(name: Name)(implicit ctx: Context) = tree match {
+        case Ident(_) => Ident(tree)(name)
+        case Select(qual, _) => Select(tree)(qual, name)
+      }
       def This(tree: Tree)(qual: untpd.Ident): This = tree match {
         case tree: This if qual eq tree.qual => tree
         case _ => finalize(tree, untpd.This(qual))

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -450,7 +450,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       } else foldOver(sym, tree)
   }
 
-  override val cpy = new TypedTreeCopier
+  override val cpy: TypedTreeCopier = // Type ascription needed to pick up any new members in TreeCopier (currently there are none)
+    new TypedTreeCopier
 
   class TypedTreeCopier extends TreeCopier {
     def postProcess(tree: Tree, copied: untpd.Tree): copied.ThisTree[Type] =