Added method to help traversing children in a TreeTraverser

Author: odersky

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

@@ -1332,6 +1332,7 @@ object Trees {
     abstract class TreeTraverser extends TreeAccumulator[Unit] {
       def traverse(tree: Tree): Unit
       def apply(x: Unit, tree: Tree) = traverse(tree)
+      protected def traverseChildren(tree: Tree) = foldOver((), tree)
     }
 
     /** Fold `f` over all tree nodes, in depth-first, prefix order */
@@ -1357,9 +1358,9 @@ object Trees {
         case tree: Bind => cpy.Bind(tree)(newName, tree.body)
         case tree: ValDef => cpy.ValDef(tree)(name = newName.asTermName)
         case tree: DefDef => cpy.DefDef(tree)(name = newName.asTermName)
+        case tree: untpd.PolyTypeDef => untpd.cpy.PolyTypeDef(tree)(tree.mods, newName.asTypeName, tree.tparams, tree.rhs)
         case tree: TypeDef => cpy.TypeDef(tree)(name = newName.asTypeName)
         case tree: SelectFromTypeTree => cpy.SelectFromTypeTree(tree)(tree.qualifier, newName)
-        case tree: untpd.PolyTypeDef => untpd.cpy.PolyTypeDef(tree)(tree.mods, newName.asTypeName, tree.tparams, tree.rhs)
       }
     }.asInstanceOf[tree.ThisTree[T]]
   }

src/dotty/tools/dotc/typer/VarianceChecker.scala

@@ -125,15 +125,15 @@ class VarianceChecker()(implicit ctx: Context) {
           ctx.debuglog(s"Skipping variance check of ${sym.showDcl}")
         case tree: TypeDef =>
           checkVariance(sym)
-          foldOver((), tree)
+          traverseChildren(tree)
         case tree: ValDef =>
           checkVariance(sym)
         case DefDef(_, _, tparams, vparamss, _, _) =>
           checkVariance(sym)
           tparams foreach traverse
           vparamss foreach (_ foreach traverse)
         case Template(_, _, _, body) =>
-          foldOver((), tree)
+          traverseChildren(tree)
         case _ =>
       }
     }