address comments

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -450,11 +450,23 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
 
   /**
    * All the nodes that will be used to generate tree string.
+   *
+   * For example:
+   *
+   *   node
+   *   :  +-  innerChildren
+   *   +-  treeChildren
    */
   protected def treeChildren: Seq[BaseType] = children
 
   /**
-   * All the nodes those are parts of this node.
+   * All the nodes that are parts of this node.
+   *
+   * innerChildren will be printed with one more level of indent, for example:
+   *
+   *   node
+   *   :  +-  innerChildren
+   *   +-  treeChildren
    */
   protected def innerChildren: Seq[BaseType] = Nil
 

sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala

@@ -348,21 +348,17 @@ case class WholeStageCodegen(child: SparkPlan) extends UnaryNode with CodegenSup
     }
   }
 
-  private[sql] override def resetMetrics(): Unit = {
-    child.foreach(_.resetMetrics())
-  }
-
   override def innerChildren: Seq[SparkPlan] = {
     child :: Nil
   }
 
-  private def collectDirectInputs(plan: SparkPlan): Seq[SparkPlan] = plan match {
+  private def collectInputs(plan: SparkPlan): Seq[SparkPlan] = plan match {
     case InputAdapter(c) => c :: Nil
-    case other => other.children.flatMap(collectDirectInputs)
+    case other => other.children.flatMap(collectInputs)
   }
 
   override def treeChildren: Seq[SparkPlan] = {
-    collectDirectInputs(child)
+    collectInputs(child)
   }
 
   override def simpleString: String = "WholeStageCodegen"