More logging of expression rewriting for GeneratedAggregate.

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

@@ -128,25 +128,28 @@ case class GeneratedAggregate(
 
     child.execute().mapPartitions { iter =>
       // Builds a new custom class for holding the results of aggregation for a group.
-      val newAggregationBuffer =
-        newProjection(computeFunctions.flatMap(_.initialValues), child.output)
+      val initialValues = computeFunctions.flatMap(_.initialValues)
+      val newAggregationBuffer = newProjection(initialValues, child.output)
+      logger.info(s"Initial values: ${initialValues.mkString(",")}")
+
+      // A projection that computes the group given an input tuple.
+      val groupProjection = newProjection(groupingExpressions, child.output)
+      logger.info(s"Grouping Projection: ${groupingExpressions.mkString(",")}")
 
       // A projection that is used to update the aggregate values for a group given a new tuple.
       // This projection should be targeted at the current values for the group and then applied
       // to a joined row of the current values with the new input row.
-      val updateProjection =
-        newMutableProjection(
-          computeFunctions.flatMap(_.update),
-          computeFunctions.flatMap(_.schema) ++ child.output)()
-
-      // A projection that computes the group given an input tuple.
-      val groupProjection = newProjection(groupingExpressions, child.output)
+      val updateExpressions = computeFunctions.flatMap(_.update)
+      val updateSchema = computeFunctions.flatMap(_.schema) ++ child.output
+      val updateProjection = newMutableProjection(updateExpressions, updateSchema)()
+      logger.info(s"Update Expressions: ${updateExpressions.mkString(",")}")
 
       // A projection that produces the final result, given a computation.
       val resultProjectionBuilder =
         newMutableProjection(
           resultExpressions,
           (namedGroups.map(_._2.toAttribute) ++ computationSchema).toSeq)
+      logger.info(s"Result Projection: ${resultExpressions.mkString(",")}")
 
       val joinedRow = new JoinedRow