[SPARK-27816][SQL] make TreeNode tag type safe

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala

@@ -1083,7 +1083,7 @@ case class OneRowRelation() extends LeafNode {
   /** [[org.apache.spark.sql.catalyst.trees.TreeNode.makeCopy()]] does not support 0-arg ctor. */
   override def makeCopy(newArgs: Array[AnyRef]): OneRowRelation = {
     val newCopy = OneRowRelation()
-    newCopy.tags ++= this.tags
+    newCopy.copyTagsFrom(this)
     newCopy
   }
 }

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

@@ -74,9 +74,8 @@ object CurrentOrigin {
   }
 }
 
-// The name of the tree node tag. This is preferred over using string directly, as we can easily
-// find all the defined tags.
-case class TreeNodeTagName(name: String)
+// A tag of a `TreeNode`, which defines name and type
+case class TreeNodeTag[T](name: String)
 
 // scalastyle:off
 abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
@@ -89,7 +88,19 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
    * A mutable map for holding auxiliary information of this tree node. It will be carried over
    * when this node is copied via `makeCopy`, or transformed via `transformUp`/`transformDown`.
    */
-  val tags: mutable.Map[TreeNodeTagName, Any] = mutable.Map.empty
+  private val tags: mutable.Map[TreeNodeTag[_], Any] = mutable.Map.empty
+
+  protected def copyTagsFrom(other: BaseType): Unit = {
+    tags ++= other.tags
+  }
+
+  def setTagValue[T](tag: TreeNodeTag[T], value: T): Unit = {
+    tags(tag) = value
+  }
+
+  def getTagValue[T](tag: TreeNodeTag[T]): Option[T] = {
+    tags.get(tag).map(_.asInstanceOf[T])
+  }
 
   /**
    * Returns a Seq of the children of this node.
@@ -418,7 +429,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
     try {
       CurrentOrigin.withOrigin(origin) {
         val res = defaultCtor.newInstance(allArgs.toArray: _*).asInstanceOf[BaseType]
-        res.tags ++= this.tags
+        res.copyTagsFrom(this)
         res
       }
     } catch {

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala

@@ -622,31 +622,33 @@ class TreeNodeSuite extends SparkFunSuite with SQLHelper {
   }
 
   test("tags will be carried over after copy & transform") {
+    val tag = TreeNodeTag[String]("test")
+
     withClue("makeCopy") {
       val node = Dummy(None)
-      node.tags += TreeNodeTagName("test") -> "a"
+      node.setTagValue(tag, "a")
       val copied = node.makeCopy(Array(Some(Literal(1))))
-      assert(copied.tags(TreeNodeTagName("test")) == "a")
+      assert(copied.getTagValue(tag) == Some("a"))
     }
 
     def checkTransform(
         sameTypeTransform: Expression => Expression,
         differentTypeTransform: Expression => Expression): Unit = {
       val child = Dummy(None)
-      child.tags += TreeNodeTagName("test") -> "child"
+      child.setTagValue(tag, "child")
       val node = Dummy(Some(child))
-      node.tags += TreeNodeTagName("test") -> "parent"
+      node.setTagValue(tag, "parent")
 
       val transformed = sameTypeTransform(node)
       // Both the child and parent keep the tags
-      assert(transformed.tags(TreeNodeTagName("test")) == "parent")
-      assert(transformed.children.head.tags(TreeNodeTagName("test")) == "child")
+      assert(transformed.getTagValue(tag) == Some("parent"))
+      assert(transformed.children.head.getTagValue(tag) == Some("child"))
 
       val transformed2 = differentTypeTransform(node)
       // Both the child and parent keep the tags, even if we transform the node to a new one of
       // different type.
-      assert(transformed2.tags(TreeNodeTagName("test")) == "parent")
-      assert(transformed2.children.head.tags.contains(TreeNodeTagName("test")))
+      assert(transformed2.getTagValue(tag) == Some("parent"))
+      assert(transformed2.children.head.getTagValue(tag) == Some("child"))
     }
 
     withClue("transformDown") {

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

@@ -33,15 +33,16 @@ import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.expressions.codegen.{Predicate => GenPredicate, _}
 import org.apache.spark.sql.catalyst.plans.QueryPlan
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.catalyst.plans.physical._
-import org.apache.spark.sql.catalyst.trees.TreeNodeTagName
+import org.apache.spark.sql.catalyst.trees.TreeNodeTag
 import org.apache.spark.sql.execution.metric.SQLMetric
 import org.apache.spark.sql.types.DataType
 
 object SparkPlan {
   // a TreeNode tag in SparkPlan, to carry its original logical plan. The planner will add this tag
   // when converting a logical plan to a physical plan.
-  val LOGICAL_PLAN_TAG_NAME = TreeNodeTagName("logical_plan")
+  val LOGICAL_PLAN_TAG = TreeNodeTag[LogicalPlan]("logical_plan")
 }
 
 /**

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

@@ -69,7 +69,7 @@ abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
         case ReturnAnswer(rootPlan) => rootPlan
         case _ => plan
       }
-      p.tags += SparkPlan.LOGICAL_PLAN_TAG_NAME -> logicalPlan
+      p.setTagValue(SparkPlan.LOGICAL_PLAN_TAG, logicalPlan)
       p
     }
   }

sql/core/src/test/scala/org/apache/spark/sql/execution/LogicalPlanTagInSparkPlanSuite.scala

@@ -21,7 +21,6 @@ import scala.reflect.ClassTag
 
 import org.apache.spark.sql.TPCDSQuerySuite
 import org.apache.spark.sql.catalyst.expressions.aggregate.{AggregateExpression, Complete, Final}
-import org.apache.spark.sql.catalyst.plans.QueryPlan
 import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Generate, Join, LocalRelation, LogicalPlan, Range, Sample, Union, Window}
 import org.apache.spark.sql.execution.aggregate.{HashAggregateExec, ObjectHashAggregateExec, SortAggregateExec}
 import org.apache.spark.sql.execution.columnar.{InMemoryRelation, InMemoryTableScanExec}
@@ -81,12 +80,12 @@ class LogicalPlanTagInSparkPlanSuite extends TPCDSQuerySuite {
       // The exchange related nodes are created after the planning, they don't have corresponding
       // logical plan.
       case _: ShuffleExchangeExec | _: BroadcastExchangeExec | _: ReusedExchangeExec =>
-        assert(!plan.tags.contains(SparkPlan.LOGICAL_PLAN_TAG_NAME))
+        assert(plan.getTagValue(SparkPlan.LOGICAL_PLAN_TAG).isEmpty)
 
       // The subquery exec nodes are just wrappers of the actual nodes, they don't have
       // corresponding logical plan.
       case _: SubqueryExec | _: ReusedSubqueryExec =>
-        assert(!plan.tags.contains(SparkPlan.LOGICAL_PLAN_TAG_NAME))
+        assert(plan.getTagValue(SparkPlan.LOGICAL_PLAN_TAG).isEmpty)
 
       case _ if isScanPlanTree(plan) =>
         // The strategies for planning scan can remove or add FilterExec/ProjectExec nodes,
@@ -120,9 +119,9 @@ class LogicalPlanTagInSparkPlanSuite extends TPCDSQuerySuite {
   }
 
   private def getLogicalPlan(node: SparkPlan): LogicalPlan = {
-    assert(node.tags.contains(SparkPlan.LOGICAL_PLAN_TAG_NAME),
-      node.getClass.getSimpleName + " does not have a logical plan link")
-    node.tags(SparkPlan.LOGICAL_PLAN_TAG_NAME).asInstanceOf[LogicalPlan]
+    node.getTagValue(SparkPlan.LOGICAL_PLAN_TAG).getOrElse {
+      fail(node.getClass.getSimpleName + " does not have a logical plan link")
+    }
   }
 
   private def assertLogicalPlanType[T <: LogicalPlan : ClassTag](node: SparkPlan): Unit = {