[SPARK-37800][SQL] TreeNode.argString incorrectly formats arguments o…

…f type Set[_]

### What changes were proposed in this pull request?

Fixing [SPARK-37800: TreeNode.argString incorrectly formats arguments of type Set\[_\]](https://issues.apache.org/jira/browse/SPARK-37800).

### Why are the changes needed?

On May 21, 2021, 746d80d by maropu introduced this bug.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

New test added to `TreeNodeSuite`.

Closes apache#35084 from ssimeonov/ss_spark37800.

Authored-by: Simeon Simeonov <sim@fastignite.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
(cherry picked from commit a8addd4)
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

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

@@ -787,7 +787,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product with Tre
       truncatedString(seq.map(formatArg(_, maxFields)), "[", ", ", "]", maxFields)
     case set: Set[_] =>
       // Sort elements for deterministic behaviours
-      truncatedString(set.toSeq.map(formatArg(_, maxFields).sorted), "{", ", ", "}", maxFields)
+      truncatedString(set.toSeq.map(formatArg(_, maxFields)).sorted, "{", ", ", "}", maxFields)
     case array: Array[_] =>
       truncatedString(array.map(formatArg(_, maxFields)), "[", ", ", "]", maxFields)
     case other =>
@@ -802,15 +802,9 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product with Tre
     case tn: TreeNode[_] => tn.simpleString(maxFields) :: Nil
     case seq: Seq[Any] if seq.toSet.subsetOf(allChildren.asInstanceOf[Set[Any]]) => Nil
     case iter: Iterable[_] if iter.isEmpty => Nil
-    case seq: Seq[_] =>
-      truncatedString(seq.map(formatArg(_, maxFields)), "[", ", ", "]", maxFields) :: Nil
-    case set: Set[_] =>
-      // Sort elements for deterministic behaviours
-      val sortedSeq = set.toSeq.map(formatArg(_, maxFields).sorted)
-      truncatedString(sortedSeq, "{", ", ", "}", maxFields) :: Nil
     case array: Array[_] if array.isEmpty => Nil
-    case array: Array[_] =>
-      truncatedString(array.map(formatArg(_, maxFields)), "[", ", ", "]", maxFields) :: Nil
+    case xs @ (_: Seq[_] | _: Set[_] | _: Array[_]) =>
+      formatArg(xs, maxFields) :: Nil
     case null => Nil
     case None => Nil
     case Some(null) => Nil

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

@@ -810,4 +810,12 @@ class TreeNodeSuite extends SparkFunSuite with SQLHelper {
         fail("TreeNode.nodeName should not throw malformed class name error")
     }
   }
+
+  test("SPARK-37800: TreeNode.argString incorrectly formats arguments of type Set[_]") {
+    case class Node(set: Set[String], nested: Seq[Set[Int]]) extends LogicalPlan with LeafNode {
+      val output: Seq[Attribute] = Nil
+    }
+    val node = Node(Set("second", "first"), Seq(Set(3, 1), Set(2, 1)))
+    assert(node.argString(10) == "{first, second}, [{1, 3}, {1, 2}]")
+  }
 }