[SPARK-24214][SS] Fix toJSON for StreamingRelationV2/StreamingExecutionRelation/ContinuousExecutionRelation

## What changes were proposed in this pull request?

We should overwrite "otherCopyArgs" to provide the SparkSession parameter otherwise TreeNode.toJSON cannot get the full constructor parameter list.

## How was this patch tested?

The new unit test.

Author: Shixiong Zhu <[email protected]>

Closes #21275 from zsxwing/SPARK-24214.

(cherry picked from commit fd1179c)
Signed-off-by: Shixiong Zhu <[email protected]>

Author: zsxwing

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamingRelation.scala

@@ -66,6 +66,7 @@ case class StreamingExecutionRelation(
     output: Seq[Attribute])(session: SparkSession)
   extends LeafNode with MultiInstanceRelation {
 
+  override def otherCopyArgs: Seq[AnyRef] = session :: Nil
   override def isStreaming: Boolean = true
   override def toString: String = source.toString
 
@@ -97,6 +98,7 @@ case class StreamingRelationV2(
     output: Seq[Attribute],
     v1Relation: Option[StreamingRelation])(session: SparkSession)
   extends LeafNode with MultiInstanceRelation {
+  override def otherCopyArgs: Seq[AnyRef] = session :: Nil
   override def isStreaming: Boolean = true
   override def toString: String = sourceName
 
@@ -116,6 +118,7 @@ case class ContinuousExecutionRelation(
     output: Seq[Attribute])(session: SparkSession)
   extends LeafNode with MultiInstanceRelation {
 
+  override def otherCopyArgs: Seq[AnyRef] = session :: Nil
   override def isStreaming: Boolean = true
   override def toString: String = source.toString
 

sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala

@@ -687,6 +687,21 @@ class StreamingQuerySuite extends StreamTest with BeforeAndAfter with Logging wi
       CheckLastBatch(("A", 1)))
   }
 
+  test("StreamingRelationV2/StreamingExecutionRelation/ContinuousExecutionRelation.toJSON " +
+    "should not fail") {
+    val df = spark.readStream.format("rate").load()
+    assert(df.logicalPlan.toJSON.contains("StreamingRelationV2"))
+
+    testStream(df)(
+      AssertOnQuery(_.logicalPlan.toJSON.contains("StreamingExecutionRelation"))
+    )
+
+    testStream(df, useV2Sink = true)(
+      StartStream(trigger = Trigger.Continuous(100)),
+      AssertOnQuery(_.logicalPlan.toJSON.contains("ContinuousExecutionRelation"))
+    )
+  }
+
   /** Create a streaming DF that only execute one batch in which it returns the given static DF */
   private def createSingleTriggerStreamingDF(triggerDF: DataFrame): DataFrame = {
     require(!triggerDF.isStreaming)