[SPARK-27917][SQL] canonical form of CaseWhen object is incorrect

## What changes were proposed in this pull request?

For caseWhen Object canonicalized is not handled

for e.g let's consider below CaseWhen Object
    val attrRef = AttributeReference("ACCESS_CHECK", StringType)()
    val caseWhenObj1 = CaseWhen(Seq((attrRef, Literal("A"))))

caseWhenObj1.canonicalized **ouput** is as below

CASE WHEN ACCESS_CHECK#0 THEN A END (**Before Fix)**

**After Fix** : CASE WHEN none#0 THEN A END

So when there will be aliasref like below statements, semantic equals will fail. Sematic equals returns true if the canonicalized form of both the expressions are same.

val attrRef = AttributeReference("ACCESS_CHECK", StringType)()
val aliasAttrRef = attrRef.withName("access_check")
val caseWhenObj1 = CaseWhen(Seq((attrRef, Literal("A"))))
val caseWhenObj2 = CaseWhen(Seq((aliasAttrRef, Literal("A"))))

**assert(caseWhenObj2.semanticEquals(caseWhenObj1.semanticEquals) fails**

**caseWhenObj1.canonicalized**

Before Fix:CASE WHEN ACCESS_CHECK#0 THEN A END
After Fix: CASE WHEN none#0 THEN A END
**caseWhenObj2.canonicalized**

Before Fix:CASE WHEN access_check#0 THEN A END
After Fix: CASE WHEN none#0 THEN A END

## How was this patch tested?
Added UT

Closes apache#24766 from sandeep-katta/caseWhenIssue.

Authored-by: sandeep katta <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

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

@@ -234,6 +234,8 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
     }
     def mapChild(child: Any): Any = child match {
       case arg: TreeNode[_] if containsChild(arg) => mapTreeNode(arg)
+      // CaseWhen Case or any tuple type
+      case (left, right) => (mapChild(left), mapChild(right))
       case nonChild: AnyRef => nonChild
       case null => null
     }
@@ -249,6 +251,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
         // `mapValues` is lazy and we need to force it to materialize
         m.mapValues(mapChild).view.force
       case arg: TreeNode[_] if containsChild(arg) => mapTreeNode(arg)
+      case Some(child) => Some(mapChild(child))
       case nonChild: AnyRef => nonChild
       case null => null
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ConditionalExpressionSuite.scala

@@ -248,4 +248,28 @@ class ConditionalExpressionSuite extends SparkFunSuite with ExpressionEvalHelper
       .contains("CASE WHEN ... THEN struct<x:int> WHEN ... THEN struct<y:int> " +
         "ELSE struct<z:int> END"))
   }
+
+  test("SPARK-27917 test semantic equals of CaseWhen") {
+    val attrRef = AttributeReference("ACCESS_CHECK", StringType)()
+    val aliasAttrRef = attrRef.withName("access_check")
+    // Test for Equality
+    var caseWhenObj1 = CaseWhen(Seq((attrRef, Literal("A"))))
+    var caseWhenObj2 = CaseWhen(Seq((aliasAttrRef, Literal("A"))))
+    assert(caseWhenObj1.semanticEquals(caseWhenObj2))
+    assert(caseWhenObj2.semanticEquals(caseWhenObj1))
+    // Test for inEquality
+    caseWhenObj2 = CaseWhen(Seq((attrRef, Literal("a"))))
+    assert(!caseWhenObj1.semanticEquals(caseWhenObj2))
+    assert(!caseWhenObj2.semanticEquals(caseWhenObj1))
+    // Test with elseValue with Equality
+    caseWhenObj1 = CaseWhen(Seq((attrRef, Literal("A"))), attrRef.withName("ELSEVALUE"))
+    caseWhenObj2 = CaseWhen(Seq((aliasAttrRef, Literal("A"))), aliasAttrRef.withName("elsevalue"))
+    assert(caseWhenObj1.semanticEquals(caseWhenObj2))
+    assert(caseWhenObj2.semanticEquals(caseWhenObj1))
+    caseWhenObj1 = CaseWhen(Seq((attrRef, Literal("A"))), Literal("ELSEVALUE"))
+    caseWhenObj2 = CaseWhen(Seq((aliasAttrRef, Literal("A"))), Literal("elsevalue"))
+    // Test with elseValue with inEquality
+    assert(!caseWhenObj1.semanticEquals(caseWhenObj2))
+    assert(!caseWhenObj2.semanticEquals(caseWhenObj1))
+  }
 }