uros-b commented on code in PR #56864:
URL: https://github.com/apache/spark/pull/56864#discussion_r3740618519


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/variant/variantExpressions.scala:
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@@ -1490,6 +1490,92 @@ object VariantArrayAppendExpressionBuilder extends 
VariantArrayAppendExpressionB
 // scalastyle:on line.size.limit
 object TryVariantArrayAppendExpressionBuilder
     extends VariantArrayAppendExpressionBuilderBase(false)
+case class VariantStripNulls(child: Expression, includeArrays: Expression)
+    extends RuntimeReplaceable
+    with ExpectsInputTypes
+    with BinaryLike[Expression]
+    with QueryErrorsBase {
+
+  override def left: Expression = child
+  override def right: Expression = includeArrays
+
+  override def inputTypes: Seq[AbstractDataType] = Seq(VariantType, 
BooleanType)
+
+  override def checkInputDataTypes(): TypeCheckResult = {
+    val result = super.checkInputDataTypes()
+    if (result.isFailure) {
+      result
+    } else if (!includeArrays.foldable) {
+      DataTypeMismatch(
+        errorSubClass = "NON_FOLDABLE_INPUT",
+        messageParameters = Map(
+          "inputName" -> toSQLId("include_arrays"),
+          "inputType" -> toSQLType(includeArrays.dataType),
+          "inputExpr" -> toSQLExpr(includeArrays)))
+    } else {
+      TypeCheckResult.TypeCheckSuccess
+    }
+  }
+
+  override lazy val replacement: Expression = StaticInvoke(
+    VariantExpressionEvalUtils.getClass,
+    VariantType,
+    "stripNulls",
+    Seq(child, includeArrays),
+    inputTypes,
+    returnNullable = false)
+
+  override def prettyName: String = "variant_strip_nulls"
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression, newRight: Expression): VariantStripNulls =
+    copy(child = newLeft, includeArrays = newRight)
+}
+
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+  usage = "_FUNC_(v[, include_arrays]) - Recursively removes object fields and 
array elements " +
+    "whose value is a variant null, unless `include_arrays` is false, in which 
case null array " +
+    "elements are kept. Returns NULL if any argument is NULL.",
+  arguments = """
+    Arguments:
+      * v - A variant value to mutate.
+      * include_arrays - An optional boolean (default true). Must be a 
constant.

Review Comment:
   Aslo, note possible issues when stripping array elements ends up renumbering 
the array. After variant_strip_nulls(v) with the current default, any 
positional path a user holds ($.a[1]) silently points at different data. That's 
a surprising side effect for a function that reads like it only removes nulls, 
so it seems better as opt-in?



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