[GitHub] [spark] amaliujia commented on a diff in pull request #38947: [SPARK-41233][SQL] Add `array_prepend` function

["amaliujia (via GitHub)" <gi...@apache.org>]

amaliujia commented on code in PR #38947:
URL: https://github.com/apache/spark/pull/38947#discussion_r1107724565


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala:
##########
@@ -1399,6 +1399,149 @@ case class ArrayContains(left: Expression, right: Expression)
     copy(left = newLeft, right = newRight)
 }
 
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+  usage =
+    "_FUNC_(array, value) - Returns an array containing value as well as all elements from array. The new element is positioned at the beginning of the array.",
+  examples = """
+    Examples:
+      > SELECT _FUNC_(array(1, 2, 3), 4);
+       [4, 1, 2, 3]
+  """,
+  group = "array_funcs",
+  since = "3.4.0")
+case class ArrayPrepend(left: Expression, right: Expression)
+  extends BinaryExpression
+    with ImplicitCastInputTypes
+    with ComplexTypeMergingExpression
+    with QueryErrorsBase {
+
+  override def nullable: Boolean = left.nullable
+
+  override def eval(input: InternalRow): Any = {
+    val value1 = left.eval(input)
+    if (value1 == null) {
+      null
+    } else {
+      val value2 = right.eval(input)
+      nullSafeEval(value1, value2)
+    }
+  }
+  override def nullSafeEval(arr: Any, value: Any): Any = {
+    val numberOfElements = arr.asInstanceOf[ArrayData].numElements()
+    if (numberOfElements + 1 > ByteArrayMethods.MAX_ROUNDED_ARRAY_LENGTH) {
+      throw QueryExecutionErrors.concatArraysWithElementsExceedLimitError(numberOfElements)
+    }
+    val newArray = new Array[Any](numberOfElements + 1)
+    newArray(0) = value
+    var pos = 1
+    arr
+      .asInstanceOf[ArrayData]
+      .foreach(
+        right.dataType,
+        (i, v) => {
+          newArray(pos) = v
+          pos += 1
+        })
+    new GenericArrayData(newArray)
+  }
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
+    val leftGen = left.genCode(ctx)
+    val rightGen = right.genCode(ctx)
+    val f = (arr: String, value: String) => {
+      val newArraySize = ctx.freshName("newArraySize")
+      val newArray = ctx.freshName("newArray")
+      val i = ctx.freshName("i")
+      val pos = ctx.freshName("pos")
+      val allocation = CodeGenerator.createArrayData(
+        newArray,
+        right.dataType,
+        newArraySize,
+        s" $prettyName failed.")
+      val assignment =
+        CodeGenerator.createArrayAssignment(newArray, right.dataType, arr, pos, i, false)
+      val newElemAssignment =
+        CodeGenerator.setArrayElement(newArray, right.dataType, pos, value, Some(rightGen.isNull))
+      s"""
+         |int $pos = 0;
+         |int $newArraySize = $arr.numElements() + 1;
+         |$allocation
+         |$newElemAssignment
+         |$pos = $pos + 1;
+         |for (int $i = 0; $i < $arr.numElements(); $i ++) {
+         |  $assignment
+         |  $pos = $pos + 1;
+         |}
+         |${ev.value} = $newArray;
+         |""".stripMargin
+    }
+    val resultCode = f(leftGen.value, rightGen.value)
+    if(nullable) {
+      val nullSafeEval = leftGen.code + rightGen.code + ctx.nullSafeExec(nullable, leftGen.isNull) {
+        s"""
+           |${ev.isNull} = false;
+           |${resultCode}
+           |""".stripMargin
+      }
+      ev.copy(code =
+        code"""
+        boolean ${ev.isNull} = true;
+        ${CodeGenerator.javaType(dataType)} ${ev.value} = ${CodeGenerator.defaultValue(dataType)};
+        $nullSafeEval
+      """)
+    } else {
+      ev.copy(code =
+        code"""
+            ${leftGen.code}
+            ${rightGen.code}
+            ${CodeGenerator.javaType(dataType)} ${ev.value} = ${CodeGenerator.defaultValue(dataType)};
+            $resultCode""", isNull = FalseLiteral)
+    }
+  }
+
+  override def prettyName: String = "array_prepend"
+
+  override protected def withNewChildrenInternal(
+      newLeft: Expression, newRight: Expression): ArrayPrepend =
+    copy(left = newLeft, right = newRight)
+
+  override def dataType: DataType = left.dataType

Review Comment:
   I guess there is a test case missing to capture this nullability case? 



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