refactor UnaryMinus serde (#2378)

Author: andygrove

spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala

@@ -138,7 +138,7 @@ object QueryPlanSerde extends Logging with CometExprShim {
     classOf[Sqrt] -> CometScalarFunction("sqrt"),
     classOf[Subtract] -> CometSubtract,
     classOf[Tan] -> CometScalarFunction("tan"),
-    // TODO UnaryMinus
+    classOf[UnaryMinus] -> CometUnaryMinus,
     classOf[Unhex] -> CometUnhex)
 
   private val mapExpressions: Map[Class[_ <: Expression], CometExpressionSerde[_]] = Map(
@@ -942,22 +942,6 @@ object QueryPlanSerde extends Logging with CometExprShim {
             None
         }
 
-      case UnaryMinus(child, failOnError) =>
-        val childExpr = exprToProtoInternal(child, inputs, binding)
-        if (childExpr.isDefined) {
-          val builder = ExprOuterClass.UnaryMinus.newBuilder()
-          builder.setChild(childExpr.get)
-          builder.setFailOnError(failOnError)
-          Some(
-            ExprOuterClass.Expr
-              .newBuilder()
-              .setUnaryMinus(builder)
-              .build())
-        } else {
-          withInfo(expr, child)
-          None
-        }
-
       // With Spark 3.4, CharVarcharCodegenUtils.readSidePadding gets called to pad spaces for
       // char types.
       // See https://github.com/apache/spark/pull/38151

spark/src/main/scala/org/apache/comet/serde/arithmetic.scala

@@ -21,7 +21,7 @@ package org.apache.comet.serde
 
 import scala.math.min
 
-import org.apache.spark.sql.catalyst.expressions.{Add, Attribute, Cast, Divide, EmptyRow, EqualTo, EvalMode, Expression, If, IntegralDivide, Literal, Multiply, Remainder, Round, Subtract}
+import org.apache.spark.sql.catalyst.expressions.{Add, Attribute, Cast, Divide, EmptyRow, EqualTo, EvalMode, Expression, If, IntegralDivide, Literal, Multiply, Remainder, Round, Subtract, UnaryMinus}
 import org.apache.spark.sql.types.{ByteType, DataType, DecimalType, DoubleType, FloatType, IntegerType, LongType, ShortType}
 
 import org.apache.comet.CometSparkSessionExtensions.withInfo
@@ -370,3 +370,25 @@ object CometRound extends CometExpressionSerde[Round] {
 
   }
 }
+object CometUnaryMinus extends CometExpressionSerde[UnaryMinus] {
+
+  override def convert(
+      expr: UnaryMinus,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[ExprOuterClass.Expr] = {
+    val childExpr = exprToProtoInternal(expr.child, inputs, binding)
+    if (childExpr.isDefined) {
+      val builder = ExprOuterClass.UnaryMinus.newBuilder()
+      builder.setChild(childExpr.get)
+      builder.setFailOnError(expr.failOnError)
+      Some(
+        ExprOuterClass.Expr
+          .newBuilder()
+          .setUnaryMinus(builder)
+          .build())
+    } else {
+      withInfo(expr, expr.child)
+      None
+    }
+  }
+}