chore: Move stringDecode() to CommonStringExprs trait

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

@@ -19,8 +19,6 @@
 
 package org.apache.comet.serde
 
-import java.util.Locale
-
 import scala.collection.JavaConverters._
 import scala.collection.mutable.ListBuffer
 
@@ -1487,30 +1485,6 @@ object QueryPlanSerde extends Logging with CometExprShim {
     })
   }
 
-  def stringDecode(
-      expr: Expression,
-      charset: Expression,
-      bin: Expression,
-      inputs: Seq[Attribute],
-      binding: Boolean): Option[Expr] = {
-    charset match {
-      case Literal(str, DataTypes.StringType)
-          if str.toString.toLowerCase(Locale.ROOT) == "utf-8" =>
-        // decode(col, 'utf-8') can be treated as a cast with "try" eval mode that puts nulls
-        // for invalid strings.
-        // Left child is the binary expression.
-        castToProto(
-          expr,
-          None,
-          DataTypes.StringType,
-          exprToProtoInternal(bin, inputs, binding).get,
-          CometEvalMode.TRY)
-      case _ =>
-        withInfo(expr, "Comet only supports decoding with 'utf-8'.")
-        None
-    }
-  }
-
   /**
    * Creates a UnaryExpr by calling exprToProtoInternal for the provided child expression and then
    * invokes the supplied function to wrap this UnaryExpr in a top-level Expr.

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

@@ -19,13 +19,16 @@
 
 package org.apache.comet.serde
 
+import java.util.Locale
+
 import org.apache.spark.sql.catalyst.expressions.{Attribute, Cast, Expression, Like, Literal, RLike, StringRPad, Substring}
 import org.apache.spark.sql.types.{DataTypes, LongType, StringType}
 
 import org.apache.comet.CometConf
 import org.apache.comet.CometSparkSessionExtensions.withInfo
+import org.apache.comet.expressions.CometEvalMode
 import org.apache.comet.serde.ExprOuterClass.Expr
-import org.apache.comet.serde.QueryPlanSerde.{createBinaryExpr, exprToProtoInternal, optExprWithInfo, scalarFunctionExprToProto}
+import org.apache.comet.serde.QueryPlanSerde.{castToProto, createBinaryExpr, exprToProtoInternal, optExprWithInfo, scalarFunctionExprToProto}
 
 object CometStringRepeat extends CometExpressionSerde {
 
@@ -180,3 +183,30 @@ object CometStringRPad extends CometExpressionSerde {
     }
   }
 }
+
+trait CommonStringExprs {
+
+  def stringDecode(
+      expr: Expression,
+      charset: Expression,
+      bin: Expression,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[Expr] = {
+    charset match {
+      case Literal(str, DataTypes.StringType)
+          if str.toString.toLowerCase(Locale.ROOT) == "utf-8" =>
+        // decode(col, 'utf-8') can be treated as a cast with "try" eval mode that puts nulls
+        // for invalid strings.
+        // Left child is the binary expression.
+        castToProto(
+          expr,
+          None,
+          DataTypes.StringType,
+          exprToProtoInternal(bin, inputs, binding).get,
+          CometEvalMode.TRY)
+      case _ =>
+        withInfo(expr, "Comet only supports decoding with 'utf-8'.")
+        None
+    }
+  }
+}

spark/src/main/spark-3.4/org/apache/comet/shims/CometExprShim.scala

@@ -19,14 +19,14 @@
 package org.apache.comet.shims
 
 import org.apache.comet.expressions.CometEvalMode
+import org.apache.comet.serde.CommonStringExprs
 import org.apache.comet.serde.ExprOuterClass.Expr
-import org.apache.comet.serde.QueryPlanSerde.stringDecode
 import org.apache.spark.sql.catalyst.expressions._
 
 /**
  * `CometExprShim` acts as a shim for for parsing expressions from different Spark versions.
  */
-trait CometExprShim {
+trait CometExprShim extends CommonStringExprs {
     /**
      * Returns a tuple of expressions for the `unhex` function.
      */

spark/src/main/spark-3.5/org/apache/comet/shims/CometExprShim.scala

@@ -19,14 +19,14 @@
 package org.apache.comet.shims
 
 import org.apache.comet.expressions.CometEvalMode
+import org.apache.comet.serde.CommonStringExprs
 import org.apache.comet.serde.ExprOuterClass.Expr
-import org.apache.comet.serde.QueryPlanSerde.stringDecode
 import org.apache.spark.sql.catalyst.expressions._
 
 /**
  * `CometExprShim` acts as a shim for for parsing expressions from different Spark versions.
  */
-trait CometExprShim {
+trait CometExprShim extends CommonStringExprs {
     /**
      * Returns a tuple of expressions for the `unhex` function.
      */

spark/src/main/spark-4.0/org/apache/comet/shims/CometExprShim.scala

@@ -19,8 +19,8 @@
 package org.apache.comet.shims
 
 import org.apache.comet.expressions.CometEvalMode
+import org.apache.comet.serde.CommonStringExprs
 import org.apache.comet.serde.ExprOuterClass.Expr
-import org.apache.comet.serde.QueryPlanSerde.stringDecode
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.expressions.objects.StaticInvoke
 import org.apache.spark.sql.internal.types.StringTypeWithCollation
@@ -29,7 +29,7 @@ import org.apache.spark.sql.types.{BinaryType, BooleanType, StringType}
 /**
  * `CometExprShim` acts as a shim for for parsing expressions from different Spark versions.
  */
-trait CometExprShim {
+trait CometExprShim extends CommonStringExprs {
     /**
      * Returns a tuple of expressions for the `unhex` function.
      */