Add missing SortPrefixUtils file

Author: JoshRosen

sql/core/src/main/scala/org/apache/spark/sql/execution/SortPrefixUtils.scala

@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.spark.sql.execution
+
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.SortOrder
+import org.apache.spark.util.collection.unsafe.sort.PrefixComparator
+
+
+object SortPrefixUtils {
+
+  /**
+   * A dummy prefix comparator which always claims that prefixes are equal. This is used in cases
+   * where we don't know how to generate or compare prefixes for a SortOrder.
+   */
+  private object NoOpPrefixComparator extends PrefixComparator {
+    override def compare(prefix1: Long, prefix2: Long): Int = 0
+  }
+
+  def getPrefixComparator(sortOrder: SortOrder): PrefixComparator = {
+    sortOrder.dataType match {
+      case _ => NoOpPrefixComparator
+    }
+  }
+
+  def getPrefixComputer(sortOrder: SortOrder): InternalRow => Long = {
+    sortOrder.dataType match {
+      case _ => (row: InternalRow) => 0L
+    }
+  }
+}