From 9f3a5c943fe86a49d8c143ba6267a9b8b7221b28 Mon Sep 17 00:00:00 2001
From: Karol Sobczak <napewnotrafi@gmail.com>
Date: Fri, 8 Dec 2023 18:30:08 +0100
Subject: [PATCH] Support for 0 length copyRegion of dictionary last position

checkValidRegion already validates that region is correct.
Therefore copyRegion for position 42 and length 0 shoudn't
fail for dictionary with 42 positions.
---
 .../src/main/java/io/trino/spi/block/DictionaryBlock.java      | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/core/trino-spi/src/main/java/io/trino/spi/block/DictionaryBlock.java b/core/trino-spi/src/main/java/io/trino/spi/block/DictionaryBlock.java
index 69c3902fd5e4..611eb63d5f89 100644
--- a/core/trino-spi/src/main/java/io/trino/spi/block/DictionaryBlock.java
+++ b/core/trino-spi/src/main/java/io/trino/spi/block/DictionaryBlock.java
@@ -420,6 +420,9 @@ public Block getRegion(int positionOffset, int length)
     public Block copyRegion(int position, int length)
     {
         checkValidRegion(positionCount, position, length);
+        if (length == 0) {
+            return dictionary.copyRegion(0, 0);
+        }
         // Avoid repeated volatile reads to the uniqueIds field
         int uniqueIds = this.uniqueIds;
         if (length <= 1 || (uniqueIds == dictionary.getPositionCount() && isSequentialIds)) {