From fd849606b1548ba0d47c01216d6fc1f7961f6e90 Mon Sep 17 00:00:00 2001
From: Pol Pinol Castuera <pol.pinol@mongodb.com>
Date: Mon, 19 Dec 2022 11:25:51 +0000
Subject: SERVER-71614 Add case to hide the index when is not compatible with
 shard key.

(cherry picked from commit 014381421c79a4d24bed1ebf82b7075db2ce7bd9)
---
 src/mongo/db/s/shard_key_index_util.cpp      |  7 +++++++
 src/mongo/db/s/shard_key_index_util.h        |  4 ++--
 src/mongo/db/s/shard_key_index_util_test.cpp | 21 +++++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/mongo/db/s/shard_key_index_util.cpp b/src/mongo/db/s/shard_key_index_util.cpp
index 542da1e129c..a97ee5167c1 100644
--- a/src/mongo/db/s/shard_key_index_util.cpp
+++ b/src/mongo/db/s/shard_key_index_util.cpp
@@ -137,6 +137,13 @@ bool isLastNonHiddenShardKeyIndex(OperationContext* opCtx,
                                   const IndexCatalog* indexCatalog,
                                   const std::string& indexName,
                                   const BSONObj& shardKey) {
+    const auto index = indexCatalog->findIndexByName(opCtx, indexName);
+    if (!index ||
+        !isCompatibleWithShardKey(
+            opCtx, collection, index->getEntry(), shardKey, false /* requireSingleKey */)) {
+        return false;
+    }
+
     return !_findShardKeyPrefixedIndex(
                 opCtx, collection, indexCatalog, indexName, shardKey, false /* requireSingleKey */)
                 .is_initialized();
diff --git a/src/mongo/db/s/shard_key_index_util.h b/src/mongo/db/s/shard_key_index_util.h
index 1fefa4af87e..c033e88be6c 100644
--- a/src/mongo/db/s/shard_key_index_util.h
+++ b/src/mongo/db/s/shard_key_index_util.h
@@ -93,8 +93,8 @@ const boost::optional<ShardKeyIndex> findShardKeyPrefixedIndex(OperationContext*
                                                                bool requireSingleKey);
 
 /**
- * Returns true if the given index name is the last remaining not hidden index that is compatible
- * with the shard key index.
+ * Returns true if the given index exists and it is the last non-hidden index compatible with the
+ * shard key. False otherwise.
  */
 bool isLastNonHiddenShardKeyIndex(OperationContext* opCtx,
                                   const CollectionPtr& collection,
diff --git a/src/mongo/db/s/shard_key_index_util_test.cpp b/src/mongo/db/s/shard_key_index_util_test.cpp
index bf1502b1ff3..73e8f78779e 100644
--- a/src/mongo/db/s/shard_key_index_util_test.cpp
+++ b/src/mongo/db/s/shard_key_index_util_test.cpp
@@ -226,5 +226,26 @@ TEST_F(ShardKeyIndexUtilTest, LastShardIndexWithMultipleCandidates) {
         opCtx(), coll(), coll()->getIndexCatalog(), "x", BSON("x" << 1)));
 }
 
+TEST_F(ShardKeyIndexUtilTest, LastShardIndexWithIncompatibleIndex) {
+    createIndex(BSON("key" << BSON("y" << 1) << "name"
+                           << "y"
+                           << "v" << kIndexVersion));
+    createIndex(BSON("key" << BSON("x" << 1) << "name"
+                           << "x"
+                           << "v" << kIndexVersion));
+
+    ASSERT_FALSE(isLastNonHiddenShardKeyIndex(
+        opCtx(), coll(), coll()->getIndexCatalog(), "y", BSON("x" << 1)));
+}
+
+TEST_F(ShardKeyIndexUtilTest, LastShardIndexWithNonExistingIndex) {
+    createIndex(BSON("key" << BSON("x" << 1) << "name"
+                           << "x"
+                           << "v" << kIndexVersion));
+
+    ASSERT_FALSE(isLastNonHiddenShardKeyIndex(
+        opCtx(), coll(), coll()->getIndexCatalog(), "y", BSON("x" << 1)));
+}
+
 }  // namespace
 }  // namespace mongo
-- 
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