SERVER-51853 Always initialize the numInserted out-parameter in AbstractIndexAccessMethod::insertKeys

(cherry picked from commit 8177334703d89a19f38246c5ca95cbf3e5470d91)

2 files changed, 13 insertions, 2 deletions

diff --git a/src/mongo/db/index/index_access_method.cpp b/src/mongo/db/index/index_access_method.cpp
index cc050e63dd8..706218c164d 100644
--- a/src/mongo/db/index/index_access_method.cpp
+++ b/src/mongo/db/index/index_access_method.cpp
@@ -218,11 +218,14 @@ Status AbstractIndexAccessMethod::insertKeys(OperationContext* opCtx,
                                              const InsertDeleteOptions& options,
                                              KeyHandlerFn&& onDuplicateKey,
                                              int64_t* numInserted) {
-    bool checkIndexKeySize = shouldCheckIndexKeySize(opCtx);
-
+    // Initialize the 'numInserted' out-parameter to zero in case the caller did not already do so.
+    if (numInserted) {
+        *numInserted = 0;
+    }
     // Add all new data keys, and all new multikey metadata keys, into the index. When iterating
     // over the data keys, each of them should point to the doc's RecordId. When iterating over
     // the multikey metadata keys, they should point to the reserved 'kMultikeyMetadataKeyId'.
+    bool checkIndexKeySize = shouldCheckIndexKeySize(opCtx);
     for (const auto keyVec : {&keys, &multikeyMetadataKeys}) {
         const auto& recordId = (keyVec == &keys ? loc : kMultikeyMetadataKeyId);
         for (const auto& key : *keyVec) {
diff --git a/src/mongo/db/index/index_access_method.h b/src/mongo/db/index/index_access_method.h
index 5fe38414125..5171c7ffef4 100644
--- a/src/mongo/db/index/index_access_method.h
+++ b/src/mongo/db/index/index_access_method.h
@@ -94,6 +94,14 @@ public:
                           KeyHandlerFn&& onDuplicateKey,
                           int64_t* numInserted) = 0;
 
+    /**
+     * Inserts the specified keys into the index, and determines whether these keys should cause the
+     * index to become multikey. If so, this method also handles the task of marking the index as
+     * multikey in the catalog, and sets the path-level multikey information if applicable. The
+     * 'numInserted' output parameter, if non-nullptr, will be reset to the number of keys inserted
+     * by this function call, or to zero in the case of either a non-OK return Status or an empty
+     * 'keys' argument.
+     */
     virtual Status insertKeys(OperationContext* opCtx,
                               const std::vector<BSONObj>& keys,
                               const std::vector<BSONObj>& multikeyMetadataKeys,