3 files changed, 25 insertions, 10 deletions

diff --git a/src/mongo/bson/mutable/damage_vector.h b/src/mongo/bson/mutable/damage_vector.h
index 8122a7c5592..29826ee0974 100644
--- a/src/mongo/bson/mutable/damage_vector.h
+++ b/src/mongo/bson/mutable/damage_vector.h
@@ -35,21 +35,35 @@
 namespace mongo {
 namespace mutablebson {
 
-// A damage event represents a change of size 'size' byte at starting at offset
-// 'target_offset' in some target buffer, with the replacement data being 'size' bytes of
-// data from the 'source' offset. The base addresses against which these offsets are to be
+// A damage event represents a change of size 'targetSize' byte at starting at offset
+// 'targetOffset' in some target buffer, with the replacement data being 'sourceSize' bytes of
+// data from the 'sourceOffset'. The base addresses against which these offsets are to be
 // applied are not captured here.
 struct DamageEvent {
     typedef uint32_t OffsetSizeType;
 
+    DamageEvent() = default;
+
+    DamageEvent(OffsetSizeType srcOffset, size_t srcSize, OffsetSizeType tgtOffset, size_t tgtSize)
+        : sourceOffset(srcOffset),
+          sourceSize(srcSize),
+          targetOffset(tgtOffset),
+          targetSize(tgtSize) {}
+
     // Offset of source data (in some buffer held elsewhere).
     OffsetSizeType sourceOffset;
 
+    // Size of the data from the source.
+    // If 'sourceSize' is zero, no new data is inserted and 'targetSize' of bytes are deleted from
+    // the target.
+    size_t sourceSize;
+
     // Offset of target data (in some buffer held elsewhere).
     OffsetSizeType targetOffset;
 
-    // Size of the damage region.
-    size_t size;
+    // Size of the data to be replaced in the target.
+    // If 'targetSize' is zero, no bytes from the target are replaced and the new data is inserted.
+    size_t targetSize;
 };
 
 typedef std::vector<DamageEvent> DamageVector;
diff --git a/src/mongo/bson/mutable/document.cpp b/src/mongo/bson/mutable/document.cpp
index b72b9d8f326..56fa36d11f5 100644
--- a/src/mongo/bson/mutable/document.cpp
+++ b/src/mongo/bson/mutable/document.cpp
@@ -1032,8 +1032,9 @@ public:
                            size_t size) {
         _damages.push_back(DamageEvent());
         _damages.back().targetOffset = targetOffset;
+        _damages.back().targetSize = size;
         _damages.back().sourceOffset = sourceOffset;
-        _damages.back().size = size;
+        _damages.back().sourceSize = size;
         if (kDebugBuild && paranoid) {
             // Force damage events to new addresses to catch invalidation errors.
             DamageVector new_damages(_damages);
@@ -1122,7 +1123,7 @@ private:
     // creating and destroying a string and its buffer each time.
     std::string _fieldNameScratch;
 
-    // Queue of damage events and status bit for whether  in-place updates are possible.
+    // Queue of damage events and status bit for whether in-place updates are possible.
     DamageVector _damages;
     Document::InPlaceMode _inPlaceMode;
 };
diff --git a/src/mongo/bson/mutable/mutable_bson_test.cpp b/src/mongo/bson/mutable/mutable_bson_test.cpp
index 7e215379cb8..95f1919b06c 100644
--- a/src/mongo/bson/mutable/mutable_bson_test.cpp
+++ b/src/mongo/bson/mutable/mutable_bson_test.cpp
@@ -954,7 +954,7 @@ void apply(mongo::BSONObj* obj, const mmb::DamageVector& damages, const char* so
     mmb::DamageVector::const_iterator where = damages.begin();
     char* const target = const_cast<char*>(obj->objdata());
     for (; where != end; ++where) {
-        std::memcpy(target + where->targetOffset, source + where->sourceOffset, where->size);
+        std::memcpy(target + where->targetOffset, source + where->sourceOffset, where->sourceSize);
     }
 }
 }  // namespace
@@ -2871,7 +2871,7 @@ TEST(DocumentInPlace, GettingInPlaceUpdatesWhenDisabledClearsArguments) {
     ASSERT_FALSE(doc.isInPlaceModeEnabled());
 
     mmb::DamageVector damages;
-    const mmb::DamageEvent event = {0};
+    const mmb::DamageEvent event{};
     damages.push_back(event);
     const char* source = "foo";
     ASSERT_FALSE(doc.getInPlaceUpdates(&damages, &source));
@@ -3244,7 +3244,7 @@ TEST(DocumentComparison, SimpleComparisonWithDeserializedElements) {
     ASSERT_EQUALS(0, doc1Copy.compareWith(doc1, nullptr));
 
     // Perform an operation on 'c' that doesn't change the serialized value, but
-    // deserializeds the node.
+    // deserializes the node.
     mmb::Document doc2(obj.getOwned());
     const mmb::Document doc2Copy(obj.getOwned());
     mmb::Element c = doc2.root()["c"];