SERVER-35172 'ns' field is no longer duplicated in response to dropCollection with WCE

(cherry picked from commit 315d216282d9182078e7ae8a994747caab812dc9)

2 files changed, 32 insertions, 1 deletions

diff --git a/jstests/noPassthrough/dropcollection_duplicate_fields.js b/jstests/noPassthrough/dropcollection_duplicate_fields.js
new file mode 100644
index 00000000000..a2a1c1c8839
--- /dev/null
+++ b/jstests/noPassthrough/dropcollection_duplicate_fields.js
@@ -0,0 +1,29 @@
+/*
+ * SERVER-35172: Test that dropCollection does not return a message containing multiple "ns" fields
+ * @tags: [requires_wiredtiger]
+ */
+
+(function() {
+    "use strict";
+    var conn = MongoRunner.runMongod();
+    var db = conn.getDB('test');
+
+    let coll = db.dropcollection_duplicate_fields;
+    // Repeat 100 times for the sake of probabilities
+    for (let i = 0; i < 100; i++) {
+        coll.drop();
+        coll.insert({x: 1});
+
+        assert.commandWorked(db.adminCommand(
+            {configureFailPoint: 'WTWriteConflictException', mode: {activationProbability: 0.1}}));
+
+        // will blow up if res is not valid
+        let res = db.runCommand({drop: 'dropcollection_duplicate_fields'});
+
+        assert.commandWorked(
+            db.adminCommand({configureFailPoint: 'WTWriteConflictException', mode: "off"}));
+    }
+
+    MongoRunner.stopMongod(conn);
+
+})();
diff --git a/src/mongo/db/catalog/drop_collection.cpp b/src/mongo/db/catalog/drop_collection.cpp
index e9e816651a2..ccfc5050987 100644
--- a/src/mongo/db/catalog/drop_collection.cpp
+++ b/src/mongo/db/catalog/drop_collection.cpp
@@ -82,7 +82,9 @@ Status dropCollection(OperationContext* opCtx,
         }
 
         WriteUnitOfWork wunit(opCtx);
-        result.append("ns", collectionName.ns());
+        if (!result.hasField("ns")) {
+            result.append("ns", collectionName.ns());
+        }
 
         if (coll) {
             invariant(!view);