SERVER-41756 source namespace is not reported correctly if $out is used

jstests/noPassthrough/aggregation_log_namespace.js

@@ -0,0 +1,54 @@
+// Tests that a source collection namespace is correctly logged in the global log for an aggregate
+// command when a pipeline contains a stage that can write into an output collection.
+// @tags: [requires_profiling]
+(function() {
+    'use strict';
+
+    load("jstests/aggregation/extras/merge_helpers.js");  // For withEachKindOfWriteStage.
+    load("jstests/libs/check_log.js");                    // For checkLogs.containsWithCount.
+
+    // Runs the given 'pipeline' and verifies that the namespace is correctly logged in the global
+    // log for the aggregate command. The 'comment' parameter is used to match a log entry against
+    // the aggregate command.
+    function verifyLoggedNamespace({pipeline, comment}) {
+        assert.commandWorked(db.runCommand(
+            {aggregate: source.getName(), comment: comment, pipeline: pipeline, cursor: {}}));
+        checkLog.containsWithCount(
+            conn,
+            `command ${source.getFullName()} appName: "MongoDB Shell" ` +
+                `command: aggregate { aggregate: "${source.getName()}", comment: "${comment}"`,
+            1);
+    }
+
+    const mongodOptions = {};
+    const conn = MongoRunner.runMongod(mongodOptions);
+    assert.neq(null, conn, `mongod failed to start with options ${tojson(mongodOptions)}`);
+
+    const db = conn.getDB(`${jsTest.name()}_db`);
+    const source = db.getCollection(`${jsTest.name()}_source`);
+    source.drop();
+    const target = db.getCollection(`${jsTest.name()}_target`);
+    target.drop();
+
+    // Make sure each command gets logged.
+    assert.commandWorked(db.setProfilingLevel(1, {slowms: 0}));
+
+    // Test stages that can write into an output collection.
+    withEachKindOfWriteStage(
+        target,
+        (stage) => verifyLoggedNamespace({pipeline: [stage], comment: Object.keys(stage)[0]}));
+
+    // Test each $merge mode.
+    withEachMergeMode(({whenMatchedMode, whenNotMatchedMode}) => verifyLoggedNamespace({
+                          pipeline: [{
+                              $merge: {
+                                  into: target.getName(),
+                                  whenMatched: whenMatchedMode,
+                                  whenNotMatched: whenNotMatchedMode
+                              }
+                          }],
+                          comment: `merge_${whenMatchedMode}_${whenNotMatchedMode}`
+                      }));
+
+    MongoRunner.stopMongod(conn);
+})();

src/mongo/db/commands/run_aggregate.cpp

@@ -784,6 +784,15 @@ Status runAggregate(OperationContext* opCtx,
         }
     }
 
+    // The aggregation pipeline may change the namespace of the curop and we need to set it back to
+    // the original namespace to correctly report command stats. One example when the namespace can
+    // be changed is when the pipeline contains an $out stage, which executes an internal command to
+    // create a temp collection, changing the curop namespace to the name of this temp collection.
+    {
+        stdx::lock_guard<Client> lk(*opCtx->getClient());
+        curOp->setNS_inlock(origNss.ns());
+    }
+
     // Any code that needs the cursor pinned must be inside the try block, above.
     return Status::OK();
 }