SERVER-29125 Add $changeNotification stage that always outputs the single last oplog entry, unmodified

This reverts commit b85788f99e2f7d309582bd9d31ffc2769de72405.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/lite_parsed_pipeline.h b/src/mongo/db/pipeline/lite_parsed_pipeline.h
index c39d9f1031e..ca2e9dfda77 100644
--- a/src/mongo/db/pipeline/lite_parsed_pipeline.h
+++ b/src/mongo/db/pipeline/lite_parsed_pipeline.h
@@ -78,6 +78,13 @@ public:
         return !_stageSpecs.empty() && _stageSpecs.front()->isCollStats();
     }
 
+    /**
+     * Returns true if the pipeline begins with a $changeNotification stage.
+     */
+    bool startsWithChangeNotification() const {
+        return !_stageSpecs.empty() && _stageSpecs.front()->isChangeNotification();
+    }
+
 private:
     std::vector<std::unique_ptr<LiteParsedDocumentSource>> _stageSpecs;
 };