SERVER-30704 Use ARM to merge agg cursors on mongos.

1 files changed, 22 insertions, 6 deletions

diff --git a/src/mongo/db/pipeline/dependencies.h b/src/mongo/db/pipeline/dependencies.h
index 9afd9adbaec..19cf3ee33f8 100644
--- a/src/mongo/db/pipeline/dependencies.h
+++ b/src/mongo/db/pipeline/dependencies.h
@@ -47,7 +47,7 @@ struct DepsTracker {
     enum MetadataAvailable { kNoMetadata = 0, kTextScore = 1 };
 
     DepsTracker(MetadataAvailable metadataAvailable = kNoMetadata)
-        : needWholeDocument(false), _metadataAvailable(metadataAvailable), _needTextScore(false) {}
+        : _metadataAvailable(metadataAvailable) {}
 
     /**
      * Returns a projection object covering the dependencies tracked by this class.
@@ -56,10 +56,6 @@ struct DepsTracker {
 
     boost::optional<ParsedDeps> toParsedDeps() const;
 
-    std::set<std::string> fields;  // names of needed fields in dotted notation
-    bool needWholeDocument;        // if true, ignore fields and assume the whole document is needed
-
-
     bool hasNoRequirements() const {
         return fields.empty() && !needWholeDocument && !_needTextScore;
     }
@@ -85,9 +81,29 @@ struct DepsTracker {
         _needTextScore = needTextScore;
     }
 
+    bool getNeedSortKey() const {
+        return _needSortKey;
+    }
+
+    void setNeedSortKey(bool needSortKey) {
+        // We don't expect to ever unset '_needSortKey'.
+        invariant(!_needSortKey || needSortKey);
+        _needSortKey = needSortKey;
+    }
+
+    std::set<std::string> fields;    // The names of needed fields in dotted notation.
+    bool needWholeDocument = false;  // If true, ignore 'fields' and assume the whole document is
+                                     // needed.
 private:
+    /**
+     * Appends the meta projections for the sort key and/or text score to 'bb' if necessary. Returns
+     * true if either type of metadata was needed, and false otherwise.
+     */
+    bool _appendMetaProjections(BSONObjBuilder* bb) const;
+
     MetadataAvailable _metadataAvailable;
-    bool _needTextScore;
+    bool _needTextScore = false;  // if true, add a {$meta: "textScore"} to the projection.
+    bool _needSortKey = false;    // if true, add a {$meta: "sortKey"} to the projection.
 };
 
 /**