SERVER-39403 Implement visitor for DocumentSource as precursor work for

encryption in agg

39 files changed, 291 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/document_source.h b/src/mongo/db/pipeline/document_source.h
index f3f67db8e0a..de0ef8b209d 100644
--- a/src/mongo/db/pipeline/document_source.h
+++ b/src/mongo/db/pipeline/document_source.h
@@ -47,6 +47,7 @@
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/pipeline/dependencies.h"
 #include "mongo/db/pipeline/document.h"
+#include "mongo/db/pipeline/document_source_visitor.h"
 #include "mongo/db/pipeline/expression_context.h"
 #include "mongo/db/pipeline/field_path.h"
 #include "mongo/db/pipeline/lite_parsed_document_source.h"
@@ -468,6 +469,12 @@ public:
         return false;
     }
 
+    /**
+     * This allows an arbitrary class to implement logic which gets dispatched to at runtime
+     * depending on the type of the DocumentSource.
+     */
+    virtual void acceptVisitor(DocumentSourceVisitor* visitor) = 0;
+
 protected:
     explicit DocumentSource(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
diff --git a/src/mongo/db/pipeline/document_source_bucket_auto.h b/src/mongo/db/pipeline/document_source_bucket_auto.h
index 961ad0f9865..0ccb3981a13 100644
--- a/src/mongo/db/pipeline/document_source_bucket_auto.h
+++ b/src/mongo/db/pipeline/document_source_bucket_auto.h
@@ -88,6 +88,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_change_stream.h b/src/mongo/db/pipeline/document_source_change_stream.h
index 077ec7ff616..c6ddf3c67c3 100644
--- a/src/mongo/db/pipeline/document_source_change_stream.h
+++ b/src/mongo/db/pipeline/document_source_change_stream.h
@@ -230,6 +230,10 @@ public:
 
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain) const final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceOplogMatch(BSONObj filter, const boost::intrusive_ptr<ExpressionContext>& expCtx);
 };
diff --git a/src/mongo/db/pipeline/document_source_change_stream_close_cursor.h b/src/mongo/db/pipeline/document_source_change_stream_close_cursor.h
index d21a2170157..b19f6861495 100644
--- a/src/mongo/db/pipeline/document_source_change_stream_close_cursor.h
+++ b/src/mongo/db/pipeline/document_source_change_stream_close_cursor.h
@@ -82,6 +82,10 @@ public:
         return MergingLogic{nullptr, this, change_stream_constants::kSortSpec};
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     /**
      * Use the create static method to create a DocumentSourceCloseCursor.
diff --git a/src/mongo/db/pipeline/document_source_change_stream_transform.h b/src/mongo/db/pipeline/document_source_change_stream_transform.h
index ca1003128fd..425995498aa 100644
--- a/src/mongo/db/pipeline/document_source_change_stream_transform.h
+++ b/src/mongo/db/pipeline/document_source_change_stream_transform.h
@@ -63,6 +63,10 @@ public:
         return DocumentSourceChangeStream::kStageName.rawData();
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     // This constructor is private, callers should use the 'create()' method above.
     DocumentSourceChangeStreamTransform(const boost::intrusive_ptr<ExpressionContext>&,
diff --git a/src/mongo/db/pipeline/document_source_check_invalidate.h b/src/mongo/db/pipeline/document_source_check_invalidate.h
index 5e5b14f69af..2870bccc7f5 100644
--- a/src/mongo/db/pipeline/document_source_check_invalidate.h
+++ b/src/mongo/db/pipeline/document_source_check_invalidate.h
@@ -72,6 +72,10 @@ public:
         return new DocumentSourceCheckInvalidate(expCtx, ignoreFirstInvalidate);
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     /**
      * Use the create static method to create a DocumentSourceCheckInvalidate.
diff --git a/src/mongo/db/pipeline/document_source_check_resume_token.h b/src/mongo/db/pipeline/document_source_check_resume_token.h
index c91c9813157..0a6d4b5e724 100644
--- a/src/mongo/db/pipeline/document_source_check_resume_token.h
+++ b/src/mongo/db/pipeline/document_source_check_resume_token.h
@@ -84,6 +84,10 @@ public:
     static boost::intrusive_ptr<DocumentSourceShardCheckResumability> create(
         const boost::intrusive_ptr<ExpressionContext>& expCtx, ResumeTokenData token);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     /**
      * Use the create static method to create a DocumentSourceShardCheckResumability.
@@ -145,6 +149,10 @@ public:
     static boost::intrusive_ptr<DocumentSourceEnsureResumeTokenPresent> create(
         const boost::intrusive_ptr<ExpressionContext>& expCtx, ResumeTokenData token);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     /**
      * Use the create static method to create a DocumentSourceEnsureResumeTokenPresent.
diff --git a/src/mongo/db/pipeline/document_source_coll_stats.h b/src/mongo/db/pipeline/document_source_coll_stats.h
index 8cea821a23a..b9d4d8e8f3d 100644
--- a/src/mongo/db/pipeline/document_source_coll_stats.h
+++ b/src/mongo/db/pipeline/document_source_coll_stats.h
@@ -96,6 +96,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     // The raw object given to $collStats containing user specified options.
     BSONObj _collStatsSpec;
diff --git a/src/mongo/db/pipeline/document_source_current_op.h b/src/mongo/db/pipeline/document_source_current_op.h
index 84340c63e71..68f8493e290 100644
--- a/src/mongo/db/pipeline/document_source_current_op.h
+++ b/src/mongo/db/pipeline/document_source_current_op.h
@@ -133,6 +133,10 @@ public:
 
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceCurrentOp(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
                             ConnMode includeIdleConnections,
diff --git a/src/mongo/db/pipeline/document_source_cursor.h b/src/mongo/db/pipeline/document_source_cursor.h
index d1ca145b886..94e34fed1f5 100644
--- a/src/mongo/db/pipeline/document_source_cursor.h
+++ b/src/mongo/db/pipeline/document_source_cursor.h
@@ -151,6 +151,10 @@ public:
         return _planSummaryStats;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     DocumentSourceCursor(Collection* collection,
                          std::unique_ptr<PlanExecutor, PlanExecutor::Deleter> exec,
diff --git a/src/mongo/db/pipeline/document_source_exchange.h b/src/mongo/db/pipeline/document_source_exchange.h
index 4b6b821be82..1c4624f78a4 100644
--- a/src/mongo/db/pipeline/document_source_exchange.h
+++ b/src/mongo/db/pipeline/document_source_exchange.h
@@ -247,6 +247,10 @@ public:
         return _consumerId;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     boost::intrusive_ptr<Exchange> _exchange;
 
diff --git a/src/mongo/db/pipeline/document_source_facet.h b/src/mongo/db/pipeline/document_source_facet.h
index 74281663fb6..8dfe289e37d 100644
--- a/src/mongo/db/pipeline/document_source_facet.h
+++ b/src/mongo/db/pipeline/document_source_facet.h
@@ -145,6 +145,10 @@ public:
     StageConstraints constraints(Pipeline::SplitState pipeState) const final;
     bool usedDisk() final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_geo_near.h b/src/mongo/db/pipeline/document_source_geo_near.h
index 749d9fee7cd..c9b50d6f586 100644
--- a/src/mongo/db/pipeline/document_source_geo_near.h
+++ b/src/mongo/db/pipeline/document_source_geo_near.h
@@ -125,6 +125,9 @@ public:
      */
     boost::optional<MergingLogic> mergingLogic() final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
 
 private:
     explicit DocumentSourceGeoNear(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
diff --git a/src/mongo/db/pipeline/document_source_graph_lookup.h b/src/mongo/db/pipeline/document_source_graph_lookup.h
index 6449560875b..2df71c08e72 100644
--- a/src/mongo/db/pipeline/document_source_graph_lookup.h
+++ b/src/mongo/db/pipeline/document_source_graph_lookup.h
@@ -105,6 +105,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_group.h b/src/mongo/db/pipeline/document_source_group.h
index b166d8e8335..f65754ab7f5 100644
--- a/src/mongo/db/pipeline/document_source_group.h
+++ b/src/mongo/db/pipeline/document_source_group.h
@@ -172,6 +172,10 @@ public:
     std::unique_ptr<GroupFromFirstDocumentTransformation> rewriteGroupAsTransformOnFirstDocument()
         const;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_index_stats.h b/src/mongo/db/pipeline/document_source_index_stats.h
index 9b162ca4575..e4a3b30292e 100644
--- a/src/mongo/db/pipeline/document_source_index_stats.h
+++ b/src/mongo/db/pipeline/document_source_index_stats.h
@@ -89,6 +89,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceIndexStats(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
diff --git a/src/mongo/db/pipeline/document_source_internal_inhibit_optimization.h b/src/mongo/db/pipeline/document_source_internal_inhibit_optimization.h
index 209c39308b8..ce99d887aed 100644
--- a/src/mongo/db/pipeline/document_source_internal_inhibit_optimization.h
+++ b/src/mongo/db/pipeline/document_source_internal_inhibit_optimization.h
@@ -68,6 +68,10 @@ public:
 
     GetNextResult getNext() final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
 };
diff --git a/src/mongo/db/pipeline/document_source_internal_split_pipeline.h b/src/mongo/db/pipeline/document_source_internal_split_pipeline.h
index b2b30952dd2..9ed1ff52741 100644
--- a/src/mongo/db/pipeline/document_source_internal_split_pipeline.h
+++ b/src/mongo/db/pipeline/document_source_internal_split_pipeline.h
@@ -74,6 +74,10 @@ public:
 
     GetNextResult getNext() final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceInternalSplitPipeline(const boost::intrusive_ptr<ExpressionContext>& expCtx,
                                         HostTypeRequirement mergeType)
diff --git a/src/mongo/db/pipeline/document_source_limit.h b/src/mongo/db/pipeline/document_source_limit.h
index 0a5ed1428a5..e6e5ce4c301 100644
--- a/src/mongo/db/pipeline/document_source_limit.h
+++ b/src/mongo/db/pipeline/document_source_limit.h
@@ -92,6 +92,10 @@ public:
         _limit = newLimit;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceLimit(const boost::intrusive_ptr<ExpressionContext>& pExpCtx, long long limit);
 
diff --git a/src/mongo/db/pipeline/document_source_list_cached_and_active_users.h b/src/mongo/db/pipeline/document_source_list_cached_and_active_users.h
index 45df30ac5d8..6cbd2115973 100644
--- a/src/mongo/db/pipeline/document_source_list_cached_and_active_users.h
+++ b/src/mongo/db/pipeline/document_source_list_cached_and_active_users.h
@@ -109,6 +109,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceListCachedAndActiveUsers(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
diff --git a/src/mongo/db/pipeline/document_source_list_local_sessions.h b/src/mongo/db/pipeline/document_source_list_local_sessions.h
index 57fcdf97a1e..0eeab06035c 100644
--- a/src/mongo/db/pipeline/document_source_list_local_sessions.h
+++ b/src/mongo/db/pipeline/document_source_list_local_sessions.h
@@ -123,6 +123,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceListLocalSessions(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
                                     const ListSessionsSpec& spec);
diff --git a/src/mongo/db/pipeline/document_source_list_sessions.h b/src/mongo/db/pipeline/document_source_list_sessions.h
index 42bfe4faf71..15238c1df92 100644
--- a/src/mongo/db/pipeline/document_source_list_sessions.h
+++ b/src/mongo/db/pipeline/document_source_list_sessions.h
@@ -96,6 +96,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceListSessions(const BSONObj& query,
                                const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
diff --git a/src/mongo/db/pipeline/document_source_lookup.h b/src/mongo/db/pipeline/document_source_lookup.h
index 1718ad5dc63..7f9bdd715cd 100644
--- a/src/mongo/db/pipeline/document_source_lookup.h
+++ b/src/mongo/db/pipeline/document_source_lookup.h
@@ -193,6 +193,10 @@ public:
         return buildPipeline(inputDoc);
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_lookup_change_post_image.h b/src/mongo/db/pipeline/document_source_lookup_change_post_image.h
index 504ad359625..3814f2245b9 100644
--- a/src/mongo/db/pipeline/document_source_lookup_change_post_image.h
+++ b/src/mongo/db/pipeline/document_source_lookup_change_post_image.h
@@ -108,6 +108,10 @@ public:
         return kStageName.rawData();
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceLookupChangePostImage(const boost::intrusive_ptr<ExpressionContext>& expCtx)
         : DocumentSource(expCtx) {}
diff --git a/src/mongo/db/pipeline/document_source_match.h b/src/mongo/db/pipeline/document_source_match.h
index 1552c5b1219..a11c846e786 100644
--- a/src/mongo/db/pipeline/document_source_match.h
+++ b/src/mongo/db/pipeline/document_source_match.h
@@ -162,6 +162,10 @@ public:
         return boost::none;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) {
+        visitor->visit(this);
+    }
+
 protected:
     DocumentSourceMatch(const BSONObj& query,
                         const boost::intrusive_ptr<ExpressionContext>& expCtx);
diff --git a/src/mongo/db/pipeline/document_source_mock.h b/src/mongo/db/pipeline/document_source_mock.h
index 3fb65ba7c13..ea1416cffcf 100644
--- a/src/mongo/db/pipeline/document_source_mock.h
+++ b/src/mongo/db/pipeline/document_source_mock.h
@@ -97,6 +97,10 @@ public:
         return boost::none;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
     // Return documents from front of queue.
     std::deque<GetNextResult> queue;
 
diff --git a/src/mongo/db/pipeline/document_source_out.h b/src/mongo/db/pipeline/document_source_out.h
index 8f313213983..fee56a03dbb 100644
--- a/src/mongo/db/pipeline/document_source_out.h
+++ b/src/mongo/db/pipeline/document_source_out.h
@@ -249,6 +249,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     // Stash the writeConcern of the original command as the operation context may change by the
     // time we start to spill $out writes. This is because certain aggregations (e.g. $exchange)
diff --git a/src/mongo/db/pipeline/document_source_plan_cache_stats.h b/src/mongo/db/pipeline/document_source_plan_cache_stats.h
index 9f5aed005b8..102496e334f 100644
--- a/src/mongo/db/pipeline/document_source_plan_cache_stats.h
+++ b/src/mongo/db/pipeline/document_source_plan_cache_stats.h
@@ -123,6 +123,10 @@ public:
         std::vector<Value>& array,
         boost::optional<ExplainOptions::Verbosity> explain = boost::none) const override;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourcePlanCacheStats(const boost::intrusive_ptr<ExpressionContext>& expCtx);
 
diff --git a/src/mongo/db/pipeline/document_source_redact.h b/src/mongo/db/pipeline/document_source_redact.h
index a05f9d2e4ff..4babb90f0a6 100644
--- a/src/mongo/db/pipeline/document_source_redact.h
+++ b/src/mongo/db/pipeline/document_source_redact.h
@@ -66,6 +66,10 @@ public:
 
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceRedact(const boost::intrusive_ptr<ExpressionContext>& expCtx,
                          const boost::intrusive_ptr<Expression>& previsit);
diff --git a/src/mongo/db/pipeline/document_source_sample.h b/src/mongo/db/pipeline/document_source_sample.h
index 3a5c7231d50..aa7c1e8aee1 100644
--- a/src/mongo/db/pipeline/document_source_sample.h
+++ b/src/mongo/db/pipeline/document_source_sample.h
@@ -66,6 +66,10 @@ public:
     static boost::intrusive_ptr<DocumentSource> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     explicit DocumentSourceSample(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
diff --git a/src/mongo/db/pipeline/document_source_sample_from_random_cursor.h b/src/mongo/db/pipeline/document_source_sample_from_random_cursor.h
index 8c9a6e99733..0f607657331 100644
--- a/src/mongo/db/pipeline/document_source_sample_from_random_cursor.h
+++ b/src/mongo/db/pipeline/document_source_sample_from_random_cursor.h
@@ -64,6 +64,10 @@ public:
         std::string idField,
         long long collectionSize);
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceSampleFromRandomCursor(const boost::intrusive_ptr<ExpressionContext>& expCtx,
                                          long long size,
diff --git a/src/mongo/db/pipeline/document_source_sequential_document_cache.h b/src/mongo/db/pipeline/document_source_sequential_document_cache.h
index fa7d9133a2b..6d529254766 100644
--- a/src/mongo/db/pipeline/document_source_sequential_document_cache.h
+++ b/src/mongo/db/pipeline/document_source_sequential_document_cache.h
@@ -83,6 +83,10 @@ public:
         _cache->abandon();
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
                                                      Pipeline::SourceContainer* container) final;
diff --git a/src/mongo/db/pipeline/document_source_single_document_transformation.h b/src/mongo/db/pipeline/document_source_single_document_transformation.h
index d9ca3a8e57b..41003ef2141 100644
--- a/src/mongo/db/pipeline/document_source_single_document_transformation.h
+++ b/src/mongo/db/pipeline/document_source_single_document_transformation.h
@@ -83,6 +83,10 @@ public:
         return _parsedTransform->isSubsetOfProjection(proj);
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_skip.h b/src/mongo/db/pipeline/document_source_skip.h
index d6bc4c88458..70ccb99b859 100644
--- a/src/mongo/db/pipeline/document_source_skip.h
+++ b/src/mongo/db/pipeline/document_source_skip.h
@@ -96,6 +96,10 @@ public:
         _nToSkip = newSkip;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     explicit DocumentSourceSkip(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
                                 long long nToSkip);
diff --git a/src/mongo/db/pipeline/document_source_sort.h b/src/mongo/db/pipeline/document_source_sort.h
index eeca2371b6e..cdb0bcadb99 100644
--- a/src/mongo/db/pipeline/document_source_sort.h
+++ b/src/mongo/db/pipeline/document_source_sort.h
@@ -140,6 +140,10 @@ public:
         return _limitSrc;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     /**
      * Attempts to absorb a subsequent $limit stage so that it an perform a top-k sort.
diff --git a/src/mongo/db/pipeline/document_source_tee_consumer.h b/src/mongo/db/pipeline/document_source_tee_consumer.h
index 3c5ae5fc729..0279c001a76 100644
--- a/src/mongo/db/pipeline/document_source_tee_consumer.h
+++ b/src/mongo/db/pipeline/document_source_tee_consumer.h
@@ -78,6 +78,10 @@ public:
 
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 protected:
     void doDispose() final;
 
diff --git a/src/mongo/db/pipeline/document_source_test_optimizations.h b/src/mongo/db/pipeline/document_source_test_optimizations.h
index 6bda5052d81..1c0bb51d25b 100644
--- a/src/mongo/db/pipeline/document_source_test_optimizations.h
+++ b/src/mongo/db/pipeline/document_source_test_optimizations.h
@@ -63,6 +63,10 @@ public:
         MONGO_UNREACHABLE;
     }
 
+    virtual void acceptVisitor(DocumentSourceVisitor* visitor) override {
+        visitor->visit(this);
+    }
+
 private:
     virtual Value serialize(boost::optional<ExplainOptions::Verbosity>) const override {
         MONGO_UNREACHABLE;
diff --git a/src/mongo/db/pipeline/document_source_unwind.h b/src/mongo/db/pipeline/document_source_unwind.h
index 7948f6fdcd6..3904cc602de 100644
--- a/src/mongo/db/pipeline/document_source_unwind.h
+++ b/src/mongo/db/pipeline/document_source_unwind.h
@@ -90,6 +90,10 @@ public:
         return _indexPath;
     }
 
+    void acceptVisitor(DocumentSourceVisitor* visitor) final {
+        visitor->visit(this);
+    }
+
 private:
     DocumentSourceUnwind(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
                          const FieldPath& fieldPath,
diff --git a/src/mongo/db/pipeline/document_source_visitor.h b/src/mongo/db/pipeline/document_source_visitor.h
new file mode 100644
index 00000000000..58a8d3aebf6
--- /dev/null
+++ b/src/mongo/db/pipeline/document_source_visitor.h
@@ -0,0 +1,133 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+namespace mongo {
+
+class DocumentSourceMergeCursors;
+class DocumentSourceSequentialDocumentCache;
+class DocumentSourceSample;
+class DocumentSourceUnwind;
+class DocumentSourceCloseCursor;
+class DocumentSourceGeoNear;
+class DocumentSourceLookUp;
+class DocumentSourceInternalInhibitOptimization;
+class DocumentSourceLookupChangePostImage;
+class DocumentSourceListCachedAndActiveUsers;
+class DocumentSourceChangeStreamTransform;
+class DocumentSourceOut;
+class DocumentSourceRedact;
+class DocumentSourceGraphLookUp;
+class DocumentSourceExchange;
+class DocumentSourceCursor;
+class DocumentSourceBucketAuto;
+class DocumentSourceSkip;
+class DocumentSourceSort;
+class DocumentSourceGroup;
+class DocumentSourceMock;
+class DocumentSourceListLocalSessions;
+class DocumentSourcePlanCacheStats;
+class DocumentSourceIndexStats;
+class DocumentSourceLimit;
+class DocumentSourceCurrentOp;
+class DocumentSourceSingleDocumentTransformation;
+class DocumentSourceChangeStream;
+class DocumentSourceShardCheckResumability;
+class DocumentSourceEnsureResumeTokenPresent;
+class DocumentSourceCheckInvalidate;
+class DocumentSourceFacet;
+class DocumentSourceInternalSplitPipeline;
+class DocumentSourceListSessions;
+class DocumentSourceCollStats;
+class DocumentSourceTeeConsumer;
+class DocumentSourceSampleFromRandomCursor;
+class DocumentSourceMatch;
+class DocumentSourceOplogMatch;
+class DocumentSourceUpdateOnAddShard;
+class DocumentSourceBackupCursorExtend;
+class DocumentSourceBackupCursor;
+class DocumentSourceTestOptimizations;
+
+/**
+ * This is a base class to allow for dynamic dispatch on a DocumentSource. It implements the visitor
+ * pattern, in which every derived class from DocumentSource implements an acceptVisitor() method,
+ * which simply calls the appropriate visit() method on the derived DocumentSourceVisitor class. The
+ * derived class can do whatever it needs to do for each specific node type in the corresponding
+ * visit() method.
+ */
+class DocumentSourceVisitor {
+public:
+    virtual ~DocumentSourceVisitor() = default;
+
+    virtual void visit(DocumentSourceMergeCursors* source) = 0;
+    virtual void visit(DocumentSourceSequentialDocumentCache* source) = 0;
+    virtual void visit(DocumentSourceSample* source) = 0;
+    virtual void visit(DocumentSourceUnwind* source) = 0;
+    virtual void visit(DocumentSourceCloseCursor* source) = 0;
+    virtual void visit(DocumentSourceGeoNear* source) = 0;
+    virtual void visit(DocumentSourceLookUp* source) = 0;
+    virtual void visit(DocumentSourceInternalInhibitOptimization* source) = 0;
+    virtual void visit(DocumentSourceLookupChangePostImage* source) = 0;
+    virtual void visit(DocumentSourceListCachedAndActiveUsers* source) = 0;
+    virtual void visit(DocumentSourceChangeStreamTransform* source) = 0;
+    virtual void visit(DocumentSourceOut* source) = 0;
+    virtual void visit(DocumentSourceRedact* source) = 0;
+    virtual void visit(DocumentSourceGraphLookUp* source) = 0;
+    virtual void visit(DocumentSourceExchange* source) = 0;
+    virtual void visit(DocumentSourceCursor* source) = 0;
+    virtual void visit(DocumentSourceBucketAuto* source) = 0;
+    virtual void visit(DocumentSourceSkip* source) = 0;
+    virtual void visit(DocumentSourceSort* source) = 0;
+    virtual void visit(DocumentSourceGroup* source) = 0;
+    virtual void visit(DocumentSourceMock* source) = 0;
+    virtual void visit(DocumentSourceListLocalSessions* source) = 0;
+    virtual void visit(DocumentSourcePlanCacheStats* source) = 0;
+    virtual void visit(DocumentSourceIndexStats* source) = 0;
+    virtual void visit(DocumentSourceLimit* source) = 0;
+    virtual void visit(DocumentSourceCurrentOp* source) = 0;
+    virtual void visit(DocumentSourceSingleDocumentTransformation* source) = 0;
+    virtual void visit(DocumentSourceOplogMatch* source) = 0;
+    virtual void visit(DocumentSourceShardCheckResumability* source) = 0;
+    virtual void visit(DocumentSourceEnsureResumeTokenPresent* source) = 0;
+    virtual void visit(DocumentSourceCheckInvalidate* source) = 0;
+    virtual void visit(DocumentSourceFacet* source) = 0;
+    virtual void visit(DocumentSourceInternalSplitPipeline* source) = 0;
+    virtual void visit(DocumentSourceListSessions* source) = 0;
+    virtual void visit(DocumentSourceCollStats* source) = 0;
+    virtual void visit(DocumentSourceTeeConsumer* source) = 0;
+    virtual void visit(DocumentSourceSampleFromRandomCursor* source) = 0;
+    virtual void visit(DocumentSourceMatch* source) = 0;
+    virtual void visit(DocumentSourceUpdateOnAddShard* source) = 0;
+    virtual void visit(DocumentSourceBackupCursorExtend* source) = 0;
+    virtual void visit(DocumentSourceBackupCursor* source) = 0;
+    virtual void visit(DocumentSourceTestOptimizations* source) = 0;
+};
+
+}  // namespace mongo