SERVER-62529: Add DocumentSourceSetVariableFromSubPipeline

1 files changed, 100 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/document_source_set_variable_from_subpipeline.h b/src/mongo/db/pipeline/document_source_set_variable_from_subpipeline.h
new file mode 100644
index 00000000000..3dd6df56bc4
--- /dev/null
+++ b/src/mongo/db/pipeline/document_source_set_variable_from_subpipeline.h
@@ -0,0 +1,100 @@
+/**
+ *    Copyright (C) 2022-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
+
+#include "mongo/db/pipeline/document_source.h"
+
+namespace mongo {
+
+
+class DocumentSourceSetVariableFromSubPipeline final : public DocumentSource {
+public:
+    static constexpr StringData kStageName = "$setVariableFromSubPipeline"_sd;
+
+    static boost::intrusive_ptr<DocumentSource> createFromBson(
+        BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);
+
+    static boost::intrusive_ptr<DocumentSourceSetVariableFromSubPipeline> create(
+        const boost::intrusive_ptr<ExpressionContext>& expCtx,
+        std::unique_ptr<Pipeline, PipelineDeleter> subpipeline,
+        Variables::Id varID);
+
+    ~DocumentSourceSetVariableFromSubPipeline() = default;
+
+    boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
+        // {shardsStage, mergingStage, sortPattern}
+        return DistributedPlanLogic{nullptr, this, boost::none};
+    }
+    const char* getSourceName() const final {
+        return kStageName.rawData();
+    }
+    StageConstraints constraints(Pipeline::SplitState) const final {
+        StageConstraints setVariableConstraints(StreamType::kStreaming,
+                                                PositionRequirement::kNone,
+                                                HostTypeRequirement::kAnyShard,
+                                                DiskUseRequirement::kNoDiskUse,
+                                                FacetRequirement::kNotAllowed,
+                                                TransactionRequirement::kNotAllowed,
+                                                LookupRequirement::kAllowed,
+                                                UnionRequirement::kAllowed);
+
+        // The constraints of the sub-pipeline determine the constraints of the
+        // $setVariableFromSubPipeline. We want to forward the strictest requirements of the stages
+        // in the sub-pipeline.
+        setVariableConstraints = StageConstraints::getStrictestConstraints(
+            _subPipeline->getSources(), setVariableConstraints);
+        return setVariableConstraints;
+    }
+
+    DepsTracker::State getDependencies(DepsTracker* deps) const final;
+
+protected:
+    /**
+     * Attempts to swap with a subsequent sharding only stage.
+     */
+    Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
+                                                     Pipeline::SourceContainer* container) final;
+    DocumentSourceSetVariableFromSubPipeline(const boost::intrusive_ptr<ExpressionContext>& expCtx,
+                                             std::unique_ptr<Pipeline, PipelineDeleter> subpipeline,
+                                             Variables::Id varID)
+        : DocumentSource(kStageName, expCtx),
+          _subPipeline(std::move(subpipeline)),
+          _variableID(varID) {}
+
+private:
+    GetNextResult doGetNext() final;
+    Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
+    std::unique_ptr<Pipeline, PipelineDeleter> _subPipeline;
+    Variables::Id _variableID;
+    // $setVariableFromSubPipeline sets the value of $$SEARCH_META only on the first call to
+    // doGetNext().
+    bool _firstCallForInput = true;
+};
+}  // namespace mongo