1 files changed, 59 insertions, 0 deletions
diff --git a/src/mongo/db/exec/sbe/stages/co_scan.h b/src/mongo/db/exec/sbe/stages/co_scan.h
new file mode 100644
index 00000000000..f88f3762852
--- /dev/null
+++ b/src/mongo/db/exec/sbe/stages/co_scan.h
@@ -0,0 +1,59 @@
+/**
+ *    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
+
+#include "mongo/db/exec/sbe/stages/stages.h"
+
+namespace mongo::sbe {
+/**
+ * This is a CoScan PlanStage. It delivers an infinite stream of getNext() calls. Also, it does not
+ * define any slots; i.e. it does not produce any results.
+ *
+ * On its face value this does not seem to be very useful but it is handy when we have to construct
+ * a data stream when there is not any physical source (i.e. no collection to read from).
+ * Typical use cases are: inner side of Traverse, outer side of Nested Loops, constants, etc.
+ */
+class CoScanStage final : public PlanStage {
+public:
+    CoScanStage();
+
+    std::unique_ptr<PlanStage> clone() const final;
+
+    void prepare(CompileCtx& ctx) final;
+    value::SlotAccessor* getAccessor(CompileCtx& ctx, value::SlotId slot) final;
+    void open(bool reOpen) final;
+    PlanState getNext() final;
+    void close() final;
+
+    std::unique_ptr<PlanStageStats> getStats() const final;
+    const SpecificStats* getSpecificStats() const final;
+    std::vector<DebugPrinter::Block> debugPrint() const final;
+};
+}  // namespace mongo::sbe