From 2273889eebfcda349c1aa9d444bbf442b88feff6 Mon Sep 17 00:00:00 2001
From: Alberto Massari <alberto.massari@mongodb.com>
Date: Tue, 6 Feb 2024 21:30:13 +0100
Subject: [PATCH] SERVER-86224 Preserve bitmap slot when clearing non-requested
 fields (#18714)

GitOrigin-RevId: 8f6c489e72b413b3daaee5bec56c5dfb345262b9
---
 .../core/timeseries/timeseries_computed_field.js   | 14 ++++++++++++++
 src/mongo/db/query/sbe_stage_builder.cpp           |  6 ++++++
 2 files changed, 20 insertions(+)

diff --git a/jstests/core/timeseries/timeseries_computed_field.js b/jstests/core/timeseries/timeseries_computed_field.js
index 3eabc3ef966f6..18275ddadba2d 100644
--- a/jstests/core/timeseries/timeseries_computed_field.js
+++ b/jstests/core/timeseries/timeseries_computed_field.js
@@ -331,6 +331,20 @@ TimeseriesTest.run((insert) => {
         assert.eq(res[2], {"obj": {}}, res);
     }
 
+    {
+        // Try a replaceRoot stage which remove all fields.
+        const res = coll.aggregate([
+                            {$match: {"time": {$gte: new Date(datePrefix + 200)}}},
+                            {$addFields: {}},
+                            {$project: {"measurement0": {$floor: "$topLevelScalar"}}},
+                            {$replaceRoot: {newRoot: {}}}
+                        ])
+                        .toArray();
+        assert.eq(res.length, 2, res);
+        assert.eq(res[0], {}, res);
+        assert.eq(res[1], {}, res);
+    }
+
     {
         const res = coll.aggregate([{
                             "$project": {
diff --git a/src/mongo/db/query/sbe_stage_builder.cpp b/src/mongo/db/query/sbe_stage_builder.cpp
index d5b193a77972d..a8858cc59a11b 100644
--- a/src/mongo/db/query/sbe_stage_builder.cpp
+++ b/src/mongo/db/query/sbe_stage_builder.cpp
@@ -496,6 +496,12 @@ std::vector<PlanStageSlots::OwnedSlotName> PlanStageSlots::getRequiredNamesInOrd
     std::vector<OwnedSlotName> names(reqs._data->slotNameSet.begin(),
                                      reqs._data->slotNameSet.end());
 
+    // Always treat as required, if it present, the slot holding the bitmap with the filtered items
+    // of block values.
+    if (has(kBlockSelectivityBitmap)) {
+        names.emplace_back(kBlockSelectivityBitmap);
+    }
+
     // If this PlanStageSlots has ResultInfo and 'reqs.hasResult()' is true, then we need
     // to get the list of changed fields and add them to 'names'.
     if (reqs.hasResult() && hasResultInfo()) {