From bcb0cf270fdbcb6d1cbf9998e29afbfe4cbeebde Mon Sep 17 00:00:00 2001
From: Mihai Andrei <mihai.andrei@10gen.com>
Date: Thu, 4 Jun 2020 11:08:11 -0400
Subject: SERVER-47223 Verify that $geoNear applies index hint correctly

(cherry picked from commit e1d82874e90ed0cb7fd6898edc54d47c1a42b97c)
---
 .../aggregation/sources/geonear/geonear_hint.js    | 53 ++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 jstests/aggregation/sources/geonear/geonear_hint.js

diff --git a/jstests/aggregation/sources/geonear/geonear_hint.js b/jstests/aggregation/sources/geonear/geonear_hint.js
new file mode 100644
index 00000000000..31c700955b3
--- /dev/null
+++ b/jstests/aggregation/sources/geonear/geonear_hint.js
@@ -0,0 +1,53 @@
+// Verify that an aggregate with $geoNear always uses the index hinted to the aggregate command.
+(function() {
+"use strict";
+
+const collName = jsTest.name();
+const coll = db[collName];
+coll.drop();
+
+// Save the names of each hinted index to use when examining the output of $indexStats.
+const simpleGeoNearIndexName = "simpleGeoNearIndex";
+const compoundGeoNearIndexName = "compoundGeoNearIndex";
+
+assert.commandWorked(coll.insert({_id: "1", state: "ACTIVE", location: [106, 10], name: "TEST"}));
+assert.commandWorked(
+    coll.createIndex({_id: 1, location: "2dsphere", state: 1}, {name: compoundGeoNearIndexName}));
+assert.commandWorked(coll.createIndex({location: "2dsphere"}, {name: simpleGeoNearIndexName}));
+
+const pipeline = [
+    {
+        $geoNear: {
+            query: {_id: {$in: ["1", "2", "3"]}, state: "ACTIVE"},
+            spherical: true,
+            near: {coordinates: [106.65589, 10.787627], type: "Point"},
+            distanceField: "distance",
+            key: "location"
+        }
+    },
+    {$project: {id: 1, name: 1, distance: 1}}
+];
+
+// Run the aggregate with two different hinted indexes and confirm that the hinted index gets
+// chosen each time. By testing that two separate index hints get used, we confirm that the
+// index in each query plan gets chosen because it was hinted to the aggregate command and not
+// because the query planner chose it over other indexes.
+for (const indexHint of [simpleGeoNearIndexName, compoundGeoNearIndexName]) {
+    // Run the aggregate with the hint and ensure that it worked.
+    const aggResult = coll.aggregate(pipeline, {hint: indexHint});
+    assert.eq(1, aggResult.itcount());
+
+    // Run $indexStats and limit the results to the hinted index.
+    const indexStats = coll.aggregate([{$indexStats: {}}, {$match: {name: indexHint}}]).toArray();
+
+    // Verify that the hinted index was used exactly once. Note that in the case of a sharded
+    // cluster, $indexStats will report per-shard stats, so we loop over the array returned by
+    // the aggregate to check the stats for each machine.
+    for (const indexEntry of indexStats) {
+        assert(indexEntry.hasOwnProperty("accesses"), indexStats);
+        const indexAccesses = indexEntry["accesses"];
+        assert(indexAccesses.hasOwnProperty("ops"), indexStats);
+        assert.eq(1, indexAccesses["ops"], indexStats);
+    }
+}
+}());
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