SERVER-36609 Modify allPaths indexes to support equality to empty array

2 files changed, 51 insertions, 0 deletions

diff --git a/jstests/noPassthroughWithMongod/all_paths_basic_index_bounds.js b/jstests/noPassthroughWithMongod/all_paths_basic_index_bounds.js
index 2c0463130b4..9eef97a7da4 100644
--- a/jstests/noPassthroughWithMongod/all_paths_basic_index_bounds.js
+++ b/jstests/noPassthroughWithMongod/all_paths_basic_index_bounds.js
@@ -73,6 +73,7 @@
         {expression: {$ne: null, $exists: true}, bounds: ['[MinKey, MaxKey]'], subpathBounds: true},
         // In principle we could have tighter bounds for this. See SERVER-36765.
         {expression: {$eq: null, $exists: true}, bounds: ['[MinKey, MaxKey]'], subpathBounds: true},
+        {expression: {$eq: []}, bounds: ['[undefined, undefined]', '[[], []]']}
     ];
 
     // Given a keyPattern and (optional) pathProjection, this function builds a $** index on the
diff --git a/jstests/noPassthroughWithMongod/wildcard_index_empty_arrays.js b/jstests/noPassthroughWithMongod/wildcard_index_empty_arrays.js
new file mode 100644
index 00000000000..77b20b5ba8e
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/wildcard_index_empty_arrays.js
@@ -0,0 +1,50 @@
+/**
+ * Tests that wildcard indexes will correctly match for empty arrays.
+ */
+(function() {
+    "use strict";
+
+    load("jstests/aggregation/extras/utils.js");  // For arrayEq.
+
+    const coll = db.wildcard_empty_arrays;
+    coll.drop();
+
+    const assertArrayEq = (l, r) => assert(arrayEq(l, r), tojson(l) + " != " + tojson(r));
+
+    // Required in order to build $** indexes.
+    assert.commandWorked(
+        db.adminCommand({setParameter: 1, internalQueryAllowAllPathsIndexes: true}));
+
+    try {
+        const indexWildcard = {"$**": 1};
+        assert.commandWorked(coll.createIndex(indexWildcard));
+
+        assert.commandWorked(coll.insert({a: 1, b: 1, c: [], d: {e: [5, 6]}}));
+        assert.commandWorked(coll.insert({a: 2, b: 2, c: [1, 2], d: {e: []}}));
+        assert.commandWorked(coll.insert({a: 1, b: 2, c: [3, 4], d: {e: [7, 8]}, f: [{g: []}]}));
+        assert.commandWorked(coll.insert({a: 2, b: [[]], c: 1, d: 4}));
+
+        // $** index matches empty array.
+        assertArrayEq(coll.find({c: []}, {_id: 0}).hint(indexWildcard).toArray(),
+                      [{a: 1, b: 1, c: [], d: {e: [5, 6]}}]);
+
+        // $** index supports equality to array offset.
+        assertArrayEq(coll.find({"c.0": 1}, {_id: 0}).hint(indexWildcard).toArray(),
+                      [{a: 2, b: 2, c: [1, 2], d: {e: []}}]);
+
+        // $** index matches empty array nested in object.
+        assertArrayEq(coll.find({"d.e": []}, {_id: 0}).hint(indexWildcard).toArray(),
+                      [{a: 2, b: 2, c: [1, 2], d: {e: []}}]);
+
+        // $** index matches empty array nested within an array of objects.
+        assertArrayEq(coll.find({"f.0.g": []}, {_id: 0}).hint(indexWildcard).toArray(),
+                      [{a: 1, b: 2, c: [3, 4], d: {e: [7, 8]}, f: [{g: []}]}]);
+
+        // $** index matches empty array nested within an array.
+        assertArrayEq(coll.find({"b": []}, {_id: 0}).hint(indexWildcard).toArray(),
+                      [{a: 2, b: [[]], c: 1, d: 4}]);
+    } finally {
+        // Disable $** indexes once the tests have either completed or failed.
+        db.adminCommand({setParameter: 1, internalQueryAllowAllPathsIndexes: false});
+    }
+})();
\ No newline at end of file