SERVER-29647 Fix $match swapping to avoid moving before $sort-$limit.

1 files changed, 20 insertions, 0 deletions

diff --git a/jstests/aggregation/bugs/match_swap_limit.js b/jstests/aggregation/bugs/match_swap_limit.js
new file mode 100644
index 00000000000..3de26d6f4b5
--- /dev/null
+++ b/jstests/aggregation/bugs/match_swap_limit.js
@@ -0,0 +1,20 @@
+/**
+ * Ensure that $match is always applied after $limit.
+ */
+(function() {
+    "use strict";
+
+    let coll = db.jstests_match_swap_limit;
+    coll.drop();
+
+    assert.writeOK(coll.insert({_id: 0, x: 1, y: 3}));
+    assert.writeOK(coll.insert({_id: 1, x: 2, y: 2}));
+    assert.writeOK(coll.insert({_id: 2, x: 3, y: 1}));
+
+    assert.eq([{_id: 1, x: 2, y: 2}],
+              coll.aggregate([{$sort: {x: -1}}, {$limit: 2}, {$match: {y: {$gte: 2}}}]).toArray());
+
+    assert.writeOK(coll.createIndex({x: 1}));
+    assert.eq([{_id: 1, x: 2, y: 2}],
+              coll.aggregate([{$sort: {x: -1}}, {$limit: 2}, {$match: {y: {$gte: 2}}}]).toArray());
+}());