SERVER-21011 Fix query correctness problem related to covered matching for 2d/text indexes.

The fix ensures that the tightness predicates over the
trailing fields of 2d/text indexes is checked. Predicates
which are INEXACT_FETCH will then get affixed to the FETCH
stage of the plan rather than incorrectly affixed to the
IXSCAN.

1 files changed, 22 insertions, 0 deletions

diff --git a/jstests/core/fts_trailing_fields.js b/jstests/core/fts_trailing_fields.js
new file mode 100644
index 00000000000..2c7f79b423d
--- /dev/null
+++ b/jstests/core/fts_trailing_fields.js
@@ -0,0 +1,22 @@
+// Tests for predicates which can use the trailing field of a text index.
+(function() {
+    "use strict";
+
+    const coll = db.fts_trailing_fields;
+
+    coll.drop();
+    assert.commandWorked(coll.createIndex({a: 1, b: "text", c: 1}));
+    assert.writeOK(coll.insert({a: 2, b: "lorem ipsum"}));
+
+    assert.eq(0, coll.find({a: 2, $text: {$search: "lorem"}, c: {$exists: true}}).itcount());
+    assert.eq(1, coll.find({a: 2, $text: {$search: "lorem"}, c: null}).itcount());
+    assert.eq(1, coll.find({a: 2, $text: {$search: "lorem"}, c: {$exists: false}}).itcount());
+
+    // An equality predicate on the leading field isn't useful, but it shouldn't cause any problems.
+    // Same with an $elemMatch predicate on one of the trailing fields.
+    coll.drop();
+    assert.commandWorked(coll.createIndex({a: 1, b: "text", "c.d": 1}));
+    assert.writeOK(coll.insert({a: 2, b: "lorem ipsum", c: {d: 3}}));
+    assert.eq(0, coll.find({a: [1, 2], $text: {$search: "lorem"}}).itcount());
+    assert.eq(0, coll.find({a: 2, $text: {$search: "lorem"}, c: {$elemMatch: {d: 3}}}).itcount());
+}());