SERVER-56819 Make indexOfCP's classic engine impl always return -1 when end is less than start

(cherry picked from commit 934d6de41bb3adbecee23e3837852e29c7ff4af6)
(cherry picked from commit 2141bb0d88dc9938fe568a7c4f4584d3c191319a)

1 files changed, 15 insertions, 1 deletions

diff --git a/jstests/aggregation/expressions/indexof_codepoints.js b/jstests/aggregation/expressions/indexof_codepoints.js
index 56d43547564..29458275233 100644
--- a/jstests/aggregation/expressions/indexof_codepoints.js
+++ b/jstests/aggregation/expressions/indexof_codepoints.js
@@ -30,7 +30,21 @@ function testExpressionCodePoints(coll, expression, result, shouldTestEquivalenc
     }
 }
 
-var coll = db.indexofcp;
+const coll = db.indexofcp;
+coll.drop();
+assert.commandWorked(coll.insert({item: 'foobar foobar', emptyStr: ''}));
+
+// Test the edge case of searching for an empty string inside an empty string, where the start index
+// is past the end index. These cases are designed to reproduce SERVER-56819.
+assert.eq(-1,
+          coll.aggregate({$project: {byteLocation: {$indexOfCP: ['', '$emptyStr', 3]}}})
+              .toArray()[0]
+              .byteLocation);
+assert.eq(-1,
+          coll.aggregate({$project: {byteLocation: {$indexOfCP: ['', '$emptyStr', 3, 1]}}})
+              .toArray()[0]
+              .byteLocation);
+
 coll.drop();
 
 // Insert a dummy document so something flows through the pipeline.