SERVER-44050 Arrays are not correctly rejected during key generation for 'hashed' indexes

(cherry picked from commit 888f7e6fc10ccb999be203b8cbad4dbe19d0a5d2)

2 files changed, 22 insertions, 8 deletions

diff --git a/jstests/core/hashindex1.js b/jstests/core/hashindex1.js
index 93986ecfd5e..09a1e1f7b47 100644
--- a/jstests/core/hashindex1.js
+++ b/jstests/core/hashindex1.js
@@ -87,3 +87,13 @@ var total = t.find().hint({"_id": 1}).toArray().length;
 var totala = t.find().hint(goodspec).toArray().length;
 assert.eq(total, totala, "non-sparse index has wrong total");
 assert.lt(totalb, totala, "sparse index should have smaller total");
+
+// Test that having arrays along the path of the index is not allowed.
+assert.commandWorked(t.createIndex({"field1.field2.0.field4": "hashed"}));
+assert.writeErrorWithCode(t.insert({field1: []}), 16766);
+assert.writeErrorWithCode(t.insert({field1: {field2: []}}), 16766);
+assert.writeErrorWithCode(t.insert({field1: {field2: {0: []}}}), 16766);
+assert.writeErrorWithCode(t.insert({field1: [{field2: {0: []}}]}), 16766);
+assert.writeErrorWithCode(t.insert({field1: {field2: {0: {field4: []}}}}), 16766);
+assert.writeOK(t.insert({field1: {field2: {0: {otherField: []}}}}));
+assert.writeOK(t.insert({field1: {field2: {0: {field4: 1}}}}));
diff --git a/src/mongo/db/index/expression_keys_private.cpp b/src/mongo/db/index/expression_keys_private.cpp
index 9fe3365f393..0a4cd2e42ed 100644
--- a/src/mongo/db/index/expression_keys_private.cpp
+++ b/src/mongo/db/index/expression_keys_private.cpp
@@ -361,7 +361,18 @@ void ExpressionKeysPrivate::getHashKeys(const BSONObj& obj,
                                         const CollatorInterface* collator,
                                         BSONObjSet* keys) {
     const char* cstr = hashedField.c_str();
-    BSONElement fieldVal = dps::extractElementAtPath(obj, cstr);
+    BSONElement fieldVal = dps::extractElementAtPathOrArrayAlongPath(obj, cstr);
+
+    // If we hit an array while traversing the path, 'cstr' will point to the path component
+    // immediately following the array, or the null termination byte if the final field in the path
+    // was an array.
+    uassert(
+        16766,
+        str::stream()
+            << "Error: hashed indexes do not currently support array values. Found array at path: "
+            << hashedField.substr(
+                   0, hashedField.size() - StringData(cstr).size() - !StringData(cstr).empty()),
+        fieldVal.type() != BSONType::Array);
 
     // Convert strings to comparison keys.
     BSONObj fieldValObj;
@@ -370,13 +381,6 @@ void ExpressionKeysPrivate::getHashKeys(const BSONObj& obj,
         CollationIndexKey::collationAwareIndexKeyAppend(fieldVal, collator, &bob);
         fieldValObj = bob.obj();
         fieldVal = fieldValObj.firstElement();
-    }
-
-    uassert(16766,
-            "Error: hashed indexes do not currently support array values",
-            fieldVal.type() != Array);
-
-    if (!fieldVal.eoo()) {
         BSONObj key = BSON("" << makeSingleHashKey(fieldVal, seed, hashVersion));
         keys->insert(key);
     } else if (!isSparse) {