Fix regression and update tests (#7616)

Fixes b4e1075

Author: jedelbo

CHANGELOG.md

@@ -19,6 +19,7 @@
   * Fixed an issue during a subsequent open of an encrypted Realm for some rare allocation patterns when the top ref was within ~50 bytes of the end of a page. This could manifest as a DecryptionFailed exception or as an assertion: `encrypted_file_mapping.hpp:183: Assertion failed: local_ndx < m_page_state.size()`. ([#7319](https://github.com/realm/realm-core/issues/7319))
 * Non-streaming download sync progress notification is fixed for flexible sync Realms where before it was sometimes stopping to emit values right after the registration of the callback (PR [#7561](https://github.com/realm/realm-core/issues/7561)).
 * Schema initialization could hit an assertion failure if the sync client applied a downloaded changeset while the Realm file was in the process of being opened ([#7041](https://github.com/realm/realm-core/issues/7041), since v11.4.0).
+* Queries using query paths on Mixed values returns inconsistent results ([#7587](https://github.com/realm/realm-core/issues/7587), since v14.0.0)
 
 ### Breaking changes
 * The following things have been renamed or moved as part of moving all of the App Services functionality to the app namespace:

src/realm/query_expression.hpp

@@ -2076,7 +2076,7 @@ class Columns<Mixed> : public SimpleQuerySupport<Mixed> {
                     }
                 }
                 if (!index.set_size(m_ctrl.matches.size())) {
-                    dest.init(true, 0);
+                    destination.init(true, 0);
                     return;
                 }
             }

test/test_query2.cpp

@@ -5630,6 +5630,51 @@ TEST_TYPES(Query_Mixed, std::true_type, std::false_type)
     CHECK_EQUAL(tv.size(), 1);
 }
 
+TEST(Query_NestedListNull)
+{
+    SHARED_GROUP_TEST_PATH(path);
+    auto hist = make_in_realm_history();
+    DBRef db = DB::create(*hist, path);
+    auto tr = db->start_write();
+    auto foo = tr->add_table("foo");
+    auto col_any = foo->add_column(type_Mixed, "mixed");
+
+    const char* listOfListOfNull = R"([[null]])";
+
+    foo->create_object().set_json(col_any, R"("not a list")");
+    foo->create_object().set_json(col_any, listOfListOfNull);
+    foo->create_object().set_json(col_any, listOfListOfNull);
+    foo->create_object().set_json(col_any, listOfListOfNull);
+
+    CHECK_EQUAL(foo->query("mixed[0][0] == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed[0][5] == null").count(), 0);
+    CHECK_EQUAL(foo->query("mixed[0][*] == null").count(), 3);
+}
+
+TEST(Query_NestedDictionaryNull)
+{
+    SHARED_GROUP_TEST_PATH(path);
+    auto hist = make_in_realm_history();
+    DBRef db = DB::create(*hist, path);
+    auto tr = db->start_write();
+    auto foo = tr->add_table("foo");
+    auto col_any = foo->add_column(type_Mixed, "mixed");
+
+    const char* dictOfDictOfNull = R"({ "nestedDict": { "nullValue": null }})";
+
+    foo->create_object().set_json(col_any, R"("not a dictionary")");
+    foo->create_object().set_json(col_any, dictOfDictOfNull);
+    foo->create_object().set_json(col_any, dictOfDictOfNull);
+    foo->create_object().set_json(col_any, dictOfDictOfNull);
+
+    CHECK_EQUAL(foo->query("mixed['nestedDict']['nullValue'] == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed.nestedDict.nullValue == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed['nestedDict']['foo'] == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed.nestedDict.foo == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed.nestedDict[*] == null").count(), 3);
+    CHECK_EQUAL(foo->query("mixed.nestedDict[*].@type == 'null'").count(), 3);
+}
+
 TEST(Query_ListOfMixed)
 {
     Group g;