Js/sectioned notification (#5926)

* repro bug

* set sectioned results previous values on the initial run

* address review feedback

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)
+* Fixed an assertion failure when observing change notifications on a sectioned result, if the first modification was to a linked property that did not cause the state of the sections to change. ([#5912](https://github.com/realm/realm-core/issues/5912), since the introduction of sectioned results in v12.3.0)
 * CompensatingWriteErrorInfo reported string primary keys as boolean values instead ([PR #5938](https://github.com/realm/realm-core/pull/5938), since the introduction of CompensatingWriteErrorInfo in 12.1.0).
 * Fix a use-after-free if the last external reference to an encrypted Realm was closed between when a client reset error was received and when the download of the new Realm began. ([PR #5949](https://github.com/realm/realm-core/pull/5949), since 12.4.0).
 

src/realm/object-store/sectioned_results.cpp

@@ -401,6 +401,14 @@ void SectionedResults::calculate_sections()
             m_row_to_index_path[i] = {section.index, section.indices.size() - 1};
         }
     }
+    if (!has_performed_initial_evalutation) {
+        REALM_ASSERT_EX(m_previous_key_to_index_lookup.size() == 0, m_previous_key_to_index_lookup.size());
+        REALM_ASSERT_EX(m_prev_section_index_to_key.size() == 0, m_prev_section_index_to_key.size());
+        for (auto& [key, section] : m_sections) {
+            m_previous_key_to_index_lookup[key] = section.index;
+            m_prev_section_index_to_key[section.index] = section.key;
+        }
+    }
 }
 
 size_t SectionedResults::size()

test/object-store/sectioned_results.cpp

@@ -1554,6 +1554,75 @@ TEST_CASE("sectioned results", "[sectioned_results]") {
     }
 }
 
+TEST_CASE("sectioned results link notification bug", "[sectioned_results]") {
+    _impl::RealmCoordinator::assert_no_open_realms();
+
+    InMemoryTestFile config;
+    config.automatic_change_notifications = false;
+
+    auto r = Realm::get_shared_realm(config);
+    r->update_schema(
+        {{"Transaction",
+          {{"_id", PropertyType::String, Property::IsPrimary{true}},
+           {"date", PropertyType::Date},
+           {"account", PropertyType::Object | PropertyType::Nullable, "Account"}}},
+         {"Account", {{"_id", PropertyType::String, Property::IsPrimary{true}}, {"name", PropertyType::String}}}});
+
+    auto coordinator = _impl::RealmCoordinator::get_coordinator(config.path);
+    auto transaction_table = r->read_group().get_table("class_Transaction");
+    transaction_table->get_column_key("date");
+    auto account_col = transaction_table->get_column_key("account");
+    auto account_table = r->read_group().get_table("class_Account");
+    auto account_name_col = account_table->get_column_key("name");
+
+    r->begin_transaction();
+    auto t1 = transaction_table->create_object_with_primary_key("t");
+    auto a1 = account_table->create_object_with_primary_key("a");
+    t1.set(account_col, a1.get_key());
+    r->commit_transaction();
+
+    Results results(r, transaction_table);
+    auto sorted = results.sort({{"date", false}});
+    auto sectioned_results = sorted.sectioned_results([](Mixed value, SharedRealm realm) {
+        auto obj = Object(realm, value.get_link());
+        auto ts = obj.get_column_value<Timestamp>("date");
+        auto tp = ts.get_time_point();
+        auto day = std::chrono::floor<std::chrono::hours>(tp);
+        return Timestamp{day};
+    });
+
+    REQUIRE(sectioned_results.size() == 1);
+    REQUIRE(sectioned_results[0].size() == 1);
+
+    SectionedResultsChangeSet changes;
+    size_t callback_count = 0;
+    auto token = sectioned_results.add_notification_callback([&](SectionedResultsChangeSet c) {
+        changes = c;
+        ++callback_count;
+    });
+    coordinator->on_change();
+    advance_and_notify(*r);
+    REQUIRE(callback_count == 1);
+    REQUIRE(changes.sections_to_insert.empty());
+    REQUIRE(changes.sections_to_delete.empty());
+    REQUIRE(changes.insertions.size() == 0);
+    REQUIRE(changes.deletions.size() == 0);
+    REQUIRE(changes.modifications.size() == 0);
+
+    r->begin_transaction();
+    a1.set(account_name_col, "a2");
+    r->commit_transaction();
+    advance_and_notify(*r);
+
+    REQUIRE(callback_count == 2);
+    REQUIRE(changes.sections_to_insert.empty());
+    REQUIRE(changes.sections_to_delete.empty());
+    REQUIRE(changes.insertions.size() == 0);
+    REQUIRE(changes.deletions.size() == 0);
+    REQUIRE(changes.modifications.size() == 1);
+    REQUIRE_INDICES(changes.modifications[0], 0);
+}
+
 namespace cf = realm::sectioned_results_fixtures;
 
 TEMPLATE_TEST_CASE("sectioned results primitive types", "[sectioned_results]", cf::MixedVal, cf::Int, cf::Bool,