Add fine-grained notifications for Results

src/collection_notifications.cpp

@@ -311,3 +311,255 @@ void CollectionChangeIndices::verify()
         REALM_ASSERT(!modifications.contains(index));
 #endif
 }
+
+namespace {
+struct RowInfo {
+    size_t shifted_row_index;
+    size_t prev_tv_index;
+    size_t tv_index;
+};
+
+void calculate_moves_unsorted(std::vector<RowInfo>& new_rows, CollectionChangeIndices& changeset,
+                              std::function<bool (size_t)> row_did_change)
+{
+    std::sort(begin(new_rows), end(new_rows), [](auto& lft, auto& rgt) {
+        return lft.tv_index < rgt.tv_index;
+    });
+
+    IndexSet::IndexInterator ins = changeset.insertions.begin(), del = changeset.deletions.begin();
+    int shift = 0;
+    for (auto& row : new_rows) {
+        while (del != changeset.deletions.end() && *del <= row.tv_index) {
+            ++del;
+            ++shift;
+        }
+        while (ins != changeset.insertions.end() && *ins <= row.tv_index) {
+            ++ins;
+            --shift;
+        }
+        if (row.prev_tv_index == npos)
+            continue;
+
+        // For unsorted, non-LV queries a row can only move to an index before
+        // its original position due to a move_last_over
+        if (row.tv_index + shift != row.prev_tv_index) {
+            --shift;
+            changeset.moves.push_back({row.prev_tv_index, row.tv_index});
+        }
+        // FIXME: currently move implies modification, and so they're mutally exclusive
+        // this is correct for sorted, but for unsorted a row can move without actually changing
+        else if (row_did_change(row.shifted_row_index)) {
+            // FIXME: needlessly quadratic
+            if (!changeset.insertions.contains(row.tv_index))
+                changeset.modifications.add(row.tv_index);
+        }
+    }
+
+    // FIXME: this is required for merge(), but it would be nice if it wasn't
+    for (auto&& move : changeset.moves) {
+        changeset.insertions.add(move.to);
+        changeset.deletions.add(move.from);
+    }
+}
+
+using items = std::vector<std::pair<size_t, size_t>>;
+
+struct Match {
+    size_t i, j, size;
+};
+
+Match find_longest_match(items const& a, items const& b,
+                         size_t begin1, size_t end1, size_t begin2, size_t end2)
+{
+    Match best = {begin1, begin2, 0};
+    std::vector<size_t> len_from_j;
+    len_from_j.resize(end2 - begin2, 0);
+    std::vector<size_t> len_from_j_prev = len_from_j;
+
+    for (size_t i = begin1; i < end1; ++i) {
+        std::fill(begin(len_from_j), end(len_from_j), 0);
+
+        size_t ai = a[i].first;
+        auto it = lower_bound(begin(b), end(b), std::make_pair(size_t(0), ai),
+                              [](auto a, auto b) { return a.second < b.second; });
+        for (; it != end(b) && it->second == ai; ++it) {
+            size_t j = it->first;
+            if (j < begin2)
+                continue;
+            if (j >= end2)
+                break;
+
+            size_t off = j - begin2;
+            size_t size = off == 0 ? 1 : len_from_j_prev[off - 1] + 1;
+            len_from_j[off] = size;
+            if (size > best.size) {
+                best.i = i - size + 1;
+                best.j = j - size + 1;
+                best.size = size;
+            }
+        }
+        len_from_j.swap(len_from_j_prev);
+    }
+    return best;
+}
+
+void find_longest_matches(items const& a, items const& b_ndx,
+                          size_t begin1, size_t end1, size_t begin2, size_t end2, std::vector<Match>& ret)
+{
+    // FIXME: recursion could get too deep here
+    Match m = find_longest_match(a, b_ndx, begin1, end1, begin2, end2);
+    if (!m.size)
+        return;
+    if (m.i > begin1 && m.j > begin2)
+        find_longest_matches(a, b_ndx, begin1, m.i, begin2, m.j, ret);
+    ret.push_back(m);
+    if (m.i + m.size < end2 && m.j + m.size < end2)
+        find_longest_matches(a, b_ndx, m.i + m.size, end1, m.j + m.size, end2, ret);
+}
+
+void calculate_moves_sorted(std::vector<RowInfo>& new_rows, CollectionChangeIndices& changeset,
+                            std::function<bool (size_t)> row_did_change)
+{
+    std::vector<std::pair<size_t, size_t>> old_candidates;
+    std::vector<std::pair<size_t, size_t>> new_candidates;
+
+    std::sort(begin(new_rows), end(new_rows), [](auto& lft, auto& rgt) {
+        return lft.tv_index < rgt.tv_index;
+    });
+
+    IndexSet::IndexInterator ins = changeset.insertions.begin(), del = changeset.deletions.begin();
+    int shift = 0;
+    for (auto& row : new_rows) {
+        while (del != changeset.deletions.end() && *del <= row.tv_index) {
+            ++del;
+            ++shift;
+        }
+        while (ins != changeset.insertions.end() && *ins <= row.tv_index) {
+            ++ins;
+            --shift;
+        }
+        if (row.prev_tv_index == npos)
+            continue;
+
+        if (row_did_change(row.shifted_row_index)) {
+            // FIXME: needlessly quadratic
+            if (!changeset.insertions.contains(row.tv_index))
+                changeset.modifications.add(row.tv_index);
+        }
+            old_candidates.push_back({row.shifted_row_index, row.prev_tv_index});
+            new_candidates.push_back({row.shifted_row_index, row.tv_index});
+//        }
+    }
+
+    std::sort(begin(old_candidates), end(old_candidates), [](auto a, auto b) {
+        if (a.second != b.second)
+            return a.second < b.second;
+        return a.first < b.first;
+    });
+
+    // First check if the order of any of the rows actually changed
+    size_t first_difference = npos;
+    for (size_t i = 0; i < old_candidates.size(); ++i) {
+        if (old_candidates[i].first != new_candidates[i].first) {
+            first_difference = i;
+            break;
+        }
+    }
+    if (first_difference == npos)
+        return;
+
+    const auto b_ndx = [&]{
+        std::vector<std::pair<size_t, size_t>> ret;
+        ret.reserve(new_candidates.size());
+        for (size_t i = 0; i < new_candidates.size(); ++i)
+            ret.push_back(std::make_pair(i, new_candidates[i].first));
+        std::sort(begin(ret), end(ret), [](auto a, auto b) {
+            if (a.second != b.second)
+                return a.second < b.second;
+            return a.first < b.first;
+        });
+        return ret;
+    }();
+
+    std::vector<Match> longest_matches;
+    find_longest_matches(old_candidates, b_ndx,
+                         first_difference, old_candidates.size(),
+                         first_difference, new_candidates.size(),
+                         longest_matches);
+    longest_matches.push_back({old_candidates.size(), new_candidates.size(), 0});
+
+    size_t i = first_difference, j = first_difference;
+    for (auto match : longest_matches) {
+        for (; i < match.i; ++i)
+            changeset.deletions.add(old_candidates[i].second);
+        for (; j < match.j; ++j)
+            changeset.insertions.add(new_candidates[j].second);
+        i += match.size;
+        j += match.size;
+    }
+
+    // FIXME: needlessly suboptimal
+    changeset.modifications.remove(changeset.insertions);
+}
+} // Anonymous namespace
+
+CollectionChangeIndices CollectionChangeIndices::calculate(std::vector<size_t> const& prev_rows,
+                                                           std::vector<size_t> const& next_rows,
+                                                           std::function<bool (size_t)> row_did_change,
+                                                           bool sort)
+{
+    CollectionChangeIndices ret;
+
+    std::vector<RowInfo> old_rows;
+    for (size_t i = 0; i < prev_rows.size(); ++i) {
+        if (prev_rows[i] == npos)
+            ret.deletions.add(i);
+        else
+            old_rows.push_back({prev_rows[i], npos, i});
+    }
+    std::stable_sort(begin(old_rows), end(old_rows), [](auto& lft, auto& rgt) {
+        return lft.shifted_row_index < rgt.shifted_row_index;
+    });
+
+    std::vector<RowInfo> new_rows;
+    for (size_t i = 0; i < next_rows.size(); ++i) {
+        new_rows.push_back({next_rows[i], npos, i});
+    }
+    std::stable_sort(begin(new_rows), end(new_rows), [](auto& lft, auto& rgt) {
+        return lft.shifted_row_index < rgt.shifted_row_index;
+    });
+
+    size_t i = 0, j = 0;
+    while (i < old_rows.size() && j < new_rows.size()) {
+        auto old_index = old_rows[i];
+        auto new_index = new_rows[j];
+        if (old_index.shifted_row_index == new_index.shifted_row_index) {
+            new_rows[j].prev_tv_index = old_rows[i].tv_index;
+            ++i;
+            ++j;
+        }
+        else if (old_index.shifted_row_index < new_index.shifted_row_index) {
+            ret.deletions.add(old_index.tv_index);
+            ++i;
+        }
+        else {
+            ret.insertions.add(new_index.tv_index);
+            ++j;
+        }
+    }
+
+    for (; i < old_rows.size(); ++i)
+        ret.deletions.add(old_rows[i].tv_index);
+    for (; j < new_rows.size(); ++j)
+        ret.insertions.add(new_rows[j].tv_index);
+
+    if (sort) {
+        calculate_moves_sorted(new_rows, ret, row_did_change);
+    }
+    else {
+        calculate_moves_unsorted(new_rows, ret, row_did_change);
+    }
+    ret.verify();
+
+    return ret;
+}

src/collection_notifications.hpp

@@ -70,6 +70,11 @@ struct CollectionChangeIndices {
                             IndexSet modification = {},
                             std::vector<Move> moves = {});
 
+    static CollectionChangeIndices calculate(std::vector<size_t> const& old_rows,
+                                             std::vector<size_t> const& new_rows,
+                                             std::function<bool (size_t)> row_did_change,
+                                             bool sort);
+
     bool empty() const { return deletions.empty() && insertions.empty() && modifications.empty() && moves.empty(); }
 
     void merge(CollectionChangeIndices&&);

src/impl/async_query.cpp

@@ -30,6 +30,7 @@ AsyncQuery::AsyncQuery(Results& target)
 , m_sort(target.get_sort())
 {
     Query q = target.get_query();
+    set_table(*q.get_table());
     m_query_handover = Realm::Internal::get_shared_group(get_realm()).export_for_handover(q, MutableSourcePayload::Move);
 }
 
@@ -62,8 +63,26 @@ void AsyncQuery::release_data() noexcept
 // destroyed while the background work is running, and to allow removing
 // callbacks from any thread.
 
+static bool map_moves(size_t& idx, CollectionChangeIndices const& changes)
+{
+    for (auto&& move : changes.moves) {
+        if (move.from == idx) {
+            idx = move.to;
+            return true;
+        }
+    }
+    return false;
+}
+
+void AsyncQuery::do_add_required_change_info(TransactionChangeInfo& info)
+{
+    REALM_ASSERT(m_query);
+    m_info = &info;
+}
+
 void AsyncQuery::run()
 {
+    REALM_ASSERT(m_info);
     m_did_change = false;
 
     {
@@ -76,6 +95,8 @@ void AsyncQuery::run()
 
     REALM_ASSERT(!m_tv.is_attached());
 
+    size_t table_ndx = m_query->get_table()->get_index_in_group();
+
     // If we've run previously, check if we need to rerun
     if (m_initial_run_complete) {
         // Make an empty tableview from the query to get the table version, since
@@ -90,6 +111,39 @@ void AsyncQuery::run()
         m_tv.sort(m_sort.column_indices, m_sort.ascending);
     }
 
+    if (m_initial_run_complete) {
+        auto changes = table_ndx < m_info->tables.size() ? &m_info->tables[table_ndx] : nullptr;
+
+        std::vector<size_t> next_rows;
+        next_rows.reserve(m_tv.size());
+        for (size_t i = 0; i < m_tv.size(); ++i)
+            next_rows.push_back(m_tv[i].get_index());
+
+        if (changes) {
+            for (auto& idx : m_previous_rows) {
+                if (changes->deletions.contains(idx))
+                    idx = npos;
+                else
+                    map_moves(idx, *changes);
+                REALM_ASSERT_DEBUG(!changes->insertions.contains(idx));
+            }
+        }
+
+        m_changes = CollectionChangeIndices::calculate(m_previous_rows, next_rows,
+                                                       [&](size_t row) { return m_info->row_did_change(*m_query->get_table(), row); },
+                                                       !!m_sort);
+        m_previous_rows = std::move(next_rows);
+        if (m_changes.empty()) {
+            m_tv = {};
+            return;
+        }
+    }
+    else {
+        m_previous_rows.resize(m_tv.size());
+        for (size_t i = 0; i < m_tv.size(); ++i)
+            m_previous_rows[i] = m_tv[i].get_index();
+    }
+
     m_did_change = true;
 }
 
@@ -105,9 +159,12 @@ bool AsyncQuery::do_prepare_handover(SharedGroup& sg)
     m_handed_over_table_version = m_tv.sync_if_needed();
     m_tv_handover = sg.export_for_handover(m_tv, MutableSourcePayload::Move);
 
+    add_changes(std::move(m_changes));
+    REALM_ASSERT(m_changes.empty());
+
     // detach the TableView as we won't need it again and keeping it around
     // makes advance_read() much more expensive
-    m_tv = TableView();
+    m_tv = {};
 
     return m_did_change;
 }

src/impl/async_query.hpp

@@ -27,11 +27,14 @@
 #include <exception>
 #include <mutex>
 #include <functional>
+#include <set>
 #include <thread>
 #include <vector>
 
 namespace realm {
 namespace _impl {
+struct TransactionChangeInfo;
+
 class AsyncQuery : public BackgroundCollection {
 public:
     AsyncQuery(Results& target);
@@ -45,6 +48,8 @@ private:
     // Returns if any callbacks need to be invoked
     bool do_deliver(SharedGroup& sg) override;
 
+    void do_add_required_change_info(TransactionChangeInfo& info) override;
+
     void release_data() noexcept override;
     void do_attach_to(SharedGroup& sg) override;
     void do_detach_from(SharedGroup& sg) override;
@@ -64,9 +69,14 @@ private:
     TableView m_tv;
     std::unique_ptr<SharedGroup::Handover<TableView>> m_tv_handover;
 
+    CollectionChangeIndices m_changes;
+    TransactionChangeInfo* m_info = nullptr;
+
     uint_fast64_t m_handed_over_table_version = -1;
     bool m_did_change = false;
 
+    std::vector<size_t> m_previous_rows;
+
     bool m_initial_run_complete = false;
 };
 

src/impl/background_collection.cpp

@@ -102,6 +102,38 @@ bool BackgroundCollection::is_alive() const noexcept
     return m_realm != nullptr;
 }
 
+// Recursively add `table` and all tables it links to to `out`
+static void find_relevant_tables(std::vector<size_t>& out, Table const& table)
+{
+    auto table_ndx = table.get_index_in_group();
+    if (find(begin(out), end(out), table_ndx) != end(out))
+        return;
+    out.push_back(table_ndx);
+
+    for (size_t i = 0, count = table.get_column_count(); i != count; ++i) {
+        if (table.get_column_type(i) == type_Link || table.get_column_type(i) == type_LinkList) {
+            find_relevant_tables(out, *table.get_link_target(i));
+        }
+    }
+}
+
+void BackgroundCollection::set_table(Table const& table)
+{
+    find_relevant_tables(m_relevant_tables, table);
+}
+
+void BackgroundCollection::add_required_change_info(TransactionChangeInfo& info)
+{
+    auto max = *max_element(begin(m_relevant_tables), end(m_relevant_tables)) + 1;
+    if (max > info.tables_needed.size())
+        info.tables_needed.resize(max, false);
+    for (auto table_ndx : m_relevant_tables) {
+        info.tables_needed[table_ndx] = true;
+    }
+
+    do_add_required_change_info(info);
+}
+
 void BackgroundCollection::prepare_handover()
 {
     REALM_ASSERT(m_sg);

src/impl/background_collection.hpp

@@ -57,7 +57,7 @@ public:
     // SharedGroup
     void detach();
 
-    virtual void add_required_change_info(TransactionChangeInfo&) { }
+    void add_required_change_info(TransactionChangeInfo&);
 
     virtual void run() { }
     void prepare_handover();
@@ -70,12 +70,14 @@ protected:
     bool have_callbacks() const noexcept { return m_have_callbacks; }
     bool have_changes() const noexcept { return !m_accumulated_changes.empty(); }
     void add_changes(CollectionChangeIndices change) { m_accumulated_changes.merge(std::move(change)); }
+    void set_table(Table const& table);
 
 private:
     virtual void do_attach_to(SharedGroup&) = 0;
     virtual void do_detach_from(SharedGroup&) = 0;
     virtual bool do_prepare_handover(SharedGroup&) = 0;
     virtual bool do_deliver(SharedGroup&) = 0;
+    virtual void do_add_required_change_info(TransactionChangeInfo&) { }
 
     const std::thread::id m_thread_id = std::this_thread::get_id();
     bool is_for_current_thread() const { return m_thread_id == std::this_thread::get_id(); }
@@ -92,6 +94,9 @@ private:
 
     uint_fast64_t m_results_version = 0;
 
+    // Tables which this collection needs change information for
+    std::vector<size_t> m_relevant_tables;
+
     struct Callback {
         CollectionChangeCallback fn;
         size_t token;

src/impl/list_notifier.cpp

@@ -26,28 +26,11 @@
 using namespace realm;
 using namespace realm::_impl;
 
-// Recursively add `table` and all tables it links to to `out`
-static void find_relevant_tables(std::vector<size_t>& out, Table const& table)
-{
-    auto table_ndx = table.get_index_in_group();
-    if (find(begin(out), end(out), table_ndx) != end(out))
-        return;
-    out.push_back(table_ndx);
-
-    for (size_t i = 0, count = table.get_column_count(); i != count; ++i) {
-        if (table.get_column_type(i) == type_Link || table.get_column_type(i) == type_LinkList) {
-            find_relevant_tables(out, *table.get_link_target(i));
-        }
-    }
-}
-
 
 ListNotifier::ListNotifier(LinkViewRef lv, std::shared_ptr<Realm> realm)
 : BackgroundCollection(std::move(realm))
 , m_prev_size(lv->size())
 {
-    find_relevant_tables(m_relevant_tables, lv->get_target_table());
-
     // Find the lv's column, since that isn't tracked directly
     size_t row_ndx = lv->get_origin_row_index();
     m_col_ndx = not_found;
@@ -60,6 +43,8 @@ ListNotifier::ListNotifier(LinkViewRef lv, std::shared_ptr<Realm> realm)
     }
     REALM_ASSERT(m_col_ndx != not_found);
 
+    set_table(lv->get_target_table());
+
     auto& sg = Realm::Internal::get_shared_group(get_realm());
     m_lv_handover = sg.export_linkview_for_handover(lv);
 }
@@ -86,7 +71,7 @@ void ListNotifier::do_detach_from(SharedGroup& sg)
     }
 }
 
-void ListNotifier::add_required_change_info(TransactionChangeInfo& info)
+void ListNotifier::do_add_required_change_info(TransactionChangeInfo& info)
 {
     REALM_ASSERT(!m_lv_handover);
     if (!m_lv) {
@@ -97,13 +82,6 @@ void ListNotifier::add_required_change_info(TransactionChangeInfo& info)
     auto& table = m_lv->get_origin_table();
     info.lists.push_back({table.get_index_in_group(), row_ndx, m_col_ndx, &m_change});
 
-    auto max = *max_element(begin(m_relevant_tables), end(m_relevant_tables)) + 1;
-    if (max > info.tables_needed.size())
-        info.tables_needed.resize(max, false);
-    for (auto table_ndx : m_relevant_tables) {
-        info.tables_needed[table_ndx] = true;
-    }
-
     m_info = &info;
 }
 

src/impl/list_notifier.hpp

@@ -47,7 +47,7 @@ private:
     void do_detach_from(SharedGroup& sg) override;
 
     void release_data() noexcept override;
-    void add_required_change_info(TransactionChangeInfo& info) override;
+    void do_add_required_change_info(TransactionChangeInfo& info) override;
 };
 }
 }

src/impl/realm_coordinator.cpp

@@ -51,11 +51,10 @@ bool TransactionChangeInfo::row_did_change(Table const& table, size_t idx, int d
     for (size_t i = 0, count = table.get_column_count(); i < count; ++i) {
         auto type = table.get_column_type(i);
         if (type == type_Link) {
-            auto& target = *table.get_link_target(i);
+            if (table.is_null_link(i, idx))
-            if (target.is_null_link(i, idx))
                 continue;
             auto dst = table.get_link(i, idx);
-            return row_did_change(target, dst, depth + 1);
+            return row_did_change(*table.get_link_target(i), dst, depth + 1);
         }
         if (type != type_LinkList)
             continue;

src/results.cpp

@@ -46,6 +46,7 @@ Results::Results(SharedRealm r, const ObjectSchema &o, Query q, SortOrder s)
 , m_sort(std::move(s))
 , m_mode(Mode::Query)
 {
+    REALM_ASSERT(m_sort.column_indices.size() == m_sort.ascending.size());
 }
 
 Results::Results(SharedRealm r, const ObjectSchema &o, Table& table)
@@ -350,6 +351,7 @@ TableView Results::get_tableview()
 
 Results Results::sort(realm::SortOrder&& sort) const
 {
+    REALM_ASSERT(sort.column_indices.size() == sort.ascending.size());
     return Results(m_realm, get_object_schema(), get_query(), std::move(sort));
 }
 
@@ -380,6 +382,12 @@ NotificationToken Results::async(std::function<void (std::exception_ptr)> target
     return {m_background_query, m_background_query->add_callback(wrap)};
 }
 
+NotificationToken Results::add_notification_callback(CollectionChangeCallback cb)
+{
+    prepare_async();
+    return {m_background_query, m_background_query->add_callback(std::move(cb))};
+}
+
 void Results::Internal::set_table_view(Results& results, realm::TableView &&tv)
 {
     // If the previous TableView was never actually used, then stop generating

src/results.hpp

@@ -177,6 +177,7 @@ public:
     // The query will be run on a background thread and delivered to the callback,
     // and then rerun after each commit (if needed) and redelivered if it changed
     NotificationToken async(std::function<void (std::exception_ptr)> target);
+    NotificationToken add_notification_callback(CollectionChangeCallback cb);
 
     bool wants_background_updates() const { return m_wants_background_updates; }
 

tests/collection_change_indices.cpp

@@ -177,6 +177,71 @@ TEST_CASE("collection change indices") {
         }
     }
 
+    SECTION("calculate") {
+        auto all_modified = [](size_t) { return true; };
+        auto none_modified = [](size_t) { return false; };
+
+        SECTION("no changes") {
+            c = CollectionChangeIndices::calculate({1, 2, 3}, {1, 2, 3}, none_modified, false);
+            REQUIRE(c.empty());
+        }
+
+        SECTION("inserting from empty") {
+            c = CollectionChangeIndices::calculate({}, {1, 2, 3}, all_modified, false);
+            REQUIRE_INDICES(c.insertions, 0, 1, 2);
+        }
+
+        SECTION("deleting all existing") {
+            c = CollectionChangeIndices::calculate({1, 2, 3}, {}, all_modified, false);
+            REQUIRE_INDICES(c.deletions, 0, 1, 2);
+        }
+
+        SECTION("all rows modified without changing order") {
+            c = CollectionChangeIndices::calculate({1, 2, 3}, {1, 2, 3}, all_modified, false);
+            REQUIRE_INDICES(c.modifications, 0, 1, 2);
+        }
+
+        SECTION("single insertion in middle") {
+            c = CollectionChangeIndices::calculate({1, 3}, {1, 2, 3}, all_modified, false);
+            REQUIRE_INDICES(c.insertions, 1);
+        }
+
+        SECTION("single deletion in middle") {
+            c = CollectionChangeIndices::calculate({1, 2, 3}, {1, 3}, all_modified, false);
+            REQUIRE_INDICES(c.deletions, 1);
+        }
+
+        SECTION("unsorted reordering") {
+            auto calc = [&](std::vector<size_t> values) {
+                return CollectionChangeIndices::calculate({1, 2, 3}, values, none_modified, false);
+            };
+
+            // The commented-out permutations are not possible with
+            // move_last_over() and so are unhandled by unsorted mode
+            REQUIRE(calc({1, 2, 3}).empty());
+            REQUIRE_MOVES(calc({1, 3, 2}), {2, 1});
+//            REQUIRE_MOVES(calc({2, 1, 3}), {1, 0});
+//            REQUIRE_MOVES(calc({2, 3, 1}), {1, 0}, {2, 1});
+            REQUIRE_MOVES(calc({3, 1, 2}), {2, 0});
+            REQUIRE_MOVES(calc({3, 2, 1}), {2, 0}, {1, 1});
+        }
+
+        SECTION("sorted reordering") {
+            auto calc = [&](std::vector<size_t> values) {
+                return CollectionChangeIndices::calculate({1, 2, 3}, values, all_modified, true);
+            };
+
+            REQUIRE(calc({1, 2, 3}).moves.empty());
+            return;
+            // none of these actually work since it just does insert+delete
+            REQUIRE_MOVES(calc({1, 3, 2}), {2, 1});
+            REQUIRE_MOVES(calc({2, 1, 3}), {1, 0});
+            REQUIRE_MOVES(calc({2, 3, 1}), {1, 0}, {2, 1});
+            REQUIRE_MOVES(calc({3, 1, 2}), {2, 0});
+            REQUIRE_MOVES(calc({3, 2, 1}), {2, 0}, {1, 1});
+        }
+    }
+
     SECTION("merge") {
         SECTION("deletions are shifted by previous deletions") {
             c = {{5}, {}, {}, {}};

tests/results.cpp

@@ -1,5 +1,6 @@
 #include "catch.hpp"
 
+#include "util/index_helpers.hpp"
 #include "util/test_file.hpp"
 
 #include "impl/realm_coordinator.hpp"
@@ -12,6 +13,8 @@
 #include <realm/group_shared.hpp>
 #include <realm/link_view.hpp>
 
+#include <unistd.h>
+
 using namespace realm;
 
 TEST_CASE("Results") {
@@ -41,76 +44,38 @@ TEST_CASE("Results") {
     r->begin_transaction();
     table->add_empty_row(10);
     for (int i = 0; i < 10; ++i)
-        table->set_int(0, i, i);
+        table->set_int(0, i, i * 2);
     r->commit_transaction();
 
-    Results results(r, *config.schema->find("object"), table->where().greater(0, 0).less(0, 5));
+    Results results(r, *config.schema->find("object"), table->where().greater(0, 0).less(0, 10));
 
-    SECTION("notifications") {
+    SECTION("unsorted notifications") {
         int notification_calls = 0;
-        auto token = results.async([&](std::exception_ptr err) {
+        CollectionChangeIndices change;
+        auto token = results.add_notification_callback([&](CollectionChangeIndices c, std::exception_ptr err) {
             REQUIRE_FALSE(err);
+            change = c;
             ++notification_calls;
         });
 
         coordinator->on_change();
         r->notify();
 
+        auto write = [&](auto&& f) {
+            r->begin_transaction();
+            f();
+            r->commit_transaction();
+            coordinator->on_change();
+            r->notify();
+        };
+
         SECTION("initial results are delivered") {
             REQUIRE(notification_calls == 1);
         }
 
-        SECTION("modifying the table sends a notification asynchronously") {
+        SECTION("notifications are sent asynchronously") {
             r->begin_transaction();
-            table->set_int(0, 0, 0);
+            table->set_int(0, 0, 4);
-            r->commit_transaction();
-
-            REQUIRE(notification_calls == 1);
-            coordinator->on_change();
-            r->notify();
-            REQUIRE(notification_calls == 2);
-        }
-
-        SECTION("modifying a linked-to table send a notification") {
-            r->begin_transaction();
-            r->read_group()->get_table("class_linked to object")->add_empty_row();
-            r->commit_transaction();
-
-            REQUIRE(notification_calls == 1);
-            coordinator->on_change();
-            r->notify();
-            REQUIRE(notification_calls == 2);
-        }
-
-        SECTION("modifying a a linking table sends a notification") {
-            r->begin_transaction();
-            r->read_group()->get_table("class_linking object")->add_empty_row();
-            r->commit_transaction();
-
-            REQUIRE(notification_calls == 1);
-            coordinator->on_change();
-            r->notify();
-            REQUIRE(notification_calls == 2);
-        }
-
-        SECTION("modifying a an unrelated table does not send a notification") {
-            r->begin_transaction();
-            r->read_group()->get_table("class_other object")->add_empty_row();
-            r->commit_transaction();
-
-            REQUIRE(notification_calls == 1);
-            coordinator->on_change();
-            r->notify();
-            REQUIRE(notification_calls == 1);
-        }
-
-        SECTION("modifications from multiple transactions are collapsed") {
-            r->begin_transaction();
-            table->set_int(0, 0, 0);
-            r->commit_transaction();
-
-            r->begin_transaction();
-            table->set_int(0, 1, 0);
             r->commit_transaction();
 
             REQUIRE(notification_calls == 1);
@@ -121,7 +86,7 @@ TEST_CASE("Results") {
 
         SECTION("notifications are not delivered when the token is destroyed before they are calculated") {
             r->begin_transaction();
-            table->set_int(0, 0, 0);
+            table->set_int(0, 0, 4);
             r->commit_transaction();
 
             REQUIRE(notification_calls == 1);
@@ -133,7 +98,7 @@ TEST_CASE("Results") {
 
         SECTION("notifications are not delivered when the token is destroyed before they are delivered") {
             r->begin_transaction();
-            table->set_int(0, 0, 0);
+            table->set_int(0, 0, 4);
             r->commit_transaction();
 
             REQUIRE(notification_calls == 1);
@@ -142,5 +107,344 @@ TEST_CASE("Results") {
             r->notify();
             REQUIRE(notification_calls == 1);
         }
+
+        SECTION("notifications are delivered when a new callback is added from within a callback") {
+            NotificationToken token2, token3;
+            bool called = false;
+            token2 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                token3 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                    called = true;
+                });
+            });
+
+            coordinator->on_change();
+            r->notify();
+
+            REQUIRE(called);
+        }
+
+        SECTION("notifications are not delivered when a callback is removed from within a callback") {
+            NotificationToken token2, token3;
+            token2 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                token3 = {};
+            });
+            token3 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                REQUIRE(false);
+            });
+
+            coordinator->on_change();
+            r->notify();
+        }
+
+        SECTION("removing the current callback does not stop later ones from being called") {
+            NotificationToken token2, token3;
+            bool called = false;
+            token2 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                token2 = {};
+            });
+            token3 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr) {
+                called = true;
+            });
+
+            coordinator->on_change();
+            r->notify();
+
+            REQUIRE(called);
+        }
+
+        SECTION("modifications to unrelated tables do not send notifications") {
+            write([&] {
+                r->read_group()->get_table("class_other object")->add_empty_row();
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("irrelevant modifications to linked tables do not send notifications") {
+            write([&] {
+                r->read_group()->get_table("class_linked to object")->add_empty_row();
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("irrelevant modifications to linking tables do not send notifications") {
+            write([&] {
+                r->read_group()->get_table("class_linking object")->add_empty_row();
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("modifications that leave a non-matching row non-matching do not send notifications") {
+            write([&] {
+                table->set_int(0, 6, 13);
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("deleting non-matching rows does not send a notification") {
+            write([&] {
+                table->move_last_over(0);
+                table->move_last_over(6);
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("modifying a matching row and leaving it matching marks that row as modified") {
+            write([&] {
+                table->set_int(0, 1, 3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.modifications, 0);
+        }
+
+        SECTION("modifying a matching row to no longer match marks that row as deleted") {
+            write([&] {
+                table->set_int(0, 2, 0);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.deletions, 1);
+        }
+
+        SECTION("modifying a non-matching row to match marks that row as inserted") {
+            write([&] {
+                table->set_int(0, 7, 3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.insertions, 4);
+        }
+
+        SECTION("deleting a matching row marks that row as deleted") {
+            write([&] {
+                table->move_last_over(3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.deletions, 2);
+        }
+
+        SECTION("moving a matching row via deletion marks that row as moved") {
+            write([&] {
+                table->where().greater_equal(0, 10).find_all().clear(RemoveMode::unordered);
+                table->move_last_over(0);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_MOVES(change, {3, 0});
+        }
+
+        SECTION("modifications from multiple transactions are collapsed") {
+            r->begin_transaction();
+            table->set_int(0, 0, 6);
+            r->commit_transaction();
+
+            r->begin_transaction();
+            table->set_int(0, 1, 0);
+            r->commit_transaction();
+
+            REQUIRE(notification_calls == 1);
+            coordinator->on_change();
+            r->notify();
+            REQUIRE(notification_calls == 2);
+        }
+    }
+
+    // Sort in descending order
+    results = results.sort({{0}, {false}});
+
+    SECTION("sorted notifications") {
+        int notification_calls = 0;
+        CollectionChangeIndices change;
+        auto token = results.add_notification_callback([&](CollectionChangeIndices c, std::exception_ptr err) {
+            REQUIRE_FALSE(err);
+            change = c;
+            ++notification_calls;
+        });
+
+        coordinator->on_change();
+        r->notify();
+
+        auto write = [&](auto&& f) {
+            r->begin_transaction();
+            f();
+            r->commit_transaction();
+            coordinator->on_change();
+            r->notify();
+        };
+
+        SECTION("modifications that leave a non-matching row non-matching do not send notifications") {
+            write([&] {
+                table->set_int(0, 6, 13);
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("deleting non-matching rows does not send a notification") {
+            write([&] {
+                table->move_last_over(0);
+                table->move_last_over(6);
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("modifying a matching row and leaving it matching marks that row as modified") {
+            write([&] {
+                table->set_int(0, 1, 3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.modifications, 3);
+        }
+
+        SECTION("modifying a matching row to no longer match marks that row as deleted") {
+            write([&] {
+                table->set_int(0, 2, 0);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.deletions, 2);
+        }
+
+        SECTION("modifying a non-matching row to match marks that row as inserted") {
+            write([&] {
+                table->set_int(0, 7, 3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.insertions, 3);
+        }
+
+        SECTION("deleting a matching row marks that row as deleted") {
+            write([&] {
+                table->move_last_over(3);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.deletions, 1);
+        }
+
+        SECTION("moving a matching row via deletion does not send a notification") {
+            write([&] {
+                table->where().greater_equal(0, 10).find_all().clear(RemoveMode::unordered);
+                table->move_last_over(0);
+            });
+            REQUIRE(notification_calls == 1);
+        }
+
+        SECTION("modifying a matching row to change its position sends insert+delete") {
+            write([&] {
+                table->set_int(0, 2, 9);
+            });
+            REQUIRE(notification_calls == 2);
+            REQUIRE_INDICES(change.deletions, 2);
+            REQUIRE_INDICES(change.insertions, 0);
+        }
+
+        SECTION("modifications from multiple transactions are collapsed") {
+            r->begin_transaction();
+            table->set_int(0, 0, 5);
+            r->commit_transaction();
+
+            r->begin_transaction();
+            table->set_int(0, 1, 0);
+            r->commit_transaction();
+
+            REQUIRE(notification_calls == 1);
+            coordinator->on_change();
+            r->notify();
+            REQUIRE(notification_calls == 2);
+        }
+    }
+}
+
+TEST_CASE("Async Results error handling") {
+    InMemoryTestFile config;
+    config.cache = false;
+    config.automatic_change_notifications = false;
+    config.schema = std::make_unique<Schema>(Schema{
+        {"object", "", {
+            {"value", PropertyTypeInt},
+        }},
+    });
+
+    auto r = Realm::get_shared_realm(config);
+    auto coordinator = _impl::RealmCoordinator::get_existing_coordinator(config.path);
+    Results results(r, *config.schema->find("object"), *r->read_group()->get_table("class_object"));
+
+    SECTION("error when opening the advancer SG") {
+        unlink(config.path.c_str());
+
+        SECTION("error is delivered asynchronously") {
+            bool called = false;
+            auto token = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                called = true;
+            });
+
+            REQUIRE(!called);
+            coordinator->on_change();
+            REQUIRE(!called);
+            r->notify();
+            REQUIRE(called);
+        }
+
+        SECTION("adding another callback does not send the error again") {
+            bool called = false;
+            auto token = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                REQUIRE_FALSE(called);
+                called = true;
+            });
+
+            coordinator->on_change();
+            r->notify();
+
+            bool called2 = false;
+            auto token2 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                REQUIRE_FALSE(called2);
+                called2 = true;
+            });
+
+            coordinator->on_change();
+            r->notify();
+
+            REQUIRE(called2);
+        }
+    }
+
+    SECTION("error when opening the executor SG") {
+        SECTION("error is delivered asynchronously") {
+            bool called = false;
+            auto token = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                called = true;
+            });
+            unlink(config.path.c_str());
+
+            REQUIRE(!called);
+            coordinator->on_change();
+            REQUIRE(!called);
+            r->notify();
+            REQUIRE(called);
+        }
+
+        SECTION("adding another callback does not send the error again") {
+            bool called = false;
+            auto token = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                REQUIRE_FALSE(called);
+                called = true;
+            });
+            unlink(config.path.c_str());
+
+            coordinator->on_change();
+            r->notify();
+
+            bool called2 = false;
+            auto token2 = results.add_notification_callback([&](CollectionChangeIndices, std::exception_ptr err) {
+                REQUIRE(err);
+                REQUIRE_FALSE(called2);
+                called2 = true;
+            });
+
+            coordinator->on_change();
+            r->notify();
+
+            REQUIRE(called2);
+        }
+
     }
 }