Resolve section aliases on the fly

The original code resolved them when the menu was requested as I thought that made constructing the dbus menu
easier as in dbus menu it's just a contiguous list of actions. However, this also changed the mapping from
dbus action to GTK action (the latter does not have a unique ID system), so when a GTK app signalled a change
(e.g. a menu item got added/removed), the signal was for the original position of the item and not the
resolved one we were using internally.
By resolving everything on the fly, the IDs stay correct, and updating the menu mostly works now.
There's still something funky going on when moving from e.g. LibreOffice splash to LibreOffice Writer
but that needs to be investigated now.

gmenu-dbusmenu-proxy/menu.cpp

@@ -251,50 +251,6 @@ void Menu::start(uint id)
                 return;
             }
 
-            // Now resolve any aliases we might have
-            // TODO Don't do this every time? ugly..
-            for (auto &menu : m_menus) {
-                for (auto &section : menu) {
-                    QMutableListIterator<QVariantMap> it(section.items);
-                    while (it.hasNext()) {
-                        auto &item = it.next();
-
-                        auto findIt = item.constFind(QStringLiteral(":section"));
-                        if (findIt != item.constEnd()) {
-                            // references another place, add it instead
-                            GMenuSection gmenuSection = qdbus_cast<GMenuSection>(findIt->value<QDBusArgument>());
-
-                            // TODO figure out what to do when menu changed since we'd end up shifting the indices around here
-                            if (item.value(QStringLiteral("section-expanded")).toBool()) {
-                                continue;
-                            }
-
-                            // TODO start subscription if we don't have it
-                            auto items = findSection(m_menus.value(gmenuSection.subscription), gmenuSection.menu).items;
-
-                            // remember that this section was already expanded, we'll keep the reference around
-                            // so we can show a separator line in the menu
-                            item.insert(QStringLiteral("section-expanded"), true);
-
-                            // Check whether it's an alias to an alias
-                            // FIXME make generic/recursive
-                            if (items.count() == 1) {
-                                const auto &aliasedItem = items.constFirst();
-                                auto findIt = aliasedItem.constFind(QStringLiteral(":section"));
-                                if (findIt != aliasedItem.constEnd()) {
-                                    GMenuSection gmenuSection2 = qdbus_cast<GMenuSection>(findIt->value<QDBusArgument>());
-                                    items = findSection(m_menus.value(gmenuSection2.subscription), gmenuSection2.menu).items;
-                                }
-                            }
-
-                            for (const auto &aliasedItem : qAsConst(items)) {
-                                it.insert(aliasedItem);
-                            }
-                        }
-                    }
-                }
-            }
-
             // TODO are we subscribed to all it returns or just to the ones we requested?
             m_subscriptions.append(id);
         }
@@ -795,17 +751,57 @@ uint Menu::GetLayout(int parentId, int recursionDepth, const QStringList &proper
         {QStringLiteral("children-display"), QStringLiteral("submenu")}
     };
 
-    auto itemsToBeAdded = section.items;
-
     int count = 0;
 
+    const auto itemsToBeAdded = section.items;
     for (const auto &item : itemsToBeAdded) {
+
         DBusMenuLayoutItem child{
             treeStructureToInt(section.id, sectionId, ++count),
-            gMenuToDBusMenuProperties(item)
+            gMenuToDBusMenuProperties(item),
+            {} // children
         };
-
         dbusItem.children.append(child);
+
+        // Now resolve section aliases
+        auto it = item.constFind(QStringLiteral(":section"));
+        if (it != item.constEnd()) {
+
+            // references another place, add it instead
+            GMenuSection gmenuSection = qdbus_cast<GMenuSection>(it->value<QDBusArgument>());
+
+            // remember where the item came from and give it an appropriate ID
+            // so updates signalled by the app will map to the right place
+            int originalSubscription = gmenuSection.subscription;
+            int originalMenu = gmenuSection.menu;
+
+            // TODO start subscription if we don't have it
+            auto items = findSection(m_menus.value(gmenuSection.subscription), gmenuSection.menu).items;
+
+            // Check whether it's an alias to an alias
+            // FIXME make generic/recursive
+            if (items.count() == 1) {
+                const auto &aliasedItem = items.constFirst();
+                auto findIt = aliasedItem.constFind(QStringLiteral(":section"));
+                if (findIt != aliasedItem.constEnd()) {
+                    GMenuSection gmenuSection2 = qdbus_cast<GMenuSection>(findIt->value<QDBusArgument>());
+                    items = findSection(m_menus.value(gmenuSection2.subscription), gmenuSection2.menu).items;
+
+                    originalSubscription = gmenuSection2.subscription;
+                    originalMenu = gmenuSection2.menu;
+                }
+            }
+
+            int aliasedCount = 0;
+            for (const auto &aliasedItem : qAsConst(items)) {
+                DBusMenuLayoutItem aliasedChild{
+                    treeStructureToInt(originalSubscription, originalMenu, ++aliasedCount),
+                    gMenuToDBusMenuProperties(aliasedItem),
+                    {} // children
+                };
+                dbusItem.children.append(aliasedChild);
+            }
+        }
     }
 
     // revision, unused in libdbusmenuqt