Fix "Pinned Chrome disappears when all Chrome windows are closed"

Summary:
It turns out that Chrome under certain conditions will change its
window metadata as it quits, causing a race we sometimes lose, failing
to reveal the associated launcher because we can no longer match it
to the window at window closing time. Instead we are now forced to
re-check all launchers after the window is gone. As a speed optimi-
zation we only consider top-level windows (and startups) as being in
a group implies matching siblings.

In addition this refactoring eliminates a use of Qt::QueuedConnection
that allowed for an unpredictable event loop spin inbetween things.

BUG:365617

Reviewers: davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3950

libtaskmanager/tasksmodel.cpp

@@ -70,6 +70,7 @@ public:
     bool launchInPlace = false;
     bool launchersEverSet = false;
     bool launcherSortingDirty = false;
+    bool launcherCheckNeeded = false;
     QList<int> sortedPreFilterRows;
     QVector<int> sortRowInsertQueue;
     QHash<QString, int> activityTaskCounts;
@@ -366,21 +367,40 @@ void TasksModel::Private::initModels()
                 }
 
                 // When a window or startup task is removed, we have to trigger a re-filter of
-                // matching launchers to (possibly) pop them back in.
-                if (!launcherTasksModel
-                      || !(sourceIndex.data(AbstractTasksModel::IsWindow).toBool()
+                // our launchers to (possibly) pop them back in.
+                // NOTE: An older revision of this code compared the window and startup tasks
+                // to the launchers to figure out which launchers should be re-filtered. This
+                // was fine until we discovered that certain applications (e.g. Google Chrome)
+                // change their window metadata specifically during tear-down, sometimes
+                // breaking TaskTools::appsMatch (it's a race) and causing the associated
+                // launcher to remain hidden. Therefore we now consider any top-level window or
+                // startup task removal a trigger to re-filter all launchers. We don't do this
+                // in response to the window metadata changes (even though it would be strictly
+                // more correct, as then-ending identity match-up was what caused the launcher
+                // to be hidden) because we don't want the launcher and window/startup task to
+                // briefly co-exist in the model.
+                if (!launcherCheckNeeded
+                      && launcherTasksModel
+                      && (sourceIndex.data(AbstractTasksModel::IsWindow).toBool()
                       || sourceIndex.data(AbstractTasksModel::IsStartup).toBool())) {
-                    continue;
+                    launcherCheckNeeded = true;
                 }
+            }
+        }
+    );
+
+    QObject::connect(filterProxyModel, &QAbstractItemModel::rowsRemoved, q,
+        [this](const QModelIndex &parent, int first, int last) {
+            Q_UNUSED(parent)
+            Q_UNUSED(first)
+            Q_UNUSED(last)
 
-                for (int j = 0; j < launcherTasksModel->rowCount(); ++j) {
-                    const QModelIndex &launcherIndex = launcherTasksModel->index(j, 0);
+            if (launcherCheckNeeded) {
+                QMetaObject::invokeMethod(launcherTasksModel, "dataChanged",
+                    Q_ARG(QModelIndex, launcherTasksModel->index(0, 0)),
+                    Q_ARG(QModelIndex, launcherTasksModel->index(launcherTasksModel->rowCount() - 1, 0)));
 
-                    if (appsMatch(sourceIndex, launcherIndex)) {
-                        QMetaObject::invokeMethod(launcherTasksModel, "dataChanged", Qt::QueuedConnection,
-                            Q_ARG(QModelIndex, launcherIndex), Q_ARG(QModelIndex, launcherIndex));
-                    }
-                }
+                launcherCheckNeeded = false;
             }
         }
     );