Prevent instantiation of QGestureManager in ~QWidget, ~QGraphicsItem()

Debugging PYSIDE-815 revealed that QGestureManager is instantiated in
the application destruction sequence. To prevent that, add a "force"
parameter defaulting to true to QGestureManager::instance() and pass
false in the destructors and QGestureManager::gesturePending().

Change-Id: I1b76173c926c2a156252b88832b032508d8e8a73
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/graphicsview/qgraphicsitem.cpp

@@ -1598,7 +1598,7 @@ QGraphicsItem::~QGraphicsItem()
 #ifndef QT_NO_GESTURES
     if (d_ptr->isObject && !d_ptr->gestureContext.isEmpty()) {
         QGraphicsObject *o = static_cast<QGraphicsObject *>(this);
-        if (QGestureManager *manager = QGestureManager::instance()) {
+        if (QGestureManager *manager = QGestureManager::instance(QGestureManager::DontForceCreation)) {
             const auto types  = d_ptr->gestureContext.keys(); // FIXME: iterate over the map directly?
             for (Qt::GestureType type : types)
                 manager->cleanupCachedGestures(o, type);

src/widgets/kernel/qapplication.cpp

@@ -4521,12 +4521,12 @@ void QApplicationPrivate::notifyDragStarted(const QDrag *drag)
 #endif // QT_CONFIG(draganddrop)
 
 #ifndef QT_NO_GESTURES
-QGestureManager* QGestureManager::instance()
+QGestureManager* QGestureManager::instance(InstanceCreation ic)
 {
     QApplicationPrivate *qAppPriv = QApplicationPrivate::instance();
     if (!qAppPriv)
         return 0;
-    if (!qAppPriv->gestureManager)
+    if (!qAppPriv->gestureManager && ic == ForceCreation)
         qAppPriv->gestureManager = new QGestureManager(qApp);
     return qAppPriv->gestureManager;
 }

src/widgets/kernel/qgesturemanager.cpp

@@ -773,7 +773,7 @@ void QGestureManager::recycle(QGesture *gesture)
 
 bool QGestureManager::gesturePending(QObject *o)
 {
-    const QGestureManager *gm = QGestureManager::instance();
+    const QGestureManager *gm = QGestureManager::instance(DontForceCreation);
     return gm && gm->m_gestureOwners.key(o);
 }
 

src/widgets/kernel/qgesturemanager_p.h

@@ -81,7 +81,9 @@ public:
     bool filterEvent(QGraphicsObject *receiver, QEvent *event);
 #endif // QT_CONFIG(graphicsview)
 
-    static QGestureManager* instance(); // declared in qapplication.cpp
+    enum InstanceCreation { ForceCreation, DontForceCreation };
+
+    static QGestureManager *instance(InstanceCreation ic = ForceCreation); // declared in qapplication.cpp
     static bool gesturePending(QObject *o);
 
     void cleanupCachedGestures(QObject *target, Qt::GestureType type);

src/widgets/kernel/qwidget.cpp

@@ -1572,7 +1572,7 @@ QWidget::~QWidget()
 #endif
 
 #ifndef QT_NO_GESTURES
-    if (QGestureManager *manager = QGestureManager::instance()) {
+    if (QGestureManager *manager = QGestureManager::instance(QGestureManager::DontForceCreation)) {
         // \forall Qt::GestureType type : ungrabGesture(type) (inlined)
         for (auto it = d->gestureContext.keyBegin(), end = d->gestureContext.keyEnd(); it != end; ++it)
             manager->cleanupCachedGestures(this, *it);