DataOffer not invalidated when client loses keyboard focus

The data_offer object should be invalidated when client loses keyboard focus.
Otherwise in following scenario, it will become zombie object: start app1 ->
copy text -> start app2 -> paste text -> close app1 -> paste again in app2 ->
seg fault in qtwayland.

The root cause is that when app2 takes focus the first time, data_device.data_offer
event was sent to it from DataDevice::setFocus. When app1 is closed, the data source
reference in data offer becomes invalid. so when trying to paste again in app2,
segmentation faults

Change-Id: I16a584e80fddaadd269b00cdf39eb405dd95b622
Task-number: QTBUG-41005
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>

src/plugins/platforms/wayland/qwaylanddatadevice.cpp

@@ -77,6 +77,11 @@ QWaylandDataOffer *QWaylandDataDevice::selectionOffer() const
     return m_selectionOffer.data();
 }
 
+void QWaylandDataDevice::invalidateSelectionOffer()
+{
+    m_selectionOffer.reset();
+}
+
 QWaylandDataSource *QWaylandDataDevice::selectionSource() const
 {
     return m_selectionSource.data();

src/plugins/platforms/wayland/qwaylanddatadevice_p.h

@@ -65,6 +65,7 @@ public:
     ~QWaylandDataDevice();
 
     QWaylandDataOffer *selectionOffer() const;
+    void invalidateSelectionOffer();
     QWaylandDataSource *selectionSource() const;
     void setSelectionSource(QWaylandDataSource *source);
 

src/plugins/platforms/wayland/qwaylandinputdevice.cpp

@@ -717,6 +717,11 @@ void QWaylandInputDevice::Keyboard::keyboard_leave(uint32_t time, struct wl_surf
     Q_UNUSED(time);
     Q_UNUSED(surface);
 
+    if (surface) {
+        QWaylandWindow *window = QWaylandWindow::fromWlSurface(surface);
+        window->unfocus();
+    }
+
     mFocus = NULL;
 
     // Use a callback to set the focus because we may get a leave/enter pair, and

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -42,6 +42,7 @@
 #include "qwaylandwindow_p.h"
 
 #include "qwaylandbuffer_p.h"
+#include "qwaylanddatadevice_p.h"
 #include "qwaylanddisplay_p.h"
 #include "qwaylandinputdevice_p.h"
 #include "qwaylandscreen_p.h"
@@ -642,6 +643,14 @@ void QWaylandWindow::requestActivateWindow()
     // we rely on compositor setting keyboard focus based on window stacking.
 }
 
+void QWaylandWindow::unfocus()
+{
+    QWaylandInputDevice *inputDevice = mDisplay->currentInputDevice();
+    if (inputDevice && inputDevice->dataDevice()) {
+        inputDevice->dataDevice()->invalidateSelectionOffer();
+    }
+}
+
 bool QWaylandWindow::isExposed() const
 {
     if (mShellSurface)

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -142,6 +142,7 @@ public:
 
     void requestActivateWindow() Q_DECL_OVERRIDE;
     bool isExposed() const Q_DECL_OVERRIDE;
+    void unfocus();
 
     QWaylandDecoration *decoration() const;
     void setDecoration(QWaylandDecoration *decoration);