Handle gracefully the removal and re-attachment of all QScreens

Don't crash; restore windows when all screens are removed and re-added.
xcb: on configure notify, check for screen change: it may be that a
window belonging to a screen which was removed has now gotten mapped
to the new screen.  On screen change, send a synthetic expose event,
because the real expose events already happened.

Task-number: QTBUG-38326
Task-number: QTBUG-32973
Task-number: QTBUG-42985
Change-Id: If334f55c248468ad3c95e7066bb14eca377d2050
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

5 files changed, 20 insertions, 10 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index d44a79b37e..92be903b41 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -2583,6 +2583,8 @@ void QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::E
         return;
 
     QWindow *window = e->exposed.data();
+    if (!window)
+        return;
     QWindowPrivate *p = qt_window_private(window);
 
     if (!p->receivedExpose) {
@@ -2598,7 +2600,7 @@ void QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::E
         p->receivedExpose = true;
     }
 
-    p->exposed = e->isExposed;
+    p->exposed = e->isExposed && window->screen();
 
     QExposeEvent exposeEvent(e->region);
     QCoreApplication::sendSpontaneousEvent(window, &exposeEvent);
diff --git a/src/gui/kernel/qplatformwindow.cpp b/src/gui/kernel/qplatformwindow.cpp
index 167bd44f0e..763ab68868 100644
--- a/src/gui/kernel/qplatformwindow.cpp
+++ b/src/gui/kernel/qplatformwindow.cpp
@@ -83,7 +83,8 @@ QPlatformWindow *QPlatformWindow::parent() const
 */
 QPlatformScreen *QPlatformWindow::screen() const
 {
-    return window()->screen()->handle();
+    QScreen *scr = window()->screen();
+    return scr ? scr->handle() : Q_NULLPTR;
 }
 
 /*!
@@ -479,7 +480,7 @@ QString QPlatformWindow::formatWindowTitle(const QString &title, const QString &
 QPlatformScreen *QPlatformWindow::screenForGeometry(const QRect &newGeometry) const
 {
     QPlatformScreen *currentScreen = screen();
-    if (!parent() && !currentScreen->geometry().intersects(newGeometry)) {
+    if (!parent() && currentScreen && !currentScreen->geometry().intersects(newGeometry)) {
         Q_FOREACH (QPlatformScreen* screen, currentScreen->virtualSiblings()) {
             if (screen->geometry().intersects(newGeometry))
                 return screen;
diff --git a/src/gui/kernel/qscreen.cpp b/src/gui/kernel/qscreen.cpp
index 8357e14354..0cc8f1082a 100644
--- a/src/gui/kernel/qscreen.cpp
+++ b/src/gui/kernel/qscreen.cpp
@@ -86,7 +86,7 @@ QScreen::~QScreen()
     if (this == primaryScreen)
         return;
 
-    bool movingFromVirtualSibling = primaryScreen->handle()->virtualSiblings().contains(handle());
+    bool movingFromVirtualSibling = primaryScreen && primaryScreen->handle()->virtualSiblings().contains(handle());
 
     // Move any leftover windows to the primary screen
     foreach (QWindow *window, QGuiApplication::topLevelWindows()) {
diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index b679dd9bfc..773cce7a7f 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -338,7 +338,7 @@ inline bool QWindowPrivate::windowRecreationRequired(QScreen *newScreen) const
 {
     Q_Q(const QWindow);
     const QScreen *oldScreen = q->screen();
-    return oldScreen != newScreen && platformWindow
+    return oldScreen != newScreen && (platformWindow || !oldScreen)
         && !(oldScreen && oldScreen->virtualSiblings().contains(newScreen));
 }
 
@@ -373,10 +373,13 @@ void QWindowPrivate::setTopLevelScreen(QScreen *newScreen, bool recreate)
     }
     if (newScreen != topLevelScreen) {
         const bool shouldRecreate = recreate && windowRecreationRequired(newScreen);
-        if (shouldRecreate)
+        const bool shouldShow = visibilityOnDestroy && !topLevelScreen;
+        if (shouldRecreate && platformWindow)
             q->destroy();
         connectToScreen(newScreen);
-        if (newScreen && shouldRecreate)
+        if (shouldShow)
+            q->setVisible(true);
+        else if (newScreen && shouldRecreate)
             create(true);
         emitScreenChangedRecursion(newScreen);
     }
@@ -1600,6 +1603,7 @@ void QWindow::destroy()
         QGuiApplicationPrivate::tabletPressTarget = parent();
 
     bool wasVisible = isVisible();
+    d->visibilityOnDestroy = wasVisible && d->platformWindow;
 
     setVisible(false);
 
@@ -1683,7 +1687,7 @@ bool QWindow::setMouseGrabEnabled(bool grab)
 QScreen *QWindow::screen() const
 {
     Q_D(const QWindow);
-    return d->parentWindow ? d->parentWindow->screen() : d->topLevelScreen;
+    return d->parentWindow ? d->parentWindow->screen() : d->topLevelScreen.data();
 }
 
 /*!
@@ -1703,7 +1707,7 @@ void QWindow::setScreen(QScreen *newScreen)
     Q_D(QWindow);
     if (!newScreen)
         newScreen = QGuiApplication::primaryScreen();
-    d->setTopLevelScreen(newScreen, true /* recreate */);
+    d->setTopLevelScreen(newScreen, newScreen != 0);
 }
 
 /*!
diff --git a/src/gui/kernel/qwindow_p.h b/src/gui/kernel/qwindow_p.h
index c496d7716b..9151e76ea4 100644
--- a/src/gui/kernel/qwindow_p.h
+++ b/src/gui/kernel/qwindow_p.h
@@ -45,6 +45,7 @@
 // We mean it.
 //
 
+#include <QtGui/qscreen.h>
 #include <QtGui/qwindow.h>
 #include <qpa/qplatformwindow.h>
 
@@ -73,6 +74,7 @@ public:
         , parentWindow(0)
         , platformWindow(0)
         , visible(false)
+        , visibilityOnDestroy(false)
         , exposed(false)
         , windowState(Qt::WindowNoState)
         , visibility(QWindow::Hidden)
@@ -147,6 +149,7 @@ public:
     QWindow *parentWindow;
     QPlatformWindow *platformWindow;
     bool visible;
+    bool visibilityOnDestroy;
     bool exposed;
     QSurfaceFormat requestedFormat;
     QString windowTitle;
@@ -175,7 +178,7 @@ public:
     int updateTimer;
 
     QPointer<QWindow> transientParent;
-    QScreen *topLevelScreen;
+    QPointer<QScreen> topLevelScreen;
 
 #ifndef QT_NO_CURSOR
     QCursor cursor;