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>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
index 8974ab549f..915287d93e 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
@@ -249,8 +249,13 @@ void *QXcbNativeInterface::nativeResourceForContext(const QByteArray &resourceSt
 
 void *QXcbNativeInterface::nativeResourceForScreen(const QByteArray &resourceString, QScreen *screen)
 {
+    if (!screen) {
+        qWarning() << "nativeResourceForScreen: null screen";
+        return Q_NULLPTR;
+    }
+
     QByteArray lowerCaseResource = resourceString.toLower();
-    void *result = handlerNativeResourceForScreen(lowerCaseResource ,screen);
+    void *result = handlerNativeResourceForScreen(lowerCaseResource, screen);
     if (result)
         return result;