Client: Fail gracefully when wl_display_connect fails

[ChangeLog][QPA plugin] If we're unable to create a connection to the Wayland
display, fail gracefully so other platform integrations can be tried instead.

This also adds QWaylandIntegration::hasFailed() which can later be extended to
report that the platform plugin is unusable for other reasons. I.e. no
compatible shell extensions or similar.

Task-number: QTBUG-59762
Change-Id: I0f1ae73982e2860814235c1a189741d130e1db3e
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/plugins/platforms/wayland/qwaylanddisplay.cpp

@@ -142,9 +142,9 @@ QWaylandDisplay::QWaylandDisplay(QWaylandIntegration *waylandIntegration)
     qRegisterMetaType<uint32_t>("uint32_t");
 
     mDisplay = wl_display_connect(nullptr);
-    if (mDisplay == nullptr) {
+    if (!mDisplay) {
-        qErrnoWarning(errno, "Failed to create display");
+        qErrnoWarning(errno, "Failed to create wl_display");
-        ::exit(1);
+        return;
     }
 
     struct ::wl_registry *registry = wl_display_get_registry(mDisplay);
@@ -170,6 +170,7 @@ QWaylandDisplay::~QWaylandDisplay(void)
 #if QT_CONFIG(wayland_datadevice)
     delete mDndSelectionHandler.take();
 #endif
+    if (mDisplay)
         wl_display_disconnect(mDisplay);
 }
 

src/plugins/platforms/wayland/qwaylandintegration.cpp

@@ -134,6 +134,10 @@ QWaylandIntegration::QWaylandIntegration()
 {
     initializeInputDeviceIntegration();
     mDisplay.reset(new QWaylandDisplay(this));
+    if (!mDisplay->isInitialized()) {
+        mFailed = true;
+        return;
+    }
 #if QT_CONFIG(clipboard)
     mClipboard.reset(new QWaylandClipboard(mDisplay.data()));
 #endif

src/plugins/platforms/wayland/qwaylandintegration_p.h

@@ -73,6 +73,8 @@ public:
     QWaylandIntegration();
     ~QWaylandIntegration();
 
+    bool hasFailed() { return mFailed; }
+
     bool hasCapability(QPlatformIntegration::Capability cap) const override;
     QPlatformWindow *createPlatformWindow(QWindow *window) const override;
 #if QT_CONFIG(opengl)
@@ -144,6 +146,7 @@ private:
 #if QT_CONFIG(accessibility)
     QScopedPointer<QPlatformAccessibility> mAccessibility;
 #endif
+    bool mFailed = false;
     bool mClientBufferIntegrationInitialized;
     bool mServerBufferIntegrationInitialized;
     bool mShellIntegrationInitialized;