Fix setting custom cursor for widgets and windows before showing them

If custom cursor was set before the window was created, it didn't
actually get set, and in some cases even caused a crash.
Fixed by making sure the cursor is correct when showing widget/window.

Task-number: QTBUG-27535
Change-Id: I3bc946a9c406c96af5b86869a3a54893f8980aba
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/gui/kernel/qwindow.cpp

@@ -286,6 +286,10 @@ void QWindow::setVisible(bool visible)
             QGuiApplicationPrivate::hideModalWindow(this);
     }
 
+#ifndef QT_NO_CURSOR
+    if (visible)
+        d->applyCursor();
+#endif
     d->platformWindow->setVisible(visible);
 
     if (!visible) {
@@ -1853,11 +1857,10 @@ QCursor QWindow::cursor() const
 void QWindow::setCursor(const QCursor &cursor)
 {
     Q_D(QWindow);
-    if (QPlatformCursor *platformCursor = d->screen->handle()->cursor()) {
-        d->cursor = cursor;
-        QCursor *oc = QGuiApplication::overrideCursor();
-        QCursor c = oc ? *oc : d->cursor;
-        platformCursor->changeCursor(&c, this);
+    d->cursor = cursor;
+    // Only attempt to set cursor and emit signal if there is an actual platform cursor
+    if (d->screen->handle()->cursor()) {
+        d->applyCursor();
         QEvent event(QEvent::CursorChange);
         QGuiApplication::sendEvent(this, &event);
     }
@@ -1868,19 +1871,20 @@ void QWindow::setCursor(const QCursor &cursor)
  */
 void QWindow::unsetCursor()
 {
-    Q_D(QWindow);
-    if (QPlatformCursor *platformCursor = d->screen->handle()->cursor()) {
-        d->cursor = Qt::ArrowCursor;
-        QCursor *oc = QGuiApplication::overrideCursor();
-        if (!oc) {
-            QCursor c = d->cursor;
-            platformCursor->changeCursor(&c, this);
-        }
-        QEvent event(QEvent::CursorChange);
-        QGuiApplication::sendEvent(this, &event);
-    }
+    setCursor(Qt::ArrowCursor);
 }
 
+void QWindowPrivate::applyCursor()
+{
+    Q_Q(QWindow);
+    if (platformWindow) {
+        if (QPlatformCursor *platformCursor = screen->handle()->cursor()) {
+            QCursor *oc = QGuiApplication::overrideCursor();
+            QCursor c = oc ? *oc : cursor;
+            platformCursor->changeCursor(&c, q);
+        }
+    }
+}
 #endif
 
 QT_END_NAMESPACE

src/gui/kernel/qwindow_p.h

@@ -97,6 +97,9 @@ public:
     }
 
     void maybeQuitOnLastWindowClosed();
+#ifndef QT_NO_CURSOR
+    void applyCursor();
+#endif
 
     QPoint globalPosition() const {
         Q_Q(const QWindow);

src/widgets/kernel/qwidget_qpa.cpp

@@ -547,6 +547,9 @@ void QWidgetPrivate::show_sys()
             }
         }
 
+#ifndef QT_NO_CURSOR
+        qt_qpa_set_cursor(q, false); // Needed in case cursor was set before show
+#endif
         invalidateBuffer(q->rect());
         window->setVisible(true);
     }