Regression: Fix setting of custom cursors for native widgets.

Currently, there is no concept of not having a cursor set on
a Window. Qt::ArrowCursor is always set instead. This causes
bugs when native child widgets are involved, for example setting
a cursor on the native widget's parent no longer works since
the child's Qt::ArrowCursor applies.

Introduce QWindowPrivate::hasCursor tracking whether a cursor
has been explicitly set and clear in QWindow::unsetCursor().

Handle 0 in QPlatformCursor::changeCursor() to mean
"unsetCursor()":
- Windows: Introduce default constructor for QWindowsWindowCursor
  meaning "0". Search for applicable parent cursor in applyCursor.
- XCB: No big changes required, set XCB_CURSOR_NONE for no cursor.
- Other platforms: Assume Qt::ArrowCursor when cursor = 0 is
  passed for now.

Task-number: QTBUG-28879
Change-Id: Id82722592f3cd5fe577a5b64dcc600c85cfea484
Reviewed-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/plugins/platforms/kms/qkmscursor.cpp b/src/plugins/platforms/kms/qkmscursor.cpp
index 9a86d6c7cb..5101b4c7e2 100644
--- a/src/plugins/platforms/kms/qkmscursor.cpp
+++ b/src/plugins/platforms/kms/qkmscursor.cpp
@@ -85,8 +85,9 @@ void QKmsCursor::changeCursor(QCursor *widgetCursor, QWindow *window)
     if (!m_moved)
         drmModeMoveCursor(m_screen->device()->fd(), m_screen->crtcId(), 0, 0);
 
-    if (widgetCursor->shape() != Qt::BitmapCursor) {
-        m_cursorImage->set(widgetCursor->shape());
+    const Qt::CursorShape newShape = widgetCursor ? widgetCursor->shape() : Qt::ArrowCursor;
+    if (newShape != Qt::BitmapCursor) {
+        m_cursorImage->set(newShape);
     } else {
         m_cursorImage->set(widgetCursor->pixmap().toImage(),
                            widgetCursor->hotSpot().x(),