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, 4 insertions, 3 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoacursor.mm b/src/plugins/platforms/cocoa/qcocoacursor.mm
index a584e22e59..238a900c08 100644
--- a/src/plugins/platforms/cocoa/qcocoacursor.mm
+++ b/src/plugins/platforms/cocoa/qcocoacursor.mm
@@ -61,8 +61,9 @@ void QCocoaCursor::changeCursor(QCursor *cursor, QWindow *window)
 {
     Q_UNUSED(window);
 
+    const Qt::CursorShape newShape = cursor ? cursor->shape() : Qt::ArrowCursor;
     // Check for a suitable built-in NSCursor first:
-    switch (cursor->shape()) {
+    switch (newShape) {
     case Qt::ArrowCursor:
         [[NSCursor arrowCursor] set];
         break;
@@ -99,14 +100,14 @@ void QCocoaCursor::changeCursor(QCursor *cursor, QWindow *window)
     default : {
         // No suitable OS cursor exist, use cursors provided
         // by Qt for the rest. Check for a cached cursor:
-        NSCursor *cocoaCursor = m_cursors.value(cursor->shape());
+        NSCursor *cocoaCursor = m_cursors.value(newShape);
         if (cocoaCursor == 0) {
             cocoaCursor = createCursorData(cursor);
             if (cocoaCursor == 0) {
                 [[NSCursor arrowCursor] set];
                 return;
             }
-            m_cursors.insert(cursor->shape(), cocoaCursor);
+            m_cursors.insert(newShape, cocoaCursor);
         }
 
         [cocoaCursor set];