dnd: send DragEnter and DragMove on DnD start

This was a regression from Qt4 and also is the documented behavior.
In addition this patch fixes various issues with cursor shape updating
that were discovered along the way and that are necessary for testing
the new changes.

The code in QGuiApplicationPrivate::processDrag() also needed a fixup,
particularly the resetting of QGuiApplicationPrivate::currentDragWindow.
Without this fix we would get DragMove (the one that immediately follows
the DragEnter) only for the first DragEnter event. For example when dnd
starts on mouse press then for mouse click we would get:

<click> DragEnter->DragMove->DragLeave <click> DragEnter->DragLeave

but the expected is:

<click> DragEnter->DragMove->DragLeave <click> DragEnter->DragMove->DragLeave

Task-number: QTBUG-34331
Change-Id: I3cc96c87d1fd5d1342c7f6c9438802ab30076e9e
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 14 insertions, 10 deletions

diff --git a/src/gui/kernel/qsimpledrag_p.h b/src/gui/kernel/qsimpledrag_p.h
index ddd32bc5a5..f9e8a83a39 100644
--- a/src/gui/kernel/qsimpledrag_p.h
+++ b/src/gui/kernel/qsimpledrag_p.h
@@ -55,13 +55,14 @@
 #include <qpa/qplatformdrag.h>
 
 #include <QtCore/QObject>
+#include <QtCore/QPointer>
+#include <QtGui/QWindow>
 
 QT_REQUIRE_CONFIG(draganddrop);
 
 QT_BEGIN_NAMESPACE
 
 class QMouseEvent;
-class QWindow;
 class QEventLoop;
 class QDropData;
 class QShapedPixmapWindow;
@@ -106,7 +107,8 @@ protected:
     QDrag *drag() const { return m_drag; }
 
 protected:
-    QWindow *m_current_window;
+    QWindow *m_sourceWindow = nullptr;
+    QPointer<QWindow> m_windowUnderCursor = nullptr;
 
 private:
     void enableEventFilter();
@@ -114,14 +116,16 @@ private:
     void restoreCursor();
     void exitDndEventLoop();
 
-    bool m_restoreCursor;
-    QEventLoop *m_eventLoop;
-    Qt::DropAction m_executed_drop_action;
-    bool m_can_drop;
-    QDrag *m_drag;
-    QShapedPixmapWindow *m_drag_icon_window;
-    bool m_useCompositing;
-    QScreen *m_screen;
+#ifndef QT_NO_CURSOR
+    bool m_dndHasSetOverrideCursor = false;
+#endif
+    QEventLoop *m_eventLoop = nullptr;
+    Qt::DropAction m_executed_drop_action = Qt::IgnoreAction;
+    bool m_can_drop = false;
+    QDrag *m_drag = nullptr;
+    QShapedPixmapWindow *m_drag_icon_window = nullptr;
+    bool m_useCompositing = true;
+    QScreen *m_screen = nullptr;
 };
 
 class Q_GUI_EXPORT QSimpleDrag : public QBasicDrag