QBasicDrag: Send QDragMoveEvent when modifiers change

... without moving the mouse.
This allows to update drop action and cursor.

Task-number: QTBUG-56218
Task-number: QTBUG-82934
Pick-to: 5.15
Change-Id: I8b0ac2a008a9dbcc4c2d6abce282e6f169c2f542
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/gui/kernel/qsimpledrag.cpp

@@ -145,15 +145,17 @@ bool QBasicDrag::eventFilter(QObject *o, QEvent *e)
                 disableEventFilter();
                 exitDndEventLoop();
 
+            } else if (ke->modifiers() != QGuiApplication::keyboardModifiers()) {
+                move(m_lastPos, QGuiApplication::mouseButtons(), ke->modifiers());
             }
             return true; // Eat all key events
         }
 
         case QEvent::MouseMove:
         {
-            QPoint nativePosition = getNativeMousePos(e, m_drag_icon_window);
+            m_lastPos = getNativeMousePos(e, m_drag_icon_window);
             auto mouseMove = static_cast<QMouseEvent *>(e);
-            move(nativePosition, mouseMove->buttons(), mouseMove->modifiers());
+            move(m_lastPos, mouseMove->buttons(), mouseMove->modifiers());
             return true; // Eat all mouse move events
         }
         case QEvent::MouseButtonRelease:
@@ -230,6 +232,7 @@ void QBasicDrag::startDrag()
         pos = QPoint();
     }
 #endif
+    m_lastPos = pos;
     recreateShapedPixmapWindow(m_screen, pos);
     enableEventFilter();
 }

src/gui/kernel/qsimpledrag_p.h

@@ -126,6 +126,7 @@ private:
     QShapedPixmapWindow *m_drag_icon_window = nullptr;
     bool m_useCompositing = true;
     QScreen *m_screen = nullptr;
+    QPoint m_lastPos;
 };
 
 class Q_GUI_EXPORT QSimpleDrag : public QBasicDrag

tests/auto/widgets/kernel/qwidget_window/tst_qwidget_window.cpp

@@ -725,7 +725,7 @@ protected:
     {
         e->accept();
         _dndEvents.append(QStringLiteral("DragMove "));
-        emit releaseMouseButton();
+        emit dragMoveReceived();
     }
     void dragLeaveEvent(QDragLeaveEvent *e)
     {
@@ -739,7 +739,7 @@ protected:
     }
 
 signals:
-    void releaseMouseButton();
+    void dragMoveReceived();
 };
 
 void tst_QWidget_window::tst_dnd_events()
@@ -774,7 +774,7 @@ void tst_QWidget_window::tst_dnd_events()
 
     // Some dnd implementation rely on running internal event loops, so we have to use
     // the following queued signal hack to simulate mouse clicks in the widget.
-    QObject::connect(&dndWidget, &DnDEventRecorder::releaseMouseButton, this, [=]() {
+    QObject::connect(&dndWidget, &DnDEventRecorder::dragMoveReceived, this, [=]() {
         QTest::mouseRelease(window, Qt::LeftButton);
     }, Qt::QueuedConnection);
 
@@ -783,6 +783,27 @@ void tst_QWidget_window::tst_dnd_events()
     QTest::mousePress(window, Qt::LeftButton);
 
     QCOMPARE(dndWidget._dndEvents, expectedDndEvents);
+
+    dndWidget._dndEvents.clear();
+    dndWidget.disconnect();
+    int step = 0;
+    QObject::connect(&dndWidget, &DnDEventRecorder::dragMoveReceived, this, [window, &step]() {
+        switch (step++) {
+        case 0:
+            QTest::keyPress(window, Qt::Key_Shift, Qt::ShiftModifier);
+            break;
+        case 1:
+            QTest::keyRelease(window, Qt::Key_Shift, Qt::NoModifier);
+            break;
+        default:
+            QTest::mouseRelease(window, Qt::LeftButton);
+            break;
+        }
+    }, Qt::QueuedConnection);
+
+    QTest::mousePress(window, Qt::LeftButton);
+    const QString expectedDndWithModsEvents = "DragEnter DragMove DragMove DragMove DropEvent ";
+    QCOMPARE(dndWidget._dndEvents, expectedDndWithModsEvents);
 }
 
 class DropTarget : public QWidget