Don't send a mouse move when we just need to do a synthetic enter/leave

[ChangeLog][QtWidgets] QApplication no longer sends a mouse move event
to the entered widget if it sends synthetic enter and leave events.

Task-number: QTBUG-67736
Change-Id: I75daaffd53f1ddc2bc4d7df67382cbc22d3eb6fc
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/kernel/qapplication.cpp

@@ -2624,7 +2624,7 @@ QWidget *QApplicationPrivate::pickMouseReceiver(QWidget *candidate, const QPoint
 bool QApplicationPrivate::sendMouseEvent(QWidget *receiver, QMouseEvent *event,
                                          QWidget *alienWidget, QWidget *nativeWidget,
                                          QWidget **buttonDown, QPointer<QWidget> &lastMouseReceiver,
-                                         bool spontaneous)
+                                         bool spontaneous, bool onlyDispatchEnterLeave)
 {
     Q_ASSERT(receiver);
     Q_ASSERT(event);
@@ -2685,11 +2685,17 @@ bool QApplicationPrivate::sendMouseEvent(QWidget *receiver, QMouseEvent *event,
     // We need this quard in case someone opens a modal dialog / popup. If that's the case
     // leaveAfterRelease is set to null, but we shall not update lastMouseReceiver.
     const bool wasLeaveAfterRelease = leaveAfterRelease != 0;
-    bool result;
-    if (spontaneous)
-        result = QApplication::sendSpontaneousEvent(receiver, event);
-    else
-        result = QApplication::sendEvent(receiver, event);
+    bool result = true;
+    // This code is used for sending the synthetic enter/leave events for cases where it is needed
+    // due to other events causing the widget under the mouse to change. However in those cases
+    // we do not want to send the mouse event associated with this call, so this enables us to
+    // not send the unneeded mouse event
+    if (!onlyDispatchEnterLeave) {
+        if (spontaneous)
+            result = QApplication::sendSpontaneousEvent(receiver, event);
+        else
+            result = QApplication::sendEvent(receiver, event);
+    }
 
     if (!graphicsWidget && leaveAfterRelease && event->type() == QEvent::MouseButtonRelease
         && !event->buttons() && QWidget::mouseGrabber() != leaveAfterRelease) {
@@ -2764,9 +2770,10 @@ void QApplicationPrivate::sendSyntheticEnterLeave(QWidget *widget)
     if (widget->data->in_destructor && qt_button_down == widget)
         qt_button_down = 0;
 
-    // Send enter/leave events followed by a mouse move on the entered widget.
+    // A mouse move is not actually sent, but we utilize the sendMouseEvent() call to send the
+    // enter/leave events as appropriate
     QMouseEvent e(QEvent::MouseMove, pos, windowPos, globalPos, Qt::NoButton, Qt::NoButton, Qt::NoModifier);
-    sendMouseEvent(widgetUnderCursor, &e, widgetUnderCursor, tlw, &qt_button_down, qt_last_mouse_receiver);
+    sendMouseEvent(widgetUnderCursor, &e, widgetUnderCursor, tlw, &qt_button_down, qt_last_mouse_receiver, true, true);
 #else // !QT_NO_CURSOR
     Q_UNUSED(widget);
 #endif // QT_NO_CURSOR

src/widgets/kernel/qapplication_p.h

@@ -226,7 +226,7 @@ public:
                                       QWidget *buttonDown, QWidget *alienWidget);
     static bool sendMouseEvent(QWidget *receiver, QMouseEvent *event, QWidget *alienWidget,
                                QWidget *native, QWidget **buttonDown, QPointer<QWidget> &lastMouseReceiver,
-                               bool spontaneous = true);
+                               bool spontaneous = true, bool onlyDispatchEnterLeave = false);
     void sendSyntheticEnterLeave(QWidget *widget);
 
     static QWindow *windowForWidget(const QWidget *widget)

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -9120,7 +9120,8 @@ void tst_QWidget::taskQTBUG_4055_sendSyntheticEnterLeave()
          void mouseMoveEvent(QMouseEvent *event)
          {
              QCOMPARE(event->button(), Qt::NoButton);
-             QCOMPARE(event->buttons(), Qt::MouseButtons(Qt::NoButton));
+             QCOMPARE(event->buttons(), QApplication::mouseButtons());
+             QCOMPARE(event->modifiers(), QApplication::keyboardModifiers());
              ++numMouseMoveEvents;
          }
          void reset() { numEnterEvents = numMouseMoveEvents = 0; }
@@ -9154,11 +9155,11 @@ void tst_QWidget::taskQTBUG_4055_sendSyntheticEnterLeave()
      child.setMouseTracking(true);
      child.show();
 
-     // Make sure the child gets enter event and mouse move event.
+     // Make sure the child gets enter event.
      // Note that we verify event->button() and event->buttons()
      // in SELChild::mouseMoveEvent().
      QTRY_COMPARE(child.numEnterEvents, 1);
-     QCOMPARE(child.numMouseMoveEvents, 1);
+     QCOMPARE(child.numMouseMoveEvents, 0);
 
      // Sending synthetic enter/leave trough the parent's mousePressEvent handler.
      parent.child = &child;
@@ -9167,10 +9168,19 @@ void tst_QWidget::taskQTBUG_4055_sendSyntheticEnterLeave()
      child.reset();
      QTest::mouseClick(&parent, Qt::LeftButton);
 
-     // Make sure the child gets enter event and one mouse move event.
+     // Make sure the child gets enter event.
      QTRY_COMPARE(child.numEnterEvents, 1);
-     QCOMPARE(child.numMouseMoveEvents, 1);
+     QCOMPARE(child.numMouseMoveEvents, 0);
 
+     child.hide();
+     child.reset();
+     QTest::keyPress(&parent, Qt::Key_Shift);
+     QTest::mouseClick(&parent, Qt::LeftButton);
+
+     // Make sure the child gets enter event
+     QTRY_COMPARE(child.numEnterEvents, 1);
+     QCOMPARE(child.numMouseMoveEvents, 0);
+     QTest::keyRelease(&child, Qt::Key_Shift);
      child.hide();
      child.reset();
      child.setMouseTracking(false);