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, 87 insertions, 0 deletions

diff --git a/tests/auto/widgets/kernel/qwidget_window/tst_qwidget_window.cpp b/tests/auto/widgets/kernel/qwidget_window/tst_qwidget_window.cpp
index 0813a13693..f0b4bd6dd9 100644
--- a/tests/auto/widgets/kernel/qwidget_window/tst_qwidget_window.cpp
+++ b/tests/auto/widgets/kernel/qwidget_window/tst_qwidget_window.cpp
@@ -83,6 +83,7 @@ private slots:
 
 #if QT_CONFIG(draganddrop)
     void tst_dnd();
+    void tst_dnd_events();
 #endif
 
     void tst_qtbug35600();
@@ -597,6 +598,92 @@ void tst_QWidget_window::tst_dnd()
 
     QCOMPARE(log, expectedLog);
 }
+
+class DnDEventRecorder : public QWidget
+{
+    Q_OBJECT
+public:
+    QString _dndEvents;
+    DnDEventRecorder() { setAcceptDrops(true); }
+
+protected:
+    void mousePressEvent(QMouseEvent *)
+    {
+        QMimeData *mimeData = new QMimeData;
+        mimeData->setData("application/x-dnditemdata", "some data");
+        QDrag *drag = new QDrag(this);
+        drag->setMimeData(mimeData);
+        drag->exec();
+    }
+
+    void dragEnterEvent(QDragEnterEvent *e)
+    {
+        e->accept();
+        _dndEvents.append(QStringLiteral("DragEnter "));
+    }
+    void dragMoveEvent(QDragMoveEvent *e)
+    {
+        e->accept();
+        _dndEvents.append(QStringLiteral("DragMove "));
+        emit releaseMouseButton();
+    }
+    void dragLeaveEvent(QDragLeaveEvent *e)
+    {
+        e->accept();
+        _dndEvents.append(QStringLiteral("DragLeave "));
+    }
+    void dropEvent(QDropEvent *e)
+    {
+        e->accept();
+        _dndEvents.append(QStringLiteral("DropEvent "));
+    }
+
+signals:
+    void releaseMouseButton();
+};
+
+void tst_QWidget_window::tst_dnd_events()
+{
+    // Note: This test is somewhat a hack as testing DnD with qtestlib is not
+    // supported at the moment. The test verifies that we get an expected event
+    // sequence on dnd operation that does not move a mouse. This logic is implemented
+    // in QGuiApplication, so we have to go via QWindowSystemInterface API (QTest::mouse*).
+    const auto platformName = QGuiApplication::platformName().toLower();
+    // The test is known to work with XCB and platforms that use the default dnd
+    // implementation QSimpleDrag (e.g. qnx). Running on XCB should be sufficient to
+    // catch regressions at cross platform code: QGuiApplication::processDrag/Leave().
+    if (platformName != "xcb")
+        return;
+
+    const QString expectedDndEvents = "DragEnter DragMove DropEvent DragEnter DragMove "
+                                      "DropEvent DragEnter DragMove DropEvent ";
+    DnDEventRecorder dndWidget;
+    dndWidget.setGeometry(100, 100, 200, 200);
+    dndWidget.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&dndWidget));
+    QVERIFY(QTest::qWaitForWindowActive(&dndWidget));
+
+    // ### FIXME - QTBUG-35117 ???
+    auto targetCenter = QPoint(dndWidget.width(), dndWidget.height()) / 2;
+    auto targetCenterGlobal = dndWidget.mapToGlobal(targetCenter);
+    QCursor::setPos(targetCenterGlobal);
+    QVERIFY(QTest::qWaitFor([&]() { return QCursor::pos() == targetCenterGlobal; }));
+    QCoreApplication::processEvents(); // clear mouse events generated from cursor
+
+    auto window = dndWidget.window()->windowHandle();
+
+    // 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, [=]() {
+        QTest::mouseRelease(window, Qt::LeftButton);
+    }, Qt::QueuedConnection);
+
+    QTest::mousePress(window, Qt::LeftButton);
+    QTest::mousePress(window, Qt::LeftButton);
+    QTest::mousePress(window, Qt::LeftButton);
+
+    QCOMPARE(dndWidget._dndEvents, expectedDndEvents);
+}
 #endif
 
 void tst_QWidget_window::tst_qtbug35600()