QAbstractItemModel::supportedDragActions: fix regression

This method now returns -1 by default, due to commit 6255cb893d
which mistakenly replaced -1 with Qt::IgnoreAction (0x0).

As a result, dropping is forbidden in a number of applications
(I detected this in zanshin).

Change-Id: I4922451216e08d5d3fe36f8ba87364a361b691bf
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

src/corelib/itemmodels/qabstractitemmodel.cpp

@@ -2044,7 +2044,7 @@ Qt::DropActions QAbstractItemModel::supportedDropActions() const
 Qt::DropActions QAbstractItemModel::supportedDragActions() const
 {
     Q_D(const QAbstractItemModel);
-    if (d->supportedDragActions != Qt::IgnoreAction)
+    if (int(d->supportedDragActions) != -1)
         return d->supportedDragActions;
     return supportedDropActions();
 }

tests/auto/corelib/itemmodels/qabstractitemmodel/tst_qabstractitemmodel.cpp

@@ -101,6 +101,7 @@ private slots:
 
     void testRoleNames();
     void testDragActions();
+    void dragActionsFallsBackToDropActions();
 
     void testFunctionPointerSignalConnection();
 
@@ -2157,6 +2158,27 @@ void tst_QAbstractItemModel::testDragActions()
     QVERIFY(actions & Qt::MoveAction);
 }
 
+class OverrideDropActions : public QStringListModel
+{
+    Q_OBJECT
+public:
+    OverrideDropActions(QObject *parent = 0)
+      : QStringListModel(parent)
+    {
+    }
+    Qt::DropActions supportedDropActions() const override
+    {
+        return Qt::MoveAction;
+    }
+};
+
+void tst_QAbstractItemModel::dragActionsFallsBackToDropActions()
+{
+    QAbstractItemModel *model = new OverrideDropActions(this);
+    QCOMPARE(model->supportedDragActions(), Qt::MoveAction);
+    QCOMPARE(model->supportedDropActions(), Qt::MoveAction);
+}
+
 class SignalConnectionTester : public QObject
 {
     Q_OBJECT

tests/auto/corelib/itemmodels/qstringlistmodel/tst_qstringlistmodel.cpp

@@ -80,6 +80,8 @@ private slots:
 
     void setData_emits_both_roles_data();
     void setData_emits_both_roles();
+
+    void supportedDragDropActions();
 };
 
 void tst_QStringListModel::rowsAboutToBeRemoved_rowsRemoved_data()
@@ -250,5 +252,12 @@ void tst_QStringListModel::setData_emits_both_roles()
              expected);
 }
 
+void tst_QStringListModel::supportedDragDropActions()
+{
+    QStringListModel model;
+    QCOMPARE(model.supportedDragActions(), Qt::CopyAction | Qt::MoveAction);
+    QCOMPARE(model.supportedDropActions(), Qt::CopyAction | Qt::MoveAction);
+}
+
 QTEST_MAIN(tst_QStringListModel)
 #include "tst_qstringlistmodel.moc"

tests/auto/gui/itemmodels/qstandarditemmodel/tst_qstandarditemmodel.cpp

@@ -125,6 +125,7 @@ private slots:
 
     void itemRoleNames();
     void getMimeDataWithInvalidModelIndex();
+    void supportedDragDropActions();
 
 private:
     QAbstractItemModel *m_model;
@@ -1666,5 +1667,12 @@ void tst_QStandardItemModel::getMimeDataWithInvalidModelIndex()
     QVERIFY(!data);
 }
 
+void tst_QStandardItemModel::supportedDragDropActions()
+{
+    QStandardItemModel model;
+    QCOMPARE(model.supportedDragActions(), Qt::CopyAction | Qt::MoveAction);
+    QCOMPARE(model.supportedDropActions(), Qt::CopyAction | Qt::MoveAction);
+}
+
 QTEST_MAIN(tst_QStandardItemModel)
 #include "tst_qstandarditemmodel.moc"