QmlDesigner: Fix item library expand issue

If a click happens on an item library item, mouse interaction
(expanding, collapsing sections, and showing context menu) is blocked
until some action happens (right-click for example). This is due
to a bug in QDrag. With this commit it is very hard to reproduce the
issue unless one's deliberately insisting to reproduce it.

Fixes: QDS-3792
Fixes: QDS-1652
Change-Id: I201b07aabf144adbb4d51e32c1fcc4990f89f5f9
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>

share/qtcreator/qmldesigner/itemLibraryQmlSources/ItemDelegate.qml

@@ -75,7 +75,7 @@ Item {
             anchors.fill: parent
 
             onPressed: {
-                rootView.startDragAndDrop(mouseRegion, itemLibraryEntry)
+                rootView.startDragAndDrop(itemLibraryEntry)
             }
         }
     }

src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp

@@ -84,6 +84,17 @@ bool ItemLibraryWidget::eventFilter(QObject *obj, QEvent *event)
     if (event->type() == QEvent::FocusOut) {
         if (obj == m_itemViewQuickWidget.data())
             QMetaObject::invokeMethod(m_itemViewQuickWidget->rootObject(), "closeContextMenu");
+    } else if (event->type() == QMouseEvent::MouseMove) {
+        if (m_itemToDrag.isValid()) {
+            ItemLibraryEntry entry = m_itemToDrag.value<ItemLibraryEntry>();
+            auto drag = new QDrag(this);
+            drag->setPixmap(Utils::StyleHelper::dpiSpecificImageFile(entry.libraryEntryIconPath()));
+            drag->setMimeData(m_itemLibraryModel->getMimeData(entry));
+            drag->exec();
+            drag->deleteLater();
+
+            m_itemToDrag = {};
+        }
     }
 
     return QObject::eventFilter(obj, event);
@@ -366,25 +377,12 @@ void ItemLibraryWidget::setResourcePath(const QString &resourcePath)
     updateSearch();
 }
 
-void ItemLibraryWidget::startDragAndDrop(QQuickItem *mouseArea, QVariant itemLibraryId)
+void ItemLibraryWidget::startDragAndDrop(const QVariant &itemLibEntry)
 {
-    m_currentitemLibraryEntry = itemLibraryId.value<ItemLibraryEntry>();
+    // Actual drag is created after mouse has moved to avoid a QDrag bug that causes drag to stay
-
+    // active (and blocks mouse release) if mouse is released at the same spot of the drag start.
-    QMimeData *mimeData = m_itemLibraryModel->getMimeData(m_currentitemLibraryEntry);
+    // This doesn't completely eliminate the bug but makes it significantly harder to produce.
-    auto drag = new QDrag(this);
+    m_itemToDrag = itemLibEntry;
-
-    drag->setPixmap(Utils::StyleHelper::dpiSpecificImageFile(
-                        m_currentitemLibraryEntry.libraryEntryIconPath()));
-    drag->setMimeData(mimeData);
-
-    /* Workaround for bug in Qt. The release event is not delivered for Qt < 5.9 if a drag is started */
-    QMouseEvent event (QEvent::MouseButtonRelease, QPoint(-1, -1), Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);
-    QApplication::sendEvent(mouseArea, &event);
-
-    QTimer::singleShot(0, [drag]() {
-        drag->exec();
-        drag->deleteLater();
-    });
 }
 
 void ItemLibraryWidget::setFlowMode(bool b)

src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.h

@@ -87,7 +87,7 @@ public:
     void setModel(Model *model);
     void setFlowMode(bool b);
 
-    Q_INVOKABLE void startDragAndDrop(QQuickItem *mouseArea, QVariant itemLibId);
+    Q_INVOKABLE void startDragAndDrop(const QVariant &itemLibEntry);
     Q_INVOKABLE void removeImport(const QString &importUrl);
 
 signals:
@@ -123,7 +123,7 @@ private:
     QShortcut *m_qmlSourceUpdateShortcut;
     AsynchronousImageCache &m_imageCache;
     QPointer<Model> m_model;
-    ItemLibraryEntry m_currentitemLibraryEntry;
+    QVariant m_itemToDrag;
     bool m_updateRetry = false;
     QString m_filterText;