Refactor and fix QMainWindow::tabifiedDockWidgets()

The method traversed QDockAreaLayoutInfo::item_list, to identify
dock widgets tabbed with the QDockWidget argument in a tab bar
It relied on bool QDockAreLayoutInfo::tabbed, which is set to true, when
a QMainWindowTabBar is to be added to a QDockAreaLayoutInfo. This flag
isn't cleared, when the second last dock widget is removed from the
tab bar. It can't be replaced by QMainWindowLayout::isDockWidgetTabbed,
because the flag also represents intermediate states, where e.g. a dock
widget is hovered over, prepares to become a floating tab and then rolls
back, because hovering doesn't result in a drop. In that case, tabbed
must become true, which the dock widget isn't actually tabbed.

Furthermore, the way to traverse item_list didn't find dock widgets
in a floating tab. In that case, tabifiedDockWidgets() wrongly returned
an empty list.

To fix both issues, refactor QMainWindow::tabifiedDockWidgets() to read
the list of dock widgets directly from the QMainWindowTabBar.

Add tests in tst_QDockWidget::floatingTabs() and
updateTabBarOnVisibilityChanged()

Fixes: QTBUG-122001
Pick-to: 6.5
Change-Id: Ia9eb3711be642101261f34ee447521cc6accc20c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit cd2a3e970aaeb8f5f92d9c6e52ede7a82f953150)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 5e89966da1a2107324171a222f27e7c02340a449)

src/widgets/widgets/qmainwindow.cpp

@@ -1123,21 +1123,8 @@ void QMainWindow::tabifyDockWidget(QDockWidget *first, QDockWidget *second)
 
 QList<QDockWidget*> QMainWindow::tabifiedDockWidgets(QDockWidget *dockwidget) const
 {
-    QList<QDockWidget*> ret;
-    const QDockAreaLayoutInfo *info = d_func()->layout->layoutState.dockAreaLayout.info(dockwidget);
-    if (info && info->tabbed && info->tabBar) {
-        for(int i = 0; i < info->item_list.size(); ++i) {
-            const QDockAreaLayoutItem &item = info->item_list.at(i);
-            if (item.widgetItem) {
-                if (QDockWidget *dock = qobject_cast<QDockWidget*>(item.widgetItem->widget())) {
-                    if (dock != dockwidget) {
-                        ret += dock;
-                    }
-                }
-            }
-        }
-    }
-    return ret;
+    Q_D(const QMainWindow);
+    return d->layout ? d->layout->tabifiedDockWidgets(dockwidget) : QList<QDockWidget *>();
 }
 #endif // QT_CONFIG(tabbar)
 

src/widgets/widgets/qmainwindowlayout.cpp

@@ -1885,6 +1885,7 @@ public:
     ~QMainWindowTabBar();
     QDockWidget *dockAt(int index) const;
     QList<QDockWidget *> dockWidgets() const;
+    bool contains(const QDockWidget *dockWidget) const;
 protected:
     bool event(QEvent *e) override;
     void mouseReleaseEvent(QMouseEvent*) override;
@@ -1892,6 +1893,17 @@ protected:
 
 };
 
+QMainWindowTabBar *QMainWindowLayout::findTabBar(const QDockWidget *dockWidget) const
+{
+     for (auto *bar : usedTabBars) {
+        Q_ASSERT(qobject_cast<QMainWindowTabBar *>(bar));
+        auto *tabBar = static_cast<QMainWindowTabBar *>(bar);
+        if (tabBar->contains(dockWidget))
+            return tabBar;
+    }
+    return nullptr;
+}
+
 QMainWindowTabBar::QMainWindowTabBar(QMainWindow *parent)
     : QTabBar(parent), mainWindow(parent)
 {
@@ -1908,6 +1920,15 @@ QList<QDockWidget *> QMainWindowTabBar::dockWidgets() const
     return docks;
 }
 
+bool QMainWindowTabBar::contains(const QDockWidget *dockWidget) const
+{
+    for (int i = 0; i < count(); ++i) {
+        if (dockAt(i) == dockWidget)
+            return true;
+    }
+    return false;
+}
+
 QDockWidget *QMainWindowTabBar::dockAt(int index) const
 {
     QMainWindowTabBar *that = const_cast<QMainWindowTabBar *>(this);
@@ -2011,21 +2032,26 @@ bool QMainWindowTabBar::event(QEvent *e)
     return true;
 }
 
+QList<QDockWidget *> QMainWindowLayout::tabifiedDockWidgets(const QDockWidget *dockWidget) const
+{
+    const auto *bar = findTabBar(dockWidget);
+    if (!bar)
+        return {};
+
+    QList<QDockWidget *> buddies = bar->dockWidgets();
+    // Return only other dock widgets associated with dockWidget in a tab bar.
+    // If dockWidget is alone in a tab bar, return an empty list.
+    buddies.removeOne(dockWidget);
+    return buddies;
+}
+
 bool QMainWindowLayout::isDockWidgetTabbed(const QDockWidget *dockWidget) const
 {
-    for (auto *bar : std::as_const(usedTabBars)) {
     // A single dock widget in a tab bar is not considered to be tabbed.
     // This is to make sure, we don't drag an empty QDockWidgetGroupWindow around.
     // => only consider tab bars with two or more tabs.
-        if (bar->count() <= 1)
-            continue;
-        auto *tabBar = qobject_cast<QMainWindowTabBar *>(bar);
-        Q_ASSERT(tabBar);
-        const auto dockWidgets = tabBar->dockWidgets();
-        if (std::find(dockWidgets.begin(), dockWidgets.end(), dockWidget) != dockWidgets.end())
-            return true;
-    }
-    return false;
+    const auto *bar = findTabBar(dockWidget);
+    return bar && bar->count() > 1;
 }
 
 QTabBar *QMainWindowLayout::getTabBar()

src/widgets/widgets/qmainwindowlayout_p.h

@@ -448,6 +448,7 @@ public:
     bool restoreState(QDataStream &stream, const QMainWindowLayoutState &oldState);
 };
 
+class QMainWindowTabBar;
 class Q_AUTOTEST_EXPORT QMainWindowLayout
     : public QLayout,
       public QMainWindowLayoutSeparatorHelper<QMainWindowLayout>
@@ -575,7 +576,11 @@ public:
 #if QT_CONFIG(dockwidget)
     QPointer<QDockWidgetGroupWindow> currentHoveredFloat; // set when dragging over a floating dock widget
     void setCurrentHoveredFloat(QDockWidgetGroupWindow *w);
+#if QT_CONFIG(tabbar)
     bool isDockWidgetTabbed(const QDockWidget *dockWidget) const;
+    QList<QDockWidget *> tabifiedDockWidgets(const QDockWidget *dockWidget) const;
+    QMainWindowTabBar *findTabBar(const QDockWidget *dockWidget) const;
+#endif
 #endif
     bool isInApplyState = false;
 

tests/auto/widgets/widgets/qdockwidget/tst_qdockwidget.cpp

@@ -698,6 +698,9 @@ void tst_QDockWidget::updateTabBarOnVisibilityChanged()
     mw.tabifyDockWidget(dw1, dw2);
     mw.tabifyDockWidget(dw2, dw3);
 
+    const auto list1 = QList<QDockWidget *>{dw1, dw2, dw3};
+    QCOMPARE(mw.tabifiedDockWidgets(dw0), list1);
+
     QTabBar *tabBar = mw.findChild<QTabBar *>();
     QVERIFY(tabBar);
     tabBar->setCurrentIndex(2);
@@ -711,6 +714,8 @@ void tst_QDockWidget::updateTabBarOnVisibilityChanged()
     dw1->hide();
     QTRY_COMPARE(tabBar->count(), 2);
     QCOMPARE(tabBar->currentIndex(), 0);
+
+    QCOMPARE(mw.tabifiedDockWidgets(dw2), {dw3});
 }
 
 Q_DECLARE_METATYPE(Qt::DockWidgetArea)
@@ -1438,6 +1443,9 @@ void tst_QDockWidget::floatingTabs()
     createFloatingTabs(mainWindow, cent, d1, d2, path1, path2);
     std::unique_ptr<QMainWindow> up_mainWindow(mainWindow);
 
+    QCOMPARE(mainWindow->tabifiedDockWidgets(d1), {d2});
+    QCOMPARE(mainWindow->tabifiedDockWidgets(d2), {d1});
+
     /*
      * unplug both dockwidgets, resize them and plug them into a joint floating tab
      * expected behavior: QDOckWidgetGroupWindow with both widgets is created
@@ -1515,6 +1523,9 @@ void tst_QDockWidget::floatingTabs()
     // Paths must be identical
     QTRY_COMPARE(layout->layoutState.indexOf(d1), path1);
     QTRY_COMPARE(layout->layoutState.indexOf(d2), path2);
+
+    QCOMPARE(mainWindow->tabifiedDockWidgets(d1), {});
+    QCOMPARE(mainWindow->tabifiedDockWidgets(d2), {});
 #else
     QSKIP("test requires -developer-build option");
 #endif // QT_BUILD_INTERNAL