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: 6.7 6.6 6.5
Change-Id: Ia9eb3711be642101261f34ee447521cc6accc20c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 39 insertions, 13 deletions

diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index 3933f2a7cd..e17fa28b83 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/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;
+    // 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.
+    const auto *bar = findTabBar(dockWidget);
+    return bar && bar->count() > 1;
 }
 
 QTabBar *QMainWindowLayout::getTabBar()