QDockWidgetGroupWindow::adjustFlags() - don't show() empty group window

The method calls show() on a dock widget group window, when the window
flags have changed. When all of its contained, tabbed dock widgets are
programmatically hidden or docked on the main window, an empty group
window is shown.

This patch implements bool hasVisibleDockWidgets(). It returns true, if
at least one of the group window's dockwidget children is not hidden.
It replaces show() by setVisible(), passing the return value of
hasVisibleChildren().

It adapts tst_QDockWidget::floatingTabs() to test the fix.
(Drive-by: remove dead code)

Fixes: QTBUG-115058
Pick-to: 6.6 6.5 6.2
Change-Id: Ifb8e2450e91a7c78decc06f592e160631ca2faf5
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 20 insertions, 1 deletions

diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index e9cfd05007..f51fc41494 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -432,6 +432,25 @@ void QDockWidgetGroupWindow::destroyOrHideIfEmpty()
     deleteLater();
 }
 
+/*!
+   \internal
+   \return \c true if the group window has at least one visible QDockWidget child,
+   otherwise false.
+ */
+bool QDockWidgetGroupWindow::hasVisibleDockWidgets() const
+{
+    const auto &children = findChildren<QDockWidget *>(Qt::FindChildrenRecursively);
+    for (auto child : children) {
+        // WA_WState_Visible is set on the dock widget, associated to the active tab
+        // and unset on all others.
+        // WA_WState_Hidden is set if the dock widgets have been explicitly hidden.
+        // This is the relevant information to check (equivalent to !child->isHidden()).
+        if (!child->testAttribute(Qt::WA_WState_Hidden))
+            return true;
+    }
+    return false;
+}
+
 /*! \internal
     Sets the flags of this window in accordance to the capabilities of the dock widgets
  */
@@ -480,7 +499,7 @@ void QDockWidgetGroupWindow::adjustFlags()
             m_removedFrameSize = QSize();
         }
 
-        show(); // setWindowFlags hides the window
+        setVisible(hasVisibleDockWidgets());
     }
 
     QWidget *titleBarOf = top ? top : parentWidget();