Make redocking floating windows with tabs possible

TitleBar::isFloating() was returning false, while it should
have returned true.

Fixed by making isFloating() simpler and dumb. isFloating() should
only say if it belongs to a floating window or not. It shouldn't
contain any logic about whether button should be visible or not.

There's already logic elsewhere that will hide the float button
in case there's nesting.

Fixes issue #96 and #44

src/private/TitleBar.cpp

@@ -366,7 +366,7 @@ void TitleBar::onCloseClicked()
 bool TitleBar::isFloating() const
 {
     if (m_floatingWindow)
-        return m_floatingWindow->hasSingleDockWidget(); // Debatable! Maybe it's always floating.
+        return true;
 
     if (m_frame)
         return m_frame->isFloating();

src/private/TitleBar_p.h

@@ -63,7 +63,7 @@ class DOCKS_EXPORT TitleBar : public QWidgetAdapter, public Draggable
 
     DockWidgetBase *singleDockWidget() const override;
 
-    ///@brief Returns true if the dock widget which has this title bar is floating
+    ///@brief Returns true if this title-bar is the title bar of a floating window
     bool isFloating() const;
 
     ///@brief the list of dockwidgets under this TitleBar.

tests/tst_docks.cpp

@@ -7655,6 +7655,26 @@ void TestDocks::tst_resizePropagatesEvenly()
     QVERIFY(qAbs(dock2->height() - dock1->height()) < 3);
 }
 
+void TestDocks::tst_unfloatTabbedFloatingWidgets()
+{
+    auto m = createMainWindow(QSize(1000, 1000), MainWindowOption_None);
+    auto dock0 = createDockWidget("dock0", new MyWidget2());
+    auto dock1 = createDockWidget("dock1", new MyWidget2());
+    m->addDockWidget(dock0, Location_OnLeft);
+    dock0->addDockWidgetAsTab(dock1);
+
+    dock0->titleBar()->onFloatClicked();
+    QVERIFY(dock0->titleBar()->isFloating());
+    QVERIFY(!dock0->mainWindow());
+
+    dock0->titleBar()->onFloatClicked();
+    QVERIFY(!dock0->titleBar()->isFloating());
+    QVERIFY(dock0->mainWindow());
+
+
+
+}
+
 void TestDocks::tst_addMDIDockWidget()
 {
     EnsureTopLevelsDeleted e;

tests/tst_docks.h

@@ -240,6 +240,7 @@ private Q_SLOTS:
     void tst_toggleTabbed();
     void tst_toggleTabbed2();
     void tst_resizePropagatesEvenly();
+    void tst_unfloatTabbedFloatingWidgets();
 
     void tst_addMDIDockWidget();
     void tst_redockToMDIRestoresPosition();