Added KDDockWidgets::InitialVisibilityOption::PreserveCurrentTab

So you can insert into a tab group without changing the current
tab, if you want.

(cherry-picked from commit 58b8633e3d)

src/KDDockWidgets.h

@@ -128,7 +128,8 @@ Q_ENUM_NS(AddingOption)
 enum class InitialVisibilityOption
 {
     StartVisible = 0, ///< The dock widget is made visible when docked
-    StartHidden ///< Don't show the dock widget when adding it
+    StartHidden, ///< Don't show the dock widget when adding it
+    PreserveCurrentTab ///< When adding as tabbed, don't change the current index
 };
 Q_ENUM_NS(InitialVisibilityOption)
 
@@ -176,6 +177,11 @@ struct InitialOption
         return visibility == InitialVisibilityOption::StartHidden;
     }
 
+    bool preservesCurrentTab() const
+    {
+        return visibility == InitialVisibilityOption::PreserveCurrentTab;
+    }
+
     int preferredLength(Qt::Orientation o) const
     {
         return o == Qt::Horizontal ? preferredSize.width()

src/controllers/DockWidget.cpp

@@ -336,6 +336,14 @@ int DockWidget::tabIndex() const
     return 0;
 }
 
+int DockWidget::currentTabIndex() const
+{
+    if (Frame *frame = d->frame())
+        return frame->currentTabIndex();
+
+    return 0;
+}
+
 void DockWidget::setIcon(const QIcon &icon, IconPlaces places)
 {
     if (places & IconPlace::TitleBar)

src/controllers/DockWidget.h

@@ -229,10 +229,17 @@ public:
     void setAsCurrentTab();
 
     /**
-     * @brief Returns which tab index this dock widget occupies in the tab widget it's contained in
+     * @brief Returns the tab index this dock widget occupies
+     * Note that dock widgets are almost always tabbed, even if you don't see the tab bar.
+     * A single floating dock widget is still tabbed on a tab widget with a single tab.
      */
     int tabIndex() const;
 
+    /**
+     * @brief Returns the index of the current tab of the tab group this dock widget is in.
+     */
+    int currentTabIndex() const;
+
     /**
      * @brief Sets an icon to show on title bars and tab bars.
      * @param places Specifies where the icon will be shown (TitleBar, TabBar, ToggleAction, or All)

src/controllers/Frame.cpp

@@ -292,6 +292,7 @@ void Frame::insertWidget(DockWidget *dockWidget, int index, InitialOption adding
     if (m_layoutItem)
         dockWidget->d->addPlaceholderItem(m_layoutItem);
 
+    const int originalCurrentIndex = currentIndex();
     insertDockWidget(dockWidget, index);
 
     if (addingOption.startsHidden()) {
@@ -307,6 +308,8 @@ void Frame::insertWidget(DockWidget *dockWidget, int index, InitialOption adding
                 // use that size as the initial suggested size.
                 view()->resize(dockWidget->size());
             }
+        } else if (addingOption.preservesCurrentTab() && originalCurrentIndex != -1) {
+            setCurrentTabIndex(originalCurrentIndex);
         }
     }