Make DockWidgetBase::setMDIPosition|setMDISize support nesting

They now honour Option_MDINestable.
Before they would bail out assuming they weren't in a MDI area.
Now they look further up the hierarchy to find our MDIArea, if any.

src/DockWidgetBase.cpp

@@ -543,8 +543,30 @@ void DockWidgetBase::Private::maybeMorphIntoFloatingWindow()
 
 MDILayoutWidget *DockWidgetBase::Private::mdiLayout() const
 {
-    if (auto mw = mainWindow())
-        return mw->mdiLayoutWidget();
+    auto p = const_cast<QObject *>(q->parent());
+    while (p) {
+        if (qobject_cast<const QWindow*>(p)) {
+            // Ignore QObject hierarchies spanning though multiple windows
+            return nullptr;
+        }
+
+        if (auto layout = qobject_cast<LayoutWidget*>(p)) {
+            // We found a layout
+            if (auto mdiLayout = qobject_cast<MDILayoutWidget*>(p)) {
+                // And it's MDI
+                return mdiLayout;
+            } else if (auto dropArea = qobject_cast<DropArea*>(p)) {
+                // It's a DropArea. But maybe it's a drop area that's just helping
+                // making the MDI windows accept drops (Option_MDINestable)
+                if (!dropArea->isMDIWrapper())
+                    return nullptr;
+
+                // It's a MDI wrapper, keep looking up.
+            }
+        }
+
+        p = p->parent();
+    }
 
     return nullptr;
 }
@@ -564,6 +586,36 @@ DropArea *DockWidgetBase::Private::mdiDropAreaWrapper() const
     return nullptr;
 }
 
+DockWidgetBase *DockWidgetBase::Private::mdiDockWidgetWrapper() const
+{
+    if (isMDIWrapper()) {
+        // We are the wrapper
+        return q;
+    }
+
+    auto p = const_cast<QObject *>(q->parent());
+    while (p) {
+        if (qobject_cast<const QWindow*>(p)) {
+            // Ignore QObject hierarchies spanning though multiple windows
+            return nullptr;
+        }
+
+        if (auto layout = qobject_cast<LayoutWidget*>(p)) {
+            if (auto dropArea = qobject_cast<DropArea*>(p)) {
+                if (dropArea->isMDIWrapper())
+                    return dropArea->mdiDockWidgetWrapper();
+
+            }
+
+            return nullptr;
+        }
+
+        p = p->parent();
+    }
+
+    return nullptr;
+}
+
 DockWidgetBase::Private *DockWidgetBase::dptr() const
 {
     return d;
@@ -852,14 +904,26 @@ int DockWidgetBase::userType() const
 
 void DockWidgetBase::setMDIPosition(QPoint pos)
 {
-    if (MDILayoutWidget *layout = d->mdiLayout())
-        layout->moveDockWidget(this, pos);
+    if (MDILayoutWidget *layout = d->mdiLayout()) {
+        if (auto wrapperDW = d->mdiDockWidgetWrapper()) {
+            // Case of using Option_MDINestable. We need to layout the actual top level DW
+            layout->moveDockWidget(wrapperDW, pos);
+        } else {
+            layout->moveDockWidget(this, pos);
+        }
+    }
 }
 
 void DockWidgetBase::setMDISize(QSize size)
 {
-    if (MDILayoutWidget *layout = d->mdiLayout())
-        layout->resizeDockWidget(this, size);
+    if (MDILayoutWidget *layout = d->mdiLayout()) {
+        if (auto wrapperDW = d->mdiDockWidgetWrapper()) {
+            // Case of using Option_MDINestable. We need to layout the actual top level DW
+            layout->resizeDockWidget(wrapperDW, size);
+        } else {
+            layout->resizeDockWidget(this, size);
+        }
+    }
 }
 
 void DockWidgetBase::setMDIZ(int z)

src/private/DockWidgetBase_p.h

@@ -143,6 +143,10 @@ public:
     /// @brief If this dock widget is an MDI wrapper (isMDIWrapper()), then returns the wrapper drop area
     DropArea *mdiDropAreaWrapper() const;
 
+    /// @brief If this dock widget is inside a drop area nested in MDI then returns the wrapper dock widget
+    /// This goes up the hierarchy, while mdiDropAreaWrapper goes down.
+    DockWidgetBase *mdiDockWidgetWrapper() const;
+
     const QString name;
     QStringList affinities;
     QString title;

src/private/DropArea_p.h

@@ -74,6 +74,9 @@ public:
     /// When DockWidget::Option_MDINestable is used, docked MDI dock widgets will be wrapped inside a DropArea, so they accept drops
     /// This DropArea is created implicitly while docking, and this function will return true
     bool isMDIWrapper() const;
+
+    /// Returns the helper dock widget for implementing DockWidget::Option_MDINestable.
+    DockWidgetBase *mdiDockWidgetWrapper() const;
 private:
     Q_DISABLE_COPY(DropArea)
     friend class Frame;
@@ -88,7 +91,6 @@ private:
     bool drop(QWidgetOrQuick *droppedwindow, KDDockWidgets::Location location, Frame *relativeTo);
     Frame *frameContainingPos(QPoint globalPos) const;
     void updateFloatingActions();
-    DockWidgetBase *mdiDockWidgetWrapper() const;
 
     bool m_inDestructor = false;
     const bool m_isMDIWrapper;

src/private/MDILayoutWidget.cpp

@@ -107,7 +107,8 @@ void MDILayoutWidget::resizeDockWidget(Frame *frame, QSize size)
 
     Layouting::Item *item = itemForFrame(frame);
     if (!item) {
-        qWarning() << Q_FUNC_INFO << "Frame not found in the layout" << frame;
+        qWarning() << Q_FUNC_INFO << "Frame not found in the layout" << frame << frame->isMDI()
+                   << frame->isMDIWrapper();
         return;
     }
 

tests/tst_docks.cpp

@@ -5213,6 +5213,42 @@ void TestDocks::tst_mdi_mixed_with_docking2()
     mdiTitleBar->onFloatClicked();
 }
 
+void TestDocks::tst_mdi_mixed_with_docking_setMDISize()
+{
+    EnsureTopLevelsDeleted e;
+    auto m = createMainWindow(QSize(1000, 500), MainWindowOption_HasCentralWidget);
+    auto dock1 = createDockWidget("1", new QPushButton("1"));
+
+    m->addDockWidget(dock1, Location_OnBottom);
+
+    auto mdiArea = new MDIArea();
+    m->setPersistentCentralWidget(mdiArea);
+
+    auto createSheet = [](int id) -> DockWidgetBase* {
+        auto dock = new DockWidget(QStringLiteral("dw-sheet-%1").arg(id), DockWidgetBase::Option_MDINestable);
+        dock->setWidget(new QPushButton(QStringLiteral("Sheet %1").arg(id)));
+        dock->setTitle(QStringLiteral("Sheet %1").arg(id));
+
+        return dock;
+    };
+
+    auto mdiWidget1 = createSheet(1);
+    auto mdiWidget2 = createSheet(2);
+
+    mdiArea->addDockWidget(mdiWidget1, QPoint(10, 10));
+    mdiArea->addDockWidget(mdiWidget2, QPoint(50, 50));
+
+    Frame *frame1 = mdiArea->frames().at(0);
+
+    const QSize sz1 = frame1->QWidgetAdapter::size();
+    const QSize increment(200, 200);
+
+    QVERIFY(mdiWidget1->d->mdiLayout());
+    mdiWidget1->setMDISize(sz1 + increment);
+
+    QCOMPARE(frame1->QWidgetAdapter::size(), sz1 + increment);
+}
+
 // No need to port to QtQuick
 void TestDocks::tst_floatingWindowDeleted()
 {

tests/tst_docks.h

@@ -252,6 +252,7 @@ private Q_SLOTS:
     void tst_mainWindowAlwaysHasCentralWidget();
     void tst_dockableMainWindows();
     void tst_mdi_mixed_with_docking2();
+    void tst_mdi_mixed_with_docking_setMDISize();
 
     // But these are fine to be widget only:
     void tst_tabsNotClickable();