nested mdi: Get rid of unneeded drop area mdi wrapper when floating

When floating, the FloatingWindow has its own DropArea for nesting.
We delete the redundant level of wrappers when floating.

src/DockWidgetBase.cpp

@@ -551,10 +551,17 @@ MDILayoutWidget *DockWidgetBase::Private::mdiLayout() const
 
 bool DockWidgetBase::Private::isMDIWrapper() const
 {
-    if (auto dropAreaGuest = qobject_cast<DropArea *>(q->widget()))
-        return dropAreaGuest->isMDIWrapper();
+    return mdiDropAreaWrapper() != nullptr;
+}
 
-    return false;
+DropArea *DockWidgetBase::Private::mdiDropAreaWrapper() const
+{
+    if (auto dropAreaGuest = qobject_cast<DropArea *>(q->widget())) {
+        if (dropAreaGuest->isMDIWrapper())
+            return dropAreaGuest;
+    }
+
+    return nullptr;
 }
 
 DockWidgetBase::Private *DockWidgetBase::dptr() const

src/private/DockWidgetBase_p.h

@@ -140,6 +140,9 @@ public:
     /// This is only used by the DockWidget::Option_MDINestable feature
     bool isMDIWrapper() const;
 
+    /// @brief If this dock widget is an MDI wrapper (isMDIWrapper()), then returns the wrapper drop area
+    DropArea *mdiDropAreaWrapper() const;
+
     const QString name;
     QStringList affinities;
     QString title;

src/private/FloatingWindow.cpp

@@ -22,6 +22,7 @@
 #include "FrameworkWidgetFactory.h"
 #include "DragController_p.h"
 #include "LayoutSaver_p.h"
+#include "DockWidgetBase_p.h"
 
 #include <QCloseEvent>
 #include <QScopedValueRollback>
@@ -146,10 +147,26 @@ FloatingWindow::FloatingWindow(Frame *frame, QRect suggestedGeometry, MainWindow
 {
     QScopedValueRollback<bool> guard(m_disableSetVisible, true);
 
-    // Adding a widget will trigger onFrameCountChanged, which triggers a setVisible(true).
-    // The problem with setVisible(true) will forget about or requested geometry and place the window at 0,0
-    // So disable the setVisible(true) call while in the ctor.
-    m_dropArea->addWidget(frame, KDDockWidgets::Location_OnTop, {});
+    if (frame->hasNestedMDIDockWidgets()) {
+        // When using DockWidget::MDINestable, the docked MDI widget is wrapped by a drop area so we can drop things into it.
+        // When floating it, we can delete that helper drop area, as FloatingWindow already has one
+
+        if (frame->dockWidgetCount() == 0) {
+            // doesn't happen
+            qWarning() << Q_FUNC_INFO << "Unexpected empty frame";
+            return;
+        }
+
+        auto dwMDIWrapper = frame->dockWidgetAt(0);
+        auto dropAreaMDIWrapper = dwMDIWrapper->d->mdiDropAreaWrapper();
+        m_dropArea->addMultiSplitter(dropAreaMDIWrapper, Location_OnTop);
+        delete dwMDIWrapper;
+    } else {
+        // Adding a widget will trigger onFrameCountChanged, which triggers a setVisible(true).
+        // The problem with setVisible(true) will forget about or requested geometry and place the window at 0,0
+        // So disable the setVisible(true) call while in the ctor.
+        m_dropArea->addWidget(frame, KDDockWidgets::Location_OnTop, {});
+    }
 }
 
 FloatingWindow::~FloatingWindow()

src/private/Frame.cpp

@@ -889,6 +889,19 @@ MDILayoutWidget *Frame::mdiLayoutWidget() const
     return qobject_cast<MDILayoutWidget *>(m_layoutWidget);
 }
 
+bool Frame::hasNestedMDIDockWidgets() const
+{
+    if (!isMDI() || dockWidgetCount() == 0)
+        return false;
+
+    if (dockWidgetCount() != 1) {
+        qWarning() << Q_FUNC_INFO << "Expected a single dock widget wrapper as frame child";
+        return false;
+    }
+
+    return dockWidgetAt(0)->d->isMDIWrapper();
+}
+
 int Frame::userType() const
 {
     return m_userType;

src/private/Frame_p.h

@@ -302,6 +302,10 @@ public:
     /// @brief Returns the MDI layout. Or nullptr if this frame isn't in a MDI layout
     MDILayoutWidget *mdiLayoutWidget() const;
 
+    /// @brief If this frame is a MDI frame (isMDI() == true), returns whether it contains nested dock widgets (DockWidget::Option_MDINestable)
+    /// @sa isMDI()
+    bool hasNestedMDIDockWidgets() const;
+
     /// @brief See DockWidgetBase::userType()
     int userType() const;
 

tests/tst_docks.cpp

@@ -5153,7 +5153,32 @@ void TestDocks::tst_mdi_mixed_with_docking2()
     QVERIFY(!mdiWidget3->isOpen());
     QVERIFY(dropArea1.isNull());
 
-    // QTest::qWait(10000);
+    // Reopen everything again:
+
+    mdiArea->addDockWidget(mdiWidget1, QPoint(10, 10));
+    mdiArea->addDockWidget(mdiWidget2, QPoint(50, 50));
+    frame1 = mdiWidget1->d->frame();
+    mdiFrame1 = frame1->mdiFrame();
+    dropArea1 = frame1->mdiDropAreaWrapper();
+    dropArea1->addDockWidget(mdiWidget3, Location_OnLeft, nullptr);
+
+    // Test floating:
+    frame2 = mdiWidget2->d->frame();
+    QPointer<DockWidgetBase> dwWrapper2 = frame2->mdiDockWidgetWrapper();
+    dropArea2 = frame2->mdiDropAreaWrapper();
+    QVERIFY(mdiWidget2->isVisible());
+    QVERIFY(frame2->isMDIWrapper());
+    QVERIFY(dwWrapper2->d->isMDIWrapper());
+    mdiWidget2->setFloating(true);
+    QVERIFY(mdiWidget2->isFloating());
+
+    QVERIFY(!mdiWidget2->d->frame()->isMDI());
+    QVERIFY(!mdiWidget2->d->frame()->isMDIWrapper());
+    QTest::qWait(500); // remove
+    QVERIFY(dropArea2.isNull());
+    QVERIFY(dwWrapper2.isNull());
+
+    // QTest::qWait(100000);
 }
 
 // No need to port to QtQuick