delete platform cursor before Application

We want the platform cursor to have roughly the same lifespan as the
application.

By using QObject parent mechanism, this gets deleted after the
Application destructor in the QObject destructor.

This causes an issue that removing an event filter (used by the X11
cursor) calls into the application singleton which is no longer valid.

BUG: 465970

src/backends/x11/standalone/x11_standalone_backend.cpp

@@ -182,19 +182,20 @@ std::unique_ptr<Edge> X11StandaloneBackend::createScreenEdge(ScreenEdges *edges)
     return std::make_unique<WindowBasedEdge>(edges);
 }
 
-void X11StandaloneBackend::createPlatformCursor(QObject *parent)
+std::unique_ptr<Cursor> X11StandaloneBackend::createPlatformCursor()
 {
 #if HAVE_X11_XINPUT
-    auto c = new X11Cursor(parent, m_xinputIntegration != nullptr);
+    auto c = std::make_unique<X11Cursor>(m_xinputIntegration != nullptr);
     if (m_xinputIntegration) {
-        m_xinputIntegration->setCursor(c);
+        m_xinputIntegration->setCursor(c.get());
         // we know we have xkb already
         auto xkb = input()->keyboard()->xkb();
         xkb->setConfig(kwinApp()->kxkbConfig());
         xkb->reconfigure();
     }
+    return c;
 #else
-    new X11Cursor(parent, false);
+    return std::make_unique<X11Cursor>(false);
 #endif
 }
 

src/backends/x11/standalone/x11_standalone_backend.h

@@ -33,6 +33,7 @@ class Edge;
 class ScreenEdges;
 class Outline;
 class OutlineVisual;
+class Cursor;
 class Compositor;
 class WorkspaceScene;
 class Window;
@@ -58,7 +59,7 @@ public:
     void updateOutputs();
 
     std::unique_ptr<Edge> createScreenEdge(ScreenEdges *parent);
-    void createPlatformCursor(QObject *parent = nullptr);
+    std::unique_ptr<Cursor> createPlatformCursor();
     void startInteractiveWindowSelection(std::function<void(KWin::Window *)> callback, const QByteArray &cursorName = QByteArray());
     void startInteractivePositionSelection(std::function<void(const QPointF &)> callback);
     PlatformCursorImage cursorImage() const;

src/backends/x11/standalone/x11_standalone_cursor.cpp

@@ -19,8 +19,8 @@
 namespace KWin
 {
 
-X11Cursor::X11Cursor(QObject *parent, bool xInputSupport)
-    : Cursor(parent)
+X11Cursor::X11Cursor(bool xInputSupport)
+    : Cursor()
     , m_timeStamp(XCB_TIME_CURRENT_TIME)
     , m_buttonMask(0)
     , m_hasXInput(xInputSupport)

src/backends/x11/standalone/x11_standalone_cursor.h

@@ -20,7 +20,7 @@ class KWIN_EXPORT X11Cursor : public Cursor
 {
     Q_OBJECT
 public:
-    X11Cursor(QObject *parent, bool xInputSupport = false);
+    X11Cursor(bool xInputSupport = false);
     ~X11Cursor() override;
 
     void schedulePoll()

src/cursor.cpp

@@ -109,9 +109,8 @@ void Cursors::emitCurrentCursorChanged()
     Q_EMIT currentCursorChanged(m_currentCursor);
 }
 
-Cursor::Cursor(QObject *parent)
-    : QObject(parent)
-    , m_mousePollingCounter(0)
+Cursor::Cursor()
+    : m_mousePollingCounter(0)
     , m_cursorTrackingCounter(0)
     , m_themeName(defaultThemeName())
     , m_themeSize(defaultThemeSize())

src/cursor.h

@@ -97,7 +97,7 @@ class KWIN_EXPORT Cursor : public QObject
 {
     Q_OBJECT
 public:
-    Cursor(QObject *parent);
+    Cursor();
     ~Cursor() override;
     void startMousePolling();
     void stopMousePolling();

src/input.cpp

@@ -1954,8 +1954,9 @@ class SurfaceCursor : public Cursor
 {
 public:
     explicit SurfaceCursor(KWaylandServer::TabletToolV2Interface *tool)
-        : Cursor(tool)
+        : Cursor()
     {
+        setParent(tool);
         connect(tool, &KWaylandServer::TabletToolV2Interface::cursorChanged, this, [this](const KWaylandServer::TabletCursorSourceV2 &cursor) {
             if (auto surfaceCursor = std::get_if<KWaylandServer::TabletSurfaceCursorV2 *>(&cursor)) {
                 // If the cursor is unset, fallback to the cross cursor.

src/main.cpp

@@ -257,7 +257,7 @@ void Application::createInput()
 #endif
     auto input = InputRedirection::create(this);
     input->init();
-    createPlatformCursor(this);
+    m_platformCursor = createPlatformCursor();
 }
 
 void Application::createAtoms()
@@ -335,9 +335,9 @@ std::unique_ptr<Edge> Application::createScreenEdge(ScreenEdges *edges)
     return std::make_unique<Edge>(edges);
 }
 
-void Application::createPlatformCursor(QObject *parent)
+std::unique_ptr<Cursor> Application::createPlatformCursor()
 {
-    new InputRedirectionCursor(parent);
+    return std::make_unique<InputRedirectionCursor>();
 }
 
 std::unique_ptr<OutlineVisual> Application::createOutline(Outline *outline)

src/main.h

@@ -37,6 +37,7 @@ class ColorManager;
 class ScreenLockerWatcher;
 class TabletModeManager;
 class XwaylandInterface;
+class Cursor;
 class Edge;
 class ScreenEdges;
 class Outline;
@@ -258,7 +259,7 @@ public:
     void destroyAtoms();
 
     virtual std::unique_ptr<Edge> createScreenEdge(ScreenEdges *parent);
-    virtual void createPlatformCursor(QObject *parent = nullptr);
+    virtual std::unique_ptr<Cursor> createPlatformCursor();
     virtual std::unique_ptr<OutlineVisual> createOutline(Outline *outline);
     virtual void createEffectsHandler(Compositor *compositor, WorkspaceScene *scene);
 
@@ -383,6 +384,7 @@ private:
 #if KWIN_BUILD_SCREENLOCKER
     std::unique_ptr<ScreenLockerWatcher> m_screenLockerWatcher;
 #endif
+    std::unique_ptr<Cursor> m_platformCursor;
 };
 
 inline static Application *kwinApp()

src/main_x11.cpp

@@ -15,6 +15,7 @@
 #include "backends/x11/standalone/x11_standalone_backend.h"
 #include "core/outputbackend.h"
 #include "core/session.h"
+#include "cursor.h"
 #include "outline.h"
 #include "screenedge.h"
 #include "sm.h"
@@ -199,9 +200,9 @@ std::unique_ptr<Edge> ApplicationX11::createScreenEdge(ScreenEdges *parent)
     return static_cast<X11StandaloneBackend *>(outputBackend())->createScreenEdge(parent);
 }
 
-void ApplicationX11::createPlatformCursor(QObject *parent)
+std::unique_ptr<Cursor> ApplicationX11::createPlatformCursor()
 {
-    static_cast<X11StandaloneBackend *>(outputBackend())->createPlatformCursor(parent);
+    return static_cast<X11StandaloneBackend *>(outputBackend())->createPlatformCursor();
 }
 
 std::unique_ptr<OutlineVisual> ApplicationX11::createOutline(Outline *outline)

src/main_x11.h

@@ -24,7 +24,7 @@ public:
     void setReplace(bool replace);
 
     std::unique_ptr<Edge> createScreenEdge(ScreenEdges *parent) override;
-    void createPlatformCursor(QObject *parent = nullptr) override;
+    std::unique_ptr<Cursor> createPlatformCursor() override;
     std::unique_ptr<OutlineVisual> createOutline(Outline *outline) override;
     void createEffectsHandler(Compositor *compositor, WorkspaceScene *scene) override;
     void startInteractiveWindowSelection(std::function<void(KWin::Window *)> callback, const QByteArray &cursorName = QByteArray()) override;

src/pointer_input.cpp

@@ -1095,8 +1095,8 @@ KXcursorTheme CursorImage::theme() const
     return m_waylandImage.theme();
 }
 
-InputRedirectionCursor::InputRedirectionCursor(QObject *parent)
-    : Cursor(parent)
+InputRedirectionCursor::InputRedirectionCursor()
+    : Cursor()
     , m_currentButtons(Qt::NoButton)
 {
     Cursors::self()->setMouse(this);

src/pointer_input.h

@@ -261,7 +261,7 @@ class InputRedirectionCursor : public KWin::Cursor
 {
     Q_OBJECT
 public:
-    explicit InputRedirectionCursor(QObject *parent);
+    explicit InputRedirectionCursor();
     ~InputRedirectionCursor() override;
 
 protected: