[platforms/x11] Properly unload effects on X11

Summary:
When Compositor finishes compositing, it destroys EffectsHandlerImpl,
which in its turn tries to unload all effects. But there is a problem...

EffectsHandlerImpl has platform-specific hooks to ungrab keyboard and
also stop mouse interception. Given that any call made to a virtual function
in the destructor of a base class(EffectsHandlerImpl) won't go to a derived
class(EffectsHandlerImplX11), keyboard won't be ungrabbed even if effect
that grabbed it is already gone.

BUG: 399572

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D19178

plugins/platforms/x11/standalone/effects_x11.cpp

@@ -43,7 +43,17 @@ EffectsHandlerImplX11::EffectsHandlerImplX11(Compositor *compositor, Scene *scen
     );
 }
 
-EffectsHandlerImplX11::~EffectsHandlerImplX11() = default;
+EffectsHandlerImplX11::~EffectsHandlerImplX11()
+{
+    // EffectsHandlerImpl tries to unload all effects when it's destroyed.
+    // The routine that unloads effects makes some calls (indirectly) to
+    // doUngrabKeyboard and doStopMouseInterception, which are virtual.
+    // Given that any call to a virtual function in the destructor of a base
+    // class will never go to a derived class, we have to unload effects
+    // here. Yeah, this is quite a bit ugly but it's fine; someday, X11
+    // will be dead (or not?).
+    unloadAllEffects();
+}
 
 bool EffectsHandlerImplX11::doGrabKeyboard()
 {

plugins/platforms/x11/standalone/effects_x11.h

@@ -35,7 +35,7 @@ class EffectsHandlerImplX11 : public EffectsHandlerImpl
     Q_OBJECT
 public:
     explicit EffectsHandlerImplX11(Compositor *compositor, Scene *scene);
-    virtual ~EffectsHandlerImplX11();
+    ~EffectsHandlerImplX11() override;
 
     void defineCursor(Qt::CursorShape shape) override;