wm: recompute WindowsetProjection.screens on each usage

Fixes potential UAF from destroyed screens not yet removed by a
wayland commit.

Author: outfoxxed

changelog/next.md

@@ -6,3 +6,4 @@
 - Fixed missing/wrong change signals on various properties.
 - Fixed session lock crashes on sleep, wake, DPMS, and unlocking.
 - QsWindow.updatesEnabled makes sure windows are redrawn when set to true.
+- Fixed potential crashes from usage of `WindowsetProjection.screens` during monitor unplug.

src/windowmanager/windowset.cpp

@@ -30,16 +30,22 @@ WindowsetProjection::WindowsetProjection(QObject* parent): QObject(parent) {
 		}
 		return result;
 	});
+}
 
-	this->bScreens.setBinding([this] {
-		QList<QuickshellScreenInfo*> screens;
+QList<QuickshellScreenInfo*> WindowsetProjection::screens() {
+	QList<QuickshellScreenInfo*> screens;
 
-		for (auto* screen: this->bQScreens.value()) {
-			screens.append(QuickshellTracked::instance()->screenInfo(screen));
+	for (auto* screen: this->bQScreens.value()) {
+		if (auto* qsScreen = QuickshellTracked::instance()->screenInfo(screen)) {
+			screens.append(qsScreen);
+		} else {
+			qCDebug(logWorkspace) << this << "screens list contains invalid screen"
+			                      << static_cast<void*>(screen)
+			                      << "which was probably removed before workspace state has settled.";
 		}
+	}
 
-		return screens;
-	});
+	return screens;
 }
 
 } // namespace qs::wm

src/windowmanager/windowset.hpp

@@ -132,17 +132,15 @@ class WindowsetProjection: public QObject {
 	QML_UNCREATABLE("");
 	// clang-format off
 	/// Screens the windowset projection spans, often a single screen or all screens.
-	Q_PROPERTY(QList<QuickshellScreenInfo*> screens READ default NOTIFY screensChanged BINDABLE bindableScreens);
+	Q_PROPERTY(QList<QuickshellScreenInfo*> screens READ screens NOTIFY screensChanged);
 	/// Windowsets that are currently present on the projection.
 	Q_PROPERTY(QList<Windowset*> windowsets READ default NOTIFY windowsetsChanged BINDABLE bindableWindowsets);
 	// clang-format on
 
 public:
 	explicit WindowsetProjection(QObject* parent);
 
-	[[nodiscard]] QBindable<QList<QuickshellScreenInfo*>> bindableScreens() const {
-		return &this->bScreens;
-	}
+	[[nodiscard]] QList<QuickshellScreenInfo*> screens();
 
 	[[nodiscard]] QBindable<QList<QScreen*>> bindableQScreens() const { return &this->bQScreens; }
 
@@ -155,12 +153,10 @@ class WindowsetProjection: public QObject {
 	void windowsetsChanged();
 
 protected:
-	Q_OBJECT_BINDABLE_PROPERTY(WindowsetProjection, QList<QScreen*>, bQScreens);
-
 	Q_OBJECT_BINDABLE_PROPERTY(
 	    WindowsetProjection,
-	    QList<QuickshellScreenInfo*>,
-	    bScreens,
+	    QList<QScreen*>,
+	    bQScreens,
 	    &WindowsetProjection::screensChanged
 	);