wayland: hook wl_proxy_get_listener avoiding QTBUG-145022 crash

Co-authored-by: Lemmy <studio@quadbyte.net>

changelog/next.md

@@ -58,6 +58,7 @@ set shell id.
 - Fixed ToplevelManager not clearing activeToplevel on deactivation.
 - Desktop action order is now preserved.
 - Fixed partial socket reads in greetd and hyprland on slow machines.
+- Worked around Qt bug causing crashes when plugging and unplugging monitors.
 
 ## Packaging Changes
 

src/wayland/CMakeLists.txt

@@ -73,6 +73,7 @@ endfunction()
 # -----
 
 qt_add_library(quickshell-wayland STATIC
+	wl_proxy_safe_deref.cpp
 	platformmenu.cpp
 	popupanchor.cpp
 	xdgshell.cpp
@@ -80,6 +81,13 @@ qt_add_library(quickshell-wayland STATIC
 	output_tracking.cpp
 )
 
+# required for wl_proxy_safe_deref
+target_link_libraries(quickshell-wayland PRIVATE ${CMAKE_DL_LIBS})
+target_link_options(quickshell PRIVATE
+	"LINKER:--export-dynamic-symbol=wl_proxy_get_listener"
+	"LINKER:--require-defined=wl_proxy_get_listener"
+)
+
 # required to make sure the constructor is linked
 add_library(quickshell-wayland-init OBJECT init.cpp)
 

src/wayland/init.cpp

@@ -10,6 +10,7 @@
 #include "wlr_layershell/wlr_layershell.hpp"
 #endif
 
+void installWlProxySafeDeref(); // NOLINT(misc-use-internal-linkage)
 void installPlatformMenuHook(); // NOLINT(misc-use-internal-linkage)
 void installPopupPositioner();  // NOLINT(misc-use-internal-linkage)
 
@@ -33,6 +34,7 @@ class WaylandPlugin: public QsEnginePlugin {
 	}
 
 	void init() override {
+		installWlProxySafeDeref();
 		installPlatformMenuHook();
 		installPopupPositioner();
 	}

src/wayland/windowmanager/windowset.cpp

@@ -8,9 +8,9 @@
 #include <qobjectdefs.h>
 #include <qproperty.h>
 
+#include "../../windowmanager/screenprojection.hpp"
 #include "../../windowmanager/windowmanager.hpp"
 #include "../../windowmanager/windowset.hpp"
-#include "../../windowmanager/screenprojection.hpp"
 #include "ext_workspace.hpp"
 
 namespace qs::wm::wayland {

src/wayland/wl_proxy_safe_deref.cpp

@@ -0,0 +1,42 @@
+
+#include <dlfcn.h>
+#include <qlogging.h>
+#include <qloggingcategory.h>
+#include <wayland-client-core.h>
+#include <wayland-util.h>
+
+#include "../core/logcat.hpp"
+
+namespace {
+QS_LOGGING_CATEGORY(logDeref, "quickshell.wayland.safederef", QtWarningMsg);
+using wl_proxy_get_listener_t = const void* (*) (wl_proxy*);
+wl_proxy_get_listener_t original_wl_proxy_get_listener = nullptr; // NOLINT
+} // namespace
+
+extern "C" {
+WL_EXPORT const void* wl_proxy_get_listener(struct wl_proxy* proxy) {
+	// Avoid null derefs of protocol objects in qtbase.
+	// https://qt-project.atlassian.net/browse/QTBUG-145022
+	if (!proxy) [[unlikely]] {
+		qCCritical(logDeref) << "wl_proxy_get_listener called with a null proxy!";
+		return nullptr;
+	}
+
+	return original_wl_proxy_get_listener(proxy);
+}
+}
+
+// NOLINTBEGIN (concurrency-mt-unsafe)
+void installWlProxySafeDeref() {
+	dlerror(); // clear old errors
+
+	original_wl_proxy_get_listener =
+	    reinterpret_cast<wl_proxy_get_listener_t>(dlsym(RTLD_NEXT, "wl_proxy_get_listener"));
+
+	if (auto* error = dlerror()) {
+		qCCritical(logDeref) << "Failed to find wl_proxy_get_listener for hooking:" << error;
+	} else {
+		qCInfo(logDeref) << "Installed wl_proxy_get_listener hook.";
+	}
+}
+// NOLINTEND