scene/subsurface_tree: fix handling subsurface destruction

This commit renames map/unmap listeners to clarify that they handle
subsurface events, and ensures the node is always destroyed before
the subsurface.

Without this patch, wl_list_remove() would operate on listener links in
already freed memory. glibc is usually lenient to bugs like this, but
musl isn't.

types/scene/subsurface_tree.c

@@ -13,15 +13,20 @@ struct wlr_scene_subsurface_tree {
 	struct wlr_surface *surface;
 	struct wlr_scene_surface *scene_surface;
 
-	struct wlr_scene_subsurface_tree *parent; // NULL for the top-level surface
-	struct wlr_addon surface_addon; // only set if there's a parent
-
 	struct wl_listener tree_destroy;
 	struct wl_listener surface_destroy;
 	struct wl_listener surface_commit;
-	struct wl_listener surface_map;
-	struct wl_listener surface_unmap;
 	struct wl_listener surface_new_subsurface;
+
+	struct wlr_scene_subsurface_tree *parent; // NULL for the top-level surface
+
+	// Only valid if the surface is a sub-surface
+
+	struct wlr_addon surface_addon;
+
+	struct wl_listener subsurface_destroy;
+	struct wl_listener subsurface_map;
+	struct wl_listener subsurface_unmap;
 };
 
 static void subsurface_tree_handle_tree_destroy(struct wl_listener *listener,
@@ -31,23 +36,17 @@ static void subsurface_tree_handle_tree_destroy(struct wl_listener *listener,
 	// tree and scene_surface will be cleaned up by scene_node_finish
 	if (subsurface_tree->parent) {
 		wlr_addon_finish(&subsurface_tree->surface_addon);
+		wl_list_remove(&subsurface_tree->subsurface_destroy.link);
+		wl_list_remove(&subsurface_tree->subsurface_map.link);
+		wl_list_remove(&subsurface_tree->subsurface_unmap.link);
 	}
 	wl_list_remove(&subsurface_tree->tree_destroy.link);
 	wl_list_remove(&subsurface_tree->surface_destroy.link);
 	wl_list_remove(&subsurface_tree->surface_commit.link);
-	wl_list_remove(&subsurface_tree->surface_map.link);
-	wl_list_remove(&subsurface_tree->surface_unmap.link);
 	wl_list_remove(&subsurface_tree->surface_new_subsurface.link);
 	free(subsurface_tree);
 }
 
-static void subsurface_tree_handle_surface_destroy(struct wl_listener *listener,
-		void *data) {
-	struct wlr_scene_subsurface_tree *subsurface_tree =
-		wl_container_of(listener, subsurface_tree, surface_destroy);
-	wlr_scene_node_destroy(&subsurface_tree->tree->node);
-}
-
 static const struct wlr_addon_interface subsurface_tree_addon_impl;
 
 static struct wlr_scene_subsurface_tree *subsurface_tree_from_subsurface(
@@ -97,6 +96,13 @@ static void subsurface_tree_reconfigure(
 	}
 }
 
+static void subsurface_tree_handle_surface_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene_subsurface_tree *subsurface_tree =
+		wl_container_of(listener, subsurface_tree, surface_destroy);
+	wlr_scene_node_destroy(&subsurface_tree->tree->node);
+}
+
 static void subsurface_tree_handle_surface_commit(struct wl_listener *listener,
 		void *data) {
 	struct wlr_scene_subsurface_tree *subsurface_tree =
@@ -106,18 +112,25 @@ static void subsurface_tree_handle_surface_commit(struct wl_listener *listener,
 	subsurface_tree_reconfigure(subsurface_tree);
 }
 
-static void subsurface_tree_handle_surface_map(struct wl_listener *listener,
+static void subsurface_tree_handle_subsurface_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_scene_subsurface_tree *subsurface_tree =
-		wl_container_of(listener, subsurface_tree, surface_map);
+		wl_container_of(listener, subsurface_tree, subsurface_destroy);
+	wlr_scene_node_destroy(&subsurface_tree->tree->node);
+}
+
+static void subsurface_tree_handle_subsurface_map(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene_subsurface_tree *subsurface_tree =
+		wl_container_of(listener, subsurface_tree, subsurface_map);
 
 	wlr_scene_node_set_enabled(&subsurface_tree->tree->node, true);
 }
 
-static void subsurface_tree_handle_surface_unmap(struct wl_listener *listener,
+static void subsurface_tree_handle_subsurface_unmap(struct wl_listener *listener,
 		void *data) {
 	struct wlr_scene_subsurface_tree *subsurface_tree =
-		wl_container_of(listener, subsurface_tree, surface_unmap);
+		wl_container_of(listener, subsurface_tree, subsurface_unmap);
 
 	wlr_scene_node_set_enabled(&subsurface_tree->tree->node, false);
 }
@@ -151,8 +164,14 @@ static bool subsurface_tree_create_subsurface(
 	wlr_addon_init(&child->surface_addon, &subsurface->surface->addons,
 		parent, &subsurface_tree_addon_impl);
 
-	wl_signal_add(&subsurface->events.map, &child->surface_map);
+	child->subsurface_destroy.notify = subsurface_tree_handle_subsurface_destroy;
-	wl_signal_add(&subsurface->events.unmap, &child->surface_unmap);
+	wl_signal_add(&subsurface->events.destroy, &child->subsurface_destroy);
+
+	child->subsurface_map.notify = subsurface_tree_handle_subsurface_map;
+	wl_signal_add(&subsurface->events.map, &child->subsurface_map);
+
+	child->subsurface_unmap.notify = subsurface_tree_handle_subsurface_unmap;
+	wl_signal_add(&subsurface->events.unmap, &child->subsurface_unmap);
 
 	return true;
 }
@@ -214,12 +233,6 @@ static struct wlr_scene_subsurface_tree *scene_surface_tree_create(
 	subsurface_tree->surface_commit.notify = subsurface_tree_handle_surface_commit;
 	wl_signal_add(&surface->events.commit, &subsurface_tree->surface_commit);
 
-	subsurface_tree->surface_map.notify = subsurface_tree_handle_surface_map;
-	wl_list_init(&subsurface_tree->surface_map.link);
-
-	subsurface_tree->surface_unmap.notify = subsurface_tree_handle_surface_unmap;
-	wl_list_init(&subsurface_tree->surface_unmap.link);
-
 	subsurface_tree->surface_new_subsurface.notify =
 		subsurface_tree_handle_surface_new_subsurface;
 	wl_signal_add(&surface->events.new_subsurface,