libweston: Add view unmap listener to pointer constraints

Since the logic of pointer constraints assumes a valid view throughout, add a
signal to disable constraints when its current view is unmapped by Weston.

The assumption that a previously unmapped view is valid already leads to the
constraints code crashing. This can happen when attaching a NULL buffer to the
surface and commiting, which effectively unmaps the view with the side effect of
clearing the surface's input region, which is then assumed valid inside
maybe_warp_confined_pointer().

Fixes: #721

Signed-off-by: Sergio Gómez <sergio.g.delreal@gmail.com>
(cherry picked from commit e3079393c400e3dc6498234d1d092f3072fa8b44)

include/libweston/libweston.h

@@ -1452,6 +1452,7 @@ struct weston_view {
 	struct weston_surface *surface;
 	struct wl_list surface_link;
 	struct wl_signal destroy_signal;
+	struct wl_signal unmap_signal;
 
 	/* struct weston_paint_node::view_link */
 	struct wl_list paint_node_list;
@@ -1605,6 +1606,7 @@ struct weston_pointer_constraint {
 	bool hint_is_pending;
 
 	struct wl_listener pointer_destroy_listener;
+	struct wl_listener view_unmap_listener;
 	struct wl_listener surface_commit_listener;
 	struct wl_listener surface_activate_listener;
 };

libweston/compositor.c

@@ -396,6 +396,7 @@ weston_view_create(struct weston_surface *surface)
 	wl_list_insert(&surface->views, &view->surface_link);
 
 	wl_signal_init(&view->destroy_signal);
+	wl_signal_init(&view->unmap_signal);
 	wl_list_init(&view->link);
 	wl_list_init(&view->layer_link.link);
 	wl_list_init(&view->paint_node_list);
@@ -2248,9 +2249,7 @@ weston_view_unmap(struct weston_view *view)
 	view->output_mask = 0;
 	weston_surface_assign_output(view->surface);
 
-	if (weston_surface_is_mapped(view->surface))
+	if (!weston_surface_is_mapped(view->surface)) {
-		return;
-
 		wl_list_for_each(seat, &view->surface->compositor->seat_list, link) {
 			struct weston_touch *touch = weston_seat_get_touch(seat);
 			struct weston_pointer *pointer = weston_seat_get_pointer(seat);
@@ -2264,6 +2263,8 @@ weston_view_unmap(struct weston_view *view)
 			if (touch && touch->focus == view)
 				weston_touch_set_focus(touch, NULL);
 		}
+	}
+	weston_signal_emit_mutable(&view->unmap_signal, view);
 }
 
 WL_EXPORT void

libweston/input.c

@@ -3713,6 +3713,8 @@ enable_pointer_constraint(struct weston_pointer_constraint *constraint,
 	constraint->view = view;
 	pointer_constraint_notify_activated(constraint);
 	weston_pointer_start_grab(constraint->pointer, &constraint->grab);
+	wl_signal_add(&constraint->view->unmap_signal,
+		      &constraint->view_unmap_listener);
 }
 
 static bool
@@ -3727,6 +3729,8 @@ weston_pointer_constraint_disable(struct weston_pointer_constraint *constraint)
 	constraint->view = NULL;
 	pointer_constraint_notify_deactivated(constraint);
 	weston_pointer_end_grab(constraint->grab.pointer);
+	wl_list_remove(&constraint->view_unmap_listener.link);
+	wl_list_init(&constraint->view_unmap_listener.link);
 }
 
 void
@@ -3931,6 +3935,16 @@ pointer_constraint_pointer_destroyed(struct wl_listener *listener, void *data)
 	weston_pointer_constraint_destroy(constraint);
 }
 
+static void
+pointer_constraint_view_unmapped(struct wl_listener *listener, void *data)
+{
+        struct weston_pointer_constraint *constraint =
+                container_of(listener, struct weston_pointer_constraint,
+                             view_unmap_listener);
+
+        disable_pointer_constraint(constraint);
+}
+
 static void
 pointer_constraint_surface_committed(struct wl_listener *listener, void *data)
 {
@@ -3992,6 +4006,8 @@ weston_pointer_constraint_create(struct weston_surface *surface,
 
 	constraint->surface_activate_listener.notify =
 		pointer_constraint_surface_activate;
+	constraint->view_unmap_listener.notify =
+		pointer_constraint_view_unmapped;
 	constraint->surface_commit_listener.notify =
 		pointer_constraint_surface_committed;
 	constraint->pointer_destroy_listener.notify =