Fix crash when deleting last child in a tabbed or stacked container

There was no `current` child because the container was destroyed. This
makes it fall back to looking in the parent's current children list.

3 files changed, 39 insertions, 12 deletions

diff --git a/include/sway/input/seat.h b/include/sway/input/seat.h
index 1f7792ba..0e440701 100644
--- a/include/sway/input/seat.h
+++ b/include/sway/input/seat.h
@@ -119,6 +119,17 @@ struct sway_container *seat_get_active_child(struct sway_seat *seat,
                 struct sway_container *container);
 
 /**
+ * Return the immediate child of container which was most recently focused, with
+ * fallback to selecting the child in the parent's `current` (rendered) children
+ * list.
+ *
+ * This is useful for when a tabbed container and its children are destroyed but
+ * still being rendered, and we have to render an appropriate child.
+ */
+struct sway_container *seat_get_active_current_child(struct sway_seat *seat,
+                struct sway_container *container);
+
+/**
  * Iterate over the focus-inactive children of the container calling the
  * function on each.
  */
diff --git a/sway/desktop/output.c b/sway/desktop/output.c
index 9db95ef5..1ca48975 100644
--- a/sway/desktop/output.c
+++ b/sway/desktop/output.c
@@ -713,7 +713,7 @@ static void render_container_tabbed(struct sway_output *output,
         }
         struct sway_seat *seat = input_manager_current_seat(input_manager);
         struct sway_container *focus = seat_get_focus(seat);
-        struct sway_container *current = seat_get_active_child(seat, con);
+        struct sway_container *current = seat_get_active_current_child(seat, con);
         struct border_colors *current_colors = NULL;
         struct sway_container_state *pstate = &con->current;
 
@@ -756,11 +756,13 @@ static void render_container_tabbed(struct sway_output *output,
         }
 
         // Render surface and left/right/bottom borders
-        if (current->type == C_VIEW) {
-                render_view(output, damage, current, current_colors);
-        } else {
-                render_container(output, damage, current,
-                                parent_focused || current == focus);
+        if (current) {
+                if (current->type == C_VIEW) {
+                        render_view(output, damage, current, current_colors);
+                } else {
+                        render_container(output, damage, current,
+                                        parent_focused || current == focus);
+                }
         }
 }
 
@@ -775,7 +777,7 @@ static void render_container_stacked(struct sway_output *output,
         }
         struct sway_seat *seat = input_manager_current_seat(input_manager);
         struct sway_container *focus = seat_get_focus(seat);
-        struct sway_container *current = seat_get_active_child(seat, con);
+        struct sway_container *current = seat_get_active_current_child(seat, con);
         struct border_colors *current_colors = NULL;
         struct sway_container_state *pstate = &con->current;
 
@@ -812,11 +814,13 @@ static void render_container_stacked(struct sway_output *output,
         }
 
         // Render surface and left/right/bottom borders
-        if (current->type == C_VIEW) {
-                render_view(output, damage, current, current_colors);
-        } else {
-                render_container(output, damage, current,
-                                parent_focused || current == focus);
+        if (current) {
+                if (current->type == C_VIEW) {
+                        render_view(output, damage, current, current_colors);
+                } else {
+                        render_container(output, damage, current,
+                                        parent_focused || current == focus);
+                }
         }
 }
 
diff --git a/sway/input/seat.c b/sway/input/seat.c
index 1ea36466..436d18e2 100644
--- a/sway/input/seat.c
+++ b/sway/input/seat.c
@@ -829,6 +829,18 @@ struct sway_container *seat_get_active_child(struct sway_seat *seat,
         return NULL;
 }
 
+struct sway_container *seat_get_active_current_child(struct sway_seat *seat,
+                struct sway_container *container) {
+        struct sway_container *child = seat_get_active_child(seat, container);
+        if (child) {
+                return child;
+        }
+        if (container->current.children->length == 1) {
+                return container->current.children->items[0];
+        }
+        return NULL;
+}
+
 struct sway_container *seat_get_focus(struct sway_seat *seat) {
         if (!seat->has_focus) {
                 return NULL;