subcompositor: consider mapping on parent map

Fixes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3654

include/types/wlr_subcompositor.h

@@ -3,6 +3,7 @@
 
 #include <wlr/types/wlr_subcompositor.h>
 
+void subsurface_consider_map(struct wlr_subsurface *subsurface);
 void subsurface_handle_parent_commit(struct wlr_subsurface *subsurface);
 
 #endif

types/wlr_compositor.c

@@ -735,6 +735,15 @@ void wlr_surface_map(struct wlr_surface *surface) {
 	}
 	assert(wlr_surface_has_buffer(surface));
 	surface->mapped = true;
+
+	struct wlr_subsurface *subsurface;
+	wl_list_for_each(subsurface, &surface->current.subsurfaces_below, current.link) {
+		subsurface_consider_map(subsurface);
+	}
+	wl_list_for_each(subsurface, &surface->current.subsurfaces_above, current.link) {
+		subsurface_consider_map(subsurface);
+	}
+
 	wl_signal_emit_mutable(&surface->events.map, NULL);
 }
 

types/wlr_subcompositor.c

@@ -189,7 +189,7 @@ const struct wlr_surface_role subsurface_role;
  * - The subsurface has a buffer
  * - Its parent is mapped
  */
-static void subsurface_consider_map(struct wlr_subsurface *subsurface) {
+void subsurface_consider_map(struct wlr_subsurface *subsurface) {
 	if (subsurface->surface->mapped || !wlr_surface_has_buffer(subsurface->surface)) {
 		return;
 	}
@@ -329,7 +329,6 @@ void subsurface_handle_parent_commit(struct wlr_subsurface *subsurface) {
 		subsurface->added = true;
 		wl_signal_emit_mutable(&subsurface->parent->events.new_subsurface,
 			subsurface);
-		subsurface_consider_map(subsurface);
 	}
 }