Fix T100394: Regression: Duplicating a modifier causes a crash

Need to update relations when modifiers are added or removed
since those create nodes in the dependency graph.

Added an assert statement to point at possible culprit so
that issues can be fixed more quickly.

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/editors/object/object_modifier.cc b/source/blender/editors/object/object_modifier.cc
index e7cfcf48fd3..010a01f9d30 100644
--- a/source/blender/editors/object/object_modifier.cc
+++ b/source/blender/editors/object/object_modifier.cc
@@ -486,6 +486,9 @@ bool ED_object_modifier_move_to_index(ReportList *reports,
     }
   }
 
+  /* NOTE: Dependency graph only uses modifier nodes for visibility updates, and exact order of
+   * modifier nodes in the graph does not matter. */
+
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
   WM_main_add_notifier(NC_OBJECT | ND_MODIFIER, ob);
 
@@ -1668,6 +1671,7 @@ static int modifier_copy_exec(bContext *C, wmOperator *op)
   }
 
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
+  DEG_relations_tag_update(bmain);
   WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, ob);
 
   return OPERATOR_FINISHED;