Fix T66944: Rigid Body Constraint in duplicated collection is not added to RigidBodyConstraints collection.

We only had a very limited, specific handling of that in collection
duplication code, but this has to be handled at a much more general
level in Object copy code itself, since it makes no sense to duplicate
rigidbody object data without adding new copy to relevant rigidbody
collections...

WARNING: This is a fairly risky rework of rigidbody handling logic
when copying an Object data-block. It is *NOT* considered safe enough
for 2.80 release.

I tried to take into account copy flags to not mess with other IDs
(collections) when we are copying outside of Main, and also not do deg
tags when this is forbidden, but risk of something going wrong here is
too high...

source/blender/blenkernel/BKE_collection.h

@@ -85,7 +85,7 @@ struct Scene *BKE_collection_master_scene_search(const struct Main *bmain,
 
 /* Collection Objects */
 
-bool BKE_collection_has_object(struct Collection *collection, struct Object *ob);
+bool BKE_collection_has_object(struct Collection *collection, const struct Object *ob);
 bool BKE_collection_has_object_recursive(struct Collection *collection, struct Object *ob);
 struct Collection *BKE_collection_object_find(struct Main *bmain,
                                               struct Scene *scene,

source/blender/blenkernel/BKE_rigidbody.h

@@ -44,8 +44,10 @@ void BKE_rigidbody_free_constraint(struct Object *ob);
 
 /* ...... */
 
-struct RigidBodyOb *BKE_rigidbody_copy_object(const struct Object *ob, const int flag);
-struct RigidBodyCon *BKE_rigidbody_copy_constraint(const struct Object *ob, const int flag);
+void BKE_rigidbody_object_copy(struct Main *bmain,
+                               struct Object *ob_dst,
+                               const struct Object *ob_src,
+                               const int flag);
 
 /* Callback format for performing operations on ID-pointers for rigidbody world. */
 typedef void (*RigidbodyWorldIDFunc)(struct RigidBodyWorld *rbw,

source/blender/blenkernel/intern/collection.c

@@ -287,16 +287,6 @@ static Collection *collection_duplicate_recursive(Main *bmain,
 
       collection_object_add(bmain, collection_new, ob_new, 0, true);
       collection_object_remove(bmain, collection_new, ob_old, false);
-
-      if (ob_new->rigidbody_object != NULL) {
-        BLI_assert(ob_old->rigidbody_object != NULL);
-        for (Scene *scene = bmain->scenes.first; scene != NULL; scene = scene->id.next) {
-          if (scene->rigidbody_world != NULL &&
-              BKE_collection_has_object(scene->rigidbody_world->group, ob_old)) {
-            collection_object_add(bmain, scene->rigidbody_world->group, ob_new, 0, true);
-          }
-        }
-      }
     }
   }
 
@@ -572,7 +562,7 @@ bool BKE_collection_object_cyclic_check(Main *bmain, Object *object, Collection
 
 /******************* Collection Object Membership *******************/
 
-bool BKE_collection_has_object(Collection *collection, Object *ob)
+bool BKE_collection_has_object(Collection *collection, const Object *ob)
 {
   if (ELEM(NULL, collection, ob)) {
     return false;

source/blender/blenkernel/intern/object.c

@@ -1417,8 +1417,7 @@ void BKE_object_copy_data(Main *bmain, Object *ob_dst, const Object *ob_src, con
     }
   }
   BKE_object_copy_softbody(ob_dst, ob_src, flag_subdata);
-  ob_dst->rigidbody_object = BKE_rigidbody_copy_object(ob_src, flag_subdata);
-  ob_dst->rigidbody_constraint = BKE_rigidbody_copy_constraint(ob_src, flag_subdata);
+  BKE_rigidbody_object_copy(bmain, ob_dst, ob_src, flag_subdata);
 
   BKE_object_copy_particlesystems(ob_dst, ob_src, flag_subdata);
 

source/blender/blenkernel/intern/rigidbody.c

@@ -34,6 +34,7 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_math.h"
+#include "BLI_listbase.h"
 
 #ifdef WITH_BULLET
 #  include "RBI_api.h"
@@ -228,7 +229,7 @@ void BKE_rigidbody_free_constraint(Object *ob)
  * be added to relevant groups later...
  */
 
-RigidBodyOb *BKE_rigidbody_copy_object(const Object *ob, const int flag)
+static RigidBodyOb *rigidbody_copy_object(const Object *ob, const int flag)
 {
   RigidBodyOb *rboN = NULL;
 
@@ -249,7 +250,7 @@ RigidBodyOb *BKE_rigidbody_copy_object(const Object *ob, const int flag)
   return rboN;
 }
 
-RigidBodyCon *BKE_rigidbody_copy_constraint(const Object *ob, const int UNUSED(flag))
+static RigidBodyCon *rigidbody_copy_constraint(const Object *ob, const int UNUSED(flag))
 {
   RigidBodyCon *rbcN = NULL;
 
@@ -268,6 +269,54 @@ RigidBodyCon *BKE_rigidbody_copy_constraint(const Object *ob, const int UNUSED(f
   return rbcN;
 }
 
+void BKE_rigidbody_object_copy(Main *bmain, Object *ob_dst, const Object *ob_src, const int flag)
+{
+  ob_dst->rigidbody_object = rigidbody_copy_object(ob_src, flag);
+  ob_dst->rigidbody_constraint = rigidbody_copy_constraint(ob_src, flag);
+
+  if (flag & LIB_ID_CREATE_NO_MAIN) {
+    return;
+  }
+
+  /* We have to ensure that duplicated object ends up in relevant rigidbody collections...
+   * Otherwise duplicating the RB data itself is meaningless. */
+  LISTBASE_FOREACH (Scene *, scene, &bmain->scenes) {
+    RigidBodyWorld *rigidbody_world = scene->rigidbody_world;
+
+    if (rigidbody_world != NULL) {
+      bool need_objects_update = false;
+      bool need_constraints_update = false;
+
+      if (ob_dst->rigidbody_object) {
+        if (BKE_collection_has_object(rigidbody_world->group, ob_src)) {
+          BKE_collection_object_add(bmain, rigidbody_world->group, ob_dst);
+          need_objects_update = true;
+        }
+      }
+      if (ob_dst->rigidbody_constraint) {
+        if (BKE_collection_has_object(rigidbody_world->constraints, ob_src)) {
+          BKE_collection_object_add(bmain, rigidbody_world->constraints, ob_dst);
+          need_constraints_update = true;
+        }
+      }
+
+      if ((flag & LIB_ID_CREATE_NO_DEG_TAG) == 0 &&
+          (need_objects_update || need_constraints_update)) {
+        BKE_rigidbody_cache_reset(rigidbody_world);
+
+        DEG_relations_tag_update(bmain);
+        if (need_objects_update) {
+          DEG_id_tag_update(&rigidbody_world->group->id, ID_RECALC_COPY_ON_WRITE);
+        }
+        if (need_constraints_update) {
+          DEG_id_tag_update(&rigidbody_world->constraints->id, ID_RECALC_COPY_ON_WRITE);
+        }
+        DEG_id_tag_update(&ob_dst->id, ID_RECALC_TRANSFORM);
+      }
+    }
+  }
+}
+
 /* ************************************** */
 /* Setup Utilities - Validate Sim Instances */
 
@@ -1983,13 +2032,8 @@ void BKE_rigidbody_do_simulation(Depsgraph *depsgraph, Scene *scene, float ctime
 #    pragma GCC diagnostic ignored "-Wunused-parameter"
 #  endif
 
-struct RigidBodyOb *BKE_rigidbody_copy_object(const Object *ob, const int flag)
+void BKE_rigidbody_object_copy(Main *bmain, Object *ob_dst, const Object *ob_src, const int flag)
 {
-  return NULL;
-}
-struct RigidBodyCon *BKE_rigidbody_copy_constraint(const Object *ob, const int flag)
-{
-  return NULL;
 }
 void BKE_rigidbody_validate_sim_world(Scene *scene, RigidBodyWorld *rbw, bool rebuild)
 {