Make `BKE_collection_duplicate able to handle master collections.

Those are then assumed already duplicated, and not touched. However, all
of ther objects and sub-collections can still be processed as with any
other regular collection...

1 files changed, 10 insertions, 9 deletions

diff --git a/source/blender/blenkernel/intern/collection.c b/source/blender/blenkernel/intern/collection.c
index 1388146eeb7..675e86b1584 100644
--- a/source/blender/blenkernel/intern/collection.c
+++ b/source/blender/blenkernel/intern/collection.c
@@ -314,9 +314,17 @@ static Collection *collection_duplicate_recursive(Main *bmain,
   Collection *collection_new;
   bool do_full_process = false;
   const int object_dupflag = (do_obdata) ? U.dupflag : 0;
+  const bool is_collection_master = (collection_old->flag & COLLECTION_IS_MASTER) != 0;
   const bool is_collection_liboverride = ID_IS_OVERRIDE_LIBRARY(collection_old);
 
-  if (!do_hierarchy || collection_old->id.newid == NULL) {
+  if (is_collection_master) {
+    /* We never duplicate master collections here, but we can still deep-copy their objects and
+     * collections. */
+    BLI_assert(parent == NULL);
+    collection_new = collection_old;
+    do_full_process = true;
+  }
+  else if (!do_hierarchy || collection_old->id.newid == NULL) {
     BKE_id_copy(bmain, &collection_old->id, (ID **)&collection_new);
 
     /* Copying add one user by default, need to get rid of that one. */
@@ -378,7 +386,7 @@ static Collection *collection_duplicate_recursive(Main *bmain,
 
   /* We can loop on collection_old's children,
    * that list is currently identical the collection_new' children, and won't be changed here. */
-  LISTBASE_FOREACH (CollectionChild *, child, &collection_old->children) {
+  LISTBASE_FOREACH_MUTABLE (CollectionChild *, child, &collection_old->children) {
     Collection *child_collection_old = child->collection;
 
     collection_duplicate_recursive(
@@ -422,13 +430,6 @@ Collection *BKE_collection_duplicate(Main *bmain,
                                      const bool do_objects,
                                      const bool do_obdata)
 {
-  /* It's not allowed to copy the master collection. */
-  BLI_assert((collection->id.flag & LIB_EMBEDDED_DATA) == 0);
-  BLI_assert((collection->flag & COLLECTION_IS_MASTER) == 0);
-  if (collection->flag & COLLECTION_IS_MASTER) {
-    return NULL;
-  }
-
   if (do_hierarchy) {
     BKE_main_id_tag_all(bmain, LIB_TAG_NEW, false);
     BKE_main_id_clear_newpoins(bmain);