Initial implementation of local ID re-use when appending.

This commit adds to ID struct a new optional 'weak reference' to a
linked ID (in the form of a blend file library path and full ID name).

This can then be used on next append to try to find a matching local ID
instead of re-making the linked data local again.

Ref. T90545

NOTE: ID re-use will be disabled for regular append for the time being
(3.0 release), and only used for assets. Therefore, this commit should
not change anything user-wise.

Differential Revision: https://developer.blender.org/D12545

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/lib_id.c b/source/blender/blenkernel/intern/lib_id.c
index 60b6d7ad66d..18824e73ee5 100644
--- a/source/blender/blenkernel/intern/lib_id.c
+++ b/source/blender/blenkernel/intern/lib_id.c
@@ -1301,6 +1301,9 @@ void BKE_libblock_copy_ex(Main *bmain, const ID *id, ID **r_newid, const int ori
     new_id->properties = IDP_CopyProperty_ex(id->properties, copy_data_flag);
   }
 
+  /* This is never duplicated, only one existing ID should have a given weak ref to library/ID. */
+  new_id->library_weak_reference = NULL;
+
   if ((orig_flag & LIB_ID_COPY_NO_LIB_OVERRIDE) == 0) {
     if (ID_IS_OVERRIDE_LIBRARY_REAL(id)) {
       /* We do not want to copy existing override rules here, as they would break the proper
@@ -2440,6 +2443,10 @@ void BKE_id_blend_write(BlendWriter *writer, ID *id)
     BKE_asset_metadata_write(writer, id->asset_data);
   }
 
+  if (id->library_weak_reference != NULL) {
+    BLO_write_struct(writer, LibraryWeakReference, id->library_weak_reference);
+  }
+
   /* ID_WM's id->properties are considered runtime only, and never written in .blend file. */
   if (id->properties && !ELEM(GS(id->name), ID_WM)) {
     IDP_BlendWrite(writer, id->properties);