ID: Add run-time flag indicating that ID is coming from copy-on-write

source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc

@@ -576,6 +576,7 @@ ID *deg_expand_copy_on_write_datablock(const Depsgraph *depsgraph,
 	if (newid != NULL) {
 		MEM_freeN(newid);
 	}
+	id_cow->tag |= LIB_TAG_COPY_ON_WRITE;
 	return id_cow;
 }
 

source/blender/depsgraph/intern/nodes/deg_node.cc

@@ -182,6 +182,7 @@ void IDDepsNode::init(const ID *id, const char *UNUSED(subdata))
 	id_cow = (ID *)BKE_libblock_alloc_notest(GS(id->name));
 	DEG_COW_PRINT("Create shallow copy for %s: id_orig=%p id_cow=%p\n",
 	              id_orig->name, id_orig, id_cow);
+	id_cow->tag |= LIB_TAG_COPY_ON_WRITE;
 #else
 	id_cow = id_orig;
 #endif

source/blender/makesdna/DNA_ID.h

@@ -363,6 +363,9 @@ enum {
 	LIB_TAG_ID_RECALC_DATA  = 1 << 13,
 	LIB_TAG_ANIM_NO_RECALC  = 1 << 14,
 	LIB_TAG_ID_RECALC_ALL   = (LIB_TAG_ID_RECALC | LIB_TAG_ID_RECALC_DATA),
+
+	/* The datablock is a copy-on-write version. */
+	LIB_TAG_COPY_ON_WRITE  = (1 << 15),
 };
 
 /* To filter ID types (filter_id) */