LibOverride: Add initial System Override flag.

This merely adds the flag, exposes it in RMA, and uses it in some of the
most common 'is editable' checks (RNA, `BASE_EDITABLE` macro...).

Next step: do_version and defining systemoverrides at creation.

Ref: {T95707}.

1 files changed, 19 insertions, 5 deletions

diff --git a/source/blender/makesrna/intern/rna_access.c b/source/blender/makesrna/intern/rna_access.c
index 67fa29adb47..5690d864a75 100644
--- a/source/blender/makesrna/intern/rna_access.c
+++ b/source/blender/makesrna/intern/rna_access.c
@@ -32,8 +32,10 @@
 #include "BKE_collection.h"
 #include "BKE_context.h"
 #include "BKE_fcurve.h"
+#include "BKE_global.h"
 #include "BKE_idprop.h"
 #include "BKE_idtype.h"
+#include "BKE_lib_override.h"
 #include "BKE_main.h"
 #include "BKE_node.h"
 #include "BKE_report.h"
@@ -1930,17 +1932,29 @@ static bool rna_property_editable_do(PointerRNA *ptr,
 
   /* Handle linked or liboverride ID cases. */
   const bool is_linked_prop_exception = (prop->flag & PROP_LIB_EXCEPTION) != 0;
-  if (ID_IS_LINKED(id) && !is_linked_prop_exception) {
+  if (ID_IS_LINKED(id)) {
+    if (is_linked_prop_exception) {
+      return true;
+    }
     if (r_info != NULL && (*r_info)[0] == '\0') {
       *r_info = N_("Can't edit this property from a linked data-block");
     }
     return false;
   }
-  if (ID_IS_OVERRIDE_LIBRARY(id) && !RNA_property_overridable_get(ptr, prop_orig)) {
-    if (r_info != NULL && (*r_info)[0] == '\0') {
-      *r_info = N_("Can't edit this property from an override data-block");
+  if (ID_IS_OVERRIDE_LIBRARY(id)) {
+    const bool is_liboverride_system = BKE_lib_override_library_is_system_defined(G_MAIN, id);
+    if (!RNA_property_overridable_get(ptr, prop_orig)) {
+      if (r_info != NULL && (*r_info)[0] == '\0') {
+        *r_info = N_("Can't edit this property from an override data-block");
+      }
+      return false;
+    }
+    if (is_liboverride_system && !is_linked_prop_exception) {
+      if (r_info != NULL && (*r_info)[0] == '\0') {
+        *r_info = N_("Can't edit this property from a system override data-block");
+      }
+      return false;
     }
-    return false;
   }
 
   /* At this point, property is owned by a local ID and therefore fully editable. */