3 files changed, 66 insertions, 1 deletions

diff --git a/source/blender/editors/geometry/geometry_attributes.cc b/source/blender/editors/geometry/geometry_attributes.cc
index ed16b8a903a..814c2639169 100644
--- a/source/blender/editors/geometry/geometry_attributes.cc
+++ b/source/blender/editors/geometry/geometry_attributes.cc
@@ -33,6 +33,7 @@
 #include "UI_interface.h"
 #include "UI_resources.h"
 
+#include "ED_geometry.h"
 #include "ED_object.h"
 
 #include "geometry_intern.hh"
@@ -572,3 +573,38 @@ void GEOMETRY_OT_attribute_convert(wmOperatorType *ot)
 }
 
 }  // namespace blender::ed::geometry
+
+using blender::CPPType;
+using blender::GVArray;
+
+bool ED_geometry_attribute_convert(Mesh *mesh,
+                                   const char *layer_name,
+                                   CustomDataType old_type,
+                                   AttributeDomain old_domain,
+                                   CustomDataType new_type,
+                                   AttributeDomain new_domain)
+{
+  CustomDataLayer *layer = BKE_id_attribute_find(&mesh->id, layer_name, old_type, old_domain);
+  const std::string name = layer->name;
+
+  if (!layer) {
+    return false;
+  }
+
+  MeshComponent mesh_component;
+  mesh_component.replace(mesh, GeometryOwnershipType::Editable);
+  GVArray src_varray = mesh_component.attribute_get_for_read(name, new_domain, new_type);
+
+  const CPPType &cpp_type = src_varray.type();
+  void *new_data = MEM_malloc_arrayN(src_varray.size(), cpp_type.size(), __func__);
+  src_varray.materialize_to_uninitialized(new_data);
+  mesh_component.attribute_try_delete(name);
+  mesh_component.attribute_try_create(name, new_domain, new_type, AttributeInitMove(new_data));
+
+  int *active_index = BKE_id_attributes_active_index_p(&mesh->id);
+  if (*active_index > 0) {
+    *active_index -= 1;
+  }
+
+  return true;
+}
diff --git a/source/blender/editors/include/ED_geometry.h b/source/blender/editors/include/ED_geometry.h
index 74ff968828c..46e6904523a 100644
--- a/source/blender/editors/include/ED_geometry.h
+++ b/source/blender/editors/include/ED_geometry.h
@@ -7,12 +7,22 @@
 
 #pragma once
 
+#include "BKE_attribute.h"
+#include "DNA_customdata_types.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-void ED_operatortypes_geometry(void);
+struct Mesh;
 
+void ED_operatortypes_geometry(void);
+bool ED_geometry_attribute_convert(struct Mesh *mesh,
+                                   const char *layer_name,
+                                   CustomDataType old_type,
+                                   AttributeDomain old_domain,
+                                   CustomDataType new_type,
+                                   AttributeDomain new_domain);
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/blender/editors/sculpt_paint/sculpt_undo.c b/source/blender/editors/sculpt_paint/sculpt_undo.c
index 1fee20444e7..4588930bdee 100644
--- a/source/blender/editors/sculpt_paint/sculpt_undo.c
+++ b/source/blender/editors/sculpt_paint/sculpt_undo.c
@@ -50,6 +50,7 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
+#include "ED_geometry.h"
 #include "ED_object.h"
 #include "ED_sculpt.h"
 #include "ED_undo.h"
@@ -1565,6 +1566,24 @@ static void sculpt_undo_set_active_layer(struct bContext *C, SculptAttrRef *attr
   CustomDataLayer *layer;
   layer = BKE_id_attribute_find(&me->id, attr->name, attr->type, attr->domain);
 
+  /* Temporary fix for T97408. This is a fundamental
+   * bug in the undo stack; the operator code needs to push
+   * an extra undo step before running an operator if a
+   * non-memfile undo system is active.
+   *
+   * For now, detect if the layer does exist but with a different
+   * domain and just unconvert it.
+   */
+  if (!layer) {
+    layer = BKE_id_attribute_search(&me->id, attr->name, CD_MASK_PROP_ALL, ATTR_DOMAIN_MASK_ALL);
+    AttributeDomain domain = layer ? BKE_id_attribute_domain(&me->id, layer) : ATTR_DOMAIN_NUM;
+
+    if (layer && ED_geometry_attribute_convert(
+                     me, attr->name, layer->type, domain, attr->type, attr->domain)) {
+      layer = BKE_id_attribute_find(&me->id, attr->name, attr->type, attr->domain);
+    }
+  }
+
   if (!layer) {
     /* Memfile undo killed the layer; re-create it. */
     CustomData *cdata = attr->domain == ATTR_DOMAIN_POINT ? &me->vdata : &me->ldata;