Assets: Disable snap-dragging for linking object assets

The location of a linked object isn't editable, or at least it will be reset
when reloading the file. So the drag & drop shouldn't even pretend like this
would work, so disable the snapping of the object and the bounding-box to show
the snapped object location while dragging.

source/blender/editors/object/object_add.c

@@ -3617,6 +3617,13 @@ static int object_transform_to_mouse_exec(bContext *C, wmOperator *op)
     BKE_report(op->reports, RPT_ERROR, "Object not found");
     return OPERATOR_CANCELLED;
   }
+
+  /* Don't transform a linked object. There's just nothing to do here in this case, so return
+   * #OPERATOR_FINISHED. */
+  if (ID_IS_LINKED(ob)) {
+    return OPERATOR_FINISHED;
+  }
+
   /* Ensure the locations are updated so snap reads the evaluated active location. */
   CTX_data_ensure_evaluated_depsgraph(C);
 

source/blender/editors/space_view3d/space_view3d.c

@@ -526,6 +526,12 @@ static void view3d_ob_drop_draw_activate(struct wmDropBox *drop, wmDrag *drag)
     return;
   }
 
+  /* Don't use the snap cursor when linking the object. Object transform isn't editable then and
+   * would be reset on reload. */
+  if (WM_drag_asset_will_import_linked(drag)) {
+    return;
+  }
+
   state = drop->draw_data = ED_view3d_cursor_snap_active();
   state->draw_plane = true;
 
@@ -552,8 +558,10 @@ static void view3d_ob_drop_draw_activate(struct wmDropBox *drop, wmDrag *drag)
 static void view3d_ob_drop_draw_deactivate(struct wmDropBox *drop, wmDrag *UNUSED(drag))
 {
   V3DSnapCursorState *state = drop->draw_data;
-  ED_view3d_cursor_snap_deactive(state);
-  drop->draw_data = NULL;
+  if (state) {
+    ED_view3d_cursor_snap_deactive(state);
+    drop->draw_data = NULL;
+  }
 }
 
 static bool view3d_ob_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
@@ -762,12 +770,14 @@ static void view3d_ob_drop_copy_external_asset(wmDrag *drag, wmDropBox *drop)
   DEG_id_tag_update(&scene->id, ID_RECALC_SELECT);
   ED_outliner_select_sync_from_object_tag(C);
 
-  V3DSnapCursorState *snap_state = ED_view3d_cursor_snap_state_get();
-  float obmat_final[4][4];
+  V3DSnapCursorState *snap_state = drop->draw_data;
+  if (snap_state) {
+    float obmat_final[4][4];
 
-  view3d_ob_drop_matrix_from_snap(snap_state, (Object *)id, obmat_final);
+    view3d_ob_drop_matrix_from_snap(snap_state, (Object *)id, obmat_final);
 
-  RNA_float_set_array(drop->ptr, "matrix", &obmat_final[0][0]);
+    RNA_float_set_array(drop->ptr, "matrix", &obmat_final[0][0]);
+  }
 }
 
 static void view3d_collection_drop_copy(wmDrag *drag, wmDropBox *drop)

source/blender/windowmanager/WM_api.h

@@ -752,6 +752,7 @@ ListBase *WM_dropboxmap_find(const char *idname, int spaceid, int regionid);
 
 /* ID drag and drop */
 ID *WM_drag_asset_id_import(wmDragAsset *asset_drag, int flag_extra);
+bool WM_drag_asset_will_import_linked(const wmDrag *drag);
 void WM_drag_add_local_ID(struct wmDrag *drag, struct ID *id, struct ID *from_parent);
 struct ID *WM_drag_get_local_ID(const struct wmDrag *drag, short idcode);
 struct ID *WM_drag_get_local_ID_from_event(const struct wmEvent *event, short idcode);

source/blender/windowmanager/intern/wm_dragdrop.c

@@ -577,6 +577,16 @@ ID *WM_drag_asset_id_import(wmDragAsset *asset_drag, const int flag_extra)
   return NULL;
 }
 
+bool WM_drag_asset_will_import_linked(const wmDrag *drag)
+{
+  if (drag->type != WM_DRAG_ASSET) {
+    return false;
+  }
+
+  const wmDragAsset *asset_drag = WM_drag_get_asset_data(drag, 0);
+  return asset_drag->import_type == FILE_ASSET_IMPORT_LINK;
+}
+
 /**
  * When dragging a local ID, return that. Otherwise, if dragging an asset-handle, link or append
  * that depending on what was chosen by the drag-box (currently append only in fact).