Fix #128744: Reverting single essentials brush reverts all

Code used library reloading which would reload all data-blocks from a
data-block library. Since the essentials brushes are stored in a single
.blend file (one per mode), they would all be reset. In general this
violates the design where multiple brushes in a single .blend file
should be usable just fine. (A single file per brush is only necessary
to allow saving edits to that file without opening it.)

Instead of library reloading, delete the brush from the current file and
re-link it.

The link/append API should probably get support for reloading a single
data-block (and optionally its dependencies) but for now this is not
supported yet.

Pull Request: https://projects.blender.org/blender/blender/pulls/129866

source/blender/blenkernel/BKE_asset_edit.hh

@@ -60,7 +60,12 @@ std::optional<std::string> asset_edit_id_save_as(Main &global_main,
                                                  ReportList &reports);
 
 bool asset_edit_id_save(Main &global_main, const ID &id, ReportList &reports);
-bool asset_edit_id_revert(Main &global_main, ID &id, ReportList &reports);
+/**
+ * Relink the asset from the library. This causes the ID to be re-allocated, so its address
+ * changes. Even in case of failure to reload the asset, \a id will be deleted.
+ * \return the new address of the reloaded \a id.
+ */
+ID *asset_edit_id_revert(Main &global_main, ID &id, ReportList &reports);
 bool asset_edit_id_delete(Main &global_main, ID &id, ReportList &reports);
 
 }  // namespace blender::bke

source/blender/blenkernel/intern/asset_edit.cc

@@ -47,7 +47,8 @@ namespace blender::bke {
 static ID *asset_link_id(Main &global_main,
                          const ID_Type id_type,
                          const char *filepath,
-                         const char *asset_name)
+                         const char *asset_name,
+                         ReportList *reports = nullptr)
 {
   /* Load asset from asset library. */
   LibraryLink_Params lapp_params{};
@@ -63,7 +64,7 @@ static ID *asset_link_id(Main &global_main,
 
   BKE_blendfile_link_append_context_init_done(lapp_context);
 
-  BKE_blendfile_link(lapp_context, nullptr);
+  BKE_blendfile_link(lapp_context, reports);
 
   BKE_blendfile_link_append_context_finalize(lapp_context);
 
@@ -248,24 +249,23 @@ static bool asset_write_in_library(Main &bmain,
   return success;
 }
 
-static void asset_reload(Main &global_main, Library *lib, ReportList &reports)
+static ID *asset_reload(Main &global_main, ID &id, ReportList *reports)
 {
-  /* Fill fresh main database with same datablock as before. */
-  LibraryLink_Params lapp_params{};
-  lapp_params.bmain = &global_main;
-  BlendfileLinkAppendContext *lapp_context = BKE_blendfile_link_append_context_new(&lapp_params);
-  BKE_blendfile_link_append_context_flag_set(
-      lapp_context, BLO_LIBLINK_FORCE_INDIRECT | BLO_LIBLINK_USE_PLACEHOLDERS, true);
+  BLI_assert(ID_IS_LINKED(&id));
 
-  BKE_blendfile_link_append_context_library_add(lapp_context, lib->runtime.filepath_abs, nullptr);
-  BKE_blendfile_library_relocate(lapp_context, &reports, lib, true);
-  BKE_blendfile_link_append_context_free(lapp_context);
+  const std::string name = BKE_id_name(id);
+  const std::string filepath = id.lib->runtime.filepath_abs;
+  const ID_Type id_type = GS(id.name);
 
-  /* Clear temporary tag from relocation. */
-  BKE_main_id_tag_all(&global_main, ID_TAG_PRE_EXISTING, false);
+  /* TODO: There's no API to reload a single data block (and its dependencies) yet. For now
+   * deleting the brush and re-linking it is the best way to get reloading to work. */
+  BKE_id_delete(&global_main, &id);
+  ID *new_id = asset_link_id(global_main, id_type, filepath.c_str(), name.c_str(), reports);
 
   /* Recreate dependency graph to include new IDs. */
   DEG_relations_tag_update(&global_main);
+
+  return new_id;
 }
 
 static AssetWeakReference asset_weak_reference_for_user_library(
@@ -357,17 +357,13 @@ bool asset_edit_id_save(Main &global_main, const ID &id, ReportList &reports)
   return true;
 }
 
-bool asset_edit_id_revert(Main &global_main, ID &id, ReportList &reports)
+ID *asset_edit_id_revert(Main &global_main, ID &id, ReportList &reports)
 {
   if (!asset_edit_id_is_editable(id)) {
-    return false;
+    return nullptr;
   }
 
-  /* Reload entire main, including texture dependencies. This relies on there
-   * being only a single asset per blend file. */
-  asset_reload(global_main, id.lib, reports);
-
-  return true;
+  return asset_reload(global_main, id, &reports);
 }
 
 bool asset_edit_id_delete(Main &global_main, ID &id, ReportList &reports)

source/blender/editors/sculpt_paint/brush_asset_ops.cc

@@ -788,7 +788,15 @@ static int brush_asset_revert_exec(bContext *C, wmOperator *op)
   Paint *paint = BKE_paint_get_active_from_context(C);
   Brush *brush = BKE_paint_brush(paint);
 
-  bke::asset_edit_id_revert(*bmain, brush->id, *op->reports);
+  if (ID *reverted_id = bke::asset_edit_id_revert(*bmain, brush->id, *op->reports)) {
+    BLI_assert(GS(reverted_id->name) == ID_BR);
+    BKE_paint_brush_set(paint, reinterpret_cast<Brush *>(reverted_id));
+  }
+  else {
+    /* bke::asset_edit_id_revert() deleted the brush for sure, even on failure. Fallback to the
+     * default. */
+    BKE_paint_brush_set_default(bmain, paint);
+  }
 
   WM_main_add_notifier(NC_BRUSH | NA_EDITED, nullptr);
   WM_main_add_notifier(NC_TEXTURE | ND_NODES, nullptr);