Assets: Abstraction for temporary loading of asset data-blocks

This is an editor-level abstraction for the `BLO_library_temp_xxx()`
API for temporary loading of data-blocks from another Blend file. It
abstracts away the asset specific code, like asset file-path handling
and local asset data-block handling.

Main use-case for this is applying assets as presets that are based on
data-blocks, like poses. Such preset assets are an important part of the
asset system design, so such an abstraction will likely find more usage
in the future.

source/blender/editors/asset/CMakeLists.txt

@@ -33,6 +33,7 @@ set(SRC
   asset_edit.cc
   asset_list.cc
   asset_ops.cc
+  asset_temp_id_consumer.cc
 )
 
 set(LIB

source/blender/editors/asset/asset_temp_id_consumer.cc

@@ -0,0 +1,113 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup edasset
+ *
+ * API for temporary loading of asset IDs.
+ * Uses the `BLO_library_temp_xxx()` API internally.
+ */
+
+#include "DNA_asset_types.h"
+#include "DNA_space_types.h"
+
+#include "BKE_report.h"
+
+#include "BLI_utility_mixins.hh"
+
+#include "BLO_readfile.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "ED_asset.h"
+
+using namespace blender;
+
+class AssetTemporaryIDConsumer : NonCopyable, NonMovable {
+  const AssetHandle &handle_;
+  TempLibraryContext *temp_lib_context_ = nullptr;
+
+ public:
+  AssetTemporaryIDConsumer(const AssetHandle &handle) : handle_(handle)
+  {
+  }
+  ~AssetTemporaryIDConsumer()
+  {
+    if (temp_lib_context_) {
+      BLO_library_temp_free(temp_lib_context_);
+    }
+  }
+
+  ID *get_local_id()
+  {
+    return ED_assetlist_asset_local_id_get(&handle_);
+  }
+
+  ID *import_id(const bContext *C,
+                const AssetLibraryReference &asset_library,
+                ID_Type id_type,
+                Main &bmain,
+                ReportList &reports)
+  {
+    const char *asset_name = ED_asset_handle_get_name(&handle_);
+    char blend_file_path[FILE_MAX_LIBEXTRA];
+    ED_asset_handle_get_full_library_path(C, &asset_library, &handle_, blend_file_path);
+
+    temp_lib_context_ = BLO_library_temp_load_id(
+        &bmain, blend_file_path, id_type, asset_name, &reports);
+
+    if (temp_lib_context_ == nullptr || temp_lib_context_->temp_id == nullptr) {
+      BKE_reportf(&reports, RPT_ERROR, "Unable to load %s from %s", asset_name, blend_file_path);
+      return nullptr;
+    }
+
+    BLI_assert(GS(temp_lib_context_->temp_id->name) == id_type);
+    return temp_lib_context_->temp_id;
+  }
+};
+
+AssetTempIDConsumer *ED_asset_temp_id_consumer_create(const AssetHandle *handle)
+{
+  if (!handle) {
+    return nullptr;
+  }
+  BLI_assert(handle->file_data->asset_data != nullptr);
+  return reinterpret_cast<AssetTempIDConsumer *>(
+      OBJECT_GUARDED_NEW(AssetTemporaryIDConsumer, *handle));
+}
+
+void ED_asset_temp_id_consumer_free(AssetTempIDConsumer **consumer)
+{
+  OBJECT_GUARDED_SAFE_DELETE(*consumer, AssetTemporaryIDConsumer);
+}
+
+ID *ED_asset_temp_id_consumer_ensure_local_id(AssetTempIDConsumer *consumer_,
+                                              const bContext *C,
+                                              const AssetLibraryReference *asset_library,
+                                              ID_Type id_type,
+                                              Main *bmain,
+                                              ReportList *reports)
+{
+  if (!(consumer_ && asset_library && bmain && reports)) {
+    return nullptr;
+  }
+  AssetTemporaryIDConsumer *consumer = reinterpret_cast<AssetTemporaryIDConsumer *>(consumer_);
+
+  if (ID *local_id = consumer->get_local_id()) {
+    return local_id;
+  }
+  return consumer->import_id(C, *asset_library, id_type, *bmain, *reports);
+}

source/blender/editors/include/ED_asset.h

@@ -33,6 +33,8 @@ struct Main;
 struct ReportList;
 struct wmNotifier;
 
+typedef struct AssetTempIDConsumer AssetTempIDConsumer;
+
 bool ED_asset_mark_id(const struct bContext *C, struct ID *id);
 bool ED_asset_clear_id(struct ID *id);
 
@@ -47,6 +49,15 @@ void ED_asset_handle_get_full_library_path(const struct bContext *C,
                                            const AssetHandle *asset,
                                            char r_full_lib_path[]);
 
+AssetTempIDConsumer *ED_asset_temp_id_consumer_create(const AssetHandle *handle);
+void ED_asset_temp_id_consumer_free(AssetTempIDConsumer **consumer);
+struct ID *ED_asset_temp_id_consumer_ensure_local_id(AssetTempIDConsumer *consumer,
+                                                     const struct bContext *C,
+                                                     const AssetLibraryReference *asset_library,
+                                                     ID_Type id_type,
+                                                     struct Main *bmain,
+                                                     struct ReportList *reports);
+
 void ED_assetlist_storage_fetch(const struct AssetLibraryReference *library_reference,
                                 const struct AssetFilterSettings *filter_settings,
                                 const struct bContext *C);