BLO: Functions for temporarily loading a single datablock

This introduces two functions to the blenloader module, here shown as
calls for brevity:

* `temp_lib_ctx = BLO_library_temp_load_id(real_main, blend_file_path, idcode, idname, reports);`
* Now the data in `temp_lib_ctx->temp_id` can be used (but ought not to
  be not assigned to non-temp datablocks).
* `BLO_library_temp_free(temp_lib_ctx);`

The first loads a datablock from a blend file, and returns it as part of
a `struct TempLibraryContext`. This struct contains the temp-loaded ID,
as well as enough information to correctly free everything again.

Differential Revision: https://developer.blender.org/D10736

1 files changed, 21 insertions, 0 deletions

diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 09f4c405613..d8c613ba900 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -18,6 +18,7 @@
  */
 #pragma once
 
+#include "BLI_listbase.h"
 #include "BLI_sys_types.h"
 
 /** \file
@@ -221,6 +222,26 @@ void BLO_library_link_end(struct Main *mainl,
 
 int BLO_library_link_copypaste(struct Main *mainl, BlendHandle *bh, const uint64_t id_types_mask);
 
+/**
+ * Struct for temporarily loading datablocks from a blend file.
+ */
+typedef struct TempLibraryContext {
+  struct Main *temp_main;
+  struct BlendHandle *blendhandle;
+  struct LibraryLink_Params liblink_params;
+  struct Library *lib;
+
+  /* The ID datablock that was loaded. Is NULL if loading failed. */
+  struct ID *temp_id;
+} TempLibraryContext;
+
+TempLibraryContext *BLO_library_temp_load_id(struct Main *real_main,
+                                             const char *blend_file_path,
+                                             const short idcode,
+                                             const char *idname,
+                                             struct ReportList *reports);
+void BLO_library_temp_free(TempLibraryContext *temp_lib_ctx);
+
 /** \} */
 
 void *BLO_library_read_struct(struct FileData *fd, struct BHead *bh, const char *blockname);