PyAPI: add bpy.types.BlendFile.temp_data for temporary library loading

This adds support for creating a `BlendFile` (internally called `Main`),
which is limited to a context.

Temporary data can now be created which can then use
`.libraries.load()` the same as with `bpy.data`.

To prevent errors caused by mixing the temporary ID's with data in
`bpy.data` they are tagged as temporary so they can't be assigned
to properties, however they can be passed as arguments to functions.

Reviewed By: mont29, sybren

Ref D10612

1 files changed, 6 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index 14f0fef5270..c708219cfe8 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -566,6 +566,12 @@ enum {
   /* RESET_AFTER_USE Used by undo system to tag unchanged IDs re-used from old Main (instead of
    * read from memfile). */
   LIB_TAG_UNDO_OLD_ID_REUSED = 1 << 19,
+
+  /* This ID is part of a temporary #Main which is expected to be freed in a short time-frame.
+   * Don't allow assigning this to non-temporary members (since it's likely to cause errors).
+   * When set #ID.session_uuid isn't initialized, since the data isn't part of the session. */
+  LIB_TAG_TEMP_MAIN = 1 << 20,
+
 };
 
 /* Tag given ID for an update in all the dependency graphs. */