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, 13 insertions, 0 deletions

diff --git a/source/blender/python/intern/bpy_rna.c b/source/blender/python/intern/bpy_rna.c
index ecaa5791e38..7a43c9cb997 100644
--- a/source/blender/python/intern/bpy_rna.c
+++ b/source/blender/python/intern/bpy_rna.c
@@ -2061,6 +2061,19 @@ static int pyrna_py_to_prop(
               Py_XDECREF(value_new);
               return -1;
             }
+
+            if (value_owner_id->tag & LIB_TAG_TEMP_MAIN) {
+              /* Allow passing temporary ID's to functions, but not attribute assignment. */
+              if (ptr->type != &RNA_Function) {
+                PyErr_Format(PyExc_TypeError,
+                             "%.200s %.200s.%.200s ID type assignment is temporary, can't assign",
+                             error_prefix,
+                             RNA_struct_identifier(ptr->type),
+                             RNA_property_identifier(prop));
+                Py_XDECREF(value_new);
+                return -1;
+              }
+            }
           }
         }