Function mk_query_stack_frame_extra 

fn mk_query_stack_frame_extra<'tcx, Cache>(
    (tcx, vtable, key): (TyCtxt<'tcx>, &'tcx QueryVTable<'tcx, Cache>, Cache::Key),
) -> QueryStackFrameExtra
where
    Cache: QueryCache,
    Cache::Key: Key,

The deferred part of a deferred query stack frame.