{"ast_node_type":"variable","tokens":[{"end":46,"kind":"keyword","start":0,"text":"let"}]}
        let param_env = tcx.param_env(def_id);
        let infcx = tcx.infer_ctxt().build(typing_mode);
        BorrowckInferCtxt { infcx, reg_var_to_origin: RefCell::new(Default::default()), param_env }