{"ast_node_type":"variable","tokens":[{"end":62,"kind":"keyword","start":0,"text":"let"}]}
                let mut params = callable_sig.params().iter();
                    db.callable_item_signature(fid.into()).substitute(Interner, &substs);
                let self_param = body.self_param.and_then(|id| Some((id, params.next()?.clone())));