{"ast_node_type":"other","tokens":[{"end":67,"kind":"keyword","start":0,"text":"shadow_arg.ty"}]}
                        shadow_arg.ty = P(assure_mut_ref(&arg.ty));
                        // We += into the shadow in reverse mode.
                        let old_name = if let PatKind::Ident(_, ident, _) = arg.pat.kind {