{"ast_node_type":"variable","tokens":[{"end":76,"kind":"keyword","start":0,"text":"let"}]}
                    let value = self.mk_expr_err(start.to(expr.span), guar);
                    let guar = err.emit();
                    return Ok(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }));