如题，演示Rust 标记一个属性或函数为废弃的基本使用方法：
示例：

use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, Serialize, Deserialize, Default)]
pub struct GrpcOptions {
    pub addr: String,
    pub max_recv_message_size: u32,
    pub max_send_message_size: u32,
    pub hostname: String,
}

#[derive(Clone, Debug, Serialize, Deserialize, Default)]
#[serde(default)]
pub struct DatanodeOptions {
    pub node_id: Option<u64>,
    pub require_lease_before_startup: bool,
    pub init_regions_in_background: bool,
    #[deprecated(note = "use `grpc.hostname` instead")]
    pub rpc_hostname: Option<String>,
    pub grpc: GrpcOptions,
}

fn main() {
    let mut datanode = DatanodeOptions::default();
    datanode.grpc.hostname = "hostname".to_string();
    datanode.rpc_hostname = Some("dep_hostname".to_string());
    println!("{:?}", datanode);
}

最后输出如下所示：