如何使用clap-derive在Rust程序的--help界面末尾添加自定义帮助消息？

当然可以实现，你只需要借助Clap-derive中#[command]属性的after_help参数，就能在所有参数标志描述之后、帮助界面的末尾插入自定义文本。

修改你的示例代码如下：

use clap::Parser;
use std::path::PathBuf;

#[derive(Parser, Debug, Default)]
#[command(about, version, after_help = "Some very long explanation that should be printed at the end of the help screen")]
pub struct Args {
    /// Path to a file.
    #[arg(short, long)]
    pub file: Option<PathBuf>,
}

fn main() {
    let _args = Args::parse();
}

如果你的自定义消息内容较长、需要换行，可以用Rust的原始字符串（r#"..."#）来定义：

#[derive(Parser, Debug, Default)]
#[command(
    about,
    version,
    after_help = r#"
Some very long explanation that should be printed at the end of the help screen
这是第二行自定义内容，支持多行展示
"#
)]
pub struct Args {
    /// Path to a file.
    #[arg(short, long)]
    pub file: Option<PathBuf>,
}

运行程序并执行--help参数后，输出会符合你的预期：

MyProgram ...

  --file FILE  Path to a file

Some very long explanation that should be printed at the end of the help screen

内容的提问来源于stack exchange，提问作者Yuri Astrakhan