clap+humantime+serde+figment

Cargo.toml

[package]
name = "clapment"
version = "0.1.0"
edition = "2021"

[dependencies]
anyhow = "1.0.72"
clap = { version = "4.3.21", features = ["derive"] }
figment = { version = "0.10.10", features = ["env", "json", "toml"] }
humantime = "2.1.0"
serde = { version = "1.0.183", features = ["derive"] }
serde_with = "3.2.0"

main.rs

use clap::Parser;
use figment::{
    providers::{Env, Serialized},
    Figment,
};
use serde::{Deserialize, Serialize};
use serde_with::{serde_as, DisplayFromStr};
use std::{path::PathBuf, time::Duration};

#[serde_as]
#[derive(Parser, Debug, Serialize, Deserialize)]
struct Arguments {
    /// Some config
    #[clap(default_value = "config.json")]
    config: PathBuf,

    /// How long
    #[clap(short, long, default_value_t = Duration::from_secs(1).into())]
    #[serde_as(as = "DisplayFromStr")]
    duration: humantime::Duration,
}

fn main() -> anyhow::Result<()> {
    let config: Arguments = Figment::new()
        .merge(Serialized::defaults(Arguments::parse()))
        .merge(Env::prefixed("CLAPMENT_"))
        .extract()?;
    dbg!(config);
    Ok(())
}