Configuration

Location

Configuration lives at ~/.{project-name}/config.toml. It is auto-created with defaults on first use.

Structure

AppConfig is the top-level struct. Each section is a nested struct tagged with #[serde(default)] so missing fields fall back to defaults.

#![allow(unused)]
fn main() {
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AppConfig {
    #[serde(default)]
    pub general: GeneralConfig,
    // add new sections here
}
}

Adding a Section

Full example adding a DownloadConfig section.

1. Define the struct with a Default impl

#![allow(unused)]
fn main() {
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DownloadConfig {
    pub output_dir: String,
    pub max_retries: u32,
}

impl Default for DownloadConfig {
    fn default() -> Self {
        Self {
            output_dir: "./downloads".into(),
            max_retries: 3,
        }
    }
}
}

2. Add to AppConfig

#![allow(unused)]
fn main() {
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AppConfig {
    #[serde(default)]
    pub general: GeneralConfig,
    #[serde(default)]
    pub download: DownloadConfig,
}
}

3. Wire the CLI helpers

Update these three functions so config set / config get work for your new fields:

• set_config_field — match on "download.output_dir", "download.max_retries", etc. and mutate the config.
• get_config_field — match on the same keys and return the current value as a string.
• config_as_map — insert each field into the map so config list can display them.

Reading

#![allow(unused)]
fn main() {
let cfg = app_config::load(); // returns &'static AppConfig (OnceLock-cached)
println!("{}", cfg.download.output_dir);
}

The config is loaded once and cached for the lifetime of the process.

Writing

#![allow(unused)]
fn main() {
let mut cfg = app_config::load().clone();
cfg.download.output_dir = "./out".into();
app_config::save(&cfg)?;
}

CLI Commands

# Set a value
myapp config set download.output_dir ./out

# Get a value
myapp config get download.output_dir