Derive Macro Config 

#[derive(Config)]
{
    // Attributes available to this derive:
    #[param]
}

Derive config loading from multiple sources for a struct.

#[derive(Config)] generates a [server_less_core::config::Config] implementation that loads values from defaults, TOML files, and environment variables, with a configurable precedence order.

Example

use server_less::Config;

#[derive(Config)]
struct AppConfig {
    #[param(default = "localhost")]
    host: String,
    #[param(default = 8080)]
    port: u16,
    #[param(env = "DATABASE_URL")]
    database_url: String,
    timeout_secs: Option<u64>,
}

let cfg = AppConfig::load(&[
    ConfigSource::Defaults,
    ConfigSource::File("app.toml".into()),
    ConfigSource::Env { prefix: Some("APP".into()) },
])?;

Field attributes

• #[param(default = value)] — compile-time default; field becomes optional in sources
• #[param(env = "VAR")] — exact env var name (overrides {PREFIX}_{FIELD} generation)
• #[param(file_key = "a.b.c")] — dotted TOML key override (default: field name)
• #[param(help = "...")] — description used by config show --schema and doc generators