Quick Start

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Add the crate and the schema/runtime libraries used by your application:

[dependencies]
rust-config-tree = "0.2"
confique = { version = "0.4", features = ["yaml", "toml", "json5"] }
figment = { version = "0.10", features = ["yaml", "toml", "json", "env"] }
schemars = { version = "1", features = ["derive"] }
serde = { version = "1", features = ["derive"] }
clap = { version = "4", features = ["derive"] }

Define a confique schema and implement ConfigSchema for the root type:

#![allow(unused)]
fn main() {
use std::path::PathBuf;

use confique::Config;
use rust_config_tree::ConfigSchema;

#[derive(Debug, Config)]
struct AppConfig {
    #[config(default = [])]
    include: Vec<PathBuf>,

    #[config(nested)]
    server: ServerConfig,
}

#[derive(Debug, Config)]
struct ServerConfig {
    #[config(default = "127.0.0.1")]
    #[config(env = "APP_SERVER_BIND")]
    bind: String,

    #[config(default = 8080)]
    #[config(env = "APP_SERVER_PORT")]
    port: u16,
}

impl ConfigSchema for AppConfig {
    fn include_paths(layer: &<Self as Config>::Layer) -> Vec<PathBuf> {
        layer.include.clone().unwrap_or_default()
    }
}
}

Load the config:

#![allow(unused)]
fn main() {
use rust_config_tree::load_config;

let config = load_config::<AppConfig>("config.yaml")?;
println!("{config:#?}");
Ok::<(), Box<dyn std::error::Error + Send + Sync>>(())
}

Use a root file with recursive includes:

# config.yaml
include:
  - config/server.yaml

# config/server.yaml
server:
  bind: 0.0.0.0
  port: 3000

The default load_config precedence is:

environment variables
  > config files, with later merged files overriding earlier files
    > confique code defaults

When includes are loaded by the high-level API, the root file has the highest file priority. Included files provide lower-priority values and can be used for defaults or section-specific files.

Command-line arguments are application-specific, so load_config does not read them automatically. Use the ConfigOverrides derive macro to build an override provider from parsed CLI flags:

#![allow(unused)]
fn main() {
use clap::Parser;
use rust_config_tree::{
    ConfigSchema,
    cli::ConfigOverrides,
    config::{build_config_figment, load_config_from_figment},
};

#[derive(Debug, Parser, ConfigOverrides)]
struct Cli {
    /// Config file path
    #[arg(long)]
    config: Option<std::path::PathBuf>,

    /// Override server port
    #[arg(long)]
    #[config_override(path = "server.port")]
    server_port: Option<u16>,

    /// Override log level
    #[arg(long)]
    #[config_override(path = "log.level")]
    log_level: Option<String>,
}

let cli = Cli::parse();
let figment = build_config_figment::<AppConfig>("config.yaml")?
    .merge(cli.config_overrides()?);
let config = load_config_from_figment::<AppConfig>(&figment)?;
let _ = config;
Ok::<(), Box<dyn std::error::Error + Send + Sync>>(())
}

The #[config_override(path = "...")] attribute maps each CLI flag to a dotted config path. Only provided flags produce override values; omitted flags disappear. The override provider is merged last, so provided flags override file and environment values:

command-line overrides
  > environment variables
    > config files
      > confique code defaults