derive(FromFile)

Procedural macro to derive configuration from files, with optional merging capabilities.

Features

• Derive Configuration: Easily load configuration from files into your Rust structs.
• Default Values: Specify default values for struct fields using the #[from_file(default = "...")] attribute.
• Optional Merging: When the merge feature is enabled, allows merging multiple configuration sources.

Usage

[dependencies]
filecaster = "0.2"

use filecaster::FromFile;

#[derive(Debug, Clone, PartialEq, FromFile)]
struct AppConfig {
    /// If the user does not specify a host, use `"127.0.0.1"`.
    #[from_file(default = "127.0.0.1")]
    host: String,

    /// Port number; defaults to `8080`.
    #[from_file(default = 8080)]
    port: u16,

    /// If not set, use `false`. Requires `bool: Default`.
    auto_reload: bool,
}

fn main() {
    // Simulate file content (e.g., from a JSON file)
    let file_content = r#"{ "host": "localhost", "port": 3000 }"#;

    // The `AppConfigFile` struct is automatically generated by `#[derive(FromFile)]`.
    // It has all fields as `Option<T>`.
    let partial_config: AppConfigFile = serde_json::from_str(file_content).unwrap();
    let partial_config2 = partial_config.clone();

    // Use the generated `from_file` method to get the final config.
    // Default values are applied for missing fields.
    let config = AppConfig::from_file(Some(partial_config));
    // or
    let config: AppConfig = partial_config2.into();

    assert_eq!(config.host, "localhost");
    assert_eq!(config.port, 3000);
    assert_eq!(config.auto_reload, false); // `bool::default()` is `false`

    println!("Final Config: {:#?}", config);

    // Example with no file content (all defaults)
    let default_config = AppConfig::from_file(None);
    assert_eq!(default_config.host, "127.0.0.1");
    assert_eq!(default_config.port, 8080);
    assert_eq!(default_config.auto_reload, false);
}

Examples

Use cargo run --example <example_name> to execute a specific example. For example:

cargo run --example simple
cargo run --example nested

Documentation

Full documentation is available at docs.rs.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is dual-licensed under either:

• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

at your option.