Crate fondant

fondant

Documentation · Architecture · Usage · Customization · Todo

fondant is a macro based library to take the boilerplate out of configuration handling. All you need to do is derive the Configure trait on your struct, and fondant will decide where to store it and and how to do so safely.

Most of fondant is based off the confy crate. fondant adds a couple of extra features:

• support for json, yaml and toml
• support for custom config paths
• support for custom config file names

Architecture

fondant is split into 3 separate crates:

• fondant_deps: external crates and utils that fondant requires
• fondant_derive: core macro definitions
• fondant: the user facing library that brings it all together

This slightly strange architecture arose because of some limitations with proc-macro crates and strict cyclic dependencies in cargo. All you need is the fondant crate.

Usage

// the struct has to derive Serialize, Deserialize and Default
#[derive(Configure, Serialize, Deserialize, Default)]
#[config_file = "config.toml"]
// `config_file` attribute sets the file name to "config.toml"
// the file format to "toml"
// and the file path to "default" (read the notes below)
struct AppConfig {
    version: u32,
    port: u32,
    username: String,
}

fn main() {
    // use `load` to load the config file
    // loads in Default::default if it can't find one
    let mut conf = AppConfig::load().unwrap();

    // do stuff with conf
    conf.version = 2;

    // call `store` to save changes
    conf.store().unwrap();
}

Notes:

• load returns Default::default if the config file is not present, and stores a serialized Default::default at the specified path
• the “default” config path varies by platform:
  • GNU/Linux: $XDG_CONFIG_HOME/my_cool_crate/config.toml (follows xdg spec)
  • MacOS: $HOME/Library/Preferences/my_cool_crate/config.toml
  • Windows: {FOLDERID_RoamingAppData}\_project_path_\config

Customization

Set your own filename, for ex.: apprc

#[derive(Configure, Serialize, Deserialize, Default)]
#[config_file = "apprc.toml"]
struct AppConfig {
    // -- snip --
}
// effective path: $XDG_CONFIG_HOME/my_cool_crate/apprc.toml
// effective format: toml

Change file format to yaml, by changing the file extension. Supported extensions are yaml, toml, json:

#[derive(Configure, Serialize, Deserialize, Default)]
#[config_file = "config.yaml"]
struct AppConfig {
    // -- snip --
}
// effective path: $XDG_CONFIG_HOME/my_cool_crate/config.yaml
// effective format: yaml

Override the default config path (not recommended), for ex.: the home directory:

#[derive(Configure, Serialize, Deserialize, Default)]
#[config_file = "~/.apprc.json"]
struct AppConfig {
    // -- snip --
}
// effective path: $HOME/.apprc.json
// effective format: json

Fondant meshes well with Serde, for ex.:

#[derive(Configure, Serialize, Deserialize, Default)]
#[config_file = "config.toml"]
struct Madagascar {
    #[serde(skip)]
    rating: u32,

    name: String,
    penguins: u32,
}

Above snippet produces this config file:

name = 'Central Park Zoo'
penguins = 4

Modules

fondant_exports

Enums

FondantError

Errors that load and store can result in

Traits

Configure

Derive this trait on a struct to mark it as a ‘configuration’ struct.

Derive Macros

Configure