rusty-figtree

A layered runtime configuration system for Rust, inspired by the Go figtree package. Supports multiple configuration sources with explicit priority resolution, per-key validators, per-key callbacks, and live mutation tracking via channels.

Repository Structure

rusty-figtree/
├── Cargo.toml           # workspace root — ties both crates together
├── VERSION              # single version file for both crates
├── build.rs             # reads VERSION, exposes APP_VERSION at compile time
├── .gitignore
├── LICENSE
├── CHANGELOG.md
├── figtree/             # primary library crate
│   ├── Cargo.toml
│   ├── README.md
│   └── src/
│       ├── lib.rs
│       ├── error.rs
│       ├── tree.rs
│       ├── fig.rs
│       ├── mutation.rs
│       ├── priority.rs
│       ├── rules.rs
│       ├── validators.rs
│       ├── callbacks.rs
│       ├── sources/
│       │   ├── mod.rs
│       │   ├── env.rs
│       │   ├── cli.rs
│       │   ├── yaml.rs
│       │   ├── json.rs
│       │   ├── ini.rs
│       │   └── embedded.rs
│       └── tests/
│           ├── tree_test.rs
│           ├── validators_test.rs
│           ├── priority_test.rs
│           ├── sources_test.rs
│           └── callbacks_test.rs
└── figtree-derive/      # procedural macro crate
    ├── Cargo.toml
    ├── README.md
    └── src/
        └── lib.rs

Two Crates, One Repository

This repository is a Cargo workspace containing two crates that are always versioned, built, tested, and published together.

figtree is the library your application depends on at runtime. figtree-derive is the procedural macro crate the Rust compiler consumes at build time to expand the #[derive(Figtree)] decorator. End users never reference figtree-derive directly in their own Cargo.toml — it is re-exported transparently by figtree.

Priority Resolution

figtree resolves configuration values in a fixed priority order. This order is inspired by PEMDAS — just as multiplication always precedes addition regardless of left-to-right reading, CLI flags always precede environment variables regardless of declaration order.

CLI flags
  > Environment Variables
    > Configuration Files (in load order)
      > Programmatic Store()
        > Default Values

The source that wins is the one highest in this hierarchy that has a value defined. A default only speaks when nothing above it does.

Feature Flags

Feature       What It Enables
-------       ---------------
std           Standard library support (enabled by default)
env           Environment variable source (enabled by default)
yaml          YAML config file source via serde_yaml
json          JSON config file source via serde_json
ini           INI config file source via rust-ini
cli           CLI flag source via clap
async         Async mutation channel via tokio
embedded      Bare metal source support, implies no_std

Versioning

Both crates share a single VERSION file at the repository root. The build.rs script reads this file at compile time and exposes the version as APP_VERSION. Bumping the version with the bump tool updates both crates atomically.

bump -patch -write
cargo build --release

License

Apache 2.0