---
nav_title: Contributing
parent: Community
nav_order: 10
---
# Contributing
Open issues, propose language changes, improve docs, or build examples around real rules. Pull requests are welcome.
## Setup
```bash
git clone https://github.com/lemma/lemma
cd lemma
cargo nextest run --workspace
```
### Optional tools
For WASM development:
```bash
cargo install wasm-pack
```
For fuzzing (requires nightly Rust):
```bash
rustup install nightly
cargo install cargo-fuzz
```
For security audits:
```bash
cargo install cargo-deny
cargo deny check --config .cargo/deny.toml
```
## Making changes
1. Write a test first
2. Make your changes
3. Run before submitting (from repo root):
```bash
cargo precommit --fuzz
```
That is what CI runs. Bare `cargo precommit` is a faster local shortcut (same gate without fuzz). The gate: versions-verify, Hex `mix precommit`, VS Code `npm precommit`, fmt, clippy (`--all-features`), `cargo check -p lemma-engine --no-default-features`, nextest (including ignored benches), WASM npm build+test, Maven `./mvnw -B verify` (after `lemma_jni` build), cargo-deny, `cargo coverage all --check`, then with `--fuzz` 30 minutes total across `engine/fuzz` targets. Requires `cargo-nextest`, `cargo-deny`, Elixir/Mix, Node.js, `wasm-pack`, and a **JDK 21+**; `--fuzz` also needs nightly and `cargo-fuzz`. Regenerate coverage with `cargo coverage all` when engine/cli sources change (`cargo-llvm-cov` required). `cargo nextest` alone is Rust tests only.
### Release version (maintainers)
The workspace release is `[workspace.package] version` in the root `Cargo.toml`. The same number must appear in path-dep pins, Hex `mix.exs`, Maven `pom.xml`, Maven install snippets in root/`engine`/`cli/documentation/tools` READMEs, `engine/README.md` Cargo example, and the VS Code extension `package.json` (see `xtask/src/versions.rs` module `tracked`).
- **`cargo bump <semver>`**: update all locations, then refresh `Cargo.lock` (`cargo generate-lockfile`), Hex `mix.lock` (`mix deps.get`), and VS Code `package-lock.json` (`npm install --package-lock-only`).
- **`cargo verify`**: confirm everything matches (`versions-verify` is also the first step of `cargo precommit`).
Do not hand-edit those copies unless you keep them in sync.
## Pull requests
CI runs `cargo precommit --fuzz`. That must pass.
## Project structure
- `cli/`: CLI application (HTTP server, MCP server, interactive mode, formatter)
- `engine/`: core parser, planner, and evaluator (parse → plan NormalForm DAG → evaluate; see [engine/README.md](https://github.com/lemma/lemma/blob/main/engine/README.md))
- `engine/fuzz/`: fuzz testing targets
- `openapi/`: Lemma-to-OpenAPI generation
## Testing
### Unit and integration tests
```bash
cargo nextest run --workspace
```
Hex NIF (ExUnit):
```bash
cd engine/packages/hex && mix test
```
See [engine/tests/README.md](https://github.com/lemma/lemma/blob/main/engine/tests/README.md) (catalog + semantics audit) and [cli/tests/README.md](https://github.com/lemma/lemma/blob/main/cli/tests/README.md).
### Fuzz testing
CI / full gate (30 minutes fuzz total after the rest of precommit):
```bash
cargo precommit --fuzz
```
Requires nightly Rust and `cargo-fuzz`. Manual single-target run:
```bash
cd engine/fuzz
cargo +nightly fuzz list
cargo +nightly fuzz run fuzz_parser -- -max_total_time=60
```
### WASM build and test
`cargo precommit` runs these from `engine/packages/npm` automatically. To run manually:
```bash
cd engine/packages/npm
node build.js # wasm-pack → lemma.bindings.js; copies entrypoints and lsp-client
node test.js
```