Contributing

Workspace Layout

Rex is a Cargo workspace. The most important crates are:

• rexlang-lexer: tokenization + spans
• rexlang-parser: parsing into a Program { decls, expr }
• rexlang-typesystem: Hindley–Milner inference + type classes + ADTs
• rexlang-engine: typed evaluation + native injection
• rexlang-proc-macro: #[derive(Rex)] bridge for Rust types ↔ Rex types/values
• rex: CLI binary

Architecture overview: ARCHITECTURE.md.

Development

Run the full test suite:

cargo test

There is also a lightweight “fuzz smoke” test that runs a deterministic lex→parse→infer→eval loop. You can scale iterations with REX_FUZZ_ITERS:

REX_FUZZ_ITERS=2000 cargo test -p rex --test fuzz_smoke

Fuzz Harnesses

For end-to-end fuzzing with external fuzzers (AFL++, honggfuzz, custom mutational drivers), the workspace includes rexlang-fuzz, a set of stdin-driven harness binaries:

cargo build -p rexlang-fuzz --bins
printf '1 + 2' | cargo run -q -p rexlang-fuzz --bin e2e
printf '(' | cargo run -q -p rexlang-fuzz --bin parse

Tuning knobs (environment variables):

• REX_FUZZ_GAS: gas budget for the harness run
• REX_FUZZ_MAX_NESTING: parser nesting cap (defaults to ParserLimits::safe_defaults())
• REX_FUZZ_STACK_MB: stack size (MiB) for the harness thread

If you edit Rust code, also run:

cargo fmt
cargo clippy

Lockfiles

This repo commits:

• Cargo.lock (workspace lockfile)
• rexlang-vscode/package-lock.json (VS Code extension)

Other lock-like files (for example under target/ or node_modules/) are build artifacts and should not be committed.