lua-rs

A pure-Rust Lua interpreter — one implementation that runs Lua 5.1, 5.2, 5.3, 5.4, and 5.5, selected per instance. Runs as a standalone binary with no C dependency, embeds in Rust programs and in the browser. The stable 5.4 backend passes the full upstream PUC-Rio test suite (44/44).

cargo install lua-cli            # crate `lua-cli`; the binary it installs is `lua-rs`
lua-rs -e 'print("hello")'
lua-rs script.lua                # run a file; `lua-rs` for the REPL

It is competitive with reference C (~1.3× geomean wall time, benchmarked per commit), not faster, and is not LuaJIT. Most crates build under #![forbid(unsafe_code)]; the trusted unsafe is budgeted in the GC, the dynamic-library loader, and the WASM pointer ABI.

Embed it in Rust

lua-rs-runtime is an embedding API shaped after mlua. Being pure Rust, it builds for wasm32-unknown-unknown and needs no C toolchain or liblua. It's young and it isn't LuaJIT, so if you need either, use mlua.

let lua = Lua::new();
let f = lua.create_function(|_, name: String| Ok(format!("hello, {name}")))?;
lua.globals().set("greet", f)?;
lua.load(r#"print(greet("lua-rs"))"#).exec()?;

Lua::scope lends Lua a non-'static borrow (e.g. a game engine's &mut World) for one call; a handle that escapes the scope errors cleanly instead of dangling. AnyUserData::delegate returns live sub-references into it.

lua.scope(|s| {
    let world = s.create_userdata_ref_mut(&lua, &mut my_world)?;
    lua.globals().set("world", &world)?;
    lua.load("world:spawn('player')").exec()
})?;

Full API on docs.rs. Worked Bevy 0.18 integration: bevy-lua-rs-starter (live demo).

Multiple Lua versions

The same API and binary run Lua 5.1 through 5.5, selected per instance:

let lua = Lua::new_versioned(LuaVersion::V51); // V51..V55; Lua::new() is 5.4

The CLI selects with LUA_RS_VERSION=5.1|5.2|5.3|5.4|5.5. All five share one core — the bytecode dispatch loop carries no per-version cost, so compute-bound code runs identically across versions; version differences (number model, globals model, stdlib roster, error wording) live in cold-path seams. Every version is verified against its unmodified upstream reference binary.

Maturity, by version:

• 5.4 — stable; passes the full upstream PUC-Rio suite (44/44).
• 5.3 / 5.5 — beta; long tails closed (compat-math, error wording, global declarations, named varargs, traceback fidelity), verified against the reference. A few documented divergences remain (see the open issues).
• 5.1 / 5.2 — supported, float-only number family (5.2 on the modern _ENV globals model; 5.1 adds fenv globals). Verified against the reference binary via a behavioral battery and the upstream example programs rather than a bundled conformance suite, so treat them as the newest backends. math.random sequences differ (host PRNG); see the changelog.

Use 5.4 for production; the others are good for running version-specific scripts and for the embedding use cases the playbook describes.

Running untrusted Lua

Bound CPU and memory and strip host access, so a buggy or hostile script can't hang the process, exhaust memory, or reach the filesystem. Limits are enforced on every thread (coroutines included) and are uncatchable — a script can't escape them with pcall. A non-sandboxed runtime pays zero overhead.

let (lua, sandbox) = Lua::sandboxed(SandboxConfig::strict())?;
match lua.load(untrusted_source).exec() {
    Ok(()) => { /* finished within limits */ }
    Err(_) => match sandbox.tripped() {
        Some(TripReason::Instructions) => { /* CPU budget hit */ }
        Some(TripReason::Memory)       => { /* memory ceiling hit */ }
        None                           => { /* ordinary Lua error */ }
    },
}
sandbox.reset(); // refill the budget before re-running

From the CLI:

lua-rs --sandbox script.lua              # strip host globals + default caps
lua-rs --max-instructions=5000000 s.lua  # CPU budget
lua-rs --max-memory=64M s.lua            # memory ceiling (K/M/G suffixes)

Design and threat model: docs/SANDBOXING_EXPLORATION.md.

Browser / WebAssembly

Ships as lua-rs-wasm (npm) for running Lua in the browser or Node without bundling the C interpreter. Try it in the playground; see harness/wasm/README.md for the host-hook API.

Sandboxing is exposed over the WASM ABI for running untrusted user scripts: lua_rs_wasm_set_limits(max_instructions, max_memory, strict) before lua_rs_wasm_run, then lua_rs_wasm_last_trip() to learn which limit (if any) stopped a run, and lua_rs_wasm_sandbox_reset() to refill the budget.

LuaRocks

Runs the stock LuaRocks 3.11.1 client and installs pure-Lua rocks (inspect, dkjson, argparse, middleclass, say, luassert). Native C rocks are not supported yet.

More

• Conformance: TEST_TIMEOUT_S=90 ./harness/run_official_all.sh runs the unmodified upstream suite against lua-rs (44/44). This is Lua source/runtime compatibility, not C API/ABI compatibility.
• Building, testing, and contributing: CONTRIBUTING.md.
• Embedding internals and roadmap: docs/EMBEDDING_API_IMPLEMENTATION.md, docs/FUTURE_GOALS.md.

License

A port of Lua (Roberto Ierusalimschy, Luiz Henrique de Figueiredo, and Waldemar Celes, PUC-Rio). Lua and this port are both MIT-licensed. See LICENSE.