luars

A Lua 5.5 interpreter written in pure Rust — embeddable, async-capable, with derive macros for UserData.

Features

• Lua 5.5 — full language semantics: compiler, register-based VM, GC
• Pure Rust — no C dependencies, no unsafe FFI
• Ergonomic API — call_global, register_function, load, dofile, TableBuilder, typed getters
• UserData — derive macros to expose Rust structs/enums to Lua (fields, methods, operators)
• Async — run async Rust functions from Lua via transparent coroutine bridging
• Closures — register Rust closures with captured state as Lua globals
• FromLua / IntoLua — automatic type conversion for seamless Rust ↔ Lua interop
• Optional Serde — JSON serialization via serde / serde_json (feature-gated)
• Standard Libraries — basic, string, table, math, io, os, coroutine, utf8, package, partial debug

Usage

[dependencies]
luars = "0.7"

# With JSON support:
luars = { version = "0.7", features = ["serde"] }

Basic Example

use luars::{LuaVM, Stdlib, LuaValue};
use luars::lua_vm::SafeOption;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut vm = LuaVM::new(SafeOption::default());
    vm.open_stdlib(Stdlib::All)?;

    // Execute Lua code
    let results = vm.execute("return 1 + 2")?;
    assert_eq!(results[0].as_integer(), Some(3));

    // Set / get globals
    vm.set_global("x", LuaValue::integer(42))?;
    let x: i64 = vm.get_global_as::<i64>("x")?.unwrap();

    // Call a Lua function
    vm.execute("function add(a,b) return a+b end")?;
    let sum = vm.call_global("add", vec![LuaValue::integer(1), LuaValue::integer(2)])?;
    assert_eq!(sum[0].as_integer(), Some(3));

    Ok(())
}

Register Rust Functions

vm.register_function("greet", |state| {
    let name = state.get_arg(1).and_then(|v| v.as_str().map(String::from))
        .unwrap_or_else(|| "World".into());
    let msg = state.create_string(&format!("Hello, {}!", name))?;
    state.push_value(msg)?;
    Ok(1)
})?;

vm.execute("print(greet('Rust'))")?;  // Hello, Rust!

Load, Dofile, Call

// Compile without executing
let f = vm.load("return 1 + 1")?;
let results = vm.call(f, vec![])?;

// Load named source
let f = vm.load_with_name("return 42", "my_chunk")?;

// Execute a file
vm.dofile("scripts/init.lua")?;

TableBuilder

use luars::TableBuilder;

let config = TableBuilder::new()
    .set("host", vm.create_string("localhost")?)
    .set("port", LuaValue::integer(8080))
    .push(LuaValue::integer(1))
    .build(&mut vm)?;
vm.set_global("config", config)?;

// Iterate
for (k, v) in vm.table_pairs(&config)? {
    println!("{:?} = {:?}", k, v);
}
let len = vm.table_length(&config)?;

Rust Closures

use std::sync::{Arc, atomic::{AtomicUsize, Ordering}};

let counter = Arc::new(AtomicUsize::new(0));
let counter_clone = counter.clone();
let func = vm.create_closure(move |state| {
    let n = counter_clone.fetch_add(1, Ordering::SeqCst);
    state.push_value(LuaValue::integer(n as i64))?;
    Ok(1)
})?;
vm.set_global("next_id", func)?;

UserData

use luars::{LuaUserData, lua_methods};

#[derive(LuaUserData)]
#[lua_impl(Display)]
struct Point { pub x: f64, pub y: f64 }

#[lua_methods]
impl Point {
    pub fn new(x: f64, y: f64) -> Self { Point { x, y } }
    pub fn distance(&self) -> f64 { (self.x * self.x + self.y * self.y).sqrt() }
}

vm.register_type_of::<Point>("Point")?;
vm.execute(r#"
    local p = Point.new(3, 4)
    print(p.x, p:distance())   -- 3.0  5.0
"#)?;

Error Handling

use luars::LuaError;

match vm.execute("error('boom')") {
    Ok(_) => {}
    Err(e) => {
        // Lightweight message
        let msg = vm.get_error_message(e);
        eprintln!("Lua error: {}", msg);

        // Rich error (implements std::error::Error)
        let full = vm.into_full_error(e);
        eprintln!("{}", full);
    }
}

LuaError is a 1-byte enum (Runtime, Syntax, OutOfMemory, MessageHandler, IndexOutOfBounds). For rich errors with messages and std::error::Error impl, use vm.into_full_error() → LuaFullError.

Selective Standard Libraries

use luars::Stdlib;

vm.open_stdlib(Stdlib::All)?;                          // everything
vm.open_stdlibs(&[Stdlib::Base, Stdlib::String])?;     // specific set

Async

use luars::AsyncReturnValue;

vm.register_async("fetch", |args| async move {
    let url = args[0].as_str().unwrap_or("").to_string();
    let body = reqwest::get(&url).await?.text().await?;
    Ok(vec![AsyncReturnValue::string(body)])
})?;

let results = vm.execute_async("return fetch('https://example.com')").await?;

Known Limitations

• UTF-8 Only Strings — unlike C Lua, strings must be valid UTF-8. Use string.pack/string.unpack for binary data.
• Custom Bytecode Format — string.dump output is not compatible with C Lua bytecode.
• No C API — pure Rust; cannot load C Lua modules.
• Partial Debug Library — debug.sethook is a stub; getinfo/getlocal/traceback work.
• No string-to-number coercion in arithmetic — "3" + 1 raises an error.

Documentation

License

MIT — see LICENSE.