Rlua + Luarocks Modules -> Fail to load

[solo-fox]

Hi Developers,

I will be fast and straightforward.

This is my rust code :

use rlua::{Lua, Result, Value};

fn main() -> Result<()> {
    // Create a new Lua context
    let lua = Lua::new();

    // Load and execute the Lua script
    lua.context(|lua_ctx| {
        lua_ctx.load(
            r#"
            function run()
                local result = 1 + 2
                print("Result: " .. result)
                return result
            end
        "#
        )
        .exec()?;

        // Get the run function as a Lua Value
        let result: Value = lua_ctx.globals().get("run")?;

        // Check if the Lua value is a function and call it
        if let Value::Function(func) = result {
            let result: i64 = func.call(())?;
            println!("Result in Rust: {}", result);
        } else {
            println!("Error: 'run' is not a function");
        }

        Ok(())
    })
    .map_err(|e| {
        eprintln!("Error: {:?}", e);
        e
    })
}

And this what I get from rlua

Error: runtime error: [string "?"]:2: module 'lrand' not found:                                                               no field package.preload['lrand']
no file '/usr/local/share/lua/5.4/lrand.lua'               no file '/usr/local/share/lua/5.4/lrand/init.lua'          no file '/usr/local/lib/lua/5.4/lrand.lua'                 no file '/usr/local/lib/lua/5.4/lrand/init.lua'            no file './lrand.lua'                                      
no file './lrand/init.lua'                         
stack traceback:                                                   [C]: in ?
        [C]: in function 'require'
        [string "?"]:2: in main chunk

But when I ran luarocks list, I get

luarocks list

Rocks installed for Lua 5.3
---------------------------

lrand
   1.0.0-0 (installed) - /usr/local/lib/luarocks/rocks-5.3

Also lrand is installed but cannot be loaded from rlua!!! Can someone please help me finding the issue!

Thanks.

[jugglerchris]

Hi,
It looks like you've configured rlua with the default "builtin-lua54", but are trying to use luarocks installed with Lua 5.3.
To use the system-installed Lua 5.3 library instead, specify the dependency liks this in Cargo.toml:

rlua = { version = "0.19", default-features = false, features=["system-lua53"] }

Second, by default rlua disables C extensions for safety. lrand is a C extension so that needs enabling. Instead of Lua::new, you can use Lua::unsafe_new_with_flags:

let lua = unsafe { Lua::unsafe_new_with_flags(rlua::StdLib::ALL, rlua::InitFlags::NONE) };

Depending on your luarocks or Lua installations, you may also need to add the luarocks path to package.cpath, but I didn't need to do that on my Ubuntu 22.04 system with luarocks installed from the Ubuntu package.

Putting it together, this worked for me: https://github.com/jugglerchris/rlua_luarocks_lrand

rlua_luarocks_lrand$ luarocks-5.3 list

Rocks installed for Lua 5.3
---------------------------

lrand
   1.0.0-0 (installed) - /usr/local/lib/luarocks/rocks-5.3

rlua_luarocks_lrand$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/rlua_luarocks_lrand`
6708800777304496116

[solo-fox]

It is so good to get solutions from expertise rather than searching for days and trying ChatGPT capabilities.

Thanks, it solved the problem!

[jugglerchris]

Glad to be able to help!