Lua

Using Lua

Overview of Lua

Several versions of the Lua interpreter are available: luajit, lua 5.1, 5.2, 5.3. The attribute lua refers to the default interpreter, it is also possible to refer to specific versions, e.g. lua5_2 refers to Lua 5.2.

Lua libraries are in separate sets, with one set per interpreter version.

The interpreters have several common attributes. One of these attributes is pkgs, which is a package set of Lua libraries for this specific interpreter. E.g., the busted package corresponding to the default interpreter is lua.pkgs.busted, and the lua 5.2 version is lua5_2.pkgs.busted. The main package set contains aliases to these package sets, e.g. luaPackages refers to lua5_1.pkgs and lua52Packages to lua5_2.pkgs.

Note that nixpkgs patches the non-luajit interpreters to avoid referring to /usr and have ;; (a placeholder replaced with the default LUA_PATH) work correctly.

Installing Lua and packages

Lua environment defined in separate `.nix` file

Create a file, e.g. build.nix, with the following expression

with import <nixpkgs> {};

lua5_2.withPackages (ps: with ps; [ busted luafilesystem ])

and install it in your profile with

nix-env -if build.nix

Now you can use the Lua interpreter, as well as the extra packages (busted, luafilesystem) that you added to the environment.

Lua environment defined in `~/.config/nixpkgs/config.nix`

If you prefer to, you could also add the environment as a package override to the Nixpkgs set, e.g. using config.nix,

{ # ...

  packageOverrides = pkgs: with pkgs; {
    myLuaEnv = lua5_2.withPackages (ps: with ps; [ busted luafilesystem ]);
  };
}

and install it in your profile with

nix-env -iA nixpkgs.myLuaEnv

The environment is installed by referring to the attribute, and considering the nixpkgs channel was used.

Lua environment defined in `/etc/nixos/configuration.nix`

For the sake of completeness, here's another example how to install the environment system-wide.

{ # ...

  environment.systemPackages = with pkgs; [
    (lua.withPackages(ps: with ps; [ busted luafilesystem ]))
  ];
}

How to override a Lua package using overlays?

Use the following overlay template:

final: prev:
{

  lua = prev.lua.override {
    packageOverrides = luaself: luaprev: {

      luarocks-nix = luaprev.luarocks-nix.overrideAttrs(oa: {
        pname = "luarocks-nix";
        src = /home/my_luarocks/repository;
      });
    };
  };

  luaPackages = lua.pkgs;
}

Temporary Lua environment with `nix-shell`

There are two methods for loading a shell with Lua packages. The first and recommended method is to create an environment with lua.buildEnv or lua.withPackages and load that. E.g.

$ nix-shell -p 'lua.withPackages(ps: with ps; [ busted luafilesystem ])'

opens a shell from which you can launch the interpreter

[nix-shell:~] lua

The other method, which is not recommended, does not create an environment and requires you to list the packages directly,

$ nix-shell -p lua.pkgs.busted lua.pkgs.luafilesystem

Again, it is possible to launch the interpreter from the shell. The Lua interpreter has the attribute pkgs which contains all Lua libraries for that specific interpreter.

Developing with lua

Now that you know how to get a working Lua environment with Nix, it is time to go forward and start actually developing with Lua. There are two ways to package lua software, either it is on luarocks and most of it can be taken care of by the luarocks2nix converter or the packaging has to be done manually. Let's present the luarocks way first and the manual one in a second time.

Packaging a library on luarocks

Luarocks.org is the main repository of lua packages. The site proposes two types of packages, the rockspec and the src.rock (equivalent of a rockspec but with the source).

Luarocks-based packages are generated in pkgs/development/lua-modules/generated-packages.nix from the whitelist maintainers/scripts/luarocks-packages.csv and updated by running the package luarocks-packages-updater:

nix-shell -p luarocks-packages-updater --run luarocks-packages-updater

luarocks2nix is a tool capable of generating nix derivations from both rockspec and src.rock (and favors the src.rock). The automation only goes so far though and some packages need to be customized. These customizations go in pkgs/development/lua-modules/overrides.nix. For instance if the rockspec defines external_dependencies, these need to be manually added to the overrides.nix.

You can try converting luarocks packages to nix packages with the command nix-shell -p luarocks-nix and then luarocks nix PKG_NAME.

Packaging a library manually

You can develop your package as you usually would, just don't forget to wrap it within a toLuaModule call, for instance

{
  mynewlib = toLuaModule ( stdenv.mkDerivation { /* ... */ });
}

There is also the buildLuaPackage function that can be used when lua modules are not packaged for luarocks. You can see a few examples at pkgs/top-level/lua-packages.nix.

Lua Reference

Lua interpreters

Versions 5.1, 5.2, 5.3 and 5.4 of the lua interpreter are available as respectively lua5_1, lua5_2, lua5_3 and lua5_4. Luajit is available too. The Nix expressions for the interpreters can be found in pkgs/development/interpreters/lua-5.

Attributes on lua interpreters packages

Each interpreter has the following attributes:

interpreter. Alias for ${pkgs.lua}/bin/lua.
buildEnv. Function to build lua interpreter environments with extra packages bundled together. See section lua.buildEnv function for usage and documentation.
withPackages. Simpler interface to buildEnv.
pkgs. Set of Lua packages for that specific interpreter. The package set can be modified by overriding the interpreter and passing packageOverrides.

`buildLuarocksPackage` function

The buildLuarocksPackage function is implemented in pkgs/development/interpreters/lua-5/build-luarocks-package.nix The following is an example:

{
  luaposix = buildLuarocksPackage {
    pname = "luaposix";
    version = "34.0.4-1";

    src = fetchurl {
      url    = "https://raw.githubusercontent.com/rocks-moonscript-org/moonrocks-mirror/master/luaposix-34.0.4-1.src.rock";
      hash = "sha256-4mLJG8n4m6y4Fqd0meUDfsOb9RHSR0qa/KD5KCwrNXs=";
    };
    disabled = (luaOlder "5.1") || (luaAtLeast "5.4");
    propagatedBuildInputs = [ bit32 lua std_normalize ];

    meta = {
      homepage = "https://github.com/luaposix/luaposix/";
      description = "Lua bindings for POSIX";
      maintainers = with lib.maintainers; [ vyp lblasc ];
      license.fullName = "MIT/X11";
    };
  };
}

The buildLuarocksPackage delegates most tasks to luarocks:

it adds luarocks as an unpacker for src.rock files (zip files really).
configurePhase writes a temporary luarocks configuration file which location is exported via the environment variable LUAROCKS_CONFIG.
the buildPhase does nothing.
installPhase calls luarocks make --deps-mode=none --tree $out to build and install the package
In the postFixup phase, the wrapLuaPrograms bash function is called to wrap all programs in the $out/bin/* directory to include $PATH environment variable and add dependent libraries to script's LUA_PATH and LUA_CPATH.

It accepts as arguments:

'luarocksConfig': a nix value that directly maps to the luarocks config used during the installation

By default meta.platforms is set to the same value as the interpreter unless overridden otherwise.

`buildLuaApplication` function

The buildLuaApplication function is practically the same as buildLuaPackage. The difference is that buildLuaPackage by default prefixes the names of the packages with the version of the interpreter. Because with an application we're not interested in multiple version the prefix is dropped.

lua.withPackages function

The lua.withPackages takes a function as an argument that is passed the set of lua packages and returns the list of packages to be included in the environment. Using the withPackages function, the previous example for the luafilesystem environment can be written like this:

lua.withPackages (ps: [ps.luafilesystem])

withPackages passes the correct package set for the specific interpreter version as an argument to the function. In the above example, ps equals luaPackages. But you can also easily switch to using lua5_1:

lua5_1.withPackages (ps: [ps.lua])

Now, ps is set to lua5_1.pkgs, matching the version of the interpreter.

Lua Contributing guidelines

Following rules should be respected:

Commit names of Lua libraries should reflect that they are Lua libraries, so write for example luaPackages.luafilesystem: 1.11 -> 1.12.

Lua