doc: update lua documentation
Reflects the recent changes to the lua infrastructure. Packaging from luarocks should be encouraged.
This commit is contained in:
Matthieu Coudron
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<xi:include href="idris.section.xml" />
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<xi:include href="ios.section.xml" />
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<xi:include href="java.xml" />
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<xi:include href="lua.xml" />
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<xi:include href="lua.section.xml" />
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<xi:include href="node.section.xml" />
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<xi:include href="ocaml.xml" />
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<xi:include href="perl.xml" />
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237
doc/languages-frameworks/lua.section.md
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237
doc/languages-frameworks/lua.section.md
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---
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title: Lua
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author: Matthieu Coudron
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date: 2019-02-05
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---
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# User's Guide to Lua Infrastructure
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## Using Lua
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### Overview of Lua
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Several versions of the Lua interpreter are available: luajit, lua5.1, 5.2, 5.3.
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The attribute `lua` refers to the default interpreter, it is also possible to refer to specific versions, e.g. `lua_52` refers to Lua 5.2.
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Lua libraries are in separate sets, with one set per interpreter version.
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The interpreters have several common attributes. One of these attributes is
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`pkgs`, which is a package set of Lua libraries for this specific
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interpreter. E.g., the `busted` package corresponding to the default interpreter
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is `lua.pkgs.busted`, and the lua 5.2 version is lua_52.pkgs.busted`.
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The main package set contains aliases to these package sets, e.g.
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`luaPackages` refers to `lua_51.pkgs` and `lua_52Packages` to
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`lua_52.pkgs`.
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### Installing Lua and packages
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#### Lua environment defined in separate `.nix` file
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Create a file, e.g. `build.nix`, with the following expression
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```nix
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with import <nixpkgs> {};
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lua_52.withPackages (ps: with ps; [ busted luafilesystem ])
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```
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and install it in your profile with
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```shell
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nix-env -if build.nix
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```
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Now you can use the Lua interpreter, as well as the extra packages (`busted`,
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`luafilesystem`) that you added to the environment.
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#### Lua environment defined in `~/.config/nixpkgs/config.nix`
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If you prefer to, you could also add the environment as a package override to the Nixpkgs set, e.g.
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using `config.nix`,
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```nix
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{ # ...
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packageOverrides = pkgs: with pkgs; {
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myLuaEnv = lua_52.withPackages (ps: with ps; [ busted luafilesystem ]);
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};
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}
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```
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and install it in your profile with
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```shell
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nix-env -iA nixpkgs.myLuaEnv
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```
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The environment is is installed by referring to the attribute, and considering
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the `nixpkgs` channel was used.
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#### Lua environment defined in `/etc/nixos/configuration.nix`
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For the sake of completeness, here's another example how to install the environment system-wide.
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```nix
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{ # ...
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environment.systemPackages = with pkgs; [
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(lua.withPackages(ps: with ps; [ busted luafilesystem ]))
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];
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}
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```
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### Temporary Lua environment with `nix-shell`
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For development you may need to use multiple environments.
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`nix-shell` gives the possibility to temporarily load another environment, akin
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to `virtualenv`.
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There are two methods for loading a shell with Lua packages. The first and recommended method
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is to create an environment with `lua.buildEnv` or `lua.withPackages` and load that. E.g.
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```sh
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$ nix-shell -p 'lua.withPackages(ps: with ps; [ busted luafilesystem ])'
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```
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opens a shell from which you can launch the interpreter
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```sh
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[nix-shell:~] lua
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```
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The other method, which is not recommended, does not create an environment and requires you to list the packages directly,
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```sh
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$ nix-shell -p lua.pkgs.busted lua.pkgs.luafilesystem
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```
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Again, it is possible to launch the interpreter from the shell.
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The Lua interpreter has the attribute `pkgs` which contains all Lua libraries for that specific interpreter.
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## Developing with Lua
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Now that you know how to get a working Lua environment with Nix, it is time
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to go forward and start actually developing with Lua. There are two ways to
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package lua software, either it is on luarocks and most of it can be taken care
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of by the luarocks2nix converter or the packaging has to be done manually.
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Let's present the luarocks way first and the manual one in a second time.
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### Packaging a library on luarocks
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[Luarocks.org](www.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). These packages can have different build types such as `cmake`, `builtin` etc (See https://github.com/luarocks/luarocks/wiki/Rockspec-format).
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Luarocks-based packages are generated in pkgs/development/lua-modules/generated-packages.nix from
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the whitelist maintainers/scripts/luarocks-packages.csv and updated by running maintainers/scripts/update-luarocks-packages.
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[luarocks2nix](https://github.com/teto/luarocks) is a tool capable of generating nix derivations from both rockspec and src.rock (and favors the src.rock).
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The automation only goes so far though and some packages need some customization.
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These go in pkgs/development/lua-modules/generated-packages.nix
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nix won't work with all packages. If the package lists `external_dependencies` in its rockspec file then it won't work.
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You can run `nix-shell -p luarocks-nix` and then `luarocks nix PKG_NAME`.
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Nix rely on luarocks to install lua packages, basically it runs:
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`luarocks make --deps-mode=none --tree $out`
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#### Packaging a library manually
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You can develop your package as you usually would, just don't forget to wrap it
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within a `toLuaModule` call, for instance
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```nix
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mynewlib = toLuaModule ( stdenv.mkDerivation { ... });
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```
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## Lua Reference
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### Lua interpreters
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Versions 5.1, 5.2 and 5.3 of the lua interpreter are available as
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respectively `lua_51`, `lua_52` and `lua_53`. The luajit interpreter is also available.
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The Nix expressions for the interpreters can be found in `pkgs/development/interpreters/lua`.
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#### Attributes on lua interpreters packages
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Each interpreter has the following attributes:
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- `interpreter`. Alias for `${lua}/bin/lua`.
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- `buildEnv`. Function to build python interpreter environments with extra packages bundled together. See section *python.buildEnv function* for usage and documentation.
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- `withPackages`. Simpler interface to `buildEnv`.
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- `pkgs`. Set of Lua packages for that specific interpreter. The package set can be modified by overriding the interpreter and passing `packageOverrides`.
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#### `buildLuarocksPackage` function
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The `buildLuarocksPackage` function is implemented in `pkgs/development/interpreters/lua-5/build-lua-package.nix`
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The following is an example:
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```nix
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luaexpat = buildLuaPackage rec {
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pname = "luaexpat";
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version = "1.3.0-1";
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src = fetchurl {
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url = https://luarocks.org/luaexpat-1.3.0-1.src.rock;
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sha256 = "15jqz5q12i9zvjyagzwz2lrpzya64mih8v1hxwr0wl2gsjh86y5a";
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};
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disabled = luaOlder "5.1";
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propagatedBuildInputs = [ lua ];
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buildType="builtin";
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meta = {
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homepage = http://www.keplerproject.org/luaexpat/;
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description="XML Expat parsing";
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license = {
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fullName = "MIT/X11";
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};
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};
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};
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```
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The `buildLuarocksPackage` delegates most tasks to luarocks:
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* it adds `luarocks` as an unpacker for `src.rock` files (in fact zip files)
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* configurePhase` writes a temporary luarocks configuration file which location
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is exported via the environment variable `LUAROCKS_CONFIG`.
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* In the `buildPhase`, nothing is done.
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* `installPhase` calls `luarocks make --deps-mode=none --tree $out` to build and
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install the package
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* In the `postFixup` phase, the `wrapLuaPrograms` bash function is called to
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wrap all programs in the `$out/bin/*` directory to include `$PATH`
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environment variable and add dependent libraries to script's `LUA_PATH` and
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`LUA_CPATH`.
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By default `meta.platforms` is set to the same value
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as the interpreter unless overridden otherwise.
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#### `buildLuaApplication` function
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The `buildLuaApplication` function is practically the same as `buildLuaPackage`.
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The difference is that `buildLuaPackage` by default prefixes the names of the packages with the version of the interpreter.
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Because with an application we're not interested in multiple version the prefix is dropped.
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#### lua.withPackages function
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The `lua.withPackages` function provides a simpler interface to the `python.buildEnv` functionality.
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It takes a function as an argument that is passed the set of python packages and returns the list
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of the packages to be included in the environment. Using the `withPackages` function, the previous
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example for the luafilesystem environment can be written like this:
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```nix
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with import <nixpkgs> {};
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lua.withPackages (ps: [ps.luafilesystem])
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```
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`withPackages` passes the correct package set for the specific interpreter version as an argument to the function. In the above example, `ps` equals `luaPackages`.
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But you can also easily switch to using lua_52:
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```nix
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with import <nixpkgs> {};
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lua_52.withPackages (ps: [ps.lua])
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```
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Now, `ps` is set to `lua_52Packages`, matching the version of the interpreter.
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### Possible Todos
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* export/use version specific variables such as LUA_PATH_5_2/LUAROCKS_CONFIG_5_2
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* let luarocks check for dependencies via exporting the different rocktrees in temporary config
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### Lua Contributing guidelines
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Following rules should be respected:
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* Make sure libraries build for all Lua interpreters.
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* Commit names of Lua libraries should reflect that they are Lua libraries, so write for example `lua.luafilesystem: 1.11 -> 1.12`.
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