Martin Helmut Fieber

Lua project setup with LuaRocks

Coming from the moon

Even though I already wrote an overview of how to set up a Lua project, this article, part of the longer Lua series, will go into more detail on specific aspects with greater focus. Going through this, the goal is to have a solid foundation to further build on in later articles of this series or for any project to come.

Running a first Lua program, using LuaRocks for dependency management, code formatting, and linting, and setting up an editor or IDE to support Lua development as well as possible. Remark: This is how I set up my projects, maybe not by the books, but the way it works best for me in all environments, repeatedly.

Lua versions

A note about versions. The latest Lua version as of this writing is 5.4 (released in June 2020). Generally, everything in this article series will work with Lua 5.1 (released in February 2006) and up. If this is not the case, a callout such as the following will signal that a higher version is required.

For instance, in a later article, I will use the meta-method __close, added in Lua 5.4, for a simple profiling tool.

An overview of the versions and their respective main features can be found on the official Lua version history page.

Installing Lua

First things first, let's check if Lua is already installed on the system by running Lua's version command lua -v in a terminal.

$ lua -v
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio

If it prints something similar to the above, it's already good to go. If not, Lua needs to be installed first.

macOS

Brew on macOS can be used to install an up-to-date version of Lua.

$ brew install lua

Linux

On Linux, installing Lua is as straight-forward as using the system package manager. For example, on Debian, Ubuntu, and Mint:

$ apt install lua5.3

Take a look at Lua's installation guide to build a more recent version from source if needed.

Windows

On Windows, there is a list of available Lua binaries, offering pre-compiled Lua versions ready to be used. Scrolling down on that page to the History section, the latest available pre-compiled versions can be found. Choosing one, for example version 5.4.2, will lead to SourceForge; click the Tools Executables folder next.

Here is the option of picking either the 32-bit or the 64-bit version, depending on the used system.

After the download, the archive contents can be extracted, finding, depending on the downloaded version, an executable. For version 5.4.x this is called lua54.

Double-clicking that file will open a terminal, from which Lua can be run. Alternatively, this file can be placed in a folder that is part of the PATH variable or made available through it.

Hello World

-- src/main.lua
local greeting = "Hello, reader."
print(greeting)

Executing that file via the terminal from inside the project directory will print the greeting.

$ lua src/main.lua
Hello, reader.

Dependency management with LuaRocks

LuaRocks, the de facto standard package manager for Lua, will be used to manage project dependencies. First, the LuaRocks command-line tool needs to be installed on the system.

macOS

Again, using brew on macOS, LuaRocks can be installed with a single command.

$ brew install luarocks

Linux

Same for Linux; a single command does the job using the system package manager.

$ apt install luarocks

Windows

First, the LuaRocks executable needs to be downloaded, either 32-bit or 64-bit. The downloads are at the top of the LuaRocks download page on GitHub. After downloading and extracting the files, the luarocks.exe needs to be added to the PATH to make it available as luarocks command from the terminal.

Project folder setup

With LuaRocks installed, the init command helps to set up a project, including local dependency management. This means dependencies will be installed inside the project folder in a lua_modules directory.

$ luarocks init --lua-versions "5.1,5.2,5.3,5.4"

The init command will do a couple of things, some of which are:

• Creating the lua_module folder and storing all installed dependencies.
• Detecting the src/main.lua as the main entry point of the program.
• Add two shortcuts that can be used for executing lua and luarocks from inside the project.
• Adding a .luarocks folder containing some configuration files and marking the directory as the root folder for LuaRocks.

And two more I'll have a more detailed look at:

• Creating or adding to an existing .gitignore file.
• Creating a .rockspec file with the base project settings and name, taken from the folder name LuaRocks was executed from.

.gitignore

The luarocks init command automatically generates a .gitignore, if not already present, or appends its entries to an existing .gitignore file. The following entries will be added.

/luarocks
/lua
/lua_modules
/.luarocks

The first two files are local shortcuts to execute lua and luarocks. Then comes the dependency folder lua_modules and the config folder .luarocks.

About .rockspec

The .rockspec file defines the project's properties, like name, version, and used dependencies. A complete list of the supported options can be found on the official LuaRocks wiki page for build rules.

-- lua-series-dev-1.rockspec
package = "lua-series"
version = "dev-1"
source = {
   url = "*** please add URL for source tarball, zip or repository here ***"
}
description = {
   homepage = "*** please enter a project homepage ***",
   license = "*** please specify a license ***"
}
dependencies = {
   "lua >= 5.1, < 5.5"
}
build = {
   type = "builtin",
   modules = {
      main = "src/main.lua"
   }
}

At the top of the file, the rockspec format will be defined, indicating the format version, the latest being version 3.

rockspec_format = "3.0"

The source.url can be many things; I usually point it to the project's git repository, but it can also be other repository types or URLs.

source = {
   url = "https://github.com/MartinHelmut/lua-series.git"
}

The description can contain a summary, the project home page, a license, and more.

description = {
   summary = "Companion repository to the Lua series.",
   homepage = "https://martin-fieber.de/series/lua/",
   license = "MIT"
}

Next comes the list of dependencies. This will hold all necessary project dependencies and one special dependency from the start: lua. Less of an actual dependency; more of the projects supported Lua versions or version range.

dependencies = {
   "lua >= 5.1, < 5.5"
}

And at last, the project's build settings and modules — not yet utilized.

build = {
   type = "builtin",
   modules = {
      main = "src/main.lua"
   }
}

To ensure all changes to a .rockspec file are valid, the luarocks lint command can be used, giving it the filename to validate.

$ luarocks lint lua-series-dev-1.rockspec

And here is the final .rockspec file.

-- lua-series-dev-1.rockspec
rockspec_format = "3.0"
package = "lua-series"
version = "dev-1"
source = {
   url = "https://github.com/MartinHelmut/lua-series.git"
}
description = {
   summary = "The companion repository to my Lua blog series.",
   homepage = "https://martin-fieber.de/series/lua/",
   license = "MIT"
}
dependencies = {
   "lua >= 5.1, < 5.5"
}
build = {
   type = "builtin",
   modules = {
      main = "src/main.lua"
   }
}

Install a module

Let's install something, finally! The inspect module is handy in general, giving an easy way to print any value in Lua for inspection or debugging.

$ luarocks install inspect

The new dependency also needs to be added to the .rockspec file to keep it on later installs.

dependencies = {
   "lua >= 5.1, < 5.5",
   "inspect >= 3.1"
}

On a fresh checkout of the project, this will ensure that inspect is installed again when running luarocks install --deps-only on the .rockspec file.

$ luarocks install --deps-only lua-series-dev-1.rockspec

Let's use inspect to print a test table.

-- src/main.lua
local inspect = require("inspect")
local output = { "Hello, reader.", 42 }

print(inspect(output))

Oh no, running this code will give an error.

$ lua src/main.lua
lua: src/main.lua:1: module 'inspect' not found:
	no field package.preload['inspect']
	no file '/opt/homebrew/share/lua/5.4/inspect.lua'
	no file '/opt/homebrew/share/lua/5.4/inspect/init.lua'
	no file '/opt/homebrew/lib/lua/5.4/inspect.lua'
	no file '/opt/homebrew/lib/lua/5.4/inspect/init.lua'
	no file './inspect.lua'
	no file './inspect/init.lua'
	no file '/opt/homebrew/lib/lua/5.4/inspect.so'
	no file '/opt/homebrew/lib/lua/5.4/loadall.so'
	no file './inspect.so'
stack traceback:
	[C]: in function 'require'
	src/main.lua:1: in main chunk
	[C]: in ?

Resolve module paths

Despite having a way to manage dependencies, Lua still needs to be told where to find modules for the project. This is done through the package.path and package.cpath variables. My preferred way is to have a src/setup.lua file defining those.

In that file, I can also put other project setup options later, as it will be loaded before running any Lua script.

-- src/setup.lua
local version = _VERSION:match("%d+%.%d+")

package.path = 'lua_modules/share/lua/' .. version ..
    '/?.lua;lua_modules/share/lua/' .. version ..
    '/?/init.lua;' .. package.path
package.cpath = 'lua_modules/lib/lua/' .. version ..
    '/?.so;' .. package.cpath

Now, there are two ways to use this setup: one is via the -l option of the lua command.

$ lua -l src/setup src/main.lua

Another option is to set the LUA_INIT environment variable. This variable can either execute Lua code before running a script or load a file when the value starts with @.

By defining the environment variable inside the terminal, Lua can be run without the -l option.

export LUA_INIT="@src/setup.lua"

Optionally, to not pollute the environment or re-set the variable every time, I use direnv, defining a .envrc with my projects' environment variables that will only be loaded when working inside the respective project folder.

Having that done, one way or another, I assume from here that the LUA_INIT variable is set and the test script with the inspect module can be run again.

$ lua src/main.lua
{ "Hello, reader.", 42 }

Remark: The package.path variable can also be used to solve inner project module resolution. Let's say all files will be located inside a src/ folder, adding 'src/?.lua' at the end will enable looking up modules from that directory.

-- src/setup.lua
-- ...

package.path = 'lua_modules/share/lua/' .. version ..
    '/?.lua;lua_modules/share/lua/' .. version ..
    '/?/init.lua;' .. package.path .. ';src/?.lua'

Rock trees

It is important to note where packages are installed when using LuaRocks. So far, having the project set up via luarocks init, all packages were installed locally, inside the project folder. This is only the case due to the presence of the .luarocks and lua_modules folders. When this is not the case, packages are installed globally by default when a config file is not present.

Another option when not in a project is using the --local flag. Be aware: this does not mean local as in "local folder", this means local as in "the user's home directory". To really get a local installation, for example, inside the current working directory, the --tree flag needs to be used, passing the path to a folder.

$ luarocks install --tree=lua_modules inspect

Enable local scripts

Before continuing to add more tools to the project setup, it is quite handy to enable the execution of local scripts. When installing an executable with LuaRocks those binaries are installed in the lua_modules/bin folder.

To execute a script, the full path needs to be used.

$ ./lua_modules/bin/some-script --argument ...

To simplify this, the local bin folder can be added to the system PATH, which is especially handy when already using direnv.

# .envrc
export LUA_INIT="@src/setup.lua"
export PATH=$PATH:./lua_modules/bin

The same example command above then becomes the following when executed inside the project directory.

$ some-script --argument ...

Auto format code

I much appreciate auto code formatting from other projects and languages, like Prettier for JavaScript and TypeScript or clang-format for C++. I also want automatic code formatting for Lua.

LuaFormatter the tool of choice, installed via LuaRocks and thereafter available via the lua_modules/bin folder.

$ luarocks install \
    --server=https://luarocks.org/dev luaformatter

Custom format options can be defined in a .lua-format YAML file inside the project root. I'll only change a few options for my projects.

# .lua-format
keep_simple_control_block_one_line: false
keep_simple_function_one_line: false
column_table_limit: 1

With the local script setup enabled or using the path to the executable, the formatter can be run, and all Lua files are automatically formatted.

$ lua-format --in-place src/**/*.lua

Static analysis

To lint the project code base, Luacheck can be used, which is an executable installed via LuaRocks into the lua_modules/bin folder.

$ luarocks install luacheck

Keeping the default options, it can be run on all files inside src. A full list of all options can be found in the official Luacheck documentation.

$ luacheck src
Checking src/main.lua                             OK
Checking src/setup.lua                            OK

Total: 0 warnings / 0 errors in 2 files

Editor setup

No project setup is complete without setting up an editor environment. To have some options, I picked two well-known ones: IntelliJ IDE from JetBrains (paid) and VSCode from Microsoft (free).

JetBrains

Using any JetBrains product (e.g. CLion) for Lua development, I use the plugin Luanalysis, an EmmyLua fork. It comes with Luacheck bundled and offers many convenient functions like Find Usage, Refactor, Go To, Parameter Hints, and Documentation support, to name a few.

I could not find a way to auto-format code on save with LuaFormatter, though.

Visual Studio Code

For VSCode three plugins do the heavy lifting — the Lua language server plugin, the plugin for Luacheck, and another plugin for LuaFormatter.

The only plugin that really needs configuration is the LuaFormatter plugin, setting the path to the LuaFormatter executable and to the .lua-format config file.

VSCode's setting "Format on Save" can be used to automatically format the code.

Honorable mentions

Even though I focused on those two editors, I wanted to mention some more options for Lua development.

One of those options is ZeroBrane Studio, an IDE focused on Lua development. It has a lot of features focused on Lua, including resources to learn the language.

Neovim is another option that comes with Lua support out-of-the-box. Lua is even built-in, and plugins for the editor are written in it.

Close to my heart, Sublime Text is a great option for development in general. For Lua, I use the LuaExtended plugin, which brings even better support to the editor.

What comes next

This article was specifically focused on getting a good environment running to develop Lua. Everything shown here can be found in the companion repository, branch part-1.

The next article focuses on creating, building, and publishing new packages; how to manage versions; and how to add documentation to them.

Until then 👋🏻