Example usage of LuaPreprocess+LÖVE.

_info.txt

I have a separate installation of Lua that I use to build the game (though you could use LÖVE too).
I run build.lua which processes all Lua files in the project and starts the game.

> lua buildSystem/build.lua

This example uses 3 folders:
- buildSystem/ for things used to build the game.
- src/ for unprocessed files.
- srcgen/ for processed/generated files.

I use a different extension for unprocessed files (.lua2p) so I don't get confused while working on the game.

build.lua

-- buildSystem/build.lua
local pp = require("buildSystem.preprocess")

-- Settings for the build system.
local OUTPUT_ZIP = false

-- Add values that all files use. The values in pp.metaEnvironment
-- will be globals in the files we're about to process.
pp.metaEnvironment.DEVELOPER_MODE    = true
pp.metaEnvironment.DISABLE_SOUNDS    = false
pp.metaEnvironment.GAME_VERSION_NAME = "v1.0.8 (Tomato)"

-- Get paths to all Lua files in the src/ folder.
local paths = getLuaFilesInDirectory("src")

for _, pathIn in ipairs(paths) do
	local pathOut = pathIn

	-- Output the files into the srcgen/ folder.
	pathOut = pathOut:gsub("^src/", "srcgen/")

	-- The unprocessed files have a different extension (.lua2p)
	-- so I don't get confused.
	pathOut = pathOut:gsub("%.lua2p$", ".lua")

	-- Output main.lua into the top folder instead of srcgen/.
	if pathOut == "srcgen/main.lua" then
		pathOut = "main.lua"
	end

	local info, err = pp.processFile{ pathIn=pathIn, pathOut=pathOut }

	-- Just exit if there was an error while processing the file.
	-- An error message should already have been printed to the console.
	if not info then  os.exit(1)  end
end

if OUTPUT_ZIP then
	-- Output a .zip file.
	os.execute("some_program_that_creates_a_zip_file.exe")
else
	-- Execute LÖVE in the top/current folder to start the game.
	os.execute("love.exe .")
end

main.lua2p

-- src/main.lua2p

-- require() should look in the top folder or the srcgen/ folder.
package.path = "?.lua;srcgen/?.lua"

function love.load()
	!if DEVELOPER_MODE then
		doDevStuff()
	!end

	require("menus")
	showMainMenu()
end

menus.lua2p

-- src/menus.lua2p

function _G.showMainMenu()
	!if not DEVELOPER_MODE then
		showSplashScreen()
	!end
end

Where is this function getLuaFilesInDirectory found?

You'll have to define it yourself. Since Lua has no way of retrieving files in a directory by default you'll have to use something like LuaFileSystem.

I suggest you also provide one?
here's a working one on my case

local getLuaFilesInDirectory = function(str)
	local f = io.popen("ls " .. str)
	if f then
		local files = {}
		for line in f:lines() do
			local path = str .. "/" .. line
			table.insert(files, path)
		end
		return files
	end
	return nil
end

I left out implementation details involving the operative system on purpose because things work differently everywhere. For Windows you'd use something like io.popen("dir /b "..str) instead of io.popen("ls "..str).

Oh yeah, got it! Thanks!