A really simple C program that lets you load Lua scripts into "Sky: Children of the Light" (desktop version) through a named pipe while it's running. The scripts run in the game's built-in Lua engine.
The provided terminal.c lets you script in a command line (like a REPL) to load scripts into the game, while hotload.c lets you load scripts from a directory.
The mod itself is comprised of debug.c (a DLL file that is loaded into the game to listen for incoming scripts) and launch.c (for launching the game and injecting debug.dll into it).
You have to do the DLL injection immediately when the game process starts, not after the game engine initializes, otherwise for some reason game output (including lines written by Lua print and io.write) doesn't get printed to stdout. It's something to do with the way the game engine initializes the console. That's why launch.c launches an executable and immediately injects the DLL into the created process rather than just being an injector. You have to pass the name of the game binary and the DLL (the game binary is Sky.exe, the DLL is debug.c). You can create a launch script called play.bat like this:
@echo off
bin\launch.exe bin\debug.dll "C:\Program Files (x86)\Steam\steamapps\common\Sky Children of the Light\Sky.exe"
bin\terminal.exe
This launches the game and opens terminal.exe (example compilation of terminal.c) automatically. (Note: in this example, terminal.exe keeps the named pipe open, so hotload.exe won't work at the same time.)
I've only tested this on Linux with wine, and haven't actually tested it on Windows, so I don't know if it works on native Windows. It works on my system at the time of writing this README file, and it has continued to work through multiple updates, so it will probably continue to work.
It's really simple since there are no dependencies besides standard built-in Windows and C stuff (windows.h, stdio.h, stdint.h, string.h, and direct.h are the only headers used). I personally use x86_64-w64-mingw32, but you can use anything:
x86_64-w64-mingw32-gcc -shared -o bin/debug.dll debug.c
x86_64-w64-mingw32-gcc -o bin/launch.exe launch.c
x86_64-w64-mingw32-gcc -o bin/terminal.exe terminal.c
x86_64-w64-mingw32-gcc -o bin/hotload.exe hotload.c -Wl,--subsystem,windows
The -Wl,--subsystem,windows is just for disabling the console, since I don't want it to flash and disrupt my input in the game when I load a script.
If it breaks, two patterns in debug.c need to be updated. debugdostring is the debug function built into the game that loads code from a Lua source string. update is nonspecific, it's just a function that runs in the game's main loop and receives a Lua state pointer - it can be replaced with any other similar function (the criteria being that it gets a Lua state and runs in the game's main update thread).
The main update thread thing is important because Lua is single-threaded, so debugdostring has to be called from within the game's main thread. If you tried calling it directly, it would cause occasional crashes.