Mods may use LuaJIT-only features, leading to incompatibility with PUC Lua 5.1

[Ratstail91]

Luanti version

Luanti 5.11.0 (Linux)
Using Lua 5.1.5
Built by GCC 12.2
Running on Linux/6.6.74 aarch64
BUILD_TYPE=Release
RUN_IN_PLACE=0
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="/usr/local/share/luanti"
STATIC_LOCALEDIR="/usr/local/share/locale"

Operating system and version

Linux raspberrypi 6.6.74+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.6.74-1+rpt1 (2025-01-27) aarch64 GNU/Linux

CPU model

No response

GPU model

No response

Active renderer

No response

Summary

Due the the currently bundled version of lua, the goto statement in a game caused an error.

The specific issue can be found here: asuna-mt/asuna#15

However, I believe that updating the lua engine to a more modern build would resolve this issue, and enable the use of the goto keyword for all projects, not just this one.

This was my very first time trying Luanti, as I was hoping to write a summary article for a gaming website - please advise if this upgrade is possible any time soon, thanks.

Steps to reproduce

Here is the process I followed:

1. Platform is a Raspberry Pi (for unrelated reasons)
2. Download the source of the latest release as a zip file
3. run sudo cmake ., installing any missing dependancies via apt
4. run sudo make install to install it properly
5. download the game "Asuna" from the game browser
6. Create a new world, and try to run it
7. You'll be met with the following error message:

ModError: Failed to load and run script from /home/kruse/.minetest/games/asuna/mods/worldgate/init.lua:
/home/kruse/.minetest/games/asuna/mods/worldgate/src/mapgen.lua:157: '=' expected near 'retry_probe'
stack traceback:
	[C]: ?
	[C]: in function 'dofile'
	.../kruse/.minetest/games/asuna/mods/worldgate/init.lua:37: in function 'load'
	.../kruse/.minetest/games/asuna/mods/worldgate/init.lua:43: in main chunk
Check debug.txt for details.

The erroneous code is:

if not heightmapy then
    goto retry_probe
end

Which is effectively the lua "continue" stand-in, using the goto keyword.

[rubenwardy]

Games should not use the goto statement as it is not supported in all Luanti builds

There are two main implementations of lua - PUC Lua (the official implementation) and LuaJIT. All official Luanti builds ship with LuaJIT, a reimplementation of Lua that is magnitudes faster. LuaJIT only supports up to 5.1 of the Lua language, with some features above that including goto. To ensure compatibility of games and mods across Luanti versions, we only support PUC Lua 5.1 as well

This is unlikely to change unless LuaJIT supports newer language versions, which they intentionally do not

[rubenwardy]

For reasons why LuaJIT only supports 5.1, see LuaJIT/LuaJIT#929 (comment)

[appgurueu]

Side note, especially when you're running a heavier game on a weaker device like a raspi, you probably really want LuaJIT.

It should also be noted that Lua 5.2+ introduce various breaking changes, so we couldn't "just" upgrade even if we wanted to.

[ryvnf]

Also note that we have gotten multiple elusive bug reports in Mineclonia which have only been reproducible on ARM:

• https://codeberg.org/mineclonia/mineclonia/issues/3072
• https://codeberg.org/mineclonia/mineclonia/issues/2989
• https://codeberg.org/mineclonia/mineclonia/issues/2971
• https://codeberg.org/mineclonia/mineclonia/issues/1627

These problems have all gone away when after compiling Luanti with -DENABLE_LUAJIT=OFF. We have not made an issue here yet because someone wanted to investigate further and make their own bug report.

I think this may be of some relevance to this issue "Lua version is several patches behind". Updating luajit may solve other problems since it appears to be somewhat unstable on ARM.

[rollerozxa]

Updating luajit may solve other problems since it appears to be somewhat unstable on ARM.

Yes, it's a well known issue that Debian ships old versions of LuaJIT that are very unstable on ARM. People running servers on a Pi will need to build the latest LuaJIT from source.

Running --version on the engine binary should show what version of LuaJIT is used, and now with LuaJIT's rolling release versioning the last version digit will show the timestamp of the commit that was built from. If it says beta3 or similar then it's a good sign it is too old.

[sfan5]

If you get a bug report with a Lua-related segfault from someone running "LuaJIT 2.1.0-beta3" you can save yourself the time and discard it immediately. As of this year that that release is 8 years old.
(Our official Android build uses LuaJIT from git, since it's now rolling release.)