Making LuaRocks (partially) compliant with the XDG Base Directory specification

LuaRocks is a community-driven package manager for the Lua programming language. LuaRocks packages can be installed globally or in the user's home directory, but sadly LuaRocks does not follow the XDG Base Directory specification. However, with a few lines of Lua code we can fix this shortcoming partially at least.

Package directory

LuaRocks's global configuration file depends on the particular version of Lua it uses. For example, if you use Lua 5.3, then file path is /etc/luarocks/config-5.3.lua. There we can adjust the rocks_trees table entry which has its name set to "user". There is one problem though: the file is loaded from within a sandbox, which means that we do not have access to the Lua standard library. Here is the adjusted table:

rocks_trees = {
   { name = "user", root = (os_getenv("XDG_DATA_HOME") or (home .. '/.local/share')) .. "/luarocks" };
   { name = "system", root = "/usr" };

The second entry is unchanged, the first entry is what we had to change. The root entry contains the path to the directory we will be using to store packages. Let me rewrite the expression a bit to be more readable:

   (os_getenv("XDG_DATA_HOME") or (home .. '/.local/share'))
   .. "/luarocks"

The first line gets either the value of the environment variable $XDG_DATA_HOME, or uses ~/.local/share as the default fallback, as defined in the specification. Note that we have to use os_getenv instead of os.getenv from the standard library because we are inside a sandbox. Please refer to the documentation for more information about the sandbox.

Be aware that this changes the directory for all users on the system. There does not seem to be a way to first check whether the directory ~/.luarocks exists from within the sandbox. This might trip up users who had already installed packages before the change. It's simply something they will have to live with.

Configuration directory

I have to pass on this one. From what I have seen there is no way of changing the location of the user configuration file. The system configuration file can be changed during compilation, or at runtime through the $LUAROCKS_CONFIG environment variable, but nothing similar exists for the user configuration file.