LuaRocks can't find the custom build back-end for the current Lua version

[jonasgeiler]

• Platform: Windows

• LuaRocks version: 3.9.2

• Configuration file:

  lua_version = "5.1"
  

• LuaRocks output from when the issue occurred:

  • LuaRocks output with --verbose
  • LuaRocks output without --verbose:

    PS C:\Users\skayo\Documents> luarocks install lua-ryaml
    Installing https://luarocks.org/lua-ryaml-0.1.0-1.src.rock
    
    lua-ryaml 0.1.0-1 depends on lua >= 5.1 (5.1-1 provided by VM)
    lua-ryaml 0.1.0-1 depends on luarocks-build-rust-mlua (0.1.0-1 installed)
    
    Error: Failed initializing build back-end for build type 'rust-mlua': module 'luarocks.build.rust-mlua' not found:
            Failed loading module luarocks.build.rust-mlua in LuaRocks rock luarocks-build-rust-mlua 0.1.0-1
            no field package.preload['luarocks.build.rust-mlua']
            no file 'C:\Program Files\LuaRocks\lua\luarocks\build\rust-mlua.lua'
            no file 'C:\Program Files\LuaRocks\lua\luarocks\build\rust-mlua\init.lua'
            no file 'C:\Program Files\LuaRocks\luarocks\build\rust-mlua.lua'
            no file 'C:\Program Files\LuaRocks\luarocks\build\rust-mlua\init.lua'
            no file 'C:\Program Files\LuaRocks\..\share\lua\5.4\luarocks\build\rust-mlua.lua'
            no file 'C:\Program Files\LuaRocks\..\share\lua\5.4\luarocks\build\rust-mlua\init.lua'
            no file '.\luarocks\build\rust-mlua.lua'
            no file '.\luarocks\build\rust-mlua\init.lua'
            no file 'C:\Users\skayo\AppData\Roaming/luarocks/share/lua/5.4/luarocks\build\rust-mlua.lua'
            no file 'C:\Users\skayo\AppData\Roaming/luarocks/share/lua/5.4/luarocks\build\rust-mlua/init.lua'
            no file 'C:\Program Files\LuaRocks\luarocks\build\rust-mlua.dll'
            no file 'C:\Program Files\LuaRocks\..\lib\lua\5.4\luarocks\build\rust-mlua.dll'
            no file 'C:\Program Files\LuaRocks\loadall.dll'
            no file '.\luarocks\build\rust-mlua.dll'
            no file 'C:\Users\skayo\AppData\Roaming/luarocks/lib/lua/5.4/luarocks\build\rust-mlua.dll'
            no file 'C:\Program Files\LuaRocks\luarocks.dll'
            no file 'C:\Program Files\LuaRocks\..\lib\lua\5.4\luarocks.dll'
            no file 'C:\Program Files\LuaRocks\loadall.dll'
            no file '.\luarocks.dll'
            no file 'C:\Users\skayo\AppData\Roaming/luarocks/lib/lua/5.4/luarocks.dll'
    

• Description:
  Okay so I installed Lua 5.1 by building from source using Visual Studio 2022, and then manually created the C:\Program Files\Lua folder and moved all the built .dll and .exe files in there, as well as create a include folder with the Lua headers and a lua\luarocks folder with all the LuaRocks files (for the loader).
  Then, I created the C:\Program Files\LuaRocks folder and put the two LuaRocks .exe in there.
  Afterwards, I told LuaRocks not to use the inbuilt Lua version using luarocks --scope system lua_version 5.1.

  The problem I am now facing is that for some reason LuaRocks won't respect this Lua version when it is searching for custom build back-ends. As you can see in the error message above, it's looking for C:\Users\skayo\AppData\Roaming/luarocks/share/lua/5.4/luarocks\build\rust-mlua.lua even though C:\Users\skayo\AppData\Roaming/luarocks/share/lua/5.1/luarocks\build\rust-mlua.lua actually exists and should be used. But it's only looking for the 5.4 version for some reason...

  I think the way I installed everything is unrelated to this bug, and that the problem lies somewhere within the LuaRocks source code. But I don't know anything about the code so correct me if I'm wrong. When I run luarocks without any arguments it shows ok for all the configuration entries.
  Also I don't think it's a problem with this custom build back-end either.
  Let me know if you need any additional info.

[jonasgeiler]

Okay so I actually looked where this error message originates from in the source code and I found it in the build.lua file. Above this line I noticed that it's just requireing the build back-end that is needed, so I tried this:

PS C:\Users\skayo\Documents> lua -l luarocks.loader
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> return pcall(require, "luarocks.build.rust-mlua")
true    table: 0000022AE1726210

So as you can see when I require the build back-end manually, it's found without problems. It's just that LuaRocks won't find it...

[jonasgeiler]

A temporary fix I've found is to create a junction/symlink like this:

mklink /j "C:\Users\skayo\AppData\Roaming\luarocks\share\lua\5.4" "C:\Users\skayo\AppData\Roaming\luarocks\share\lua\5.1"