Motivation for this change

mpv scripts were unable to import luasocket modules. Running mpv /dev/null --script=/tmp/path_to_script.lua with the following script:

-- test whether lua scripts can import luasocket modules
require("socket")
require("mime")
print("import successful")

failed with a Lua error: /tmp/script.lua:2: module 'socket' not found: error message.

Things done

Add LUA_CPATH LUA_PATH environment variables to the wrapped mpv binary.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.