fix(neovim): guard NixOS module to Linux for nix-darwin compatibility 🔧

- wrap Neovim module in `lib.mkIf pkgs.stdenv.isLinux` (no-op on macOS)
- add `lib` to module args
- fix Lua message var: use `config_file` instead of undefined `file`
- keep existing plugins and customRC on Linux unchanged

nixos/hosts/macos.nix

@@ -62,6 +62,7 @@
     fzf
     cowsay
     lolcat
+    neovim
   ];
 
   # Keep for darwin as well (tracks defaults across upgrades)

nixos/neovim.nix

@@ -1,9 +1,12 @@
-{ config, pkgs, ... }:
+{ lib, config, pkgs, ... }:
 
 {
+  # Only apply the Neovim NixOS module options on Linux.
+  config = lib.mkIf pkgs.stdenv.isLinux {
     programs.neovim = {
       enable = true;
       defaultEditor = true;
+
       configure = {
         customRC = ''
           set title
@@ -15,10 +18,9 @@
 
           lua << EOF
             local config_file = os.getenv("HOME")..'/.local/share/nvim_color_scheme'
-          local f=io.open(config_file, "r")
-          if f~=nil then 
+            local f = io.open(config_file, "r")
+            if f ~= nil then
                 local system_theme = f:read()
-              -- f:close()
                 io.close(f)
                 if system_theme == 'dark' then
                     vim.cmd("set bg=dark")
@@ -27,11 +29,11 @@
                 else
                     print('warning: expected value "light" or "dark"')
                     print('  got:', system_theme)
-                  print('  expected path:', file)
+                    print('  expected path:', config_file)
                 end
             else
                 print('warning: nvim color scheme not found')
-              print('  expected path:', file)
+                print('  expected path:', config_file)
             end
           EOF
 
@@ -56,14 +58,15 @@
           set spell spelllang=en_us
           setlocal spell! spelllang=en_us
         '';
+
         # vimPlugins inspired from Alexnortung
         # https://discourse.nixos.org/t/neovim-no-longer-uses-config-or-plugins/13399/4
         packages.nix = with pkgs.vimPlugins; {
           start = [
             vim-surround    # shortcuts for setting () {} etc.
             vim-gitgutter   # git diff in sign column
-          # vim-airline   # nice and light status bar # doesn't work nicely with tmux
-          # coc-nvim coc-git coc-highlight coc-python coc-rls coc-vetur coc-vimtex coc-yaml coc-html coc-json # auto completion
+            # vim-airline   # nice and light status bar (disabled for tmux)
+            # coc-nvim coc-* plugins (disabled for now)
             vim-nix         # nix highlight
             vimtex          # latex stuff
             fzf-vim         # fuzzy finder through vim
@@ -78,5 +81,5 @@
         };
       };
     };
+  };
 }
-