neovim: Add missing newlines to init.lua

When generating `init.lua` the Lua config would be placed immediately
after the nvim config without a new line.

```
vim.cmd [[source /nix/store/cs3al9x1ml5ds3n6n433wcdxp89awac4-nvim-init-home-manager.vim]]--first line of Lua config
```

This change places a newline after each config portion.

```
vim.cmd [[source /nix/store/cs3al9x1ml5ds3n6n433wcdxp89awac4-nvim-init-home-manager.vim]]
--first line of Lua config
```

modules/programs/neovim.nix

@@ -392,22 +392,21 @@ in {
 
     home.sessionVariables = mkIf cfg.defaultEditor { EDITOR = "nvim"; };
 
-    xdg.configFile =
-      let hasLuaConfig = hasAttr "lua" config.programs.neovim.generatedConfigs;
+    xdg.configFile = let
+      hasLuaConfig = hasAttr "lua" config.programs.neovim.generatedConfigs;
+      vimRcContent = lib.optionalString (neovimConfig != "") pkgs.writeText
+        "nvim-init-home-manager.vim" neovimConfig.neovimRcContent;
+      luaRcContent = lib.concatStringsSep "\n" (lib.remove "" [
+        (lib.optionalString (vimRcContent != "")
+          "vim.cmd [[source ${vimRcContent}]]")
+        (config.programs.neovim.extraLuaConfig)
+        (lib.optionalString hasLuaConfig
+          config.programs.neovim.generatedConfigs.lua)
+      ]);
     in mkMerge (
       # writes runtime
       (map (x: x.runtime) pluginsNormalized) ++ [{
-          "nvim/init.lua" = let
-            luaRcContent =
-              lib.optionalString (neovimConfig.neovimRcContent != "")
-              "vim.cmd [[source ${
-                pkgs.writeText "nvim-init-home-manager.vim"
-                neovimConfig.neovimRcContent
-              }]]" + config.programs.neovim.extraLuaConfig
-              + lib.optionalString hasLuaConfig
-              config.programs.neovim.generatedConfigs.lua;
-          in mkIf (luaRcContent != "") { text = luaRcContent; };
-
+        "nvim/init.lua" = mkIf (luaRcContent != "") { text = luaRcContent; };
         "nvim/coc-settings.json" = mkIf cfg.coc.enable {
           source = jsonFormat.generate "coc-settings.json" cfg.coc.settings;
         };

tests/modules/programs/neovim/default.nix

@@ -6,4 +6,5 @@
   # waiting for a nixpkgs patch
   neovim-no-init = ./no-init.nix;
   neovim-extra-lua-init = ./extra-lua-init.nix;
+  neovim-init-newline = ./init-newline.nix;
 }

tests/modules/programs/neovim/init-newline.nix

@@ -0,0 +1,28 @@
+{ config, lib, pkgs, ... }:
+with lib;
+let
+  extraConfig = ''
+    echo extraConfigVim
+  '';
+in {
+  config = {
+    programs.neovim = {
+      enable = true;
+      inherit extraConfig;
+      extraLuaConfig = ''
+        -- extraLuaConfig
+      '';
+    };
+    nmt.script = ''
+      nvimFolder="home-files/.config/nvim"
+      assertFileContent "$nvimFolder/init.lua" ${
+        pkgs.writeText "init.lua-expected" ''
+          vim.cmd [[source ${
+            pkgs.writeText "nvim-init-home-manager.vim" extraConfig
+          }]]
+          -- extraLuaConfig
+        ''
+      }
+    '';
+  };
+}