[backport #3639] programs.neovim: add extraLuaConfig (#3727)

Co-authored-by: Guillaume Desforges <guillaume.desforges.pro@gmail.com>

modules/programs/neovim.nix

@@ -240,6 +240,17 @@ in {
         '';
       };
 
+      extraLuaConfig = mkOption {
+        type = types.lines;
+        default = "";
+        example = ''
+          vim.opt.nobackup = true
+        '';
+        description = ''
+          Custom lua lines.
+        '';
+      };
+
       extraPackages = mkOption {
         type = with types; listOf package;
         default = [ ];
@@ -373,6 +384,7 @@ in {
             luaRcContent =
               lib.optionalString (neovimConfig.neovimRcContent != "")
               "vim.cmd [[source ${config.xdg.configHome}/nvim/init-home-manager.vim]]"
+              + config.programs.neovim.extraLuaConfig
               + lib.optionalString hasLuaConfig
               config.programs.neovim.generatedConfigs.lua;
           in mkIf (luaRcContent != "") { text = luaRcContent; };

tests/modules/programs/neovim/default.nix

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

tests/modules/programs/neovim/extra-lua-init.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    programs.neovim = {
+      enable = true;
+
+      extraLuaConfig = ''
+        -- extraLuaConfig
+      '';
+    };
+    nmt.script = ''
+      nvimFolder="home-files/.config/nvim"
+      assertFileContent "$nvimFolder/init.lua" ${
+        pkgs.writeText "init.lua-expected" ''
+          -- extraLuaConfig
+        ''
+      }
+    '';
+  };
+}