neovim/basic: add undofile options (#367)

`vim.undoFile.enable` and `vim.undoFile.path` can be used to manipulate whether undofile will be enabled, and the location if it is enabled.

modules/neovim/init/basic.nix

@@ -3,11 +3,13 @@
   lib,
   ...
 }: let
-  inherit (lib.options) mkOption literalExpression;
+  inherit (lib.options) mkOption mkEnableOption literalExpression literalMD;
   inherit (lib.strings) optionalString;
-  inherit (lib.types) enum bool str int;
+  inherit (lib.types) enum bool str int either;
+  inherit (lib.generators) mkLuaInline;
   inherit (lib.nvim.dag) entryAfter;
   inherit (lib.nvim.lua) toLuaObject;
+  inherit (lib.nvim.types) luaInline;
 
   cfg = config.vim;
 in {
@@ -158,9 +160,29 @@ in {
       default = "sensitive";
       description = "Set the case sensitivity of search";
     };
+
+    undoFile = {
+      enable = mkEnableOption "undofile for persistent undo behaviour";
+      path = mkOption {
+        type = either str luaInline;
+        default = mkLuaInline "vim.fn.stdpath('state') .. '/undo'";
+        defaultText = literalMD ''
+          ```nix
+          mkLuaInline "vim.fn.stdpath('state') .. '/undo'"
+          ```
+        '';
+        example = literalMD ''
+          ```nix
+          mkLuaInline "os.getenv('XDG_DATA_HOME') .. '/nvf/undo'"
+          ```
+        '';
+        description = "Path to the directory in which undo history will be stored";
+      };
+    };
   };
 
-  config.vim.luaConfigRC.basic = entryAfter ["globalsScript"] ''
+  config = {
+    vim.luaConfigRC.basic = entryAfter ["globalsScript"] ''
       -- Settings that are set for everything
       vim.o.encoding = "utf-8"
       vim.o.hidden = true
@@ -178,6 +200,11 @@ in {
       vim.g.mapleader = ${toLuaObject cfg.leaderKey}
       vim.g.maplocalleader = ${toLuaObject cfg.leaderKey}
 
+      ${optionalString cfg.undoFile.enable ''
+        vim.o.undofile = true
+        vim.o.undodir = ${toLuaObject cfg.undoFile.path}
+      ''}
+
       ${optionalString cfg.splitBelow ''
         vim.o.splitbelow = true
       ''}
@@ -266,4 +293,5 @@ in {
         vim.o.ignorecase = false
       ''}
     '';
+  };
 }