nixos/pkgsets/emacs/undo-tree.nix

{
  config,
  lib,
  ...
}:
with lib;
  mkIf (elem "emacs::undo-tree" config.machine.pkgs) {
    programs.emacs.init.usePackage.undo-tree = {
      enable = true;
      hook = ["(after-init . global-undo-tree-mode)"];
      config = ''
        (setq undo-tree-visualizer-diff 't)
        (setq undo-tree-auto-save-history 't)
        (setq undo-tree-enable-undo-in-region 't)
        (setq undo-tree-history-directory-alist '(("." . "~/.emacs_undo")))
      '';
    };
  }