如何相对于.dir-locals.el文件位置设置目录局部变量？

我经常遇到被告知将相对路径作为目录局部变量的情况。例如cmake-ide的cmake-ide-project-dir和cmake-ide-build-dir。当然，这不是很方便。

所以代替

.dir-locals.el：

((nil . ((cmake-ide-project-dir . "/home/user/code/project"))))

我想要类似的东西

((nil . ((cmake-ide-project-dir . directory-of-current-dir-locals-file))))

如何定义这样的变量directory-of-current-dir-locals-file？举例来说cmake-ide-build-dir，我该如何设置(concat directory-of-current-dir-locals-file "build")？

到目前为止，我的解决方案（基于此Stackoverflow答案）：

.dir-locals.el：

;;; Directory Local Variables
;;; For more information see (info "(emacs) Directory Variables")

((nil . ((eval . (set (make-local-variable 'my-project-path)
                      (file-name-directory
                       (let ((d (dir-locals-find-file ".")))
                         (if (stringp d) d (car d))))))
         (cmake-ide-project-dir . my-project-path)
         (eval . (setq cmake-ide-build-dir (concat my-project-path "build")))
         )))

您可以使用定义变量(defvar directory-of-current-dir-locals-file "/home/user/code/project")。