.dir-local.el misunderstanding

Question

I generated a .dir-locals.el by calling the function add-dir-local-variable, giving it the path for the project for which I want the variable, the variable itself, and its value.

The generated file went to my home directory (not the project path as I expected), and had the following content:

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

(("~/tmp/test_test_dir_local"
  (indent-tabs-mode . t)))

Then I went on and created a file a.c in that directory, and copied .dir-locals.el there for good measure.

The indent in that file is still set as spaces, as per my ~/.emacs.d/init.el. I expected it to be tabs, as per the local .dir-locals.el. I tried restarting emacs, but that did not work either.

What did I do wrong, or misunderstand?

I am on Mac OS Sierra.

Answer 1

When you call add-dir-local-variable, it assumes you are already in the directory you want to apply the directory-local variable to. When it prompts for a directory, it's asking if you want the variable applied to a subdirectory of your current directory.

So I expect giving it the absolute path to a directory is causing your problem. In your case, I think what you need is a .dir-locals.el file in the directory you're targeting (i.e., ~/tmp/test_test_dir_local) that contains the following:

((nil
  (indent-tabs-mode . t)))

The nil symbol indicates that this variable will be applied to all files in all subdirectories of the ~/tmp/test_test_dir_local. You can change it to indicate you only want it applied to a certain subdirectory (in quotes):

(("src"
  (indent-tabs-mode . t)))

Or a particular major mode (no quotes):

((c-mode
  (indent-tabs-mode . t)))