Permanently Set File-Local Variables in Doom Emacs

From time to time, it’s useful to set local variables within an org file. For instance, I have a file whose subsections I’d like to encrypt. This being the case, I need to turn off autosave (since this could save plain text). To do this for the buffer, I add this to the top:

# -*- buffer-auto-save-file-name: nil; -*-

Emacs is understandably wary of running elisp simply because it exists in the file, however. Upon opening this buffer, it warns:

The local variables list in [filename] contains variables that are risky

This is followed by a question about allowing them on this occasion only. Globally, the level of wariness is controlled by the variable enable-local-variables, whose explanation is given here: File Local Variables - GNU Emacs Lisp Reference Manual.

I would, however, like to avoid setting this globally. I’d prefer that Emacs adds safe variables to a whitelist. I’d consider turning off autosave to be reasonably safe, so the first thing I tried was adding it to the whitelist. The safe variable is called safe-local-variable-values and is defined in the Emacs installation itself (i.e. in /usr/local, where my Emacs installation lives).

Because I use Doom Emacs, I put the following into my ./config/Doom/config.el (which is actually tangled from my config.org):

  (add-to-list 'safe-local-variable-values '("buffer-auto-save-filename" . "nil") t)

But this didn’t work. At first, I thought that perhaps the above elisp is running too early, as the list when I inspected it after opening Emacs showed only the original values (referring to variables relevant to other files). How late, I wondered, could I make this code run? After the org module is loaded?1

(after! org
  (add-to-list 'safe-local-variable-values '("buffer-auto-save-filename" . "nil") t)
  )

Still no luck.

It turns out that safe-local-variables was being set in /.config/Doom/init.el–this should have been before my config.el, and yet my config.el code was not modifying the variable.

Fine, I thought–I’ll carefully edit the part of the init.el setting safe-local-variables. But I still saw the same behaviour in my target file: I was being asked, temporarily, if I wanted to permit the variable buffer-auto-save-file-name to be set. Why wouldn’t my method work? I wasn’t sure. But since Doom had set the variables successfully before from other org files previousl, writing them to safe-local-variables in its own init.el, I had a look at how those files set variables and I saw that it was done in a slightly different manner:

* Local variables :noexport:
# local variables:
# +org-export-directory: "projects/"
# end:

I tried this with my problematic file. First schoolboy error: I didn’t place it at the end of the file. This fixed, I tried again. But Emacs persisted in prompting me to only allow setting buffer-auto-save-filename temporarily. Why not permanently?

I went back and looked again at the elisp in my /.config/Doom/init.el and realised that I had put NIL in quotes. Second schoolboy error. Of course, it shouldn’t have quotes—it needs to be plain old NIL. The correct code in the .init is thus:

(custom-set-variables
 ;; custom-set-variables was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 '(custom-safe-themes
   (quote
    ("427fa665823299f8258d8e27c80a1481edbb8f5463a6fb2665261e9076626710" "e838d6375a73fda607820c65eb3ea1f9336be7bd9a5528c9161e10c4aa663b5b" "80365dd15f97396bdc38490390c23337063c8965c4556b8f50937e63b5e9a65c" "fe666e5ac37c2dfcf80074e88b9252c71a22b6f5d2f566df9a7aa4f9bea55ef8" default)))
 '(safe-local-variable-values
   (quote
    ((+org-export-directory . "projects/")
     (+org-export-directory . "projects/cccuWorkloadModel")
     (+org-export-dir . "projects/cccuWorkloadModel")
     (buffer-auto-save-file-name . nil)))))

  1. The after! org is a Doom wrapper function that ensures the elisp codes that follows is evaluated after a given module is loaded. [return]
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