Can I mark a local variable as safe for a single file only?

Question

I have a LaTeX-file (thesis.tex) which I edit daily. Some LaTeX-package I use requires me to compile the file with --shell-escape, so I added the file-local variable

%%% TeX-command-extra-options: "--shell-escape"

at the end of my file. This variable is considered risky, so every time I open my file, emacs asks me to confirm this variable is safe for this file. This is a bit annoying.

For arbitrary files I totally agree with the reasoning that --shell-escape is unsafe, so I do not want to mark this value as safe for arbitrary files by customizing safe-local-variable-values, as described in the documentation.

Is it possible to mark this local variable safe only for thesis.tex?

Answer 1

In the elisp manual at C-hig (elisp)File Local Variables we find:

You can specify safe values for a variable with a ‘safe-local-variable’ property. The property has to be a function of one argument; any value is safe if the function returns non-‘nil’ given that value. Many commonly-encountered file variables have ‘safe-local-variable’ properties; these include ‘fill-column’, ‘fill-prefix’, and ‘indent-tabs-mode’. For boolean-valued variables that are safe, use ‘booleanp’ as the property value.

Hence in your config you can set this to a function which approves your specific file.

(put 'TeX-command-extra-options 'safe-local-variable
     (lambda (value)
       (and (equal value "--shell-escape")
            (equal buffer-file-name "/path/to/thesis.tex"))))