bug#70136: 30.0.50; compilation-mode [was: comint-mode] doesn't call hack-dir-local-variables-non-file-buffer

[Eli Zaretskii]

> From: Augusto Stoffel <arstoffel@gmail.com>
> Cc: 70136@debbugs.gnu.org,  Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Sun, 14 Apr 2024 11:27:28 +0200
> 
> Since compilation buffers go as far as to print the directory they're
> running on at the top of the buffer, I think it's pretty clear they
> should receive dir-local variables.
> 
> So I'd suggest the attached patch, which does that and also removes a
> more limited mechanism I added some time ago to allow compilation with
> project-specific settings.  I've CC'ed Stefan since at the time he kind
> of supported the changes I'm now suggesting to remove.

Thanks, but I think this should be optional behavior, by default off,
because it could cause trouble in directory trees which already have
.dir-locals.el that were not intended to affect compilation-mode (and
its descendants, like Grep).

Also, this needs a NEWS entry, I think.

> +  (unless (buffer-file-name)
> +    (let ((sym (make-symbol "hack-dir-local-variables-non-file-buffer")))
> +      (set sym #'hack-dir-local-variables-non-file-buffer)
> +      ;; Ensure hack-dir-locals is called only after a derived mode is set.
> +      (push sym delayed-mode-hooks)))

Why such a complicated way of using the symbol of a function that's
defined in a preloaded Lisp file?  Am I missing some subtlety here?