Re: [PATCH] Automatically set `geiser-guile-load-path' from .dir-locals

[Maxim Cournoyer]

Hello Christopher,

CC'ing Ludovic since they had that problem as well, so might be
interested in testing your solution.

Christopher Lemmer Webber <cwebber@dustycloud.org> writes:

[...]

> I figured out what was happening!  The bug is *technically* in vc-mode.
> However, nontheless it manifested here...
>
> Here's what happened.  vc-mode has some various hacks, as you can see
> above with "hack-local-variables-apply"... which traverses the dirlocals
> stuff.  (Not sure what the purpose is, didn't look too long.)
>
> However for whatever reason, vc-mode also seems to be reusing buffers
> such as `*vc-diff*'... and somehow still is left in the directory
> context it *first* was used in.
>
> Thus if I C-x v = in a guix-oriented buffer first, and then switch to
> another completely different project and do the same, it's loading the
> dirlocals from Guix(...!!!!)
>
> This is clearly a bug in vc-mode, I'll try to report it as such.

Thank you for the investigation.  I'd be really happy if you could
report the problem upstream (M-x report-emacs-bug) and link to it here!
Be sure to include a very detailed description of how to reproduce; I
for one still am unable to reproduce with the above instructions.  I've
tried many ways, using a pure environment, not loading my Emacs init
file, etc. based on what Miguel had written in IRC at the time of the
initial report, but to no avail.

> In the meanwhile, I used this hacky "fix".  Maybe worth applying for the
> moment... what do you think of it?

I'd like to have the upstream bug linked in that fix rather than the
Guix one; that way it'll be possible to track upstream resolution and
know when the workaround can be removed.

> #+BEGIN_SRC diff
> diff --git a/.dir-locals.el b/.dir-locals.el
> index 8e5d3902e3..2aa446a4f6 100644
> --- a/.dir-locals.el
> +++ b/.dir-locals.el
> @@ -17,17 +17,19 @@
>       ;; Geiser
>       ;; This allows automatically setting the `geiser-guile-load-path'
>       ;; variable when using various Guix checkouts (e.g., via git worktrees).
> -     (eval . (let* ((root-dir (expand-file-name
> -                               (locate-dominating-file
> -                                default-directory ".dir-locals.el")))
> -                    ;; Workaround for bug https://issues.guix.gnu.org/43818.
> -                    (root-dir* (directory-file-name root-dir)))
> -               (unless (boundp 'geiser-guile-load-path)
> -                 (defvar geiser-guile-load-path '()))
> -               (make-local-variable 'geiser-guile-load-path)
> -               (require 'cl-lib)
> -               (cl-pushnew root-dir* geiser-guile-load-path
> -                           :test #'string-equal)))))
> +     (eval . (let ((root-dir-unexpanded (locate-dominating-file
> +                                         default-directory 
> ".dir-locals.el")))
> +               (when root-dir-unexpanded
> +                 (let* ((root-dir (expand-file-name root-dir-unexpanded))
> +                        ;; Workaround for bug 
> https://issues.guix.gnu.org/43818.
> +                        (root-dir* (directory-file-name root-dir)))
> +
> +                   (unless (boundp 'geiser-guile-load-path)
> +                     (defvar geiser-guile-load-path '()))
> +                   (make-local-variable 'geiser-guile-load-path)
> +                   (require 'cl-lib)
> +                   (cl-pushnew root-dir* geiser-guile-load-path
> +                               :test #'string-equal)))))))
>
>   (c-mode          . ((c-file-style . "gnu")))
>   (scheme-mode
> #+END_SRC
>
> Btw, I'm not very familiar with dirlocals.  I see that setq is used in
> the previous definition.  Woudl setq-local be better... or does it do
> that by default?

Good observation.  The `guix-directory' is set globally.  It could be
neater if we made it also a buffer-local variable like the
`geiser-guile-load-path' below.

Thank you for having persevered in understanding the root cause of the
issue you had, and sharing the details here.

Maxim