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

[Christopher Lemmer Webber]

Also, I hope this email isn't interpreted as being dismissive or negative
about what looks like it's probably a real usability improvement for
hacking on Guix!  I just thought my experience indicated maybe there are
additional considerations to address.

Christopher Lemmer Webber writes:

> Maxim Cournoyer writes:
>
>> Hello Guix!
>>
>> I've been experimenting with the following modification to the
>> .dir-locals file shipped with Guix, that allows setting per-buffer
>> variables within Emacs when visiting a file in the same directory (or in
>> one of its sub-directories).
>>
>> This makes life a bit easier, by ensuring that a Geiser REPL started
>> with C-c C-a in a file of either the main 'guix' checkout, a
>> 'guix-core-updates' worktree or a 'guix-staging' worktree will set up
>> the GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH correctly (via the
>> `geiser-guile-load-path' Elisp variable).
>>
>> The only requirement for it to work reliably is that any Guix checkout
>> or worktree name should start with "guix".
>>
>> It doesn't require Geiser to be installed (it will just set the above
>> variable uselessly if it isn't used -- not a big deal).
>>
>> What do you think?  Is it useful?  Should we include this as part of the
>> default .dir-locals of Guix?
>>
>> Patch to follow!
>>
>> Thanks,
>>
>> Maxim
>
> I'm a bit unsure what the implications fully are with this change, but
> here was my user experience:
>
>  - Did a pull using magit to guix
>  - Suddenly every file I open in Guix is prompting me if I want to
>    enable these dir-locals, I notice some have "eval" and I don't know
>    what it's doing so I say no
>  - But it's asking me every file
>  - And oh no, it's asking me about ten times for every magit operation!
>    (Presumably due to the reload operation.)  Fine okay fine, YES, okay
>    cool it's quiet now... I hope that was safe.
>
> Later...
>
>  - I'm hacking on another file in another repo
>  - C-x v = (check to see a diff of the work-in-progress changes of the
>    file I'm working on)
>  - Error in the minibuffer!  "Wrong type argument: stringp, nil"
>  - wtf, okay M-x toggle-debug-on-error
>
> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>   expand-file-name(nil)
>   (let* ((root-dir (expand-file-name (locate-dominating-file 
> default-directory ".dir-locals.el"))) (root-dir* (directory-file-name 
> root-dir))) (unless (boundp 'geiser-guile-load-path) (defvar 
> geiser-guile-load-path 'nil)) (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 (expand-file-name (locate-dominating-file 
> default-directory ".dir-locals.el"))) (root-dir* (directory-file-name 
> root-dir))) (unless (boundp 'geiser-guile-load-path) (defvar 
> geiser-guile-load-path 'nil)) (make-local-variable 'geiser-guile-load-path) 
> (require 'cl-lib) (cl-pushnew root-dir* geiser-guile-load-path :test 
> #'string-equal)))
>   hack-one-local-variable(eval (let* ((root-dir (expand-file-name 
> (locate-dominating-file default-directory ".dir-locals.el"))) (root-dir* 
> (directory-file-name root-dir))) (unless (boundp 'geiser-guile-load-path) 
> (defvar geiser-guile-load-path 'nil)) (make-local-variable 
> 'geiser-guile-load-path) (require 'cl-lib) (cl-pushnew root-dir* 
> geiser-guile-load-path :test #'string-equal)))
>   hack-local-variables-apply()
>   hack-dir-local-variables-non-file-buffer()
>   diff-mode()
>   vc-diff-internal(t (Git 
> ("/home/cwebber/devel/scribble/scribble-lib/scribble...")) nil nil t)
>   vc-diff(nil t)
>   funcall-interactively(vc-diff nil t)
>   call-interactively(vc-diff nil nil)
>   command-execute(vc-diff)
>  
>  - Oh... it's whatever thing I enabled earlier in the guix repo.  Well
>    now my vc-diff is broken outside of there... :\
>
> I'm presuming that if I understood whatever this is doing, it's probably
> something that gives me a better user experience if I accept it while
> working on Guix.  But a) for whatever reason Emacs' dir-locals stuff is
> written in such a way that it antagonizes me for not accepting it and I
> didn't know what it eval was (maybe this is a lack of understanding in
> how to "say no and get it to listen to me"... I didn't resist for too
> long) and b) it seems like this change isn't scoped to Guix's checkout
> itself somehow...