GNU bug report logs - #79975
14.1.0; void-function error in `preview-auto-reveal`

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
To: bug-auctex <at> gnu.org
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: 14.1.0; void-function error in `preview-auto-reveal`
Date: Tue, 09 Dec 2025 11:58:25 +0100

I am getting the error `(void-function closure)` on Emacs 29.4 (but not
on 31.0.50 FWIW) when the default value of the function
`preview-auto-reveal` is executed. I am able to reproduce the error on
Emacs 29.4 with this

(require 'preview)
(apply preview-auto-reveal)

*IF* the preview.el file is not compiled. I can also reproduce the error
 (assuming lexical-binding is t) by using its default value:

(apply `(eval . ((apply #'preview-arrived-via
                   (mapcar ,(lambda (cmd)
                              (if (and (listp cmd) (eq (car cmd) 'key-binding))
                                  (eval cmd t)
                                cmd))
                           preview-auto-reveal-commands))
            t)))

or simply with the stripped down version:

(apply `(eval . ((apply #'ignore (mapcar ,(lambda (cmd) nil) nil)) t)))


Removing `,` before the (lambda ...) fixes the error, but I am not sure
why it was there in the first place.

-- Al

Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
Cc: bug-auctex <at> gnu.org
Subject: Re: 14.1.0; void-function error in `preview-auto-reveal`
Date: Tue, 09 Dec 2025 07:31:45 -0500

> I am getting the error `(void-function closure)` on Emacs 29.4 (but not
[...]
> (apply `(eval . ((apply #'preview-arrived-via
>                    (mapcar ,(lambda (cmd)
>                               (if (and (listp cmd) (eq (car cmd) 'key-binding))
>                                   (eval cmd t)
>                                 cmd))
>                            preview-auto-reveal-commands))
>             t)))

Indeed, in Emacs<30, function values are not always self-quoting, so you
need a quote before the comma.
[ note: the problem should disappear if you compile the file, because
  compiled function values *are* self-quoting even in Emacs<30.  ]


        Stefan

Message #11 received at 79975 <at> debbugs.gnu.org (full text, mbox):

From: David Kastrup <dak <at> gnu.org>
To: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
Cc: 79975 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#79975: 14.1.0; void-function error in `preview-auto-reveal`
Date: Tue, 09 Dec 2025 13:33:28 +0100

Al Haji-Ali <abdo.haji.ali <at> gmail.com> writes:

> I am getting the error `(void-function closure)` on Emacs 29.4 (but not
> on 31.0.50 FWIW) when the default value of the function
> `preview-auto-reveal` is executed. I am able to reproduce the error on
> Emacs 29.4 with this
>
> (require 'preview)
> (apply preview-auto-reveal)
>
> *IF* the preview.el file is not compiled. I can also reproduce the error
>  (assuming lexical-binding is t) by using its default value:
>
> (apply `(eval . ((apply #'preview-arrived-via
>                    (mapcar ,(lambda (cmd)
>                               (if (and (listp cmd) (eq (car cmd) 'key-binding))
>                                   (eval cmd t)
>                                 cmd))
>                            preview-auto-reveal-commands))
>             t)))
>
> or simply with the stripped down version:
>
> (apply `(eval . ((apply #'ignore (mapcar ,(lambda (cmd) nil) nil)) t)))
>
>
> Removing `,` before the (lambda ...) fixes the error, but I am not sure
> why it was there in the first place.

To create a closure at the point where the function is being written.
Maybe 29.4 has a problem with the function cell/data cell retainment in
this expression?

Does preceding ,(lambda ...) with #' help?  That would add a
function-quote around the finished closure.  Which should really not do
anything in this context, but then we should not be getting this error
in the first place.

-- 
David Kastrup

Message #14 received at 79975 <at> debbugs.gnu.org (full text, mbox):

From: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
To: David Kastrup <dak <at> gnu.org>
Cc: 79975 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#79975: 14.1.0; void-function error in `preview-auto-reveal`
Date: Tue, 09 Dec 2025 15:38:25 +0100

On 09/12/2025, David Kastrup wrote:
> Does preceding ,(lambda ...) with #' help?  That would add a
> function-quote around the finished closure.  Which should really not do
> anything in this context, but then we should not be getting this error
> in the first place.

Yes indeed. Adding ' or #' before the comma resolves the issue on Emacs
29.4. It also doesn't break Emacs 31.0.50, even though 

`(eval . ((apply #'ignore (mapcar #',(lambda (cmd) nil) nil)) t))

produces an additional quote on Emacs 31.0.50, as in:

(eval (apply #'ignore (mapcar #'#[(cmd) (nil) (t)] nil)) t)

compared to.
`(eval . ((apply #'ignore (mapcar ,(lambda (cmd) nil) nil)) t))

which gives
(eval (apply #'ignore (mapcar #[(cmd) (nil) (t)] nil)) t)

Can someone with write access to AUCTeX make this change to
`preview-auto-reveal`?

-- Al

Message #17 received at 79975 <at> debbugs.gnu.org (full text, mbox):

From: Arash Esbati <arash <at> gnu.org>
To: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
Cc: 79975 <at> debbugs.gnu.org, David Kastrup <dak <at> gnu.org>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#79975: 14.1.0; void-function error in `preview-auto-reveal`
Date: Wed, 10 Dec 2025 08:28:18 +0100

Hi all,

Al Haji-Ali <abdo.haji.ali <at> gmail.com> writes:

> Can someone with write access to AUCTeX make this change to
> `preview-auto-reveal`?

Are you thinking about something like this:

--8<---------------cut here---------------start------------->8---
diff --git a/preview.el b/preview.el
index 94812886..8b757c84 100644
--- a/preview.el
+++ b/preview.el
@@ -1746,10 +1746,12 @@ This list is consulted by the default value of `preview-auto-reveal'."

 (defcustom preview-auto-reveal
   `(eval . ((apply #'preview-arrived-via
-                   (mapcar ,(lambda (cmd)
-                              (if (and (listp cmd) (eq (car cmd) 'key-binding))
-                                  (eval cmd t)
-                                cmd))
+                   ;; Quote the function value for interpreted code in
+                   ;; Emacs<30 (bug#79975):
+                   (mapcar #',(lambda (cmd)
+                                (if (and (listp cmd) (eq (car cmd) 'key-binding))
+                                    (eval cmd t)
+                                  cmd))
                            preview-auto-reveal-commands))
             t))
   "Cause previews to open automatically when entered.
--8<---------------cut here---------------end--------------->8---

Best, Arash

Message #20 received at 79975 <at> debbugs.gnu.org (full text, mbox):

From: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
To: Arash Esbati <arash <at> gnu.org>
Cc: 79975 <at> debbugs.gnu.org, David Kastrup <dak <at> gnu.org>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#79975: 14.1.0; void-function error in `preview-auto-reveal`
Date: Wed, 10 Dec 2025 09:18:51 +0100

Hello Arash,


On 10/12/2025, Arash Esbati wrote:
> Are you thinking about something like this:

Yes exactly. Assuming it does not break anything in Emacs >30 (I am not
experienced enough with self-quoting expressions to judge).

Best regards,
-- Al

Message #25 received at 79975-done <at> debbugs.gnu.org (full text, mbox):

From: Arash Esbati <arash <at> gnu.org>
To: Al Haji-Ali <abdo.haji.ali <at> gmail.com>
Cc: 79975-done <at> debbugs.gnu.org, David Kastrup <dak <at> gnu.org>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#79975: 14.1.0; void-function error in `preview-auto-reveal`
Date: Wed, 10 Dec 2025 09:49:37 +0100

Hi Al,

Al Haji-Ali <abdo.haji.ali <at> gmail.com> writes:

> Yes exactly.

Thanks, and pushed.

> Assuming it does not break anything in Emacs >30 (I am not experienced
> enough with self-quoting expressions to judge).

I trust Stefan's and your judgement in this case.  But we can revisit
this if people on Emacs>30 complain.  I'm closing this report for now.

Best, Arash

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