bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Sebastian Miele]

In an emacs -Q, evaluate

  (add-hook 'kill-emacs-query-functions
            'custom-prompt-customize-unsaved-options)

  (progn
    ;; Somthing like the following may be done, e.g., by
    ;; ‘activate-transient-input-method’:
    (setq default-transient-input-method "TeX")
    (customize-mark-as-set 'default-transient-input-method))

and hit C-x C-c.  When asked about whether to examine the unsaved
options, say yes.

Expected: Emacs does not terminate, so that I can examine.

Actual behavior: Emacs terminates.

The following diff fixes this issue (and a documentation bug):

diff --git a/lisp/cus-edit.el b/lisp/cus-edit.el
index c2ddaeb7b1..77840c4b65 100644
--- a/lisp/cus-edit.el
+++ b/lisp/cus-edit.el
@@ -1531,12 +1531,11 @@ customize-apropos-groups
 ;;;###autoload
 (defun custom-prompt-customize-unsaved-options ()
   "Prompt user to customize any unsaved customization options.
-Return non-nil if user chooses to customize, for use in
+Return nil if user chooses to customize, for use in
 `kill-emacs-query-functions'."
   (not (and (custom-unsaved-options)
            (yes-or-no-p "Some customized options have not been saved; Examine? ")
-           (customize-unsaved)
-           t)))
+           (prog1 t (customize-unsaved)))))

 ;;; Buffer.

Best wishes,
Sebastian Miele

In GNU Emacs 28.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.33, cairo version 1.17.4)
 of 2022-03-10 built on huette
Repository revision: d184773c2e2a69bea9b96190c83727b4e7a16542
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Arch Linux

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bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Eli Zaretskii]

> From: Sebastian Miele <iota@whxvd.name>
> Date: Thu, 10 Mar 2022 17:19:07 +0100
> 
> In an emacs -Q, evaluate
> 
>   (add-hook 'kill-emacs-query-functions
>             'custom-prompt-customize-unsaved-options)
> 
>   (progn
>     ;; Somthing like the following may be done, e.g., by
>     ;; ‘activate-transient-input-method’:
>     (setq default-transient-input-method "TeX")
>     (customize-mark-as-set 'default-transient-input-method))
> 
> and hit C-x C-c.  When asked about whether to examine the unsaved
> options, say yes.
> 
> Expected: Emacs does not terminate, so that I can examine.
> 
> Actual behavior: Emacs terminates.
> 
> The following diff fixes this issue (and a documentation bug):
> 
> diff --git a/lisp/cus-edit.el b/lisp/cus-edit.el
> index c2ddaeb7b1..77840c4b65 100644
> --- a/lisp/cus-edit.el
> +++ b/lisp/cus-edit.el
> @@ -1531,12 +1531,11 @@ customize-apropos-groups
>  ;;;###autoload
>  (defun custom-prompt-customize-unsaved-options ()
>    "Prompt user to customize any unsaved customization options.
> -Return non-nil if user chooses to customize, for use in
> +Return nil if user chooses to customize, for use in

If you want to prevent Emacs from terminating, you can simply return
nil from your hook function.  I see no reason to change the semantics
of the return value for a single use case: this function was evidently
assuming a different use case, and it exists in this shape long enough
to prevent us to change its behavior in such a radical way.

Thanks.

bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Sebastian Miele]

Hi Eli,

Eli Zaretskii <eliz@gnu.org>:
> If you want to prevent Emacs from terminating, you can simply return
> nil from your hook function.  I see no reason to change the semantics
> of the return value for a single use case: this function was evidently
> assuming a different use case, and it exists in this shape long enough
> to prevent us to change its behavior in such a radical way.

This is not about me wanting to change the behavior of
‘custom-prompt-customize-unsaved-options’.  It definitely is a bug in
Emacs 28.  The definition

  (defun custom-prompt-customize-unsaved-options ()
    (not (and (custom-unsaved-options)
              (yes-or-no-p "Some customized options have not been saved; Examine? ")
              (customize-unsaved)
              t)))

seems to be unchanged from Emacs 27.2 to Emacs 28.  However, in Emacs
27.2, it did work as I expect and as I understand the Emacs manual:

  Please note that any customizations you have not chosen to save for
  future sessions will be lost when you terminate Emacs.  If you’d
  like to be prompted about unsaved customizations at termination
  time, add the following to your initialization file:

       (add-hook 'kill-emacs-query-functions
                 'custom-prompt-customize-unsaved-options)

(For ‘custom-prompt-customize-unsaved-options’ to have a/the sensible
meaning as a member of ‘kill-emacs-query-functions’, it must return
nil when there are unsaved options and the user answered "yes".)

The reason that the behavior of
‘custom-prompt-customize-unsaved-options’ changed from version 27.2 to
28 almost certainly is the following:

‘custom-prompt-customize-unsaved-options’ calls ‘customize-unsaved’
which ends with call to ‘custom-buffer-create’.  The definition of
‘custom-buffer-create’ changed from Emacs 27.2 to Emacs 28.  In Emacs
27.2 it probably always returned non-nil.  In Emacs 28 it always
returns nil.

However, the (and ...) form in
‘custom-prompt-customize-unsaved-options’ depends on
‘customize-unsaved’ to always return non-nil in order to be correct.

‘custom-prompt-customize-unsaved-options’ always had the bug reported
here.  It just did not manifest before ‘custom-buffer-create’ was
changed from Emacs 27.2 to Emacs 28.

Best wishes,
Sebastian

bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Eli Zaretskii]

> From: Sebastian Miele <iota@whxvd.name>
> Cc: 54329@debbugs.gnu.org
> Date: Thu, 10 Mar 2022 18:17:02 +0100
> 
> The reason that the behavior of
> ‘custom-prompt-customize-unsaved-options’ changed from version 27.2 to
> 28 almost certainly is the following:
> 
> ‘custom-prompt-customize-unsaved-options’ calls ‘customize-unsaved’
> which ends with call to ‘custom-buffer-create’.  The definition of
> ‘custom-buffer-create’ changed from Emacs 27.2 to Emacs 28.  In Emacs
> 27.2 it probably always returned non-nil.  In Emacs 28 it always
> returns nil.
> 
> However, the (and ...) form in
> ‘custom-prompt-customize-unsaved-options’ depends on
> ‘customize-unsaved’ to always return non-nil in order to be correct.
> 
> ‘custom-prompt-customize-unsaved-options’ always had the bug reported
> here.  It just did not manifest before ‘custom-buffer-create’ was
> changed from Emacs 27.2 to Emacs 28.

Thanks, this was the information I missed.

I installed a minor variation of your changes on the emacs-28 branch.
Please take a look.

bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Sebastian Miele]

Eli Zaretskii <eliz@gnu.org>:
> I installed a minor variation of your changes on the emacs-28 branch.
> Please take a look.

Thank you.  Looks good and seems to work.

bug#54329: 28.0.91; custom-prompt-customize-unsaved-options does not return nil

[Eli Zaretskii]

> From: Sebastian Miele <iota@whxvd.name>
> Cc: 54329@debbugs.gnu.org
> Date: Thu, 10 Mar 2022 19:55:55 +0100
> 
> Eli Zaretskii <eliz@gnu.org>:
> > I installed a minor variation of your changes on the emacs-28 branch.
> > Please take a look.
> 
> Thank you.  Looks good and seems to work.

Great, I'm therefore closing this bug.

Thanks.