bug#48531: Error on `Apply and Save` when using customize

[Mauro Aranda]

Mikhail P <mikpom@fastmail.com> writes:

> Greetings!
>
> I started to see problems with customizing anything using M-x customize. 
>
> When I change something and then press Apply and Save I get an error. 
> Attached is what
> I got in the trace when applying and saving debug-on-error . 
>
> Unfortunately I could not reproduce it with -Q because the feature Apply and 
> Save
> becomes unavailable. However I could reproduce it without any .emacs file. 
>
> Below is what report-emacs-bug has generated. Thanks for any help. 
>

> Debugger entered--Lisp error: (void-function nil)
>   nil(nil)
>   widget-apply(nil :value-get)
>   widget-value(nil)
>   custom-variable-modified-p((custom-variable :tag "Debug Ignored Errors" 
> :value debug-ignored-errors :custom-form edit :custom-magic (custom-magic 
> :args (nil) :parent #1 :indent 0 :children nil :from #<marker (moves after 
> insertion) at 236 in *Customize Apropos*> :to #<marker at 236 in *Customize 
> Apropos*> :buttons nil :value nil) :buttons ((documentation-string :args nil 
> :value "List of errors for which the debugger should not b..." :indent 3 
> :visibility-widget custom-visibility :parent #1 :doc-overlay #<overlay from 
> 236 to 299 in *Customize Apropos*> :buttons ((custom-visibility :args nil 
> :value nil :help-echo "Show or hide rest of the documentation." :on "Hide" 
> :off "More" :always-active t :action widget-parent-action :parent #13 :indent 
> 3 :button-overlay #<overlay from 299 to 303 in *Customize Apropos*> :from 
> #<marker (moves after insertion) at 299 in *Customize Apropos*> :to #<marker 
> at 303 in *Customize Apropos*>)) :from #<marker (moves after insertion) at 
> 236 in *Customize Apropos*> :to #<marker at 304 in *Customize Apropos*>) 
> (custom-magic :args (nil) :parent #1 :indent 0 :children nil :from #<marker 
> (moves after insertion) at 236 in *Customize Apropos*> :to #<marker at 236 in 
> *Customize Apropos*> :buttons nil :value nil) (item :format "%{%t%} " 
> :sample-face custom-variable-tag :tag "Debug Ignored Errors" :parent #1 
> :indent 0 :sample-overlay #<overlay from 214 to 234 in *Customize Apropos*> 
> :from #<marker (moves after insertion) at 214 in *Customize Apropos*> :to 
> #<marker at 235 in *Customize Apropos*>) (custom-visibility :args nil :value 
> nil :help-echo "Show the value of this option." :on-glyph "down" :on "Hide" 
> :off-glyph "right" :off "Show Value" :action custom-toggle-hide-variable 
> :parent #1 :indent 0 :suppress-face t :button-overlay #<overlay from 203 to 
> 213 in *Customize Apropos*> :from #<marker (moves after insertion) at 203 in 
> *Customize Apropos*> :to #<marker at 213 in *Customize Apropos*>)) 
> :documentation-indent 3 :children nil :custom-state hidden :from #<marker 
> (moves after insertion) at 203 in *Customize Apropos*> :to #<marker at 304 in 
> *Customize Apropos*>))

Thanks for the bug report.  This looks like Bug#40853 (and Bug#42801),
which was fixed in the development branch with this fix:

commit 5c39f6f1165a33f5714eedd3a413f786dffbb5a2
Author: Mauro Aranda <maurooaranda@gmail.com>
Date:   Fri Aug 14 16:40:40 2020 +0200

    Make sure we only act on edited widgets in Custom-save
    
    * lisp/cus-edit.el (Custom-save): Only act on edited widgets in the
    buffer.  If we attempt to redraw all widgets, we confuse
    custom-variable-modified-p, or we end up drawing State buttons for
    all options, including the hidden ones (bug#42801).

Would it be possible for you to build Emacs from the master branch and
see if you can reproduce it?

Alternatively, maybe you can try to redefine Custom-save as below in
your Emacs session, and see if you can reproduce it.

(defun Custom-save (&rest _ignore)
  "Set all edited settings, then save all settings that have been set.
If a setting was edited and set before, this saves it.  If a
setting was merely edited before, this sets it then saves it."
  (interactive)
  (let (edited-widgets)
    (when (custom-command-apply
           (lambda (child)
             (when (memq (widget-get child :custom-state)
                         '(modified set changed rogue))
               (push child edited-widgets)
               (widget-apply child :custom-mark-to-save)))
           "Save all settings in this buffer? " t)
      ;; Save changes to buffer.
      (custom-save-all)
      ;; Redraw and recalculate the state when necessary.
      (dolist (widget edited-widgets)
        (widget-apply widget :custom-state-set-and-redraw)))))