bug#44598: [PATCH] Do not show obsolete options in customize

[Eli Zaretskii <eliz@gnu.org>]

> Cc: eliz@gnu.org
> From: Stefan Kangas <stefan@marxist.se>
> Date: Thu, 12 Nov 2020 15:56:24 -0500
> 
> In a recent discussion on emacs-devel,[1]

You mean this one:

  https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg01617.html

> > IMO, we shouldn't show obsolete options at all in a Custom buffer, for
> > the same reason why we remove them from the manuals.
> 
> How about the attached patch?

Thanks, some comments:

> +** Customize
> +
> +*** Customize will no longer show obsolete user options.

This is too general, it sounds like those options will not be shown
even if the user types "M-x customize-variable" to explicitly
customize an obsolete option.  That's not what the patch does, does
it?

> -(defface custom-variable-obsolete
> -  '((((class color) (background dark))
> -     :foreground "light blue")
> -    (((min-colors 88) (class color) (background light))
> -     :foreground "blue1")
> -    (((class color) (background light))
> -     :foreground "blue")
> -    (t :slant italic))
> -  "Face used for obsolete variables."
> -  :version "27.1"
> -  :group 'custom-faces)

You are removing the face, but then how will we display obsolete
options when the user actually asks to customize them by name?

> +(defun custom--filter-obsolete-variables (items)
> +  "Filter obsolete variables from ITEMS."

This doesn't say what kind of object is ITEMS expected to be.

> +  (seq-filter (lambda (item)
> +                (not (and (eq (nth 1 item) 'custom-variable)
> +                          (get (nth 0 item) 'byte-obsolete-variable))))
> +              items))

Do we really need the power of seq.el here? wouldn't mapcar do the job
nicely, since we have a simple list here?  OTOH, if you do use seq.el,
why seq-filter and not seq-remove?

> +(ert-deftest cus-edit-tests-customize-group/no-obsolete ()
> +  "Check that obsolete variables do not show up."
> +  (save-window-excursion
> +    (unwind-protect
> +        (progn
> +          (customize-group 'cus-edit-tests)
> +          (should-not (search-forward "Cus Edit Testvar Obsolete" nil t)))
> +      (when-let ((buf (get-buffer "*Customize Group: Cus Edit Tests*")))
> +        (kill-buffer buf)))))

This test will fail when we remove the obsolete option, right?  How
can we come up with a test that doesn't suffer from such maintenance
problems?