Stefan Kangas <stefan@marxist.se> writes:

> --- a/etc/NEWS
> +++ b/etc/NEWS
> @@ -706,6 +706,10 @@ This file was a compatibility kludge which is no
longer needed.
>  To revert to the previous behavior,
>  '(setq lisp-indent-function 'lisp-indent-function)' from
'lisp-mode-hook'.
>
> +** Customize
> +
> +*** Customize will no longer show obsolete user options.
> +

Only when customizing a group, it seems.  They still show up when using
customize-apropos (quite common), customize-saved (for an old setting,
it could be somewhat common), or when asking to customize them directly
(although that could be less common).  I don't know what others think,
but perhaps customize-saved should still show them: after all, it is a
current user saved setting.

> --- a/lisp/cus-edit.el
> +++ b/lisp/cus-edit.el
> @@ -2505,18 +2505,6 @@ custom-comment-invisible-p
>
>  ;;; The `custom-variable' Widget.
>
> -(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)
> -

Because of the above, perhaps it's too early to remove it?

> @@ -2544,7 +2532,7 @@ custom-variable-documentation
>  Normally just return the docstring.  But if VARIABLE automatically
>  becomes buffer local when set, append a message to that effect.
>  Also append any obsolescence information."
> -  (format "%s%s%s" (documentation-property variable
'variable-documentation t)
> +  (format "%s%s" (documentation-property variable
'variable-documentation t)
>    (if (and (local-variable-if-set-p variable)
>     (or (not (local-variable-p variable))
>         (with-temp-buffer
> @@ -2552,21 +2540,7 @@ custom-variable-documentation
>        "\n
>  This variable automatically becomes buffer-local when set outside Custom.
>  However, setting it through Custom sets the default value."
> -    "")
> -  ;; This duplicates some code from describe-variable.
> -  ;; TODO extract to separate utility function?
> -  (let* ((obsolete (get variable 'byte-obsolete-variable))
> - (use (car obsolete)))
> -    (if obsolete
> - (concat "\n
> -This variable is obsolete"
> - (if (nth 2 obsolete)
> -    (format " since %s" (nth 2 obsolete)))
> - (cond ((stringp use) (concat ";\n" use))
> -      (use (format-message ";\nuse `%s' instead."
> -   (car obsolete)))
> -      (t ".")))
> -      ""))))
> +            "")))

And the same goes for this: if the option is still likely to pop up in
some other Custom buffer, then this is useful information we might want
to keep showing to the user.

> +(defun custom--filter-obsolete-variables (items)
> +  "Filter obsolete variables from ITEMS."
> +  (seq-filter (lambda (item)
> +                (not (and (eq (nth 1 item) 'custom-variable)
> +                          (get (nth 0 item) 'byte-obsolete-variable))))
> +              items))
> +

Nit: perhaps seq-remove?