Subject: bug#30101: 25.3; defcustom does not clear old :options when reevaluated

From: Tim Landscheidt <[email-masked]>
Date: Sun, 14 Jan 2018 20:32:19 +0000

Further reading shows that this cumultative behaviour is
needed via custom-add-option by various files that enhance
the options of a different file's variables with it:

| [tim@passepartout ~/src/emacs]$ git grep custom-add-option -- \*.el
| lisp/calendar/diary-lib.el:(custom-add-option 'gnus-article-prepare-hook 'diary-from-outlook-gnus)
| lisp/custom.el:                      (custom-add-option symbol option))
| lisp/custom.el:(defun custom-add-option (symbol option)
| lisp/custom.el:(defalias 'custom-add-frequent-value 'custom-add-option)
| lisp/emacs-lisp/checkdoc.el:(custom-add-option 'emacs-lisp-mode-hook 'checkdoc-minor-mode)
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-pre-command-hook 'eshell-push-command-mark)
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-pre-command-hook 'eshell-push-command-mark)
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-input-filter-functions 'eshell-kill-new)
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-output-filter-functions
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-output-filter-functions
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-output-filter-functions
| lisp/eshell/esh-mode.el:(custom-add-option 'eshell-output-filter-functions
| lisp/gnus/message.el:(custom-add-option 'message-setup-hook 'message-check-recipients)
| lisp/gnus/nnmail.el:(custom-add-option 'nnmail-prepare-incoming-header-hook
| lisp/simple.el:(custom-add-option 'text-mode-hook 'turn-on-auto-fill)
| lisp/textmodes/flyspell.el:(custom-add-option 'text-mode-hook 'turn-on-flyspell)
| [tim@passepartout ~/src/emacs]$

So this behaviour cannot be changed, but should be document-
ed.