GNU bug report logs - #22703
24.5; PROPOSAL: Is there a way to update available choices for defcustom variable?

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Oleksandr Gavenko <gavenkoa <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5;
 PROPOSAL: Is there a way to update available choices for defcustom
 variable?
Date: Tue, 16 Feb 2016 20:20:23 +0200

Recently I ask question:

  http://emacs.stackexchange.com/questions/20350/defcustom-values-for-selecting-from-function-call

because I didn't understand show to build code from that I read in docs.

While answer to question help me to build my first "customize" code it miss
main point and I think because the way Emacs customize API works, so nobody
even think about doing as I asked.

I have values:

  (defvar my/python-checker-alist
    '((pylint . (my/python-pylint-command my/python-pylint-args))
      (pep8 . (my/python-pep8-command my/python-pep8-args))
      (pyflakes . (my/python-pyflakes-command my/python-pyflakes-args)))
    "Known Python source code checkers.")

and want to build `defcustom' definition based on that values:

  (choice (const . pylint) (const . pep8) (const . pyflakes))

  (defcustom my/python-default-checker 'pyflakes
    "Default Python source code checker. See `my/python-checker-alist' for full alist."
    :group 'my/python
    :type (cons 'choice (mapcar (lambda (e) (cons 'const (car e))) my/python-checker-alist)) )

I am worrying is there a mechanic that **automatically** update `:type' value when
user visit:

  M-x customize-group
  M-x customize-variable

with my variable?

Official info states:

  The argument of ‘:type’ is evaluated, but only once when the
  ‘defcustom’ is executed, so it isn’t useful for the value to vary.

If someone potentially extend my/python-checker-alist his addition would be
invisible in my/python-default-checker.

I thing it is wrong to ask someone not only to update possible values:

  (with-eval-after-load 'my/python
    (add-to-list 'my/python-checker-alist ...))

but also somehow to update default values (for my/python-default-checker)
synchronously.

Are there standard convention for such situation?

I see ":options" and "custom-add-frequent-value" but this is not useful when
":type (choice ...)" used. Also it cumbersome even in case of :options ask any
extension developers to call "custom-add-frequent-value" for their additions.

":set" function called after user see menu with pre-filled values while
desired situation when used see updated list of available options.

Solution to this request is to allow value of ":type" be a function which is
evaluated on   M-x customize-group /  M-x customize-variable.

-- 
http://defun.work/

Message #8 received at 22703 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Oleksandr Gavenko <gavenkoa <at> gmail.com>
Cc: 22703 <at> debbugs.gnu.org
Subject: Re: bug#22703: 24.5; PROPOSAL: Is there a way to update available
 choices for defcustom variable?
Date: Thu, 01 Aug 2019 14:44:22 +0200

Oleksandr Gavenko <gavenkoa <at> gmail.com> writes:

> Recently I ask question:
>
>   http://emacs.stackexchange.com/questions/20350/defcustom-values-for-selecting-from-function-call
>
> because I didn't understand show to build code from that I read in docs.
>
> While answer to question help me to build my first "customize" code it miss
> main point and I think because the way Emacs customize API works, so nobody
> even think about doing as I asked.
>
> I have values:
>
>   (defvar my/python-checker-alist
>     '((pylint . (my/python-pylint-command my/python-pylint-args))
>       (pep8 . (my/python-pep8-command my/python-pep8-args))
>       (pyflakes . (my/python-pyflakes-command my/python-pyflakes-args)))
>     "Known Python source code checkers.")
>
> and want to build `defcustom' definition based on that values:
>
>   (choice (const . pylint) (const . pep8) (const . pyflakes))
>
>   (defcustom my/python-default-checker 'pyflakes
>     "Default Python source code checker. See `my/python-checker-alist' for full alist."
>     :group 'my/python
>     :type (cons 'choice (mapcar (lambda (e) (cons 'const (car e))) my/python-checker-alist)) )
>
> I am worrying is there a mechanic that **automatically** update `:type' value when
> user visit:
>
>   M-x customize-group
>   M-x customize-variable
>
> with my variable?
>
> Official info states:
>
>   The argument of ‘:type’ is evaluated, but only once when the
>   ‘defcustom’ is executed, so it isn’t useful for the value to vary.
>
> If someone potentially extend my/python-checker-alist his addition would be
> invisible in my/python-default-checker.
>
> I thing it is wrong to ask someone not only to update possible values:
>
>   (with-eval-after-load 'my/python
>     (add-to-list 'my/python-checker-alist ...))
>
> but also somehow to update default values (for my/python-default-checker)
> synchronously.
>
> Are there standard convention for such situation?

(I'm going through old bug reports that have unfortunately not gotten
any responses.)

Yes, the person extending the defcustom can call
`custom-declare-variable' with the new :type, too.  This should be
mentioned in the doc string for `defcustom', I think, and I'm making
that change on the Emacs trunk now.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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