bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

[Drew Adams]

This bug exists since at least Emacs 22.

emacs -Q

(defcustom bar nil
  "@@@"
  :type 'boolean :group 'convenience)

M-x customize-set-variable bar
Set variable: bar

The prompt for the Boolean value is this:

[boolean] Set customized value for bar to: (y or n)

Set it to WHAT?

It turns out that `y' sets the value to `t' and `n' sets the value to
`nil'.  But there's no way of knowing that.

The fault is with function `custom-prompt-variable', or more precisely,
with `widget-prompt-value', and then with `widget-boolean-prompt-value'.
It's the latter that calls `y-or-n-p'.

The value returned by `y-or-n-p' is t or nil, which is OK.  But the
prompt and the expected inputs are wrong.

Even if the prompt said "[boolean] Set customized value for bar to `t':
(y or n)" it would be inadequate, because it suggests that if you reply
`n' then the variable value remains unchanged.  `y-or-n-p' is just wrong
here.

The comment for `widget-boolean-prompt-value' says that it toggles.  But
it does NOT toggle.  And `customize-set-variable' should NOT just toggle
the current value anyway.  It should always prompt you for the new
value, which may or may not be already the current value.  The command
needs to be consistent.

Maybe the `boolean' widget should be changed to use `widge-prompt-value,
not `widget-boolean-prompt-value' or something?  That it inherits from
the `toggle' widget is fine - that's for the Toggle button in the
Customize UI.  But `customize-set-variable' needs a better prompt
(better behavior).

In GNU Emacs 27.1 (build 1, x86_64-w64-mingw32)
 of 2020-08-12 built on CIRROCUMULUS
Repository revision: 86d8d76aa36037184db0b2897c434cdaab1a9ae8
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.18362
System Description: Microsoft Windows 10 Pro (v10.0.1903.18362.1082)

bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

[Eli Zaretskii]

> Date: Thu, 24 Sep 2020 10:09:57 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> emacs -Q
> 
> (defcustom bar nil
>   "@@@"
>   :type 'boolean :group 'convenience)
> 
> M-x customize-set-variable bar
> Set variable: bar
> 
> The prompt for the Boolean value is this:
> 
> [boolean] Set customized value for bar to: (y or n)
> 
> Set it to WHAT?

To 'y' or to 'n'.

FWIW, I see no problem here, and would understand immediately what is
meant.  We do this kind of "translation" of boolean values a'll the
time in Customize.  Let's keep in mind that Customize is for users
that aren't Lisp programmers, so we don't want to request them to know
what Lisp boolean data looks like.

bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

[Drew Adams]

> FWIW, I see no problem here, and would understand immediately what is
> meant.  We do this kind of "translation" of boolean values a'll the
> time in Customize.  Let's keep in mind that Customize is for users
> that aren't Lisp programmers, so we don't want to request them to know
> what Lisp boolean data looks like.

I understand what you're saying.  I don't agree that
it's clear now for a user.

If the prompt said something like this it would be
clearer:

 Set customized value for bar to true (y) or false (n): (y or n)

It's wrong to suggest that this is about setting
the value to `y' or `n'.

And users are used to "(y or n)" being used primarily
(almost exclusively) for confirming something.

I think the (ab)use of the `y-or-n-p' UI is unhelpful
here (misleading, unclear).

bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

[Lars Ingebrigtsen]

Drew Adams <drew.adams@oracle.com> writes:

> If the prompt said something like this it would be
> clearer:
>
>  Set customized value for bar to true (y) or false (n): (y or n)
>
> It's wrong to suggest that this is about setting
> the value to `y' or `n'.

Yes, I agree that it's kinda obscure.  The proposed prompt here is a bit
long though, so I've gone with this instead in Emacs 28:

"Set customized value for bar to true: (y or n)"

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

bug#43593: [External] : Re: bug#43593: 27.1; `customize-set-variable': wrong prompt for Boolean value

[Drew Adams]

> >  Set customized value for bar to true (y) or false (n): (y or n)
> 
> Yes, I agree that it's kinda obscure.  The proposed prompt here is a bit
> long though, so I've gone with this instead in Emacs 28:
> 
> "Set customized value for bar to true: (y or n)"

Yes, that's fine.  Thx.