linux-kernel - Re: kconfig - a suggestion how to fix the select issue

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Message-id: <481DB230.30907@sun.com>
Date:	Sun, 04 May 2008 08:55:12 -0400
From:	David Collier-Brown <davecb@....com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Roman Zippel <zippel@...ux-m68k.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: kconfig - a suggestion how to fix the select issue

Sam Ravnborg wrote:
[Snipped]
> The suggestion is to introduce a "require" term used
> like this:
> 
> config A
>         bool "a"
> 
> config B
>         bool "b"
>         depends on A
> 
> config C
>         bool "c"
>         require B
> 
> The require dependency will have impact on visibility.
> C shall only be visible if all symbols it require are
> visible. Note that visible does not imply 'chosen'.
> In this case C would be visible when A is chosen.
> 
> When the user then choose C and B is not chosen 
> then the user is prompted to choose B.
> 
> So user has to chose B in order to have C chosen.
> 
> This would make it visible for the user that choosing
> a camera had the side-effect that USB had to be enabled too.
> But if we have some general option that prevents the
> visibility of USB we would not be offered the camara
> in the first place

In the example you suggest, the user would not see the
option of choosing the camera at C unless they selected
USB at A, and would wonder where the camera disappeared
to...

I speculate that having two ways to express a dependency,
and the addtition of visibility control makes the
dependency tree-walk into a problem which is no longer
solvable in trivial logic. That in turn makes my head 
explode (;-))

I wonder if one could simplify back into a flat set of
selections without visibility rules and a backwards-
chaining "you need to select these too" message emitter,
and if that would be worthwhile.

--dave (who used to do formal logics) c-b
-- 
David Collier-Brown            | Always do right. This will gratify
Sun Microsystems, Toronto      | some people and astonish the rest
davecb@....com                 |                      -- Mark Twain
(905) 943-1983, cell: (647) 833-9377, (800) 555-9786 x56583
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