GNU bug report logs - #19324
25.0.50; add-function and nil

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Leo Liu <sdl.web <at> gmail.com>
Subject: bug#19324: closed (Re: bug#19324: 25.0.50; add-function and nil)
Date: Fri, 12 Dec 2014 00:45:03 +0000

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Your bug report

#19324: 25.0.50; add-function and nil

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 19324 <at> debbugs.gnu.org.

-- 
19324: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19324
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Leo Liu <sdl.web <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 19324-done <at> debbugs.gnu.org
Subject: Re: bug#19324: 25.0.50; add-function and nil
Date: Fri, 12 Dec 2014 08:44:11 +0800

On 2014-12-11 14:11 -0500, Stefan Monnier wrote:
> No I don't have a fix for this.
> `add-function' is designed to work on places that only hold functions,
> so any other value (such as nil) will create problems.
>
> IOW a variable that can hold "either nil or a function" is not something
> that add-function supports.
>
> I guess we could treat nil as an alias for `ignore' in the "proxy
> function", which would fix this particular issue.  See patch below.
> But I don't intend to handle all the cases in which a "nil function" can
> show up.  Many/most uses of `foo-function' actually give a special
> meaning to nil which is different from `ignore'.
> So I'm not sure we should cater to this particular case.

Thanks, Stefan, for the explanation. In that case maybe the workaround
isn't needed because we still cannot tell if ORIG is missing. I consider
the bug closed.

Leo

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From: Leo Liu <sdl.web <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.50; add-function and nil
Date: Tue, 09 Dec 2014 12:55:22 +0800

1. Goto a buffer (e.g. text-mode) with eldoc-documentation-function nil
2. (add-function :after-until (local 'eldoc-documentation-function) #'ignore)
3. Move around to trigger eldoc error: (void-function nil)

Looks like the orig function is unconditionally called without checking
it's a function object.

Leo

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