GNU bug report logs - #8657
24.0.50; Emacs code that seems to use `*-single-char-property-change' incorrectly

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

From: "Drew Adams" <drew.adams <at> oracle.com>
To: <bug-gnu-emacs <at> gnu.org>
Subject: 24.0.50; Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Wed, 11 May 2011 13:54:57 -0700

`(next|previous)-single-char-property-change' behaves differently in a
couple of ways from `(next|previous)-single-property-change', besides
the difference of overlay vs text properties.
 
In particular, IIUC, the return value can never be nil.
Yet I see code such as this:
 
gnus-summary-show-thread:
(or (next-single-char-property-change end 'invisible) (point-max))
 
comint-next-prompt:
(setq pos (next-single-char-property-change pos 'field))
(cond (or (null pos)...
 
Isn't this incorrect?

In GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600)
 of 2011-05-10 on 3249CTO
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.5) --no-opt --cflags
-Ic:/build/include'
 

Message #8 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: "Drew Adams" <drew.adams <at> oracle.com>
Cc: 8657 <at> debbugs.gnu.org
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Thu, 12 May 2011 00:05:46 -0300

> In particular, IIUC, the return value can never be nil.
> Yet I see code such as this:
 
> gnus-summary-show-thread:
> (or (next-single-char-property-change end 'invisible) (point-max))
 
> comint-next-prompt:
> (setq pos (next-single-char-property-change pos 'field))
> (cond (or (null pos)...
 
> Isn't this incorrect?

The behavior might have changed at some point in time, explaining the
above code.


        Stefan

Message #11 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 8657 <at> debbugs.gnu.org, drew.adams <at> oracle.com
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Thu, 12 May 2011 00:44:33 -0400

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Date: Thu, 12 May 2011 00:05:46 -0300
> Cc: 8657 <at> debbugs.gnu.org
> 
> > In particular, IIUC, the return value can never be nil.
> > Yet I see code such as this:
>  
> > gnus-summary-show-thread:
> > (or (next-single-char-property-change end 'invisible) (point-max))
>  
> > comint-next-prompt:
> > (setq pos (next-single-char-property-change pos 'field))
> > (cond (or (null pos)...
>  
> > Isn't this incorrect?
> 
> The behavior might have changed at some point in time, explaining the
> above code.

Or maybe the author was confusing next-single-char-property-change
with next-single-property-change.

In any case, those tests are redundant, because
next-single-char-property-change already returns point-max when it
finds no change in properties.

Message #14 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: "Drew Adams" <drew.adams <at> oracle.com>
To: "'Eli Zaretskii'" <eliz <at> gnu.org>,
	"'Stefan Monnier'" <monnier <at> iro.umontreal.ca>
Cc: 8657 <at> debbugs.gnu.org
Subject: RE: bug#8657: 24.0.50; Emacs code that seems to use
	`*-single-char-property-change'incorrectly
Date: Thu, 12 May 2011 06:44:22 -0700

> Or maybe the author was confusing next-single-char-property-change
> with next-single-property-change.
> 
> In any case, those tests are redundant, because
> next-single-char-property-change already returns point-max when it
> finds no change in properties.

Yes, what Eli says is what I was suggesting; that's my guess too.

Message #17 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Chong Yidong <cyd <at> gnu.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 8657 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>,
	drew.adams <at> oracle.com
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Mon, 06 Feb 2012 22:00:21 +0800

Eli Zaretskii <eliz <at> gnu.org> writes:

>> The behavior might have changed at some point in time, explaining the
>> above code.
>
> Or maybe the author was confusing next-single-char-property-change
> with next-single-property-change.
>
> In any case, those tests are redundant, because
> next-single-char-property-change already returns point-max when it
> finds no change in properties.

I went ahead and fixed them accordingly.

Message #22 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Katsumi Yamaoka <yamaoka <at> jpl.org>
To: Chong Yidong <cyd <at> gnu.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 8657 <at> debbugs.gnu.org
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Tue, 07 Feb 2012 07:56:54 +0900

Chong Yidong wrote:
> Eli Zaretskii <eliz <at> gnu.org> writes:
>>> The behavior might have changed at some point in time, explaining the
>>> above code.
>>
>> Or maybe the author was confusing next-single-char-property-change
>> with next-single-property-change.
>>
>> In any case, those tests are redundant, because
>> next-single-char-property-change already returns point-max when it
>> finds no change in properties.

> I went ahead and fixed them accordingly.

But in XEmacs next-single-char-property-change will return nil
if no property change is found.  So I've modified the gnus-sum.el
code into:

  (if (featurep 'xemacs)
      (or (next-single-char-property-change end 'invisible)
          (point-max))
    (next-single-char-property-change end 'invisible))

Message #25 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Chong Yidong <cyd <at> gnu.org>
To: Katsumi Yamaoka <yamaoka <at> jpl.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 8657 <at> debbugs.gnu.org
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Tue, 07 Feb 2012 13:57:45 +0800

Katsumi Yamaoka <yamaoka <at> jpl.org> writes:

> But in XEmacs next-single-char-property-change will return nil
> if no property change is found.

Ah OK, thanks for checking.

> So I've modified the gnus-sum.el code into:
>
>   (if (featurep 'xemacs)
>       (or (next-single-char-property-change end 'invisible)
>           (point-max))
>     (next-single-char-property-change end 'invisible))

I suggest just restoring the old code, and adding a comment about why
the `or' is there.

Message #28 received at 8657 <at> debbugs.gnu.org (full text, mbox):

From: Katsumi Yamaoka <yamaoka <at> jpl.org>
To: Chong Yidong <cyd <at> gnu.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 8657 <at> debbugs.gnu.org
Subject: Re: bug#8657: 24.0.50;
	Emacs code that seems to use `*-single-char-property-change'
	incorrectly
Date: Tue, 07 Feb 2012 15:34:01 +0900

Chong Yidong wrote:
> Katsumi Yamaoka <yamaoka <at> jpl.org> writes:

>> But in XEmacs next-single-char-property-change will return nil
>> if no property change is found.

> Ah OK, thanks for checking.

>> So I've modified the gnus-sum.el code into:
>>
>>   (if (featurep 'xemacs)
>>       (or (next-single-char-property-change end 'invisible)
>>           (point-max))
>>     (next-single-char-property-change end 'invisible))

> I suggest just restoring the old code, and adding a comment about why
> the `or' is there.

Ok.  Done.

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