GNU bug report logs - #846
Bug in handling invisible text, and bug in Pmail.

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: "Richard M. Stallman" <rms <at> gnu.org>
To: pmr <at> pajato.com, emacs-pretest-bug <at> gnu.org
Subject: Bug in handling invisible text, and bug in Pmail.
Date: Mon, 01 Sep 2008 02:11:33 -0400

In Pmail I had a message that looked like this
(I changed his host name for privacy's sake):

----------------------------------------------------------------------
To: rms <at> gnu.org
Subject: sorry that I was distracted with phone calls 
From: Brand <at> xyzxysxysbb.com
Reply-to: brand <at> xyzxysxysbb.com
Date: Thu, 21 Aug 2008 18:46:37 -0700
X-BABYL-V6-ATTRIBUTES: A------



Two other ideas to run past you when time permits.

/w

----------------------------------------------------------------------

and I wanted to copy that into an outgoing message.
So I typed C-x h M-w, went to *mail* and inserted it.
What this inserted appears below.  It was quite a surprise.

It seems there is a lot of invisible text at the beginning of
the buffer, and two different values of point display at the same
place on the screen.  These places are 934995 and 9351405.
(point-min) returns 934995, and that's where M-< moves point to.
Typing C-f C-b moves point to 9351405.  I gather that those two
positions surround the invisible text.	

I think this is a bug in the command loop's handling of invisible
text -- it should not be the case that C-f C-b changes point.

I think it is also a bug in Pmail.  Pmail should set the buffer boundaries
after that text, rather than making it invisible.

If Pmail is fixed, then it won't trigger the invisible text bug.
But I think it needs to be fixed anyway.


----------------------------------------------------------------------
From Brand <at> xyzxysxysbb.com  Fri Aug 22 01:11:22 2008
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To: rms <at> gnu.org
Subject: sorry that I was distracted with phone calls 
From: Brand <at> xyzxysxysbb.com
Reply-to: brand <at> xyzxysxysbb.com
Date: Thu, 21 Aug 2008 18:46:37 -0700
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Two other ideas to run past you when time permits.

/w

----------------------------------------------------------------------

Message #10 received at 846 <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Chong Yidong <cyd <at> stupidchicken.com>
To: rms <at> gnu.org
Cc: 846 <at> debbugs.gnu.org
Subject: Re: Bug in C-n
Date: Mon, 01 Sep 2008 14:12:10 -0400

I can't reproduce this.  However, I fixed a similar bug a couple of days
ago; could you try to reproduce this problem with the latest sources?

Message #15 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: rms <at> gnu.org
Cc: 846 <at> debbugs.gnu.org, pmr <at> pajato.com, emacs-pretest-bug <at> gnu.org
Subject: Re: bug#846: Bug in handling invisible text, and bug in Pmail.
Date: Mon, 01 Sep 2008 16:37:39 -0400

> I think this is a bug in the command loop's handling of invisible
> text -- it should not be the case that C-f C-b changes point.

There are various desirable behaviors w.r.t invisible text, and you
can't have them all at the same time.  I.e. the above "bug" is
a conscious decision.

It's been with us for a while now and hasn't caused any real bug report
yet (other than reports such as this one, that is; which complain on
principle rather than because of some real problem introduced by this
behavior).  So I'd rather leave it as is.

Now as for the Pmail-specific part of your bug-report, I can't help you
right now.  Is this different from Rmail's behavior?


        Stefan

Message #25 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: "Richard M. Stallman" <rms <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>, 846 <at> debbugs.gnu.org
Cc: pmr <at> pajato.com, 846 <at> debbugs.gnu.org, emacs-pretest-bug <at> gnu.org,
        bug-gnu-emacs <at> gnu.org
Subject: Re: bug#846: Bug in handling invisible text, and bug in Pmail.
Date: Mon, 01 Sep 2008 21:09:53 -0400

    > I think this is a bug in the command loop's handling of invisible
    > text -- it should not be the case that C-f C-b changes point.

    There are various desirable behaviors w.r.t invisible text, and you
    can't have them all at the same time.

I know that better than anyone, and I thought about this a long time.
The command loop used to have code to make sure that there weren't
two different possible point values that would display as the same place.

    It's been with us for a while now

Did you change my decision?  If so, when did that happen?

				      and hasn't caused any real bug report
    yet (other than reports such as this one, that is; which complain on
    principle rather than because of some real problem

It was a real problem, even though Pmail should not use invisible text
for this.  It led to confusing behavior in this case, and it will be
confusing in every case where invisible text is used.

If people have not complained, maybe it is because the use of 
invisible text is rare.  What other modes use invisible text?

Message #40 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: rms <at> gnu.org
Cc: 846 <at> debbugs.gnu.org, pmr <at> pajato.com, emacs-pretest-bug <at> gnu.org,
        bug-gnu-emacs <at> gnu.org
Subject: Re: bug#846: Bug in handling invisible text, and bug in Pmail.
Date: Mon, 01 Sep 2008 22:36:44 -0400

>> I think this is a bug in the command loop's handling of invisible
>> text -- it should not be the case that C-f C-b changes point.

>     There are various desirable behaviors w.r.t invisible text, and you
>     can't have them all at the same time.

> I know that better than anyone, and I thought about this a long time.
> The command loop used to have code to make sure that there weren't
> two different possible point values that would display as the same place.

When was that?  How did it do that?

>     It's been with us for a while now
> Did you change my decision?

What decision?

> If so, when did that happen?

The relevant piece of code is adjust_point_for_property, which used to
make point move over images and char-compositions and which I extended
in Emacs-22 (IIRC) to move over invisible text as well (making it
automatically somewhat-intangible).

> 				      and hasn't caused any real bug report
>     yet (other than reports such as this one, that is; which complain on
>     principle rather than because of some real problem

> It was a real problem, even though Pmail should not use invisible text
> for this.  It led to confusing behavior in this case, and it will be
> confusing in every case where invisible text is used.

Could you re-explain the problem you encountered, then?  Re-reading your
original bug-report I still can't see where this difference between point
before and after C-f C-b introduced a problem.

> If people have not complained, maybe it is because the use of 
> invisible text is rare.  What other modes use invisible text?

Indeed, most complaints around invisible text have to do with the
invisibility itself rather than details of how point is handed in
its presence.  So invisible text is rare because it's inherently
problematic (and should hence be avoided whenever possible).


        Stefan

Message #57 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Reiner Steib <reinersteib+gmane <at> imap.cc>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 846 <at> debbugs.gnu.org, rms <at> gnu.org, pmr <at> pajato.com,
        bug-gnu-emacs <at> gnu.org, emacs-pretest-bug <at> gnu.org
Subject: Re: bug#846: Bug in handling invisible text, and bug in Pmail.
Date: Tue, 23 Sep 2008 22:44:49 +0200

On Tue, Sep 02 2008, Stefan Monnier wrote:

>> If people have not complained, maybe it is because the use of 
>> invisible text is rare.  What other modes use invisible text?
>
> Indeed, most complaints around invisible text have to do with the
> invisibility itself rather than details of how point is handed in
> its presence.  So invisible text is rare because it's inherently
> problematic (and should hence be avoided whenever possible).

Gnus message mode used invisible text to hide headers while composing
a news/mail message.  But it was changed to use narrowing instead:

,----[ gnus/ChangeLog ]
| 2004-11-22  Romain Francoise  <romain <at> orebokech.com>
| 
| 	* message.el (message-header-format-alist): Add `From' in list
| 	so that it can be sorted.
| 	(message-fix-before-sending): Widen and sort headers before
| 	sending.
| 	(message-hide-headers): Use narrowing to hide headers by moving
| 	them to the top of the buffer and narrowing to the region
| 	underneath.
`----

Bye, Reiner.
-- 
       ,,,
      (o o)
---ooO-(_)-Ooo---  |  PGP key available  |  http://rsteib.home.pages.de/

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