GNU bug report logs - #64988
30.0.50; move-to-column can move across lines if there is a text with display property

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#64988: closed (30.0.50; move-to-column can move across lines
 if there is a text with display property)
Date: Sat, 02 Sep 2023 16:40:03 +0000

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Your message dated Sat, 2 Sep 2023 09:38:50 -0700
with message-id <CADwFkmnWLH1hXQrGka6HjU1F-q1tFZQUWP=7pzE7NmvT8KvDnA <at> mail.gmail.com>
and subject line Re: bug#64988: 30.0.50; move-to-column can move across lines if there is a text with display property
has caused the debbugs.gnu.org bug report #64988,
regarding 30.0.50; move-to-column can move across lines if there is a text with display property
to be marked as done.

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64988: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64988
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From: Herman, Géza <geza.herman <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; move-to-column can move across lines if there is a text with
 display property
Date: Tue, 1 Aug 2023 12:53:57 +0200

If there is a text with display property in a buffer, then 
move-to-column can move across lines.

Repro:
* emacs -Q
* in the scratch buffer, move the cursor to the top, and put an empty 
line at the beginning of the buffer
* execute 'M-: (put-text-property 1 2 'display "line\n")' (note: it's 
likely that the "\n" causes the problem)
* notice that the empty line becomes "line"
* while the cursor still on the first line, execute 'M-: (move-to-column 
20)'

The last command will move the cursor to the next line at column 16, 
instead of staying at the first line.

Note: I noticed this problem while using this package: 
https://github.com/jdtsmith/indent-bars.

The problem doesn't happen with emacs 28, this is the commit that 
introduced the issue:

4243747b1b8c3b7e3463822804b32e83febe2878 Fix 'current-column' in the 
presence of display strings

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From: Stefan Kangas <stefankangas <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 64988-done <at> debbugs.gnu.org, geza.herman <at> gmail.com
Subject: Re: bug#64988: 30.0.50; move-to-column can move across lines if there
 is a text with display property
Date: Sat, 2 Sep 2023 09:38:50 -0700

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

> tags 64988 notabug wontfix
> thanks
[...]
> So I'm sorry, but unless someone comes with an idea for how to handle
> these situations in a sensible way (and I thought long and hard about
> it, but couldn't find such ideas), this will remain a limitation of
> move-to-column, and one of the complications introduced by display
> strings with embedded newlines in general.  The affected packages will
> have to adapt to this change in some ways.  Since the original code
> also produced incorrect results, just different incorrect results, I
> don't see this as a serious problem, just as a bug that wasn't fixed,
> but changed its buggy behavior.

I'm therefore closing this bug report.

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