bug#64988: closed (30.0.50; move-to-column can move across lines if there is a text with display property)

[GNU bug Tracking System]

Your message dated Sat, 2 Sep 2023 09:38:50 -0700
with message-id 
<CADwFkmnWLH1hXQrGka6HjU1F-q1tFZQUWP=7pzE7NmvT8KvDnA@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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> --- Begin Message ---
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> Subject: 
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> 30.0.50; move-to-column can move across lines if there is a text with display property
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> Date: 
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> Tue, 1 Aug 2023 12:53:57 +0200
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> User-agent: 
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> Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.1
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> 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
>
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
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> Subject: 
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> Re: bug#64988: 30.0.50; move-to-column can move across lines if there is a text with display property
>
>
>
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> Date: 
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> Sat, 2 Sep 2023 09:38:50 -0700
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>
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> Eli Zaretskii <eliz@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.
>
>
> --- End Message ---