Bug#1027733: libc6: new libc6 breaks GNU Screen handling of some Unicode characters

[Sven Joachim <svenjoac@gmx.de>]

On 2023-01-02 16:34 +0100, Vincent Lefevre wrote:

> Package: libc6
> Version: 2.36-7
> Severity: serious
>
> The new libc6 appears to have some change related to Unicode that
> yields display issues in screen 4.9.0-3, such as horizontal and/or
> vertical text shifting. A consequence of this text shifting is that
> in Mutt (in particular with arrow_cursor), one may select a message
> to be deleted, but a different message is actually deleted.
>
> There is no such issue under bullseye (Debian 11.6), which also has
> GNU Screen 4.09.00, so the breakage appears to be due to libc6.

Without having looked at the problem: this appears to be a rather bold
conclusion.  There are also newer versions of mutt, ncurses and a few
other libraries which mutt or screen depend upon that could be
responsible.

> Example to reproduce the issue with the U+1FAF6 HEART HANDS character
> under Debian/unstable:
>
> 1. Run "screen" in a 80-column terminal.
>
> 2. Open this mailbox with "mutt -F /dev/null -f heart-hands.mbox".
>    Result: line 10 is shifted 1 column to the right, and character "v"
>    appears on the following line.

I failed to reproduce that step, the 'v' appears on the last column for
me.

Cheers,
       Sven