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



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.

If the change has been done on purpose, then there are missing
dependency relationships that should prevent the installation
of incompatible software until such software has been updated
to support this change.

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.

3. Create a new Screen window and switch back to the original window.
   Result: messages 1 to 9 are shifted upward.

-- System Information:
Debian Release: bookworm/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 'stable-security'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
merged-usr: no
Architecture: amd64 (x86_64)

Kernel: Linux 6.0.0-6-amd64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=POSIX, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libc6 depends on:
ii  libgcc-s1  12.2.0-12

Versions of packages libc6 recommends:
ii  libidn2-0  2.3.3-1+b1

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]  1.5.81
ii  glibc-doc              2.36-7
ii  libc-l10n              2.36-7
pn  libnss-nis             <none>
pn  libnss-nisplus         <none>
ii  locales                2.36-7

-- debconf information:
  glibc/disable-screensaver:
* glibc/restart-services: postfix ssh cups cron atd
  glibc/kernel-too-old:
* libraries/restart-without-asking: false
  glibc/restart-failed:
  glibc/kernel-not-supported:
  glibc/upgrade: true

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Attachment: heart-hands.mbox
Description: application/mbox


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