gtksourceview3 was superseded in 2018 by gtksourceview4 (a new major
upstream release, but still using GTK 3). There's a porting guide here,
which is mostly "stop using deprecated APIs" plus a few function renames:
https://gnome.pages.gitlab.gnome.org/gtksourceview/gtksourceview5/porting-guide-3-to-4.html

gtksourceview3 is unmaintained and hasn't had an upstream release for more
than 5 years, so it would be great if the remaining gtksourceview3
applications can move to gtksourceview4 before trixie.

This particular package uses gtksourceview3 indirectly via the C++ binding
libgtksourceviewmm, which seems to have become unmaintained upstream (see
#1079433). If it is desirable to keep this package in Debian, then someone
with an interest in gtksourceview C++ bindings should take over upstream
maintenance of libgtksourceviewmm and finish releasing a 4.x version.

Thanks,
    smcv

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I have filed an upstream PR that can be used to fix this.

Hello,

Bug #1079437 in gimagereader reported by you has been fixed in the
Git repository and is awaiting an upload. You can see the commit
message below and you can check the diff of the fix at:

https://salsa.debian.org/debian/gimagereader/-/commit/b7ec22cff75b5e9470ab357f269ff122411a2d2d

(this message was generated automatically)
-- 
Greetings

https://bugs.debian.org/1079437

I am uploading the changes in git as NMU to DELAYED/10.

We believe that the bug you reported is fixed in the latest version of
gimagereader, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1079437@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Bastian Germann <bage@debian.org> (supplier of updated gimagereader package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Thu, 01 Oct 2026 16:36:19 +0200
Source: gimagereader
Architecture: source
Version: 3.4.3-2.1
Distribution: unstable
Urgency: medium
Maintainer: Philip Rinn <rinni@debian.org>
Changed-By: Bastian Germann <bage@debian.org>
Closes: 1079437
Changes:
 gimagereader (3.4.3-2.1) unstable; urgency=medium
 .
   * Non-maintainer upload
   * Forwarded libxml++5 patch
   * Migrate to gtksourceview4 (Closes: #1079437)
Checksums-Sha1:
 e5877ff456b6c55973659ee6ccb9448d1cc54360 2922 gimagereader_3.4.3-2.1.dsc
 7539747644f9c652abe51b9829e412e5e12af9d6 11804 gimagereader_3.4.3-2.1.debian.tar.xz
 ae044368f75f5adf821de463b5bc1921f7164d25 7364 gimagereader_3.4.3-2.1_source.buildinfo
Checksums-Sha256:
 94c564b2e032a065387d5c34e8ae6fe8a5f567ba7b993d4c6d2d87b36af525a1 2922 gimagereader_3.4.3-2.1.dsc
 589c3a5d6cae0563542dd40fd25767002c269064f0bd054bb7cc3ebc6ae7d357 11804 gimagereader_3.4.3-2.1.debian.tar.xz
 e2947d86daaf1ff123ce0abe7c6e4a6afed792dd7f40e877a52c4e3b725bfe59 7364 gimagereader_3.4.3-2.1_source.buildinfo
Files:
 8e0b15a4bbddb18a9137d608090f2a6d 2922 graphics optional gimagereader_3.4.3-2.1.dsc
 cf4c497e89a69e863314024ea35f72ce 11804 graphics optional gimagereader_3.4.3-2.1.debian.tar.xz
 91b5b1b505fdd880a03f5f92da1bf4d9 7364 graphics optional gimagereader_3.4.3-2.1_source.buildinfo
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