Bug#1110900: apt update misleadingly says "All packages are up-to-date" when no package sources are configured

Package: apt
Followup-For: Bug #1110900
X-Debbugs-Cc: [email protected]

Dear Maintainer,

the issue in question is still present in apt version 3.0.3 (amd64),
cf. the transcript below:

Transcript:
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root@debiantutor:/etc/apt# cat /etc/debian_version
13.0
root@debiantutor:/etc/apt# cat /etc/issue.net
Debian GNU/Linux 13
root@debiantutor:/etc/apt# apt-cache policy apt
apt:
  Installed: 3.0.3
  Candidate: 3.0.3
  Version table:
 *** 3.0.3 100
        100 /var/lib/dpkg/status
root@debiantutor:/etc/apt# apt --version
apt 3.0.3 (amd64)
root@debiantutor:/etc/apt#
root@debiantutor:/etc/apt# apt update
Get:1 https://security.debian.org/debian-security trixie-security InRelease [43.4 kB]
Hit:2 https://linux.teamviewer.com/deb stable InRelease
Get:3 https://security.debian.org/debian-security trixie-security/main amd64 Packages [8236 B]
Get:4 https://security.debian.org/debian-security trixie-security/main i386 Packages [4800 B]
Get:5 https://security.debian.org/debian-security trixie-security/main Translation-en [8632 B]
Get:6 https://deb.debian.org/debian trixie InRelease [138 kB]
Get:7 https://deb.debian.org/debian trixie-updates InRelease [47.1 kB]
Get:8 https://deb.debian.org/debian trixie/main amd64 Packages [9668 kB]
Get:9 https://deb.debian.org/debian trixie/main i386 Packages [9428 kB]
Get:10 https://deb.debian.org/debian trixie/main Translation-en [6484 kB]
Get:11 https://deb.debian.org/debian trixie/main amd64 Components [5175 kB]
Get:12 https://deb.debian.org/debian trixie/main Icons (48x48) [3626 kB]
Get:13 https://deb.debian.org/debian trixie/main Icons (64x64) [7367 kB]
Get:14 https://deb.debian.org/debian trixie/contrib amd64 Packages [53.8 kB]
Get:15 https://deb.debian.org/debian trixie/contrib i386 Packages [44.1 kB]
Get:16 https://deb.debian.org/debian trixie/contrib Translation-en [49.6 kB]
Get:17 https://deb.debian.org/debian trixie/contrib amd64 Components [41.5 kB]
Get:18 https://deb.debian.org/debian trixie/contrib Icons (48x48) [60.1 kB]
Get:19 https://deb.debian.org/debian trixie/contrib Icons (64x64) [132 kB]
Get:20 https://deb.debian.org/debian trixie/non-free i386 Packages [72.6 kB]
Get:21 https://deb.debian.org/debian trixie/non-free amd64 Packages [100 kB]
Get:22 https://deb.debian.org/debian trixie/non-free Translation-en [67.1 kB]
Get:23 https://deb.debian.org/debian trixie/non-free amd64 Components [3784 B]
Get:24 https://deb.debian.org/debian trixie/non-free Icons (48x48) [578 B]
Get:25 https://deb.debian.org/debian trixie/non-free Icons (64x64) [10.4 kB]
Get:26 https://deb.debian.org/debian trixie/non-free-firmware i386 Packages [6540 B]
Get:27 https://deb.debian.org/debian trixie/non-free-firmware amd64 Packages [6868 B]
Get:28 https://deb.debian.org/debian trixie/non-free-firmware Translation-en [4704 B]
Get:29 https://deb.debian.org/debian trixie/non-free-firmware amd64 Components [24.3 kB]
Get:30 https://deb.debian.org/debian trixie/non-free-firmware Icons (48x48) [29 B]
Get:31 https://deb.debian.org/debian trixie/non-free-firmware Icons (64x64) [29 B]
Get:32 https://deb.debian.org/debian trixie-updates/main amd64 Packages [2432 B]
Get:33 https://deb.debian.org/debian trixie-updates/main i386 Packages [2432 B]
Get:34 https://deb.debian.org/debian trixie-updates/main Translation-en [396 B]
Fetched 42.7 MB in 8s (5242 kB/s)
7 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@debiantutor:/etc/apt#
root@debiantutor:/etc/apt# mv -v sources.list.d/debian.sources{,.disabled}
renamed 'sources.list.d/debian.sources' -> 'sources.list.d/debian.sources.disabled'
root@debiantutor:/etc/apt# mv -v sources.list.d/teamviewer.list{,.disabled}
renamed 'sources.list.d/teamviewer.list' -> 'sources.list.d/teamviewer.list.disabled'
root@debiantutor:/etc/apt# apt update
All packages are up to date.
root@debiantutor:/etc/apt#
root@debiantutor:/etc/apt# mv -v sources.list.d/teamviewer.list.disabled sources.list.d/teamviewer.list
renamed 'sources.list.d/teamviewer.list.disabled' -> 'sources.list.d/teamviewer.list'
root@debiantutor:/etc/apt# mv -v sources.list.d/debian.sources.disabled sources.list.d/debian.sources
renamed 'sources.list.d/debian.sources.disabled' -> 'sources.list.d/debian.sources'
root@debiantutor:/etc/apt# apt update
Get:1 https://linux.teamviewer.com/deb stable InRelease [11.9 kB]
Get:2 https://deb.debian.org/debian trixie InRelease [138 kB]
Get:3 https://linux.teamviewer.com/deb stable/main amd64 Packages [6747 B]
Get:4 https://linux.teamviewer.com/deb stable/main i386 Packages [6244 B]
Get:5 https://security.debian.org/debian-security trixie-security InRelease [43.4 kB]
Get:6 https://deb.debian.org/debian trixie-updates InRelease [47.1 kB]
Get:7 https://security.debian.org/debian-security trixie-security/main i386 Packages [4800 B]
Get:8 https://deb.debian.org/debian trixie/main i386 Packages [9428 kB]
Get:9 https://security.debian.org/debian-security trixie-security/main amd64 Packages [8236 B]
Get:10 https://security.debian.org/debian-security trixie-security/main Translation-en [8632 B]
Get:11 https://deb.debian.org/debian trixie/main amd64 Packages [9668 kB]
Get:12 https://deb.debian.org/debian trixie/main Translation-en [6484 kB]
Get:13 https://deb.debian.org/debian trixie/main amd64 Components [5175 kB]
Get:14 https://deb.debian.org/debian trixie/main Icons (48x48) [3626 kB]
Get:15 https://deb.debian.org/debian trixie/main Icons (64x64) [7367 kB]
Get:16 https://deb.debian.org/debian trixie/contrib amd64 Packages [53.8 kB]
Get:17 https://deb.debian.org/debian trixie/contrib i386 Packages [44.1 kB]
Get:18 https://deb.debian.org/debian trixie/contrib Translation-en [49.6 kB]
Get:19 https://deb.debian.org/debian trixie/contrib amd64 Components [41.5 kB]
Get:20 https://deb.debian.org/debian trixie/contrib Icons (48x48) [60.1 kB]
Get:21 https://deb.debian.org/debian trixie/contrib Icons (64x64) [132 kB]
Get:22 https://deb.debian.org/debian trixie/non-free i386 Packages [72.6 kB]
Get:23 https://deb.debian.org/debian trixie/non-free amd64 Packages [100 kB]
Get:24 https://deb.debian.org/debian trixie/non-free Translation-en [67.1 kB]
Get:25 https://deb.debian.org/debian trixie/non-free amd64 Components [3784 B]
Get:26 https://deb.debian.org/debian trixie/non-free Icons (48x48) [578 B]
Get:27 https://deb.debian.org/debian trixie/non-free Icons (64x64) [10.4 kB]
Get:28 https://deb.debian.org/debian trixie/non-free-firmware amd64 Packages [6868 B]
Get:29 https://deb.debian.org/debian trixie/non-free-firmware i386 Packages [6540 B]
Get:30 https://deb.debian.org/debian trixie/non-free-firmware Translation-en [4704 B]
Get:31 https://deb.debian.org/debian trixie/non-free-firmware amd64 Components [24.3 kB]
Get:32 https://deb.debian.org/debian trixie/non-free-firmware Icons (48x48) [29 B]
Get:33 https://deb.debian.org/debian trixie/non-free-firmware Icons (64x64) [29 B]
Get:34 https://deb.debian.org/debian trixie-updates/main amd64 Packages [2432 B]
Get:35 https://deb.debian.org/debian trixie-updates/main i386 Packages [2432 B]
Get:36 https://deb.debian.org/debian trixie-updates/main Translation-en [396 B]
Fetched 42.7 MB in 7s (5846 kB/s)
7 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@debiantutor:/etc/apt#
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Also note the repeated transfer of arguably the same information after restoring the sources.