[Impact]
If there is a network hiccup at the right moment it's possible that some sources.list entries will be disabled when a release upgrade is calculated and then people could upgrade with surprising results e.g. universe being missing.
[Test Case]
This is somewhat convoluted as we need to create the network error only when a specific line is is being tested by the dist-upgrader.
1) Use a system on xenial or bionic and ensure prompt is set appropriately (lts for xenial, normal for bionic)
2) Edit your /etc/apt/sources.list file so that universe is a separate line from main, restricted, and multiverse
3) Run do-release-upgrade
4) Cancel the release upgrade
5) cd to /tmp/ubuntu-release-upgrader-$tmpname
6) edit DistUpgradeController.py with the attached patch which will cause the url check for the universe line to fail
7) run 'sudo ./$release-upgrading-to'
8) wait until you receive the message regarding quantities of packages to install, upgrade, etc
9) look at /etc/apt/sources.list file and notice that the lines with universe are disabled
With the release-upgrader from -proposed you'll need to follow the same steps and you'll notice that the lines with universe are not disabled.
[Regression Potential]
Because we are checking each unique uri in sources.list only one time its possible that if the first check fails then the upgrade will fail to be calculated. That is better than upgrading and having components disabled though.
[Original Description]
I took a bionic system and stepped through bionic->cosmic->disco via do-release-upgrade.
Upon finishing I noticed that universe was "gone" and all packages from universe were removed from the system. Based on the files on my system, it looks like it happened during the bionic->cosmic upgrade. You'll see in the sources.list that cosmic-updates universe pocket is that but not cosmic universe.
ProblemType: BugDistroRelease: Ubuntu 19.04
Package: ubuntu-release-upgrader-core 1:19.04.13
ProcVersionSignature: Ubuntu 5.0.0-8.9-generic 5.0.1
Uname: Linux 5.0.0-8-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.10-0ubuntu23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Tue Apr 2 16:04:34 2019
InstallationDate: Installed on 2018-07-24 (252 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180724)
PackageArchitecture: all
ProcEnviron:
TERM=xterm
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bashSourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to disco on 2019-04-02 (0 days ago)
VarLogDistupgradeXorgFixuplog:
INFO:root:/usr/bin/do-release-upgrade running
INFO:root:No xorg.conf, exiting
mtime.conffile..etc.update-manager.release-upgrades: 2019-04-02T08:18:06.798258
The timestamp on /etc/apt/