One good example is that even though PKGBUILDs can contain version constraints (see an example here[1]), that metadata is not always present and so it is underutilized. Pacman doesn't support ‘partial upgrades’[2] (once you refresh your package lists, installing anything is ‘unsupported’ until you upgrade everything), and this is why.

(I also think that paper's notion of ‘completeness’ could probably be enriched somehow, because I've seen situations where `apt-get` will crap out but `aptitude` will offer a ‘compromise’ solution which involves downgrading some packages or removing some, and generally package managers based on libsolv do even better IME. Here Arch likely falls flatter.)

Another depsolver related issue in Pacman (related to the lack of partial upgrades) is the lack of distinction between upgrades and dist-upgrades. In apt and dnf, upgrades are non-destructive by default, meaning that they don't offer solutions that involve removing or downgrading user-selected packages. Pacman has no such distinction.

> I never had dependency resolution issues. Can you help me understand with concrete examples?

One fairly common case is that Arch just ignores the dependencies of AUR-installed packages at install time, freely upgrading packages without respect to reverse-dependencies that aren't declared in a repo.[4] Hence, ‘if packages in the official repositories are updated, you will need to rebuild any AUR packages that depend on those libraries’... every single time you upgrade, if you've installed anything from the AUR, it can leave your system with broken packages. Apt and dnf, in contrast, treat every package you install the same way. Additionally, Arch packages don't always declare version constraints for their library dependencies, and there's no CI that tests for ABI changes (there is some in Debian, although such tools can't work perfectly). So you have to use another tool (apparently one popular choice is some script from the Arch forums in 2005, lol[5]) to scan for such breakages, or else just discover them when packages don't work.

On the other hand, when Arch does consider the version constraints of installed packages, the lack of partial upgrades can be problematic for downstream distros. Any version constraints placed by downstream repos on dependencies shared with upstream can just leave you totally unable to upgrade anything at all for a while.[6]

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1: https://github.com/archlinux/svntogit-packages/blob/master/d...

2: https://wiki.archlinux.org/title/System_maintenance#Partial_...

3: https://wiki.archlinux.org/title/Pacman/Rosetta#Basic_operat...

4: https://wiki.archlinux.org/title/Arch_User_Repository#Instal...

5: https://bbs.archlinux.org/viewtopic.php?id=13882

6: https://superuser.com/questions/1497098/pacman-unable-to-upd...