Hi release team, as part of finishing the /usr-merge, I've written down the most important bits at https://subdivi.de/~helmut/dep17.html. In this mail, I'm concerned with P6, i.e. loss of empty directories. The general scenario is that one package ships an empty directory and another package also ships that directory (empty or not) with different aliasing (e.g. one package has an empty /usr/lib/foo and the other has /lib/foo). When removing (or upgrading) the other package, the empty directory may be deleted causing an inconsistency between the dpkg database and the filesystem. This inconsistency is detected e.g. by piuparts, which may fail. This is how Andreas Beckmann originally discovered this problem class.
As a result, I've started filing patches for this problem class. https://udd.debian.org/cgi-bin/bts-usertags.cgi?user=helmutg%40debian.org&tag=dep17p6 In the majority of cases, such empty directories are more of a bug than a feature and we can simply delete them. In some cases, they really are used though. When they are used, we need to do something about that deletion and I've submitted e.g. https://salsa.debian.org/systemd-team/systemd/-/merge_requests/208 where I got negative feedback on the need to address this. So how important is it to have these empty directories? I concur with Michael on the aspect that their loss rarely poses a practical issue. It can make piuparts fail however and when it does, the failing package tends to not be the one that is able to fix the failure. So in effect, keeping these bugs would cause latent migration blockers. For this reason, I was assuming the bug class to be release critical. Do you concur? If we want it to not be release critical, I think we'd have to augment piuparts in a way that it ignores such directory loss. On the flip side, systemd has been the last package for me to file a patch where this issue has practical consequences already. All others have been filed already. Beyond these, there are five more cases on the horizon that likely need to be mitigated when we lift the moratorium. So while the mitigation is ugly, the low number of affected packages and the temporary nature of the mitigation made me conclude that doing this is a reasonable trade-off. Do you agree? Another example for the ugliness is #1050412. Helmut
