Package: debian-policy Severity: normal Section 8.1 starts with the following:
+--- | The run-time shared library must be placed in a package whose name | changes whenever the SONAME of the shared library changes. This | allows several versions of the shared library to be installed at the | same time [...] +--- This has two issues: 1. It is not needed to change package names for this. One can also use "Provides: <something-that-changes-with-soname>" and have packages depend on that. 2. It does not allow coinstallability without other constraints. There are several common patterns like depending on a libfoo-bin or libfoo-common package which then would also be required to work with both versions. I think I've also seen libfooX-bin packages that were not coinstallable as helper binaries were not installed into a path that changes with soname. There is also a footnote that states +--- | There are some exceptional situations in which co-installation of | two versions of a shared library is not safe, and the new shared | library package has to conflict with the previous shared library | package. This is never desirable, since it causes significant | disruption during upgrades and potentially breaks unpackaged | third-party binaries, but is sometimes unavoidable. These situations | are sufficiently rare that they usually warrant project-wide | discussion, and are complex enough that the rules for them cannot be | codified in Debian Policy. +--- which seems to contradict current practice as I don't remember a single project-wide discussion about -common or -bin packages cuasing this. It also doesn't seem warranted for libraries with few reverse dependencies. So I suggest: 1. Policy should document current practices and also allow other methods that ensure dependencies are satisfied. Note that some ecosystems like Perl do similar things with perlapi-X (where different perlapi-X providers are in general not coinstallable). 2. Coinstallability should be mentioned as a concern for libraries with many reverse dependencies, but should explictly state that this requires the entire dependency chain to be coinstallable. Note that "Depends: libfoo-common (>= X)" runs into the risk that newer libfoo-common packages break older library versions and are safe only when extraordinary care is taken; the same is true for "libfoo-bin". (One could use libfooX-common, libfooX-bin packages where data and helper binaries are installed into paths that change with the SONAME such as /usr/lib/libfooX/libfoo-helper.) 3. The footnote about "exceptional situations" should be removed. Ansgar
