Hi, Some time ago we've got bug #510780 [1] asking us to bump subslot on LLVM even though the new version was ABI-compatible with previous one. It was because it introduced new APIs which applications could make use of. Since I believe this is a wider issue, I would like to know the opinion of our community about this.
More specifically: do we want subslots to change only when backwards- incompatible ABI changes are done -- alike SONAME -- or whenever any ABI change is done? The problem seems a bit complex. Considering the libtool versioning, there are two kinds of library bumps relevant to us: 1) when ABI is altered in backwards-compatible way (so old stuff is not touched), 2) when ABI is altered in backwards-incompatible way. Option 1) corresponds to bumping minor libtool version, option 2) to bumping SONAME. I think most of the packages follow SONAME in subslots and therefore care only about 2). If we decide to keep bumping subslots only when SONAME changes, this has two implications: a) new features introduced libraries are not used by packages built prior to upgrading the library, b) packages built after upgrading the library may be broken when it is downgraded (if they use the newer ABI). I think a) is not *that* a big deal since usually new ABIs involve new APIs, and those involve code changes in the reverse dependency. Then we can usually assume that the new version of reverse dependency will be added (and therefore upgraded to) after the library in question. I have no strong opinion about b). This is a known issue with SONAMEs, and I'm not sure if we really support people downgrading. It is worth noting, however, that sometimes we ourselves force downgrades due to issues with new versions. If we decide to bump subslots to match major+minor ABI version, we force the reverse dependencies to always use the ABI corresponding to installed library version. However, this means that we force much more rebuilds than necessary. For example, glib-2 often introduces new APIs while packages obviously don't use them immediately or at all. We will be forcing rebuild of every reverse dependency at glib-2 upgrade, while the user will most likely need to wait for another version bump (and rebuild) to get the new glib-2 features used. What do you think? [1]:https://bugs.gentoo.org/show_bug.cgi?id=510780 -- Best regards, Michał Górny
signature.asc
Description: PGP signature
