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Re: Auto-update for sid? Auto-backport?

On Thu, 16 Nov 2017 at 17:02:00 +0000, Holger Levsen wrote:
> On Thu, Nov 16, 2017 at 05:53:40PM +0100, Wouter Verhelst wrote:
> > Yes; and semver.org is a formalized system for version numbering stuff.
> > If upstream has committed to it (and does not make mistakes), then the c
> > versions in the above example MUST (in the RFC definition of that word)
> > only contain bugfixes, and no interface changes.
> oh shiny! thanks for pointing out semver.org!

Semantic versioning is not a panacea: it assumes that a developer can
know in advance whether changes are a compatibility break or not. In
simple cases where a bug fix or a new feature never causes any unintended
regressions, that's easy; but if there were no regressions, then we'd
all run unstable on servers.

Because we live in the messy real world where unintended regressions
happen, developers frequently want to branch versions and apply
policies to the changes they contain, with different subsets of bugfixes
(for example security fixes only, or fixes that have been judged to be
low-regression-risk only), or different subsets of new APIs, on different
branches. Unfortunately, because semver versions are a deterministic
product of the previous release and the changes since that release,
they can break the ability to branch. If I release Foo 1.2.3, it gets
shipped in Debian 10, and I subsequently release Foo 1.2.4 with a mixture
of high- and low-risk bug fixes, then semver offers no way to go back
and release a version aimed at a Debian 10 point release with just the
low-risk fixes included (except by releasing Foo, which is not
a valid version according to semver).

In simple cases, semantic versioning is fine; it's certainly better than
having no conceptual model at all. In the more complicated cases that
are probably of more practical interest, it's an oversimplification.

A semver-like scheme in which higher-risk bugfixes and internal changes
are treated as though they were new API, even if they aren't (i.e. bumping
the minor instead of micro version) is a common way out of this, and is
fine as long as you don't want to offer "long term supported" branches.