[Haskell-cafe] How to determine correct dependency versions for a library?
troplin at bluewin.ch
Fri Nov 16 20:19:47 CET 2012
Peter Simons <simons at cryp.to> wrote:
> Hi Tobias,
> > A 126.96.36.199 build-depends: B ==2.5.* C ==3.7.* (overspecified)
> > B 188.8.131.52 build-depends: C ==3.* (underspecified)
> > C 184.108.40.206
> > Everything works nice until C-220.127.116.11 appears with incompatible changes
> > that break B, but not A.
> > Now both A and B have to update their dependencies and we have now:
> > A 18.104.22.168 build-depends: B ==2.5.* C >=3.7 && <3.9
> > B 22.214.171.124 build-depends: C >=3 && <3.8
> > C 126.96.36.199
> > And now the following combination is still valid:
> > A 188.8.131.52
> > B 184.108.40.206 (old version)
> > C 220.127.116.11
> > Bang!
> thank you for contributing this insightful example.
> When such a situation has arisen in the past, it's my experience that the
> author of B typically releases an update to fix the issue with the latest
> version of C:
> B 18.104.22.168 build-depends: C >= 3.8
> So that particular conflict does hardly ever occur in practice.
And what if the maintainer of a takes the chance to make some major updates
and directly releases 2.6? Then all packages depending on 2.5.* will
> Note that package A would build just fine after that update of B -- if the
> author of A hadn't overspecified its dependencies. As it is, however, a
> new version of A has to released that changes no code, but only the Cabal
But all this boils down to a system where only a combination of latest
versions will be stable. So why restrict dependencies anyway?
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