On Sat, 2008-12-06 at 02:03 +0000, Ian Lynagh wrote: > On Fri, Dec 05, 2008 at 05:53:52PM +0000, Duncan Coutts wrote: > > > > The way the solver works is that it does not commit to using the > > installed version until the last possible minute. It does this because > > the installed versions have much tighter constraints on dependencies. It > > does a pass at the end to improve the solution by replacing available > > packages by already installed ones wherever possible. > > > > Currently it does that by checking if all the deps are exactly the same. > > If they are not then it decides it's not suitable. We could relax that > > slightly by instead checking if all the constraints that picking the > > installed instance are consistent with the existing constraints. If they > > are consistent then we can pick the installed one (and add the > > constraints to the constraint set). If the conflict then we have to pick > > the available version and do a re-install.
I just pushed this change to the development version of cabal-install. It seems to do the right thing in a few simple scenarios. Wider testing would be much appreciated. > If I understand correctly what happens, I think the current > cabal-install behaviour is a bug (and the above change will make it less > likely to happen, but not fix it): > > If cabal-install reinstalls foo-0.1 with different deps, and you have > bar-0.1 installed which depends on foo-0.1, then cabal-install also > needs to reinstall bar-0.1. Right. > And it should check that it will be able to > do so before it reinstalls foo-0.1 (so in particular, it would fail when > trying to replace a dependency of the ghc package). Right. We do not do that yet. See http://hackage.haskell.org/trac/hackage/ticket/371 > It would also be nice if it told you what it was going to do in advance, > and gave you the opportunity to abort, similar to: We could make it print the install list when it is non-trivial. That lets someone hit ^C if they're quick. > $ sudo apt-get install libc6 > The following extra packages will be installed: > libc6-dbg libc6-dev libc6-i386 > The following packages will be upgraded: > libc6 libc6-dbg libc6-dev libc6-i386 > Do you want to continue [Y/n]? We'd need a wider discussion with existing users if we want to make cabal-install interactive. Duncan _______________________________________________ Cvs-ghc mailing list Cvs-ghc@haskell.org http://www.haskell.org/mailman/listinfo/cvs-ghc
