On Fri, 2009-01-30 at 18:29 -0600, John Goerzen wrote:
On Fri, Jan 30, 2009 at 03:50:30PM -0800, Michael Snoyman wrote:
[3 of 7] Compiling Database.HDBC.Statement ( Database/HDBC/Statement.hs, dist/build/Database/HDBC/Statement.o )
Database/HDBC/Statement.hs:113:9: Type constructor `Exception' used as a class In the instance declaration for `Exception SqlError' cabal: Error: some packages failed to install: HDBC-2.0.0 failed during the building phase. The exception was: exit: ExitFailure 1
That's *WEIRD*.
It's as if you have the old base from GHC 6.8. Is cabal-install doing something (weird|evil|smart) here?
Yes.
Leads me to think even more that there's cabal-install trickery here.
Yup.
Can someone enlighten us on that? Is cabal-install playing tricks with base?
Yes. The difference (in the released version of cabal-install) between the configure and install commands is that configure uses a dumb algorithm for deciding what versions of dependencies to use while install uses a smarter algorithm. Obviously this is confusing and in the next release configure will use the smart algorithm too. At the moment configure picks the latest versions of all packages irrespective of whether this is likely to work or not. For developers using ghc-6.10 with base 3 and 4 this means they end up with base 4. They then likely do not notice that their package actually needs base version 4. The install command uses the constraint solver and takes into account some global preferences from hackage. These are soft preferences / soft constraints. They do not override constraints specified in the .cabal file or on the command line. However for the huge number of packages on hackage that worked with ghc-6.8 but failed to specify a constraint on the version of base, using a preference of base 3 over base 4 enables those packages to continue to build. So in the next cabal-install release (which should be pretty soon now) configure will do the same thing and pick base 3 unless you specify build-depends base >= 4. So the solution is for HDBC-2.0 to specify the version of base that it needs more accurately. It appears that it does need version 4 so it should use: build-depends: base == 4.* On a similar issue, I am going to make Hackage enforce that packages specify an upper bounds on the version of base. Hopefully doing that will make people also consider the appropriate lower bound. I don't see an obvious way of automatically requiring accuracy in selecting the base version between 3 and 4. It is perfectly possible to have a package that works with both. Perhaps we should make not-specifying an upper bound an error and not specifying a lower bound a warning. Thoughts? Duncan