RFC: Cabal-Configurations patch(es)

[Thomas Schilling]

Hi,

you just received a longish patch bundle, that together implement  
Cabal configurations.  I realized too late that there's a way to  
combine this mail with the actual patch, so consider this an addendum.

The implementation can read all old Cabal-files (and should do the  
same), but unfortunately, I had to change the interface of the  
confHook function, which I assume will break some setup files.  The  
documentation states, that you shouldn't depend on that interface,  
but then again do people have to use them if they have special  
requirements.

The most important change is, that Cabal files are now parsed to  
'PreparedPackageDescription' which requires a run of  
'finalizePackageDescription' to get to the actual  
'PackageDescription'.  This resolving process is potentially very  
slow (exponential in the number of flags), especially if there is no  
possible flag assignment.  I plan to correct this by adding some  
minimum SAT solving capabilities,  which will however still be  
exponential in the worst case.  For now, the current implementation  
should be sufficient, though.

My testing is far from exhaustive, as I haven't yet found a good way  
of setting up a suitable test environment without endangering to  
break my current setup.  I am setting up a ghc-HEAD installation, but  
there is currently a build error stopping me from it.  Incidentally,  
Cabal itself now needs configurations to build with ghc-head as well  
as ghc-6.6.1.


That said, I'd like to ask you to review the patches and possibly  
also test it on your projects.  A preliminary HOWTO is at:

   http://hackage.haskell.org/trac/hackage/wiki/CabalConfigurations

Thanks,

/ Thomas