On Tue, 2005-05-10 at 10:51 +0100, Simon Marlow wrote:
Yes, the module overlap restriction has started to bite us. It now turns out that you can't build GHC from CVS if you have wxHaskell installed.
Why? Because wxHaskell depends on some older non-hierarchical packages (util in particular, which itself depends on lang). These package populate the top-level module namespace, and steal a bunch of module names that you might want to use in your program.
There are a few libs that do this and it makes them essentially unpackagable when using ghc 6.4. Not because of conflicts with ghc itself but just conflicts with each other and totally unrelated packages. Just to make it clear to people how annoying it is, suppose I create a library with this cabal description: name: dummy version: 1.0 depends: util-1.0 exposed: True and then I register this package (to show the problem, this package doesn't need to expose any modules or contain any object code) $ ghc-pkg register dummy.cabal --user Now if we try to compile any package that contains a module called GetOpt (and lets face it there are dozens of programs that have made local copies of this module): GetOpt.hs: module GetOpt where -- module needn't have any code in it Now if we try to compile it: $ ghc-6.4 -c GetOpt.hs GetOpt.hs:1:0 Module `GetOpt` is a mamber of package util-1.0 To compile this module, please use -ignore-package util-1.0. So what this means is that by having *any* package registered on the system that is exposed by default and depends on the old util package from hslibs, then *any* other program or library that you try to compile that has a GetOpt module (and there are lots of those) will not work. We discovered this in Gentoo, when after installing Cabal-0.5 (which is exposed by default and uses the util package), compiling happy failed. Our intrim policy in Gentoo Haskell packaging land is that we cannot package any library that is exposed by default and depends on any of the old hslibs packages because it will cause compile failures in unrelated programs. (We didn't realise wxhaskell did this too)
Thoughts?
Ditch hslibs asap! We can probably draw up a list of the packages we know about that do this. Duncan