I guess you could indicate that a package won't build in some configuration using the buildable field. Hackage ought to learn to use that too.
Oh you mean we should say:
if os(windows) -- this package is known not to work on windows buildable: false
and then cabal should fail on configuration, and cabal-install should not consider depending on that package in that configuration?
if hackage started to display platform dependencies, that might help to get .cabal authors to document them. but there would need to be a single convention for documenting this, and it would have to be advertized and promoted, perhaps even enforced. having lots of packages is no good unless they work on your platform, and being explicit about which platforms a package does not (currently, for lack of porting, or ever, for hardwired dependencies) work is the first step toward improving the situation. i'd much rather have hackage tell me which packages are usable with my platform (build-reports verifying .cabal file accuracy), than tell me how many people on other platforms are using those packages without caring about portability to other platforms!-) claus