b) putting Gtk2HsSetup.hs in either gtk2hs-buildtools or any other library means that ./Setup.hs has to run to realize that this library is missing and that it needs to be downloaded. However, ./Setup.hs cannot be run because it imports Gtk2HsSetup.hs which is not yet available.
There is MIN_VERSION_<package>(), so you might be able to check whether it is defined/has the right version, if it comes with the tools package.
Does that work in Setup.hs? I thought that these CPP macros were generated by the 'confgure' step, which may not have been run yet.
argh. You're right - the macros are not available in Setup.hs. I keep forgetting that because it would be useful to have them there http://hackage.haskell.org/trac/hackage/ticket/326 So, if putting the file into the tools package doesn't suffice, we'd be back to passing in CPP macros from .cabal files (or using a front Setup.hs to check the configuration info before calling out to a version-specific SetupX.hs). Claus