From http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=293523
Specify include and library paths that are used for building the
package only, and do not end up in the GHC packages file.
I think this needs more explanation.
There is certainly a use case for includes that are used to pre-process Haskell code since they are never needed when building dependent packages. On the other hand, library paths to find libraries to link to are always required by dependent packages as far as I know since to link an executable using a package that uses a library we have to specify the library and search path.
There is no way with GHC to limit where a C header file might be needed. If a header file is needed to compile a package, then the header file might also be needed to compile code that uses the package due to cross-package inlining. If GHC does gain the feature to limit the scope of where C headers are required then we will want to support that in Cabal, possibly via package-local headers.
