I have added some suggestions about conditional compilation to https://www.haskell.org/haskellwiki/Cabal/FAQ#Conditional_compilation Maybe my suggestion about using Hs-Source-Dirs for conditional compilation can be added to http://www.haskell.org/cabal/release/cabal-latest/doc/users-guide/authors.ht... I'm confused with a paragraph from http://www.haskell.org/ghc/docs/latest/html/Cabal/authors.html "If dependencies were missing, the last flag (as by the order in which the flags were introduced in the package description) is tried with its alternative value and so on. This continues until either an assignment is found where all dependencies can be satisfied, or all possible flag assignments have been tried." I assumed that the automatic search for appropriate flag assignments is only done by cabal-install, not by Cabal.