haskell/Cabal/Setup.hs for buildnumber module auto-generation

Setup.hs

import Distribution.Simple
import Distribution.PackageDescription
import Distribution.Simple.Program
import Distribution.Simple.Command
import Distribution.Simple.PreProcess
import Distribution.Simple.Setup
import Distribution.Simple.LocalBuildInfo
import Distribution.Simple.BuildPaths
import Distribution.Simple.BuildTarget
import System.Process
import System.Directory
import System.FilePath ( (</>), (<.>) )
import System.Environment ( getArgs )



main = do
  let hooks = simpleUserHooks
        { instHook  = \pkgdescr lbi userhooks instflags -> do
                       buildNoAction lbi
                       instHook simpleUserHooks pkgdescr lbi userhooks instflags
        -- , buildHook = \pkgdescr lbi userhooks buildflags -> do
        --                buildNoAction lbi
        --                buildHook simpleUserHooks pkgdescr lbi userhooks buildflags
        , postConf  = \_args _confflags _pkgdescr lbi -> do
                       buildNoAction lbi
        }
  defaultMainWithHooks hooks

buildNoAction :: LocalBuildInfo
              -> IO ()
buildNoAction lbi = do
  -- putStrLn "Generating build number file and module."
  let dir = autogenModulesDir lbi
  createDirectoryIfMissing True dir
  let buildNoModulePath = dir </> "BuildNo_examplepackage.hs"
  buildNo <- (read :: String -> Int) <$> readProcess "buildno" [] ""
  writeFile buildNoModulePath
    $ unlines
    [ "module BuildNo_examplepackage"
    , "  ( buildNo"
    , "  )"
    , "where"
    , ""
    , ""
    , ""
    , "import Prelude ( Int )"
    , ""
    , ""
    , ""
    , "buildNo :: Int"
    , "buildNo = " ++ show buildNo
    ]
  return ()