Factor out postProcessPackageData to Util.hs.

src/Package.hs

@@ -122,15 +122,13 @@ buildPackageData pkg @ (Package name path _) (stage, dist, settings) =
           "inplace-pkg-config",
           "setup-config",
           "build" </> "autogen" </> "cabal_macros.h",
-          "build" </> "autogen" </> ("Paths_" ++ name) <.> "hs" -- TODO: Is this needed? What's up with Paths_cpsa.hs?
+          "build" </> "autogen" </> ("Paths_" ++ name) <.> "hs" -- TODO: Is this needed? Also check out Paths_cpsa.hs.
         ] &%> \_ -> do
             need [path </> name <.> "cabal"]
             when (doesFileExist $ path </> "configure.ac") $ need [path </> "configure"]
             run GhcCabal cabalArgs
             when (registerPackage settings) $ run (GhcPkg stage) ghcPkgArgs
-            let pkgDataFile = path </> dist </> "package-data.mk"                 
-            pkgData <- lines <$> liftIO (readFile pkgDataFile)
-            length pkgData `seq` writeFileLines pkgDataFile $ map (replaceIf isSlash '_') $ filter ('$' `notElem`) pkgData
+            postProcessPackageData $ path </> dist </> "package-data.mk"
               where
                 cabalArgs, ghcPkgArgs :: Args
                 cabalArgs = mconcat

src/Util.hs

 module Util (
     module Data.Char,
     isSlash,
-    replaceIf, replaceEq
+    replaceIf, replaceEq,
+    postProcessPackageData
     ) where
 
+import Base
 import Data.Char
 
 isSlash :: Char -> Bool
@@ -14,3 +16,11 @@ replaceIf p to = map (\from -> if p from then to else from)
 
 replaceEq :: Eq a => a -> a -> [a] -> [a]
 replaceEq from = replaceIf (== from)
+
+-- Prepare a given 'packaga-data.mk' file for parsing by readConfigFile:
+-- 1) Drop lines containing '$'
+-- 2) Replace '/' and '\' with '_'
+postProcessPackageData :: FilePath -> Action ()
+postProcessPackageData file = do
+    pkgData <- (filter ('$' `notElem`) . lines) <$> liftIO (readFile file)
+    length pkgData `seq` writeFileLines file $ map (replaceIf isSlash '_') pkgData