made parentDir return a Maybe FilePath; removed most uses of it

parentDir is less safe than takeDirectory, especially when working
with relative FilePaths. It's really only useful in loops that
want to terminate at /

This commit was sponsored by Audric SCHILTKNECHT.

Utility/Daemon.hs

@@ -83,7 +83,7 @@ foreground pidfile a = do
  - Fails if the pid file is already locked by another process. -}
 lockPidFile :: FilePath -> IO ()
 lockPidFile pidfile = do
-	createDirectoryIfMissing True (parentDir pidfile)
+	createDirectoryIfMissing True (takeDirectory pidfile)
 #ifndef mingw32_HOST_OS
 	fd <- openFd pidfile ReadWrite (Just stdFileMode) defaultFileFlags
 	locked <- catchMaybeIO $ setLock fd (WriteLock, AbsoluteSeek, 0, 0)
@@ -176,6 +176,6 @@ winLockFile pid pidfile = do
 	prefix = pidfile ++ "."
 	suffix = ".lck"
 	cleanstale = mapM_ (void . tryIO . removeFile) =<<
-		(filter iswinlockfile <$> dirContents (parentDir pidfile))
+		(filter iswinlockfile <$> dirContents (takeDirectory pidfile))
 	iswinlockfile f = suffix `isSuffixOf` f && prefix `isPrefixOf` f
 #endif

Utility/FreeDesktop.hs

@@ -27,7 +27,6 @@ module Utility.FreeDesktop (
 ) where
 
 import Utility.Exception
-import Utility.Path
 import Utility.UserInfo
 import Utility.Process
 import Utility.PartialPrelude
@@ -79,7 +78,7 @@ buildDesktopMenuFile d = unlines ("[Desktop Entry]" : map keyvalue d) ++ "\n"
 
 writeDesktopMenuFile :: DesktopEntry -> String -> IO ()
 writeDesktopMenuFile d file = do
-	createDirectoryIfMissing True (parentDir file)
+	createDirectoryIfMissing True (takeDirectory file)
 	writeFile file $ buildDesktopMenuFile d
 
 {- Path to use for a desktop menu file, in either the systemDataDir or

Utility/LinuxMkLibs.hs

@@ -28,14 +28,14 @@ installLib installfile top lib = ifM (doesFileExist lib)
 	( do
 		installfile top lib
 		checksymlink lib
-		return $ Just $ parentDir lib
+		return $ Just $ takeDirectory lib
 	, return Nothing
 	)
   where
 	checksymlink f = whenM (isSymbolicLink <$> getSymbolicLinkStatus (inTop top f)) $ do
 		l <- readSymbolicLink (inTop top f)
-		let absl = absPathFrom (parentDir f) l
-		let target = relPathDirToFile (parentDir f) absl
+		let absl = absPathFrom (takeDirectory f) l
+		let target = relPathDirToFile (takeDirectory f) absl
 		installfile top absl
 		nukeFile (top ++ f)
 		createSymbolicLink target (inTop top f)

Utility/Path.hs

@@ -77,14 +77,12 @@ absNormPathUnix dir path = todos <$> MissingH.absNormPath (fromdos dir) (fromdos
 	todos = replace "/" "\\"
 #endif
 
-{- Returns the parent directory of a path.
- -
- - To allow this to be easily used in loops, which terminate upon reaching the
- - top, the parent of / is "" -}
-parentDir :: FilePath -> FilePath
+{- Just the parent directory of a path, or Nothing if the path has no
+ - parent (ie for "/") -}
+parentDir :: FilePath -> Maybe FilePath
 parentDir dir
-	| null dirs = ""
-	| otherwise = joinDrive drive (join s $ init dirs)
+	| null dirs = Nothing
+	| otherwise = Just $ joinDrive drive (join s $ init dirs)
   where
 	-- on Unix, the drive will be "/" when the dir is absolute, otherwise ""
 	(drive, path) = splitDrive dir
@@ -94,8 +92,8 @@ parentDir dir
 prop_parentDir_basics :: FilePath -> Bool
 prop_parentDir_basics dir
 	| null dir = True
-	| dir == "/" = parentDir dir == ""
-	| otherwise = p /= dir
+	| dir == "/" = parentDir dir == Nothing
+	| otherwise = p /= Just dir
   where
 	p = parentDir dir