Split packages into hpath{,-io,-filepath}

2020-01-04 17:52:21 +01:00
parent 4e07fcf5b2
commit 09eea518b8
61 changed files with 349 additions and 229 deletions
--- a/hpath-filepath/src/System/Posix/FilePath.hs
+++ b/hpath-filepath/src/System/Posix/FilePath.hs
@@ -0,0 +1,824 @@
+-- |
+-- Module      :  System.Posix.FilePath
+-- Copyright   :  © 2016 Julian Ospald
+-- License     :  BSD3
+--
+-- Maintainer  :  Julian Ospald <hasufell@posteo.de>
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- The equivalent of "System.FilePath" on raw (byte string) file paths.
+--
+-- Not all functions of "System.FilePath" are implemented yet. Feel free to contribute!
+
+
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE TupleSections #-}
+
+{-# OPTIONS_GHC -Wall #-}
+
+
+module System.Posix.FilePath (
+
+  -- * Separator predicates
+  pathSeparator
+, isPathSeparator
+, searchPathSeparator
+, isSearchPathSeparator
+, extSeparator
+, isExtSeparator
+
+  -- * $PATH methods
+, splitSearchPath
+, getSearchPath
+
+  -- * Extension functions
+, splitExtension
+, takeExtension
+, replaceExtension
+, dropExtension
+, addExtension
+, hasExtension
+, (<.>)
+, splitExtensions
+, dropExtensions
+, takeExtensions
+, stripExtension
+
+  -- * Filename\/directory functions
+, splitFileName
+, takeFileName
+, replaceFileName
+, dropFileName
+, takeBaseName
+, replaceBaseName
+, takeDirectory
+, replaceDirectory
+, combine
+, (</>)
+, splitPath
+, joinPath
+, splitDirectories
+
+  -- * Trailing slash functions
+, hasTrailingPathSeparator
+, addTrailingPathSeparator
+, dropTrailingPathSeparator
+
+  -- * File name manipulations
+, normalise
+, makeRelative
+, equalFilePath
+, isRelative
+, isAbsolute
+, isValid
+, makeValid
+, isFileName
+, hasParentDir
+, hiddenFile
+
+, module System.Posix.ByteString.FilePath
+) where
+
+import           Data.ByteString (ByteString)
+import qualified Data.ByteString as BS
+import Data.String (fromString)
+import           System.Posix.ByteString.FilePath
+import qualified System.Posix.Env.ByteString as PE
+
+import           Data.Maybe (isJust)
+import           Data.Word8
+#if !MIN_VERSION_bytestring(0,10,8)
+import qualified Data.List as L
+#endif
+import           Control.Arrow (second)
+
+-- $setup
+-- >>> import Data.Char
+-- >>> import Data.Maybe
+-- >>> import Data.Word8
+-- >>> import Test.QuickCheck
+-- >>> import Control.Applicative
+-- >>> import qualified Data.ByteString as BS
+-- >>> instance Arbitrary ByteString where arbitrary = BS.pack <$> arbitrary
+-- >>> instance CoArbitrary ByteString where coarbitrary = coarbitrary . BS.unpack
+--
+-- >>> let _chr :: Word8 -> Char; _chr = chr . fromIntegral
+
+
+
+------------------------
+-- Separator predicates
+
+
+-- | Path separator character
+pathSeparator :: Word8
+pathSeparator = _slash
+
+
+-- | Check if a character is the path separator
+--
+-- prop> \n ->  (_chr n == '/') == isPathSeparator n
+isPathSeparator :: Word8 -> Bool
+isPathSeparator = (== pathSeparator)
+
+
+-- | Search path separator
+searchPathSeparator :: Word8
+searchPathSeparator = _colon
+
+
+-- | Check if a character is the search path separator
+--
+-- prop> \n -> (_chr n == ':') == isSearchPathSeparator n
+isSearchPathSeparator :: Word8 -> Bool
+isSearchPathSeparator = (== searchPathSeparator)
+
+
+-- | File extension separator
+extSeparator :: Word8
+extSeparator = _period
+
+
+-- | Check if a character is the file extension separator
+--
+-- prop> \n -> (_chr n == '.') == isExtSeparator n
+isExtSeparator :: Word8 -> Bool
+isExtSeparator = (== extSeparator)
+
+
+
+------------------------
+-- $PATH methods
+
+
+-- | Take a ByteString, split it on the 'searchPathSeparator'.
+-- Blank items are converted to @.@.
+--
+-- Follows the recommendations in
+-- <http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html>
+--
+-- >>> splitSearchPath "File1:File2:File3"
+-- ["File1","File2","File3"]
+-- >>> splitSearchPath "File1::File2:File3"
+-- ["File1",".","File2","File3"]
+-- >>> splitSearchPath ""
+-- ["."]
+splitSearchPath :: ByteString -> [RawFilePath]
+splitSearchPath = f
+  where
+    f bs = let (pre, post) = BS.break isSearchPathSeparator bs
+           in if BS.null post
+                 then g pre
+                 else g pre ++ f (BS.tail post)
+    g x
+      | BS.null x = [BS.singleton _period]
+      | otherwise = [x]
+
+
+-- | Get a list of 'RawFilePath's in the $PATH variable.
+getSearchPath :: IO [RawFilePath]
+getSearchPath = fmap (maybe [] splitSearchPath) (PE.getEnv $ fromString "PATH")
+
+
+
+------------------------
+-- Extension functions
+
+-- | Split a 'RawFilePath' into a path+filename and extension
+--
+-- >>> splitExtension "file.exe"
+-- ("file",".exe")
+-- >>> splitExtension "file"
+-- ("file","")
+-- >>> splitExtension "/path/file.tar.gz"
+-- ("/path/file.tar",".gz")
+--
+-- prop> \path -> uncurry (BS.append) (splitExtension path) == path
+splitExtension :: RawFilePath -> (RawFilePath, ByteString)
+splitExtension x = if BS.null basename
+    then (x,BS.empty)
+    else (BS.append path (BS.init basename),BS.cons extSeparator fileExt)
+  where
+    (path,file) = splitFileNameRaw x
+    (basename,fileExt) = BS.breakEnd isExtSeparator file
+
+
+-- | Get the final extension from a 'RawFilePath'
+--
+-- >>> takeExtension "file.exe"
+-- ".exe"
+-- >>> takeExtension "file"
+-- ""
+-- >>> takeExtension "/path/file.tar.gz"
+-- ".gz"
+takeExtension :: RawFilePath -> ByteString
+takeExtension = snd . splitExtension
+
+
+-- | Change a file's extension
+--
+-- prop> \path -> let ext = takeExtension path in replaceExtension path ext == path
+replaceExtension :: RawFilePath -> ByteString -> RawFilePath
+replaceExtension path ext = dropExtension path <.> ext
+
+
+-- | Drop the final extension from a 'RawFilePath'
+--
+-- >>> dropExtension "file.exe"
+-- "file"
+-- >>> dropExtension "file"
+-- "file"
+-- >>> dropExtension "/path/file.tar.gz"
+-- "/path/file.tar"
+dropExtension :: RawFilePath -> RawFilePath
+dropExtension = fst . splitExtension
+
+
+-- | Add an extension to a 'RawFilePath'
+--
+-- >>> addExtension "file" ".exe"
+-- "file.exe"
+-- >>> addExtension "file.tar" ".gz"
+-- "file.tar.gz"
+-- >>> addExtension "/path/" ".ext"
+-- "/path/.ext"
+addExtension :: RawFilePath -> ByteString -> RawFilePath
+addExtension file ext
+    | BS.null ext = file
+    | isExtSeparator (BS.head ext) = BS.append file ext
+    | otherwise = BS.intercalate (BS.singleton extSeparator) [file, ext]
+
+
+-- | Check if a 'RawFilePath' has an extension
+--
+-- >>> hasExtension "file"
+-- False
+-- >>> hasExtension "file.tar"
+-- True
+-- >>> hasExtension "/path.part1/"
+-- False
+hasExtension :: RawFilePath -> Bool
+hasExtension = isJust . BS.elemIndex extSeparator . takeFileName
+
+
+-- | Operator version of 'addExtension'
+(<.>) :: RawFilePath -> ByteString -> RawFilePath
+(<.>) = addExtension
+
+
+-- | Split a 'RawFilePath' on the first extension.
+--
+-- >>> splitExtensions "/path/file.tar.gz"
+-- ("/path/file",".tar.gz")
+--
+-- prop> \path -> uncurry addExtension (splitExtensions path) == path
+splitExtensions :: RawFilePath -> (RawFilePath, ByteString)
+splitExtensions x = if BS.null basename
+    then (path,fileExt)
+    else (BS.append path basename,fileExt)
+  where
+    (path,file) = splitFileNameRaw x
+    (basename,fileExt) = BS.break isExtSeparator file
+
+
+-- | Remove all extensions from a 'RawFilePath'
+--
+-- >>> dropExtensions "/path/file.tar.gz"
+-- "/path/file"
+dropExtensions :: RawFilePath -> RawFilePath
+dropExtensions = fst . splitExtensions
+
+
+-- | Take all extensions from a 'RawFilePath'
+--
+-- >>> takeExtensions "/path/file.tar.gz"
+-- ".tar.gz"
+takeExtensions :: RawFilePath -> ByteString
+takeExtensions = snd . splitExtensions
+
+
+-- | Drop the given extension from a FilePath, and the @\".\"@ preceding it.
+-- Returns 'Nothing' if the FilePath does not have the given extension, or
+-- 'Just' and the part before the extension if it does.
+--
+-- This function can be more predictable than 'dropExtensions',
+-- especially if the filename might itself contain @.@ characters.
+--
+-- >>> stripExtension "hs.o" "foo.x.hs.o"
+-- Just "foo.x"
+-- >>> stripExtension "hi.o" "foo.x.hs.o"
+-- Nothing
+-- >>> stripExtension ".c.d" "a.b.c.d"
+-- Just "a.b"
+-- >>> stripExtension ".c.d" "a.b..c.d"
+-- Just "a.b."
+-- >>> stripExtension "baz"  "foo.bar"
+-- Nothing
+-- >>> stripExtension "bar"  "foobar"
+-- Nothing
+--
+-- prop> \path -> stripExtension "" path == Just path
+-- prop> \path -> dropExtension path  == fromJust (stripExtension (takeExtension path) path)
+-- prop> \path -> dropExtensions path == fromJust (stripExtension (takeExtensions path) path)
+stripExtension :: ByteString -> RawFilePath -> Maybe RawFilePath
+stripExtension bs path
+  | BS.null bs = Just path
+  | otherwise  = stripSuffix' dotExt path
+  where
+    dotExt = if isExtSeparator $ BS.head bs
+                then bs
+                else extSeparator `BS.cons` bs
+#if MIN_VERSION_bytestring(0,10,8)
+    stripSuffix' = BS.stripSuffix
+#else
+    stripSuffix' xs ys = fmap (BS.pack . reverse) $ L.stripPrefix (reverse $ BS.unpack xs) (reverse $ BS.unpack ys)
+#endif
+
+
+------------------------
+-- Filename/directory functions
+
+
+-- | Split a 'RawFilePath' into (path,file).  'combine' is the inverse
+--
+-- >>> splitFileName "path/file.txt"
+-- ("path/","file.txt")
+-- >>> splitFileName "path/"
+-- ("path/","")
+-- >>> splitFileName "file.txt"
+-- ("./","file.txt")
+--
+-- prop> \path -> uncurry combine (splitFileName path) == path || fst (splitFileName path) == "./"
+splitFileName :: RawFilePath -> (RawFilePath, RawFilePath)
+splitFileName x = if BS.null path
+    then (dotSlash, file)
+    else (path,file)
+  where
+    (path,file) = splitFileNameRaw x
+    dotSlash = _period `BS.cons` (BS.singleton pathSeparator)
+
+
+-- | Get the file name
+--
+-- >>> takeFileName "path/file.txt"
+-- "file.txt"
+-- >>> takeFileName "path/"
+-- ""
+takeFileName :: RawFilePath -> RawFilePath
+takeFileName = snd . splitFileName
+
+
+-- | Change the file name
+--
+-- prop> \path -> replaceFileName path (takeFileName path) == path
+replaceFileName :: RawFilePath -> ByteString -> RawFilePath
+replaceFileName x y = fst (splitFileNameRaw x) </> y
+
+
+-- | Drop the file name
+--
+-- >>> dropFileName "path/file.txt"
+-- "path/"
+-- >>> dropFileName "file.txt"
+-- "./"
+dropFileName :: RawFilePath -> RawFilePath
+dropFileName = fst . splitFileName
+
+
+-- | Get the file name, without a trailing extension
+--
+-- >>> takeBaseName "path/file.tar.gz"
+-- "file.tar"
+-- >>> takeBaseName ""
+-- ""
+takeBaseName :: RawFilePath -> ByteString
+takeBaseName = dropExtension . takeFileName
+
+
+-- | Change the base name
+--
+-- >>> replaceBaseName "path/file.tar.gz" "bob"
+-- "path/bob.gz"
+--
+-- prop> \path -> replaceBaseName path (takeBaseName path) == path
+replaceBaseName :: RawFilePath -> ByteString -> RawFilePath
+replaceBaseName path name = combineRaw dir (name <.> ext)
+  where
+    (dir,file) = splitFileNameRaw path
+    ext = takeExtension file
+
+
+-- | Get the directory, moving up one level if it's already a directory
+--
+-- >>> takeDirectory "path/file.txt"
+-- "path"
+-- >>> takeDirectory "file"
+-- "."
+-- >>> takeDirectory "/path/to/"
+-- "/path/to"
+-- >>> takeDirectory "/path/to"
+-- "/path"
+takeDirectory :: RawFilePath -> RawFilePath
+takeDirectory x = case () of
+    () | x == BS.singleton pathSeparator -> x
+       | BS.null res && not (BS.null file) -> file
+       | otherwise -> res
+  where
+    res = fst $ BS.spanEnd isPathSeparator file
+    file = dropFileName x
+
+
+-- | Change the directory component of a 'RawFilePath'
+--
+-- prop> \path -> replaceDirectory path (takeDirectory path) `equalFilePath` path || takeDirectory path == "."
+replaceDirectory :: RawFilePath -> ByteString -> RawFilePath
+replaceDirectory file dir = combineRaw dir (takeFileName file)
+
+
+-- | Join two paths together
+--
+-- >>> combine "/" "file"
+-- "/file"
+-- >>> combine "/path/to" "file"
+-- "/path/to/file"
+-- >>> combine "file" "/absolute/path"
+-- "/absolute/path"
+combine :: RawFilePath -> RawFilePath -> RawFilePath
+combine a b | not (BS.null b) && isPathSeparator (BS.head b) = b
+            | otherwise = combineRaw a b
+
+
+-- | Operator version of combine
+(</>) :: RawFilePath -> RawFilePath -> RawFilePath
+(</>) = combine
+
+-- | Split a path into a list of components:
+--
+-- >>> splitPath "/path/to/file.txt"
+-- ["/","path/","to/","file.txt"]
+--
+-- prop> \path -> BS.concat (splitPath path) == path
+splitPath :: RawFilePath -> [RawFilePath]
+splitPath = splitter
+  where
+    splitter x
+      | BS.null x = []
+      | otherwise = case BS.elemIndex pathSeparator x of
+            Nothing -> [x]
+            Just ix -> case BS.findIndex (not . isPathSeparator) $ BS.drop (ix+1) x of
+                          Nothing -> [x]
+                          Just runlen -> uncurry (:) . second splitter $ BS.splitAt (ix+1+runlen) x
+
+
+-- | Join a split path back together
+--
+-- prop> \path -> joinPath (splitPath path) == path
+--
+-- >>> joinPath ["path","to","file.txt"]
+-- "path/to/file.txt"
+joinPath :: [RawFilePath] -> RawFilePath
+joinPath = foldr (</>) BS.empty
+
+
+-- | Like 'splitPath', but without trailing slashes
+--
+-- >>> splitDirectories "/path/to/file.txt"
+-- ["/","path","to","file.txt"]
+-- >>> splitDirectories ""
+-- []
+splitDirectories :: RawFilePath -> [RawFilePath]
+splitDirectories x
+    | BS.null x = []
+    | isPathSeparator (BS.head x) = let (root,rest) = BS.splitAt 1 x
+                                    in root : splitter rest
+    | otherwise = splitter x
+  where
+    splitter = filter (not . BS.null) . BS.split pathSeparator
+
+
+
+------------------------
+-- Trailing slash functions
+
+-- | Check if the last character of a 'RawFilePath' is '/'.
+--
+-- >>> hasTrailingPathSeparator "/path/"
+-- True
+-- >>> hasTrailingPathSeparator "/"
+-- True
+-- >>> hasTrailingPathSeparator "/path"
+-- False
+hasTrailingPathSeparator :: RawFilePath -> Bool
+hasTrailingPathSeparator x
+  | BS.null x = False
+  | otherwise = isPathSeparator $ BS.last x
+
+
+-- | Add a trailing path separator.
+--
+-- >>> addTrailingPathSeparator "/path"
+-- "/path/"
+-- >>> addTrailingPathSeparator "/path/"
+-- "/path/"
+-- >>> addTrailingPathSeparator "/"
+-- "/"
+addTrailingPathSeparator :: RawFilePath -> RawFilePath
+addTrailingPathSeparator x = if hasTrailingPathSeparator x
+    then x
+    else x `BS.snoc` pathSeparator
+
+
+-- | Remove a trailing path separator
+--
+-- >>> dropTrailingPathSeparator "/path/"
+-- "/path"
+-- >>> dropTrailingPathSeparator "/path////"
+-- "/path"
+-- >>> dropTrailingPathSeparator "/"
+-- "/"
+-- >>> dropTrailingPathSeparator "//"
+-- "/"
+dropTrailingPathSeparator :: RawFilePath -> RawFilePath
+dropTrailingPathSeparator x
+  | x == BS.singleton pathSeparator = x
+  | otherwise = if hasTrailingPathSeparator x
+                  then dropTrailingPathSeparator $ BS.init x
+                  else x
+
+
+
+------------------------
+-- File name manipulations
+
+
+-- |Normalise a file.
+--
+-- >>> normalise "/file/\\test////"
+-- "/file/\\test/"
+-- >>> normalise "/file/./test"
+-- "/file/test"
+-- >>> normalise "/test/file/../bob/fred/"
+-- "/test/file/../bob/fred/"
+-- >>> normalise "../bob/fred/"
+-- "../bob/fred/"
+-- >>> normalise "./bob/fred/"
+-- "bob/fred/"
+-- >>> normalise "./bob////.fred/./...///./..///#."
+-- "bob/.fred/.../../#."
+-- >>> normalise "."
+-- "."
+-- >>> normalise "./"
+-- "./"
+-- >>> normalise "./."
+-- "./"
+-- >>> normalise "/./"
+-- "/"
+-- >>> normalise "/"
+-- "/"
+-- >>> normalise "bob/fred/."
+-- "bob/fred/"
+-- >>> normalise "//home"
+-- "/home"
+normalise :: RawFilePath -> RawFilePath
+normalise filepath =
+  result `BS.append`
+  (if addPathSeparator
+       then BS.singleton pathSeparator
+       else BS.empty)
+  where
+    result = let n = f filepath
+             in if BS.null n
+                then BS.singleton _period
+                else n
+    addPathSeparator = isDirPath filepath &&
+      not (hasTrailingPathSeparator result)
+    isDirPath xs = hasTrailingPathSeparator xs
+        || not (BS.null xs) && BS.last xs == _period
+           && hasTrailingPathSeparator (BS.init xs)
+    f = joinPath . dropDots . propSep . splitDirectories
+    propSep :: [ByteString] -> [ByteString]
+    propSep (x:xs)
+      | BS.all (== pathSeparator) x = BS.singleton pathSeparator : xs
+      | otherwise                   = x : xs
+    propSep [] = []
+    dropDots :: [ByteString] -> [ByteString]
+    dropDots = filter (BS.singleton _period /=)
+
+
+
+-- | Contract a filename, based on a relative path. Note that the resulting
+-- path will never introduce @..@ paths, as the presence of symlinks
+-- means @..\/b@ may not reach @a\/b@ if it starts from @a\/c@. For a
+-- worked example see
+-- <http://neilmitchell.blogspot.co.uk/2015/10/filepaths-are-subtle-symlinks-are-hard.html this blog post>.
+--
+-- >>> makeRelative "/directory" "/directory/file.ext"
+-- "file.ext"
+-- >>> makeRelative "/Home" "/home/bob"
+-- "/home/bob"
+-- >>> makeRelative "/home/" "/home/bob/foo/bar"
+-- "bob/foo/bar"
+-- >>> makeRelative "/fred" "bob"
+-- "bob"
+-- >>> makeRelative "/file/test" "/file/test/fred"
+-- "fred"
+-- >>> makeRelative "/file/test" "/file/test/fred/"
+-- "fred/"
+-- >>> makeRelative "some/path" "some/path/a/b/c"
+-- "a/b/c"
+--
+-- prop> \p -> makeRelative p p == "."
+-- prop> \p -> makeRelative (takeDirectory p) p `equalFilePath` takeFileName p
+-- prop \x y -> equalFilePath x y || (isRelative x && makeRelative y x == x) || equalFilePath (y </> makeRelative y x) x
+makeRelative :: RawFilePath -> RawFilePath -> RawFilePath
+makeRelative root path
+  | equalFilePath root path = BS.singleton _period
+  | takeAbs root /= takeAbs path = path
+  | otherwise = f (dropAbs root) (dropAbs path)
+  where
+    f x y
+      | BS.null x = BS.dropWhile isPathSeparator y
+      | otherwise = let (x1,x2) = g x
+                        (y1,y2) = g y
+                    in if equalFilePath x1 y1 then f x2 y2 else path
+    g x = (BS.dropWhile isPathSeparator a, BS.dropWhile isPathSeparator b)
+      where (a, b) = BS.break isPathSeparator $ BS.dropWhile isPathSeparator x
+    dropAbs x = snd $ BS.span (== _slash) x
+    takeAbs x = fst $ BS.span (== _slash) x
+
+
+-- |Equality of two filepaths. The filepaths are normalised
+-- and trailing path separators are dropped.
+--
+-- >>> equalFilePath "foo" "foo"
+-- True
+-- >>> equalFilePath "foo" "foo/"
+-- True
+-- >>> equalFilePath "foo" "./foo"
+-- True
+-- >>> equalFilePath "" ""
+-- True
+-- >>> equalFilePath "foo" "/foo"
+-- False
+-- >>> equalFilePath "foo" "FOO"
+-- False
+-- >>> equalFilePath "foo" "../foo"
+-- False
+--
+-- prop> \p -> equalFilePath p p
+equalFilePath :: RawFilePath -> RawFilePath -> Bool
+equalFilePath p1 p2 = f p1 == f p2
+  where
+    f x = dropTrailingPathSeparator $ normalise x
+
+
+-- | Check if a path is relative
+--
+-- prop> \path -> isRelative path /= isAbsolute path
+isRelative :: RawFilePath -> Bool
+isRelative = not . isAbsolute
+
+
+-- | Check if a path is absolute
+--
+-- >>> isAbsolute "/path"
+-- True
+-- >>> isAbsolute "path"
+-- False
+-- >>> isAbsolute ""
+-- False
+isAbsolute :: RawFilePath -> Bool
+isAbsolute x
+    | BS.length x > 0 = isPathSeparator (BS.head x)
+    | otherwise = False
+
+
+-- | Is a FilePath valid, i.e. could you create a file like it?
+--
+-- >>> isValid ""
+-- False
+-- >>> isValid "\0"
+-- False
+-- >>> isValid "/random_ path:*"
+-- True
+isValid :: RawFilePath -> Bool
+isValid filepath
+  | BS.null filepath        = False
+  | _nul `BS.elem` filepath = False
+  | otherwise               = True
+
+
+-- | Take a FilePath and make it valid; does not change already valid FilePaths.
+--
+-- >>> makeValid ""
+-- "_"
+-- >>> makeValid "file\0name"
+-- "file_name"
+--
+-- prop> \p -> if isValid p then makeValid p == p else makeValid p /= p
+-- prop> \p -> isValid (makeValid p)
+makeValid :: RawFilePath -> RawFilePath
+makeValid path
+  | BS.null path = BS.singleton _underscore
+  | otherwise    = BS.map (\x -> if x == _nul then _underscore else x) path
+
+
+-- | Is the given path a valid filename? This includes
+-- "." and "..".
+--
+-- >>> isFileName "lal"
+-- True
+-- >>> isFileName "."
+-- True
+-- >>> isFileName ".."
+-- True
+-- >>> isFileName ""
+-- False
+-- >>> isFileName "\0"
+-- False
+-- >>> isFileName "/random_ path:*"
+-- False
+isFileName :: RawFilePath -> Bool
+isFileName filepath =
+  not (BS.singleton pathSeparator `BS.isInfixOf` filepath) &&
+  not (BS.null filepath) &&
+  not (_nul `BS.elem` filepath)
+
+
+-- | Check if the filepath has any parent directories in it.
+--
+-- >>> hasParentDir "/.."
+-- True
+-- >>> hasParentDir "foo/bar/.."
+-- True
+-- >>> hasParentDir "foo/../bar/."
+-- True
+-- >>> hasParentDir "foo/bar"
+-- False
+-- >>> hasParentDir "foo"
+-- False
+-- >>> hasParentDir ""
+-- False
+-- >>> hasParentDir ".."
+-- False
+hasParentDir :: RawFilePath -> Bool
+hasParentDir filepath =
+    (pathSeparator `BS.cons` pathDoubleDot)
+     `BS.isSuffixOf` filepath
+   ||
+    (BS.singleton pathSeparator
+        `BS.append` pathDoubleDot
+        `BS.append` BS.singleton pathSeparator)
+     `BS.isInfixOf`  filepath
+   ||
+    (pathDoubleDot `BS.append` BS.singleton pathSeparator)
+      `BS.isPrefixOf` filepath
+  where
+    pathDoubleDot = BS.pack [_period, _period]
+
+
+-- | Whether the file is a hidden file.
+--
+-- >>> hiddenFile ".foo"
+-- True
+-- >>> hiddenFile "..foo.bar"
+-- True
+-- >>> hiddenFile "some/path/.bar"
+-- True
+-- >>> hiddenFile "..."
+-- True
+-- >>> hiddenFile "dod.bar"
+-- False
+-- >>> hiddenFile "."
+-- False
+-- >>> hiddenFile ".."
+-- False
+-- >>> hiddenFile ""
+-- False
+hiddenFile :: RawFilePath -> Bool
+hiddenFile fp
+  | fn == BS.pack [_period, _period] = False
+  | fn == BS.pack [_period]          = False
+  | otherwise                        = BS.pack [extSeparator]
+                                         `BS.isPrefixOf` fn
+  where
+    fn = takeFileName fp
+
+
+
+------------------------
+-- internal stuff
+
+-- Just split the input FileName without adding/normalizing or changing
+-- anything.
+splitFileNameRaw :: RawFilePath -> (RawFilePath, RawFilePath)
+splitFileNameRaw = BS.breakEnd isPathSeparator
+
+-- | Combine two paths, assuming rhs is NOT absolute.
+combineRaw :: RawFilePath -> RawFilePath -> RawFilePath
+combineRaw a b | BS.null a = b
+                  | BS.null b = a
+                  | isPathSeparator (BS.last a) = BS.append a b
+                  | otherwise = BS.intercalate (BS.singleton pathSeparator) [a, b]
+