Add unsafeToString methods

doctests-hpath.hs

@@ -8,6 +8,7 @@ main =
     doctest
       ["-isrc"
       , "-XOverloadedStrings"
+      , "-XScopedTypeVariables"
       , "src/HPath.hs"
       ]
 

src/HPath.hs

@@ -10,12 +10,14 @@
 -- Support for well-typed paths.
 
 
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE EmptyDataDecls #-}
 #if __GLASGOW_HASKELL__ >= 708
 {-# LANGUAGE PatternSynonyms #-}
 #endif
+{-# LANGUAGE ScopedTypeVariables #-}
 
 module HPath
   (
@@ -39,6 +41,8 @@ module HPath
   ,fromAbs
   ,fromRel
   ,toFilePath
+  ,unsafeToString
+  ,unsafeToString'
   -- * Path Operations
   ,(</>)
   ,basename
@@ -53,8 +57,10 @@ module HPath
   )
   where
 
-import           Control.Exception (Exception)
+import           Control.Exception (IOException, Exception, catch)
+import           Control.Monad ((<$!>))
 import           Control.Monad.Catch (MonadThrow(..))
+import           Data.ByteString.Unsafe(unsafeUseAsCStringLen)
 #if MIN_VERSION_bytestring(0,10,8)
 import           Data.ByteString(ByteString, stripPrefix)
 #else
@@ -65,10 +71,17 @@ import qualified Data.ByteString as BS
 import           Data.Data
 import           Data.Maybe
 import           Data.Word8
+import           GHC.Foreign(peekCStringLen)
+import           GHC.IO.Encoding(getLocaleEncoding, TextEncoding)
 import           HPath.Internal
+import           System.IO.Unsafe(unsafePerformIO)
 import           System.Posix.FilePath hiding ((</>))
 
 
+-- $setup
+-- >>> import GHC.IO.Encoding(utf8)
+
+
 --------------------------------------------------------------------------------
 -- Types
 
@@ -232,6 +245,41 @@ fromAbs = toFilePath
 fromRel :: RelC r => Path r -> ByteString
 fromRel = toFilePath
 
+-- | This converts the underlying bytestring of the path to an unsafe
+-- FilePath by assuming the encoding of the current locale setting. This
+-- may be utterly wrong, but isn't particularly worse than what the
+-- base library does. Blows up on decoding errors.
+--
+-- >>> unsafeToString (MkPath "/lal/lad")
+-- "/lal/lad"
+-- >>> unsafeToString (MkPath "/")
+-- "/"
+-- >>> unsafeToString (MkPath "lad")
+-- "lad"
+-- >>> catch (Just <$> unsafeToString (MkPath "<22>")) (\(_ :: IOException) -> pure Nothing)
+-- Nothing
+unsafeToString :: Path b -> IO FilePath
+unsafeToString (MkPath p) = do
+  enc <- getLocaleEncoding
+  unsafeUseAsCStringLen p (peekCStringLen enc)
+
+-- | Same as @unsafeToString@, except requires the encoding
+-- to be passed explicitly. This uses 'unsafePerformIO' and
+-- returns 'Nothing' on decoding errors.
+--
+-- >>> unsafeToString' (MkPath "/lal/lad") utf8
+-- Just "/lal/lad"
+-- >>> unsafeToString' (MkPath "/") utf8
+-- Just "/"
+-- >>> unsafeToString' (MkPath "lad") utf8
+-- Just "lad"
+-- >>> unsafeToString' (MkPath "<22>") utf8
+-- Nothing
+unsafeToString' :: Path b -> TextEncoding -> Maybe FilePath
+unsafeToString' (MkPath !p) enc =
+  unsafePerformIO $!
+    catch (Just <$!> unsafeUseAsCStringLen p (peekCStringLen enc))
+          (\(_ :: IOException) -> pure Nothing)
 
 
 --------------------------------------------------------------------------------