LIB: add canOpenDirectory and throwCantOpenDirectory

src/HSFM/FileSystem/Errors.hs

@@ -51,6 +51,7 @@ import System.IO.Error
   )
 
 import qualified System.Posix.Files as PF
+import qualified System.Posix.Directory as PFD
 
 
 data FmIOException = FileDoesNotExist String
@@ -66,6 +67,7 @@ data FmIOException = FileDoesNotExist String
                    | IsSymlink String
                    | InvalidOperation String
                    | InvalidFileName
+                   | Can'tOpenDirectory String
   deriving (Show, Typeable)
 
 
@@ -139,6 +141,18 @@ doesDirectoryExist fp =
     return $ PF.isDirectory fs
 
 
+canOpenDirectory :: Path Abs -> IO Bool
+canOpenDirectory fp =
+  handleIOError (\_ -> return False) $ do
+    dirstream <- PFD.openDirStream . P.fromAbs $ fp
+    PFD.closeDirStream dirstream
+    return True
+
+
+throwCantOpenDirectory :: Path Abs -> IO ()
+throwCantOpenDirectory fp =
+  unlessM (canOpenDirectory fp) (throw $ Can'tOpenDirectory $ P.fromAbs fp)
+
 
 
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