Remove race conditions checking file existence before reading

src/Unused/Cache.hs

@@ -5,11 +5,13 @@ module Unused.Cache
 
 import Control.Monad.IO.Class (liftIO)
 import Control.Monad.Trans.Reader
-import System.Directory
 import Data.Csv (FromRecord, ToRecord, HasHeader(..), encode, decode)
 import Data.Vector (toList)
+import System.Directory (createDirectoryIfMissing)
 import qualified Data.ByteString.Lazy as BS
+import qualified Data.ByteString.Lazy.Char8 as C
 import Unused.Cache.DirectoryFingerprint
+import Unused.Util (safeReadFile)
 
 newtype CacheFileName = CacheFileName String
 type Cache = ReaderT CacheFileName IO
@@ -31,11 +33,11 @@ writeCache contents = do
 readCache :: FromRecord a => Cache (Maybe [a])
 readCache = do
     (CacheFileName fileName) <- ask
-    exists <- liftIO $ doesFileExist fileName
 
-    if exists
-        then fmap processCsv (decode NoHeader <$> liftIO (BS.readFile fileName))
-        else return Nothing
+    either
+        (const Nothing)
+        (processCsv . decode NoHeader . C.pack)
+        <$> (liftIO $ safeReadFile fileName)
   where
     processCsv = either (const Nothing) (Just . toList)
 

src/Unused/ResultsClassifier/Config.hs

@@ -4,12 +4,11 @@ module Unused.ResultsClassifier.Config
     ) where
 
 import qualified Data.Yaml as Y
-import qualified Data.ByteString as BS
 import qualified Data.ByteString.Char8 as C
 import qualified Data.Either as E
 import qualified Data.Bifunctor as B
 import System.FilePath ((</>))
-import System.Directory (getHomeDirectory, doesFileExist)
+import System.Directory (getHomeDirectory)
 import Paths_unused (getDataFileName)
 import Unused.ResultsClassifier.Types (LanguageConfiguration, ParseConfigError(..))
 import Unused.Util (safeReadFile)
@@ -17,11 +16,11 @@ import Unused.Util (safeReadFile)
 loadConfig :: IO (Either String [LanguageConfiguration])
 loadConfig = do
     configFileName <- getDataFileName ("data" </> "config.yml")
-    exists <- doesFileExist configFileName
 
-    if exists
-        then Y.decodeEither <$> BS.readFile configFileName
-        else return $ Left "default config not found"
+    either
+        (const $ Left "default config not found")
+        (Y.decodeEither . C.pack)
+        <$> safeReadFile configFileName
 
 loadAllConfigurations :: IO (Either [ParseConfigError] [LanguageConfiguration])
 loadAllConfigurations = do