Write cache files atomically

Fixes #1540.

Author: sjakobi

dhall/dhall.cabal

@@ -405,6 +405,7 @@ Library
         aeson                       >= 1.0.0.0  && < 1.5 ,
         aeson-pretty                               < 0.9 ,
         ansi-terminal               >= 0.6.3.1  && < 0.11,
+        atomic-write                >= 0.2.0.6  && < 0.3 ,
         bytestring                                 < 0.11,
         case-insensitive                           < 1.3 ,
         cborg                       >= 0.2.0.0  && < 0.3 ,

dhall/src/Dhall/Import.hs

@@ -200,6 +200,7 @@ import qualified Dhall.Map
 import qualified Dhall.Parser
 import qualified Dhall.Pretty.Internal
 import qualified Dhall.TypeCheck
+import qualified System.AtomicWrite.Writer.ByteString
 import qualified System.Environment
 import qualified System.Info
 import qualified System.IO
@@ -554,7 +555,7 @@ writeToSemanticCache :: Dhall.Crypto.SHA256Digest -> Data.ByteString.ByteString
 writeToSemanticCache hash bytes = do
     _ <- Maybe.runMaybeT $ do
         cacheFile <- getCacheFile "dhall" hash
-        liftIO (Data.ByteString.writeFile cacheFile bytes)
+        liftIO (System.AtomicWrite.Writer.ByteString.atomicWriteFile cacheFile bytes)
     return ()
 
 -- Check the "semi-semantic" disk cache, otherwise typecheck and normalise from
@@ -669,7 +670,7 @@ writeToSemisemanticCache :: Dhall.Crypto.SHA256Digest -> Data.ByteString.ByteStr
 writeToSemisemanticCache semisemanticHash bytes = do
     _ <- Maybe.runMaybeT $ do
         cacheFile <- getCacheFile "dhall-haskell" semisemanticHash
-        liftIO (Data.ByteString.writeFile cacheFile bytes)
+        liftIO (System.AtomicWrite.Writer.ByteString.atomicWriteFile cacheFile bytes)
     return ()
 
 -- Fetch source code directly from disk/network