Continuous integration on Windows and Linux

1 files changed, 29 insertions, 1 deletions

diff --git a/lib/Hakyll/Core/Util/File.hs b/lib/Hakyll/Core/Util/File.hs
index 9db6b11..02b8ece 100644
--- a/lib/Hakyll/Core/Util/File.hs
+++ b/lib/Hakyll/Core/Util/File.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE CPP                 #-}
 --------------------------------------------------------------------------------
 -- | A module containing various file utility functions
 module Hakyll.Core.Util.File
@@ -8,10 +10,12 @@ module Hakyll.Core.Util.File
 
 
 --------------------------------------------------------------------------------
+import           Control.Concurrent  (threadDelay)
+import           Control.Exception   (SomeException, catch)
 import           Control.Monad       (filterM, forM, when)
 import           System.Directory    (createDirectoryIfMissing,
                                       doesDirectoryExist, getDirectoryContents,
-                                      removeDirectoryRecursive)
+                                      removeDirectoryRecursive, removePathForcibly)
 import           System.FilePath     (takeDirectory, (</>))
 
 
@@ -51,6 +55,30 @@ getRecursiveContents ignore top = go ""
 
 --------------------------------------------------------------------------------
 removeDirectory :: FilePath -> IO ()
+#ifndef mingw32_HOST_OS
 removeDirectory fp = do
     e <- doesDirectoryExist fp
     when e $ removeDirectoryRecursive fp
+#else
+-- Deleting files on Windows is unreliable. If a file/directory is open by a program (e.g. antivirus),
+-- then removing related directories *quickly* may fail with strange messages.
+-- See here for discussions:
+--      https://github.com/haskell/directory/issues/96
+--      https://github.com/haskell/win32/pull/129
+--
+-- The hacky solution is to retry deleting directories a few times, 
+-- with a delay, on Windows only.
+removeDirectory = retryWithDelay 10 . removePathForcibly
+#endif
+
+
+--------------------------------------------------------------------------------
+-- | Retry an operation at most /n/ times (/n/ must be positive).
+--   If the operation fails the /n/th time it will throw that final exception.
+--   A delay of 100ms is introduced between every retry.
+retryWithDelay :: Int -> IO a -> IO a
+retryWithDelay i x 
+    | i <= 0    = error "Hakyll.Core.Util.File.retry: retry count must be 1 or more"
+    | i == 1    = x
+    | otherwise = catch x $ \(_::SomeException) -> threadDelay 100 >> retryWithDelay (i-1) x
+