1 files changed, 41 insertions, 4 deletions
diff --git a/compiler/utils/Fingerprint.hsc b/compiler/utils/Fingerprint.hsc
index 95f31c08bb..9a55e385b3 100644
--- a/compiler/utils/Fingerprint.hsc
+++ b/compiler/utils/Fingerprint.hsc
@@ -1,25 +1,33 @@
 -- ----------------------------------------------------------------------------
--- 
+--
 --  (c) The University of Glasgow 2006
 --
 -- Fingerprints for recompilation checking and ABI versioning.
 --
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/RecompilationAvoidance
+-- http://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/RecompilationAvoidance
 --
 -- ----------------------------------------------------------------------------
 
-{-# OPTIONS_GHC -fno-warn-orphans #-}
 module Fingerprint (
         Fingerprint(..), fingerprint0,
         readHexFingerprint,
         fingerprintData,
-        fingerprintString
+        fingerprintString,
+        -- Re-exported from GHC.Fingerprint for GHC >= 7.7, local otherwise
+        getFileHash
    ) where
 
 #include "md5.h"
 ##include "HsVersions.h"
 
 import Numeric          ( readHex )
+#if __GLASGOW_HASKELL__ < 707
+-- Only needed for getFileHash below.
+import Foreign
+import Panic
+import System.IO
+import Control.Monad    ( when )
+#endif
 
 import GHC.Fingerprint
 
@@ -30,3 +38,32 @@ readHexFingerprint s = Fingerprint w1 w2
        [(w1,"")] = readHex s1
        [(w2,"")] = readHex (take 16 s2)
 
+
+#if __GLASGOW_HASKELL__ < 707
+-- Only use this if we're smaller than GHC 7.7, otherwise
+-- GHC.Fingerprint exports a better version of this function.
+
+-- | Computes the hash of a given file.
+-- It loads the full file into memory an does not work with files bigger than
+-- MAXINT.
+getFileHash :: FilePath -> IO Fingerprint
+getFileHash path = withBinaryFile path ReadMode $ \h -> do
+
+  fileSize <- toIntFileSize `fmap` hFileSize h
+
+  allocaBytes fileSize $ \bufPtr -> do
+    n <- hGetBuf h bufPtr fileSize
+    when (n /= fileSize) readFailedError
+    fingerprintData bufPtr fileSize
+
+  where
+    toIntFileSize :: Integer -> Int
+    toIntFileSize size
+      | size > fromIntegral (maxBound :: Int) = throwGhcException $
+          Sorry $ "Fingerprint.getFileHash: Tried to calculate hash of file "
+                  ++ path ++ " with size > maxBound :: Int. This is not supported."
+      | otherwise = fromIntegral size
+
+    readFailedError = throwGhcException $
+        Panic $ "Fingerprint.getFileHash: hGetBuf failed on interface file"
+#endif