allow building w/o cryptohash

Mostly for the debian stable autobuilds, which have a too old version
to use the Crypto.Hash module.

Backend/Hash.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE CPP #-}
+
 module Backend.Hash (backends) where
 
 import Common.Annex
@@ -27,7 +29,9 @@ type HashSize = Int
 hashes :: [Hash]
 hashes = concat 
 	[ map SHAHash [256, 1, 512, 224, 384]
+#ifdef WITH_CRYPTOHASH
 	, map SkeinHash [256, 512]
+#endif
 	]
 
 {- The SHA256E backend is the default, so genBackendE comes first. -}
@@ -143,7 +147,7 @@ shaHasher hashsize filesize
 	| hashsize == 224 = use SysConfig.sha224 sha224
 	| hashsize == 384 = use SysConfig.sha384 sha384
 	| hashsize == 512 = use SysConfig.sha512 sha512
-	| otherwise = error $ "bad sha size " ++ show hashsize
+	| otherwise = error $ "unsupported sha size " ++ show hashsize
   where
 	use Nothing hasher = Left $ show . hasher
 	use (Just c) hasher
@@ -157,6 +161,8 @@ shaHasher hashsize filesize
 
 skeinHasher :: HashSize -> (L.ByteString -> String)
 skeinHasher hashsize 
+#ifdef WITH_CRYPTOHASH
 	| hashsize == 256 = show . skein256
 	| hashsize == 512 = show . skein512
-	| otherwise = error $ "bad skein size " ++ show hashsize
+#endif
+	| otherwise = error $ "unsupported skein size " ++ show hashsize

BuildFlags.hs

@@ -53,5 +53,11 @@ buildFlags = filter (not . null)
 #endif
 #ifdef WITH_QUVI
 	, "Quvi"
+#endif
+#ifdef WITH_TDFA
+	, "TDFA"
+#endif
+#ifdef WITH_CRYPTOHASH
+	, "CryptoHash"
 #endif
 	]

Utility/Hash.hs

@@ -1,13 +1,30 @@
 {- Convenience wrapper around cryptohash.
- -
+ - Falls back to SHA if it's not available.
- - The resulting Digests can be shown to get a canonical hash encoding. -}
+ -}
 
-module Utility.Hash where
+{-# LANGUAGE CPP #-}
+
+module Utility.Hash (
+	sha1,
+	sha224,
+	sha256,
+	sha384,
+	sha512,
+#ifdef WITH_CRYPTOHASH
+	skein256,
+	skein512,
+#endif
+	prop_hashes_stable
+) where
 
-import Crypto.Hash
 import qualified Data.ByteString.Lazy as L
 import qualified Data.ByteString.Char8 as C8
 
+#ifndef WITH_CRYPTOHASH
+import Data.Digest.Pure.SHA
+#else
+import Crypto.Hash
+
 sha1 :: L.ByteString -> Digest SHA1
 sha1 = hashlazy
 
@@ -33,6 +50,8 @@ skein256 = hashlazy
 skein512 :: L.ByteString -> Digest Skein512_512
 skein512 = hashlazy
 
+#endif
+
 {- Check that all the hashes continue to hash the same. -}
 prop_hashes_stable :: Bool
 prop_hashes_stable = all (\(hasher, result) -> hasher foo == result)
@@ -41,8 +60,10 @@ prop_hashes_stable = all (\(hasher, result) -> hasher foo == result)
 	, (show . sha256, "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae")
 	, (show . sha384, "98c11ffdfdd540676b1a137cb1a22b2a70350c9a44171d6b1180c6be5cbb2ee3f79d532c8a1dd9ef2e8e08e752a3babb")
 	, (show . sha512, "f7fbba6e0636f890e56fbbf3283e524c6fa3204ae298382d624741d0dc6638326e282c41be5e4254d8820772c5518a2c5a8c0c7f7eda19594a7eb539453e1ed7")
+#ifdef WITH_CRYPTOHASH
 	, (show . skein256, "a04efd9a0aeed6ede40fe5ce0d9361ae7b7d88b524aa19917b9315f1ecf00d33")
 	, (show . skein512, "fd8956898113510180aa4658e6c0ac85bd74fb47f4a4ba264a6b705d7a8e8526756e75aecda12cff4f1aca1a4c2830fbf57f458012a66b2b15a3dd7d251690a7")
+#endif
 	]
   where
 	foo = L.fromChunks [C8.pack "foo"]

doc/install/fromscratch.mdwn

@@ -7,7 +7,7 @@ quite a lot.
   * [MissingH](http://github.com/jgoerzen/missingh/wiki)
   * [utf8-string](http://hackage.haskell.org/package/utf8-string)
   * [SHA](http://hackage.haskell.org/package/SHA)
-  * [cryptohash](http://hackage.haskell.org/package/cryptohash)
+  * [cryptohash](http://hackage.haskell.org/package/cryptohash) (optional but recommended)
   * [dataenc](http://hackage.haskell.org/package/dataenc)
   * [monad-control](http://hackage.haskell.org/package/monad-control)
   * [QuickCheck 2](http://hackage.haskell.org/package/QuickCheck)

git-annex.cabal

@@ -71,12 +71,15 @@ Flag Feed
 Flag Quvi
   Description: Enable use of quvi to download videos
 
+Flag CryptoHash
+  Description: Enable use of cryptohash for checksumming
+
 Executable git-annex
   Main-Is: git-annex.hs
   Build-Depends: MissingH, hslogger, directory, filepath,
    containers, utf8-string, network (>= 2.0), mtl (>= 2),
    bytestring, old-locale, time, HTTP,
-   extensible-exceptions, dataenc, SHA, cryptohash, process, json,
+   extensible-exceptions, dataenc, SHA, process, json,
    base (>= 4.5 && < 4.8), monad-control, MonadCatchIO-transformers,
    IfElse, text, QuickCheck >= 2.1, bloomfilter, edit-distance, process,
    SafeSemaphore, uuid, random, dlist, unix-compat
@@ -107,6 +110,10 @@ Executable git-annex
     Build-Depends: regex-tdfa
     CPP-Options: -DWITH_TDFA
   
+  if flag(CryptoHash)
+    Build-Depends: cryptohash (>= 0.10.0)
+    CPP-Options: -DWITH_CRYPTOHASH
+
   if flag(S3)
     Build-Depends: hS3
     CPP-Options: -DWITH_S3