sync: Automatically resolves merge conflicts.

untested, but it compiles :)

Command/Sync.hs

@@ -15,15 +15,21 @@ import Command
 import qualified Remote
 import qualified Annex
 import qualified Annex.Branch
+import qualified Annex.Queue
+import Annex.Content
+import Annex.CatFile
 import qualified Git.Command
+import qualified Git.LsFiles as LsFiles
 import qualified Git.Merge
 import qualified Git.Branch
 import qualified Git.Ref
 import qualified Git
+import Git.Types (BlobType(..))
 import qualified Types.Remote
 import qualified Remote.Git
 
 import qualified Data.Map as M
+import qualified Data.ByteString.Lazy as L
 
 def :: [Command]
 def = [command "sync" (paramOptional (paramRepeating paramRemote))
@@ -161,7 +167,11 @@ mergeFrom branch = do
 	ok <- inRepo $ Git.Merge.mergeNonInteractive branch
 	if ok
 		then return ok
-		else resolveMerge
+		else do
+			merged <- resolveMerge
+			when merged $
+				showNote "merge conflict automatically resolved"
+			return merged
 
 {- Resolves a conflicted merge. It's important that any conflicts be
  - resolved in a way that itself avoids later merge conflicts, since
@@ -171,15 +181,48 @@ mergeFrom branch = do
  - handle.
  -
  - This uses the Keys pointed to by the files to construct new
- - filenames. So a conflicted merge of file foo will delete it,
- - and add files foo.KEYA and foo.KEYB. 
+ - filenames. So when both sides modified file foo, 
+ - it will be deleted, and replaced with files foo.KEYA and foo.KEYB.
  -
- - A conflict can also result due to 
+ - On the other hand, when one side deleted foo, and the other modified it,
+ - it will be deleted, and the modified version stored as file
+ - foo.KEYA (or KEYB).
  -}
 resolveMerge :: Annex Bool
 resolveMerge = do
-	
+	top <- fromRepo Git.repoPath
+	all id <$> (mapM resolveMerge' =<< inRepo (LsFiles.unmerged [top]))
 
+resolveMerge' :: LsFiles.Unmerged -> Annex Bool
+resolveMerge' u
+	| issymlink LsFiles.valUs && issymlink LsFiles.valThem = do
+		keyUs <- getkey LsFiles.valUs
+		keyThem <- getkey LsFiles.valThem
+		if (keyUs == keyThem)
+			then makelink keyUs (file ++ "." ++ show keyUs)
+			else do
+				void $ liftIO $ tryIO $ removeFile file
+				Annex.Queue.addCommand "rm" [Params "--quiet -f --"] [file]
+				makelink keyUs (file ++ "." ++ show keyUs)
+				makelink keyThem (file ++ "." ++ show keyThem)
+		return True
+	| otherwise = return False
+	where
+		file = LsFiles.unmergedFile u
+		issymlink select = any (select (LsFiles.unmergedBlobType u) ==)
+			[Just SymlinkBlob, Nothing]
+		makelink (Just key) f = do
+			l <- calcGitLink file key
+			liftIO $ createSymbolicLink l f
+			Annex.Queue.addCommand "add" [Param "--force", Param "--"] [f]
+		makelink _ _ = noop
+		getkey select = do
+			let msha = select $ LsFiles.unmergedSha u
+			case msha of
+				Nothing -> return Nothing
+				Just sha -> fileKey . takeFileName
+					. encodeW8 . L.unpack <$> catObject sha
+				
 changed :: Remote -> Git.Ref -> Annex Bool
 changed remote b = do
 	let r = remoteBranch remote b

Git/LsFiles.hs

@@ -88,9 +88,6 @@ data Conflicting v = Conflicting
 	, valThem :: Maybe v
 	} deriving (Show)
 
-isConflicting :: Eq a => Conflicting a -> Bool
-isConflicting (Conflicting a b) = a /= b
-
 data Unmerged = Unmerged
 	{ unmergedFile :: FilePath
 	, unmergedBlobType :: Conflicting BlobType
@@ -124,7 +121,7 @@ parseUnmerged :: String -> Maybe InternalUnmerged
 parseUnmerged s
 	| null file || length ws < 3 = Nothing
 	| otherwise = do
-		stage <- readish (ws !! 2)
+		stage <- readish (ws !! 2) :: Maybe Int
 		unless (stage == 2 || stage == 3) $
 			fail undefined -- skip stage 1
 		blobtype <- readBlobType (ws !! 0)
@@ -148,9 +145,9 @@ reduceUnmerged c (i:is) = reduceUnmerged (new:c) rest
 			, unmergedSha = Conflicting shaA shaB
 			}
 		findsib templatei [] = ([], deleted templatei)
-		findsib templatei (i:is)
-			| ifile i == ifile templatei = (is, i)
-			| otherwise = (i:is, deleted templatei)
+		findsib templatei (l:ls)
+			| ifile l == ifile templatei = (ls, l)
+			| otherwise = (l:ls, deleted templatei)
 		deleted templatei = templatei
 			{ isus = not (isus templatei)
 			, iblobtype = Nothing

Git/Types.hs

@@ -51,6 +51,7 @@ type Tag = Ref
 
 {- Types of objects that can be stored in git. -}
 data ObjectType = BlobObject | CommitObject | TreeObject
+	deriving (Eq)
 
 instance Show ObjectType where
 	show BlobObject = "blob"
@@ -65,6 +66,7 @@ readObjectType _ = Nothing
 
 {- Types of blobs. -}
 data BlobType = FileBlob | ExecutableBlob | SymlinkBlob
+	deriving (Eq)
 
 {- Git uses magic numbers to denote the type of a blob. -}
 instance Show BlobType where

debian/changelog

@@ -9,6 +9,7 @@ git-annex (3.20120625) UNRELEASED; urgency=low
   * Accept arbitrarily encoded repository filepaths etc when reading
     git config output. This fixes support for remotes with unusual characters
     in their names.
+  * sync: Automatically resolves merge conflicts.
 
  -- Joey Hess <joeyh@debian.org>  Mon, 25 Jun 2012 11:38:12 -0400
 

doc/git-annex.mdwn

@@ -135,6 +135,11 @@ subdirectories).
   commands to do each of those steps by hand, or if you don't want to
   worry about the details, you can use sync.
 
+  Merge conflicts are automatically resolved by sync. When two conflicting
+  versions of a file have been committed, both will be added to the tree,
+  under different filenames. For example, file "foo" would be replaced
+  with "foo.somekey" and "foo.otherkey".
+
   Note that syncing with a remote will not update the remote's working
   tree with changes made to the local repository. However, those changes
   are pushed to the remote, so can be merged into its working tree