rework Differences data type

Eliminated complexity and future proofed. The most important change is that
all functions over Difference are now total; any Difference that can be
expressed should be handled. Avoids needs for sanity checking of inputs,
and version skew with the future.

Also, the difference.log now serializes a [Difference], not a Differences.
This saves space and keeps it simpler.

Note that [Difference] might contain conflicting differences (eg,
[Version5, Version6]. In this case, one of them needs to consistently win
over the others, probably based on Ord.

Annex/Difference.hs

@@ -31,9 +31,7 @@ import qualified Data.Map as M
 setDifferences :: Annex ()
 setDifferences = do
 	u <- getUUID
-	otherds <- either error return 
-		=<< sanityCheckDifferences . allDifferences
-			<$> recordedDifferences
+	otherds <- allDifferences <$> recordedDifferences
 	ds <- mappend otherds . annexDifferences <$> Annex.getGitConfig
 	when (ds /= mempty) $ do
 		ds'@(Differences l) <- ifM (isJust <$> getVersion)

Locations.hs

@@ -135,7 +135,7 @@ gitAnnexLocation' key r config crippled
 	 -}
 	| Git.repoIsLocalBare r 
 		|| crippled 
-		|| hasDifference (== ObjectHashLower True) (annexDifferences config) =
+		|| hasDifference (== ObjectHashLower) (annexDifferences config) =
 			check $ map inrepo $ annexLocations key
 	{- Non-bare repositories only use hashDirMixed, so
 	 - don't need to do any work to check if the file is

Logs/Difference.hs

@@ -24,10 +24,11 @@ import Logs.UUIDBased
 import Logs.Difference.Pure
 
 recordDifferences :: Differences -> UUID -> Annex ()
-recordDifferences differences uuid = do
+recordDifferences (Differences differences) uuid = do
 	ts <- liftIO getPOSIXTime
 	Annex.Branch.change differenceLog $
 		showLog id . changeLog ts uuid (show differences) . parseLog Just
+recordDifferences UnknownDifferences _ = return ()
 
 -- Map of UUIDs that have Differences recorded.
 -- If a new version of git-annex has added a Difference this version

Logs/Difference/Pure.hs

@@ -19,7 +19,7 @@ import Logs.UUIDBased
 
 parseDifferencesLog :: String -> (M.Map UUID Differences)
 parseDifferencesLog = simpleMap 
-	. parseLog (Just . fromMaybe UnknownDifferences . readish)
+	. parseLog (Just . maybe UnknownDifferences Differences . readish)
 
 -- The sum of all recorded differences, across all UUIDs.
 allDifferences :: M.Map UUID Differences -> Differences

Types/Difference.hs

@@ -9,123 +9,74 @@ module Types.Difference (
 	Difference(..),
 	Differences(..),
 	getDifferences,
-	sanityCheckDifferences,
 	differenceConfigKey,
 	differenceConfigVal,
 	hasDifference,
 ) where
 
-import Utility.PartialPrelude
 import qualified Git
 import qualified Git.Config
 
 import Data.List
 import Data.Maybe
 import Data.Monoid
-import Control.Applicative
 
 -- Describes differences from the v5 repository format.
 --
--- The serilization is stored in difference.log, so avoid changes that
+-- The serialization is stored in difference.log, so avoid changes that
 -- would break compatability.
 --
--- Not breaking comparability is why a list of Differences is used, rather
+-- Not breaking compatability is why a list of Differences is used, rather
 -- than a sum type. With a sum type, adding a new field for some future
 -- difference would serialize to a value that an older version could not
 -- parse, even if that new field was not used. With the Differences list,
 -- old versions can still parse it, unless the new Difference constructor 
 -- is used.
+--
+-- The constructors intentionally do not have parameters; this is to
+-- ensure that any Difference that can be expressed is supported.
+-- So, a new repository version would be Version6, rather than Version Int.
 data Difference
-	= Version Int
-	| ObjectHashLower Bool
-	| ObjectHashDirectories Int
-	| BranchHashDirectories Int
-	deriving (Show, Read, Ord)
-
-instance Eq Difference where
-	Version a == Version b = a == b
-	ObjectHashLower a == ObjectHashLower b = a == b
-	ObjectHashDirectories a == ObjectHashDirectories b = a == b
-	BranchHashDirectories a == BranchHashDirectories b = a == b
-	_ == _ = False
+	= ObjectHashLower
+	| OneLevelObjectHash
+	| OneLevelBranchHash
+	deriving (Show, Read, Ord, Eq, Enum, Bounded)
 
 data Differences
 	= Differences [Difference]
 	| UnknownDifferences
-	deriving (Show, Read, Ord)
 
 instance Eq Differences where
-	Differences a == Differences b = simplify (defver:a) == simplify (defver:b)
-	_ == _ = False
+	Differences a == Differences b = canon a == canon b
+	_ == _ = False -- UnknownDifferences cannot be equal
 
 instance Monoid Differences where
 	mempty = Differences []
-	mappend (Differences l1) (Differences l2) = Differences (simplify (l1 ++ l2))
+	mappend (Differences l1) (Differences l2) = Differences (canon (l1 ++ l2))
 	mappend _ _ = UnknownDifferences
 
--- This is the default repository version that is assumed when no other one
--- is given. Note that [] == [Version 5]
-defver :: Difference
-defver = Version 5
-
--- Given [Version 6, Version 5], returns [Version 6]
-simplify :: [Difference] -> [Difference]
-simplify = go . sort
-  where
-	go [] = []
-	go (d:[]) = [d]
-	go (d1:d2:ds)
-		| like d1 d2 = go (d2:ds)
-		| otherwise = d1 : go (d2:ds)
-
-	like (Version _) (Version _) = True
-	like _ _ = False
+canon :: [Difference] -> [Difference]
+canon = nub . sort
 
 getDifferences :: Git.Repo -> Differences
-getDifferences r = checksane $ Differences $ catMaybes
-	[ ObjectHashLower 
-		<$> getmaybebool (differenceConfigKey (ObjectHashLower undefined))
-	, ObjectHashDirectories 
-		<$> getmayberead (differenceConfigKey (ObjectHashDirectories undefined))
-	, BranchHashDirectories
-		<$> getmayberead (differenceConfigKey (BranchHashDirectories undefined))
-	]
+getDifferences r = Differences $ catMaybes $
+	map getmaybe [minBound .. maxBound]
   where
-	getmaybe k = Git.Config.getMaybe k r
-	getmayberead k = readish =<< getmaybe k
-	getmaybebool k = Git.Config.isTrue =<< getmaybe k
-	checksane = either error id . sanityCheckDifferences
+	getmaybe d = case Git.Config.isTrue =<< Git.Config.getMaybe (differenceConfigKey d) r of
+		Just True -> Just d
+		_ -> Nothing
 
 differenceConfigKey :: Difference -> String
-differenceConfigKey (Version _) = "annex.version"
-differenceConfigKey (ObjectHashLower _) = tunable "objecthashlower"
-differenceConfigKey (ObjectHashDirectories _) = tunable "objecthashdirectories"
-differenceConfigKey (BranchHashDirectories _) = tunable "branchhashdirectories"
+differenceConfigKey ObjectHashLower = tunable "objecthashlower"
+differenceConfigKey OneLevelObjectHash = tunable "objecthash1"
+differenceConfigKey OneLevelBranchHash = tunable "branchhash1"
 
 differenceConfigVal :: Difference -> String
-differenceConfigVal (Version v) = show v
-differenceConfigVal (ObjectHashLower b) = Git.Config.boolConfig b
-differenceConfigVal (ObjectHashDirectories n) = show n
-differenceConfigVal (BranchHashDirectories n) = show n
+differenceConfigVal _ = Git.Config.boolConfig True
 
 tunable :: String -> String
 tunable k = "annex.tune." ++ k
 
-sanityCheckDifferences :: Differences -> Either String Differences
-sanityCheckDifferences d@(Differences l)
-	| null problems = Right d
-	| otherwise = Left (intercalate "; " problems)
-  where
-	problems = catMaybes (map check l)
-	check (ObjectHashDirectories n)
-		| n == 1 || n == 2 = Nothing
-		| otherwise = Just $ "Bad value for objecthashdirectories -- should be 1 or 2, not " ++ show n
-	check (BranchHashDirectories n)
-		| n == 1 || n == 2 = Nothing
-		| otherwise = Just $ "Bad value for branhhashdirectories -- should be 1 or 2, not " ++ show n
-	check _ = Nothing
-sanityCheckDifferences UnknownDifferences = Left "unknown differences detected; update git-annex"
-
 hasDifference :: (Difference -> Bool) -> Differences -> Bool
 hasDifference f (Differences l) = any f l
 hasDifference _ UnknownDifferences = False

doc/git-annex.mdwn

@@ -1839,7 +1839,7 @@ Here are all the supported configuration settings.
   Used by hook special remotes and external special remotes to record
   the type of the remote.
 
-* `annex.tune.objecthashdirectories`, `annex.tune.objecthashlower`, `annex.tune.branchhashdirectories`
+* `annex.tune.objecthash1`, `annex.tune.objecthashlower`, `annex.tune.branchhash1`
 
   These can be passed to `git annex init` to tune the repository.
   They cannot be safely changed in a running repository.

doc/internals.mdwn

@@ -265,4 +265,4 @@ that should prevent merging.
 
 Example:
 
-	e605dca6-446a-11e0-8b2a-002170d25c55 [Version 5] timestamp=1422387398.30395s
+	e605dca6-446a-11e0-8b2a-002170d25c55 [ObjectHashLower] timestamp=1422387398.30395s

doc/tuning.mdwn

@@ -12,7 +12,7 @@ done by passing `-c name=value` parameters to `git annex init`.
 For example, this will make git-annex use only 1 level for hash directories
 in `.git/annex/objects`:
 
-	git -c annex.tune.objecthashdirectories=1 annex init
+	git -c annex.tune.objecthash1=true annex init
 
 It's very important to keep in mind that this makes a nonstandard format
 git-annex repository. In general, this cannot safely be used with
@@ -29,16 +29,18 @@ Again, tuned repositories are an experimental feature; use with caution!
 
 The following tuning parameters are available:
 
-* `annex.tune.objecthashdirectories` (default: 2)  
-  Sets the number of hash directories to use in `.git/annex/objects/`
+* `annex.tune.objecthash1=true`  
+  Use just one level of hash directories in `.git/annex/objects/`,
+  instead of the default two levels.
 
-* `annex.tune.objecthashlower` (default: false)
-  Set to true to make the hash directories in `.git/annex/objects/` use
-  all lower-case.
+* `annex.tune.objecthashlower=true`  
+  Make the hash directories in `.git/annex/objects/` use
+  all lower-case, instead of the default mixed-case.
 
-* `annex.tune.branchhashdirectories` (default: 2)
-  Sets the number of hash directories to use in the git-annex branch.
+* `annex.tune.branchhash1=true`  
+  Use just one level of hash directories in the git-annex branch,
+  instead of the default two levels.
 
 Note that git-annex will automatically propigate these setting to
-`.git/config` for tuned repsitories. You should never directly change
+`.git/config` for tuned repositories. You should never directly change
 these settings in `.git/config`