enable LambdaCase and convert around 10% of places that could use it

Needs ghc 7.6.1, so minimum base version increased slightly. All builds
are well above this version of ghc, and debian oldstable is as well.

Code that could use lambdacase can be found by running:
git grep -B 1 'case ' | less
and searching in less for "<-"

This commit was sponsored by andrea rota.

Annex/AdjustedBranch.hs

@@ -80,9 +80,8 @@ adjustTreeItem UnlockAdjustment = ifSymlink adjustToPointer noAdjust
 adjustTreeItem LockAdjustment = ifSymlink noAdjust adjustToSymlink
 adjustTreeItem FixAdjustment = ifSymlink adjustToSymlink noAdjust
 adjustTreeItem UnFixAdjustment = ifSymlink (adjustToSymlink' gitAnnexLinkCanonical) noAdjust
-adjustTreeItem HideMissingAdjustment = \ti@(TreeItem _ _ s) -> do
-	mk <- catKey s
-	case mk of
+adjustTreeItem HideMissingAdjustment = \ti@(TreeItem _ _ s) ->
+	catKey s >>= \case
 		Just k -> ifM (inAnnex k)
 			( return (Just ti)
 			, return Nothing
@@ -99,9 +98,7 @@ noAdjust :: TreeItem -> Annex (Maybe TreeItem)
 noAdjust = return . Just
 
 adjustToPointer :: TreeItem -> Annex (Maybe TreeItem)
-adjustToPointer ti@(TreeItem f _m s) = do
-	mk <- catKey s
-	case mk of
+adjustToPointer ti@(TreeItem f _m s) = catKey s >>= \case
 	Just k -> do
 		Database.Keys.addAssociatedFile k f
 		Just . TreeItem f (fromBlobType FileBlob)
@@ -112,9 +109,7 @@ adjustToSymlink :: TreeItem -> Annex (Maybe TreeItem)
 adjustToSymlink = adjustToSymlink' gitAnnexLink
 
 adjustToSymlink' :: (FilePath -> Key -> Git.Repo -> GitConfig -> IO FilePath) -> TreeItem -> Annex (Maybe TreeItem)
-adjustToSymlink' gitannexlink ti@(TreeItem f _m s) = do
-	mk <- catKey s
-	case mk of
+adjustToSymlink' gitannexlink ti@(TreeItem f _m s) = catKey s >>= \case
 	Just k -> do
 		absf <- inRepo $ \r -> absPath $
 			fromTopFilePath f r
@@ -438,9 +433,7 @@ updateAdjustedBranch tomerge (origbranch, adj) mergeconfig canresolvemerge commi
 		return True
 	reparent _ _ Nothing = return False
 
-	getcurrentcommit = do
-		v <- inRepo Git.Branch.currentUnsafe
-		case v of
+	getcurrentcommit = inRepo Git.Branch.currentUnsafe >>= \case
 		Nothing -> return Nothing
 		Just c -> catCommit c
 
@@ -463,15 +456,11 @@ propigateAdjustedCommits'
 	-> Adjustment
 	-> CommitsPrevented
 	-> Annex (Maybe Sha, Annex ())
-propigateAdjustedCommits' origbranch adj _commitsprevented = do
-	ov <- inRepo $ Git.Ref.sha basis
-	case ov of
-		Just origsha -> do
-			cv <- catCommit currbranch
-			case cv of
-				Just currcommit -> do
-					v <- newcommits >>= go origsha False
-					case v of
+propigateAdjustedCommits' origbranch adj _commitsprevented =
+	inRepo (Git.Ref.sha basis) >>= \case
+		Just origsha -> catCommit currbranch >>= \case
+			Just currcommit ->
+				newcommits >>= go origsha False >>= \case
 					Left e -> do
 						warning e
 						return (Nothing, return ())
@@ -492,15 +481,13 @@ propigateAdjustedCommits' origbranch adj _commitsprevented = do
 		setBasisBranch (BasisBranch basis) parent
 		inRepo $ Git.Branch.update' origbranch parent
 		return (Right parent)
-	go parent pastadjcommit (sha:l) = do
-		mc <- catCommit sha
-		case mc of
+	go parent pastadjcommit (sha:l) = catCommit sha >>= \case
 		Just c
 			| commitMessage c == adjustedBranchCommitMessage ->
 				go parent True l
-				| pastadjcommit -> do
-					v <- reverseAdjustedCommit parent adj (sha, c) origbranch
-					case v of
+			| pastadjcommit ->
+				reverseAdjustedCommit parent adj (sha, c) origbranch
+					>>= \case
 						Left e -> return (Left e)
 						Right commit -> go commit pastadjcommit l
 		_ -> go parent pastadjcommit l

Annex/AutoMerge.hs

@@ -217,9 +217,8 @@ resolveMerge' unstagedmap (Just us) them inoverlay u = do
 
 	makepointer key dest destmode = do
 		unless inoverlay $ 
-			unlessM (reuseOldFile unstagedmap key file dest) $ do
-				r <- linkFromAnnex key dest destmode
-				case r of
+			unlessM (reuseOldFile unstagedmap key file dest) $
+				linkFromAnnex key dest destmode >>= \case
 					LinkAnnexFailed -> liftIO $
 						writePointerFile dest key destmode
 					_ -> noop

Annex/Branch.hs

@@ -446,9 +446,7 @@ stageJournal jl = withIndex $ do
 			[genstream dir h jh jlogh]
 	return $ cleanup dir jlogh jlogf
   where
-	genstream dir h jh jlogh streamer = do
-		v <- readDirectory jh
-		case v of
+	genstream dir h jh jlogh streamer = readDirectory jh >>= \case
 		Nothing -> return ()
 		Just file -> do
 			unless (dirCruft file) $ do

Annex/ChangedRefs.hs

@@ -39,18 +39,15 @@ data ChangedRefsHandle = ChangedRefsHandle DirWatcherHandle (TBMChan Git.Sha)
 -- When possible, coalesce ref writes that occur closely together
 -- in time. Delay up to 0.05 seconds to get more ref writes.
 waitChangedRefs :: ChangedRefsHandle -> IO ChangedRefs
-waitChangedRefs (ChangedRefsHandle _ chan) = do
-	v <- atomically $ readTBMChan chan
-	case v of
+waitChangedRefs (ChangedRefsHandle _ chan) =
+	atomically (readTBMChan chan) >>= \case
 		Nothing -> return $ ChangedRefs []
 		Just r -> do
 			threadDelay 50000
 			rs <- atomically $ loop []
 			return $ ChangedRefs (r:rs)
   where
-	loop rs = do
-		v <- tryReadTBMChan chan
-		case v of
+	loop rs = tryReadTBMChan chan >>= \case
 		Just (Just r) -> loop (r:rs)
 		_ -> return rs
 
@@ -59,9 +56,7 @@ waitChangedRefs (ChangedRefsHandle _ chan) = do
 drainChangedRefs :: ChangedRefsHandle -> IO ()
 drainChangedRefs (ChangedRefsHandle _ chan) = atomically go
   where
-	go = do
-		v <- tryReadTBMChan chan
-		case v of
+	go = tryReadTBMChan chan >>= \case
 		Just (Just _) -> go
 		_ -> return ()
 

Annex/Content.hs

@@ -149,17 +149,13 @@ inAnnexSafe key = inAnnex' (fromMaybe True) (Just False) go key
 			( checkOr is_unlocked lockfile
 			, return is_missing
 			)
-	checkOr d lockfile = do
-		v <- checkLocked lockfile
-		return $ case v of
+	checkOr d lockfile = checkLocked lockfile >>= return . \case
 		Nothing -> d
 		Just True -> is_locked
 		Just False -> is_unlocked
 #else
 	checkindirect f = liftIO $ ifM (doesFileExist f)
-		( do
-			v <- lockShared f
-			case v of
+		( lockShared f >>= \case
 			Nothing -> return is_locked
 			Just lockhandle -> do
 				dropLock lockhandle
@@ -170,9 +166,8 @@ inAnnexSafe key = inAnnex' (fromMaybe True) (Just False) go key
 	 - remove the lock file to clean up after ourselves. -}
 	checkdirect contentfile lockfile =
 		ifM (liftIO $ doesFileExist contentfile)
-			( modifyContent lockfile $ liftIO $ do
-				v <- lockShared lockfile
-				case v of
+			( modifyContent lockfile $ liftIO $
+				lockShared >>= \case
 					Nothing -> return is_locked
 					Just lockhandle -> do
 						dropLock lockhandle
@@ -428,8 +423,7 @@ checkDiskSpace' need destdir key alreadythere samefilesystem = ifM (Annex.getSta
 		inprogress <- if samefilesystem
 			then sizeOfDownloadsInProgress (/= key)
 			else pure 0
-		free <- liftIO . getDiskFree =<< dir
-		case free of
+		dir >>= liftIO . getDiskFree >>= \case
 			Just have -> do
 				reserve <- annexDiskReserve <$> Annex.getGitConfig
 				let delta = need + reserve - have - alreadythere + inprogress
@@ -581,9 +575,8 @@ data FromTo = From | To
  -}
 linkAnnex :: FromTo -> Key -> FilePath -> Maybe InodeCache -> FilePath -> Maybe FileMode -> Annex LinkAnnexResult
 linkAnnex _ _ _ Nothing _ _ = return LinkAnnexFailed
-linkAnnex fromto key src (Just srcic) dest destmode = do
-	mdestic <- withTSDelta (liftIO . genInodeCache dest)
-	case mdestic of
+linkAnnex fromto key src (Just srcic) dest destmode =
+	withTSDelta (liftIO . genInodeCache dest) >>= \case
 		Just destic -> do
 			cs <- Database.Keys.getInodeCaches key
 			if null cs
@@ -602,9 +595,7 @@ linkAnnex fromto key src (Just srcic) dest destmode = do
 	failed = do
 		Database.Keys.addInodeCaches key [srcic]
 		return LinkAnnexFailed
-	checksrcunchanged = do
-		mcache <- withTSDelta (liftIO . genInodeCache src)
-		case mcache of
+	checksrcunchanged = withTSDelta (liftIO . genInodeCache src) >>= \case
 		Just srcic' | compareStrong srcic srcic' -> do
 			destic <- withTSDelta (liftIO . genInodeCache dest)
 			Database.Keys.addInodeCaches key $

Annex/Direct.hs

@@ -111,9 +111,8 @@ preCommitDirect = do
 		withkey (DiffTree.srcsha diff) (DiffTree.srcmode diff) removeAssociatedFile
 		withkey (DiffTree.dstsha diff) (DiffTree.dstmode diff) addAssociatedFile
 	  where
-		withkey sha _mode a = when (sha /= nullSha) $ do
-			k <- catKey sha
-			case k of
+		withkey sha _mode a = when (sha /= nullSha) $
+			catKey sha >>= \case
 				Nothing -> noop
 				Just key -> void $ a key $
 					makeabs $ DiffTree.file diff
@@ -427,9 +426,7 @@ setDirect wantdirect = do
 			then moveconfig coreworktree indirectworktree
 			else moveconfig indirectworktree coreworktree
 		setConfig (ConfigKey Git.Config.coreBare) val
-	moveconfig src dest = do
-		v <- getConfigMaybe src
-		case v of
+	moveconfig src dest = getConfigMaybe src >>= \case
 		Nothing -> noop
 		Just wt -> do
 			unsetConfig src
@@ -474,8 +471,7 @@ switchHEADBack = maybe noop switch =<< inRepo Git.Branch.currentUnsafe
   where
 	switch currhead = do
 		let orighead = fromDirectBranch currhead
-		v <- inRepo $ Git.Ref.sha currhead
-		case v of
+		inRepo (Git.Ref.sha currhead) >>= \case
 			Just headsha
 				| orighead /= currhead -> do
 					inRepo $ Git.Branch.update "leaving direct mode" orighead headsha

Annex/FileMatcher.hs

@@ -133,9 +133,7 @@ mkLargeFilesParser = do
 #ifdef WITH_MAGICMIME
 	magicmime <- liftIO $ catchMaybeIO $ do
 		m <- magicOpen [MagicMimeType]
-		liftIO $ do
-			md <- getEnv "GIT_ANNEX_DIR"
-			case md of
+		liftIO $ getEnv "GIT_ANNEX_DIR" >>= \case
 			Nothing -> magicLoadDefault m
 			Just d -> magicLoad m
 				(d </> "magic" </> "magic.mgc")

Annex/Ingest.hs

@@ -169,9 +169,8 @@ ingest' preferredbackend (Just (LockedDown cfg source)) mk = withTSDelta $ \delt
 			)
 	go _ _ _ = failure "failed to generate a key"
 
-	golocked key mcache s = do
-		v <- tryNonAsync (moveAnnex key $ contentLocation source)
-		case v of
+	golocked key mcache s =
+		tryNonAsync (moveAnnex key $ contentLocation source) >>= \case
 			Right True -> do
 				populateAssociatedFiles key source
 				success key mcache s		
@@ -184,8 +183,7 @@ ingest' preferredbackend (Just (LockedDown cfg source)) mk = withTSDelta $ \delt
 		-- already has a hard link.
 		cleanCruft source
 		cleanOldKeys (keyFilename source) key
-		r <- linkToAnnex key (keyFilename source) (Just cache)
-		case r of
+		linkToAnnex key (keyFilename source) (Just cache) >>= \case
 			LinkAnnexFailed -> failure "failed to link to annex"
 			_ -> do
 				finishIngestUnlocked' key source
@@ -259,8 +257,7 @@ cleanOldKeys file newkey = do
 			fs <- filter (/= ingestedf)
 				. map (`fromTopFilePath` g)
 				<$> Database.Keys.getAssociatedFiles key
-			fs' <- filterM (`sameInodeCache` caches) fs
-			case fs' of
+			filterM (`sameInodeCache` caches) fs >>= \case
 				-- If linkToAnnex fails, the associated 
 				-- file with the content is still present,
 				-- so no need for any recovery.
@@ -342,9 +339,7 @@ cachedCurrentBranch = maybe cache (return . Just)
 	=<< Annex.getState Annex.cachedcurrentbranch
   where
 	cache :: Annex (Maybe Git.Branch)
-	cache = do
-		mb <- inRepo Git.Branch.currentUnsafe
-		case mb of
+	cache = inRepo Git.Branch.currentUnsafe >>= \case
 		Nothing -> return Nothing
 		Just b -> do
 			Annex.changeState $ \s ->
@@ -389,9 +384,7 @@ addAnnexedFile file key mtmp = ifM (addUnlocked <&&> not <$> isDirect)
 			Nothing -> return True
 	)
   where
-	linkunlocked mode = do
-		r <- linkFromAnnex key file mode
-		case r of
+	linkunlocked mode = linkFromAnnex key file mode >>= \case
 		LinkAnnexFailed -> liftIO $
 			writePointerFile file key mode
 		_ -> return ()

Annex/Init.hs

@@ -93,8 +93,7 @@ initialize' mversion = do
 	whenM versionSupportsUnlockedPointers $ do
 		configureSmudgeFilter
 		scanUnlockedFiles
-	v <- checkAdjustedClone
-	case v of
+	checkAdjustedClone >>= \case
 		NeedUpgradeForAdjustedClone -> 
 			void $ upgrade True  versionForAdjustedClone
 		InAdjustedClone -> return ()

Annex/LockPool/PosixOrPid.hs

@@ -49,9 +49,7 @@ tryLockExclusive m f = tryPidLock m f $ Posix.tryLockExclusive m f
 checkLocked :: LockFile -> Annex (Maybe Bool)
 checkLocked f = Posix.checkLocked f `pidLockCheck` checkpid
   where
-	checkpid pidlock = do
-		v <- Pid.checkLocked pidlock
-		case v of
+	checkpid pidlock = Pid.checkLocked pidlock >>= \case
 		-- Only return true when the posix lock file exists.
 		Just _ -> Posix.checkLocked f
 		Nothing -> return Nothing

Annex/MetaData.hs

@@ -39,8 +39,7 @@ import Data.Time.Clock.POSIX
  -}
 genMetaData :: Key -> FilePath -> FileStatus -> Annex ()
 genMetaData key file status = do
-	v <- catKeyFileHEAD file
-	case v of
+	catKeyFileHEAD file >>= \case
 		Nothing -> noop
 		Just oldkey -> 
 			whenM (copyMetaData oldkey key)

Annex/Perms.hs

@@ -112,7 +112,7 @@ isContentWritePermOk file = ifM crippledFileSystem
 	go AllShared = want writeModes
 	go _ = return True
 	want wantmode = do
-		mmode <- liftIO $ catchMaybeIO $ fileMode <$> getFileStatus file
+		liftIO $ catchMaybeIO $ fileMode <$> getFileStatus file
 		return $ case mmode of
 			Nothing -> True
 			Just havemode -> havemode == combineModes (havemode:wantmode)

git-annex.cabal

@@ -306,7 +306,7 @@ source-repository head
 Executable git-annex
   Main-Is: git-annex.hs
   Build-Depends:
-   base (>= 4.5 && < 5.0),
+   base (>= 4.6 && < 5.0),
    optparse-applicative (>= 0.11.0), 
    containers (>= 0.5.0.0),
    exceptions (>= 0.6),
@@ -360,7 +360,7 @@ Executable git-annex
    split
   CC-Options: -Wall
   GHC-Options: -Wall -fno-warn-tabs
-  Extensions: PackageImports
+  Extensions: PackageImports, LambdaCase
   -- Some things don't work with the non-threaded RTS.
   GHC-Options: -threaded
   Other-Extensions: TemplateHaskell