configuration to disable automatic merge conflict resolution

* Added annex.resolvemerge configuration, which can be set to false to
  disable the usual automatic merge conflict resolution done by git-annex
  sync and the assistant.
* sync: Added --no-resolvemerge option.

Note that disabling merge conflict resolution is probably not a good idea
in a direct mode repo or adjusted branch. Since updates to both are done
outside the usual work tree, if it fails the tree is not left in a
conflicted state, and it would be hard to manually resolve the conflict.
Still, made annex.resolvemerge be supported in those cases for consistency.

This commit was sponsored by Riku Voipio.

14 files changed, 89 insertions, 29 deletions

diff --git a/Annex/AdjustedBranch.hs b/Annex/AdjustedBranch.hs
index c0225540a..52f73e638 100644
--- a/Annex/AdjustedBranch.hs
+++ b/Annex/AdjustedBranch.hs
@@ -318,8 +318,8 @@ findAdjustingCommit (AdjBranch b) = go =<< catCommit b
 {- Update the currently checked out adjusted branch, merging the provided
  - branch into it. Note that the provided branch should be a non-adjusted
  - branch. -}
-updateAdjustedBranch :: Branch -> (OrigBranch, Adjustment) -> [Git.Merge.MergeConfig] -> Git.Branch.CommitMode -> Annex Bool
-updateAdjustedBranch tomerge (origbranch, adj) mergeconfig commitmode = catchBoolIO $
+updateAdjustedBranch :: Branch -> (OrigBranch, Adjustment) -> [Git.Merge.MergeConfig] -> Annex Bool -> Git.Branch.CommitMode -> Annex Bool
+updateAdjustedBranch tomerge (origbranch, adj) mergeconfig canresolvemerge commitmode = catchBoolIO $
 	join $ preventCommits go
   where
 	adjbranch@(AdjBranch currbranch) = originalToAdjusted origbranch adj
@@ -417,7 +417,7 @@ updateAdjustedBranch tomerge (origbranch, adj) mergeconfig commitmode = catchBoo
 		-- this commit will be a fast-forward.
 		adjmergecommitff <- commitAdjustedTree' adjtree (BasisBranch mergecommit) [currbranch]
 		showAction "Merging into adjusted branch"
-		ifM (autoMergeFrom adjmergecommitff (Just currbranch) mergeconfig commitmode)
+		ifM (autoMergeFrom adjmergecommitff (Just currbranch) mergeconfig canresolvemerge commitmode)
 			( reparent adjtree adjmergecommit =<< getcurrentcommit
 			, return False
 			)
diff --git a/Annex/AutoMerge.hs b/Annex/AutoMerge.hs
index 7f982e515..91f8fc99e 100644
--- a/Annex/AutoMerge.hs
+++ b/Annex/AutoMerge.hs
@@ -43,18 +43,18 @@ import qualified Data.ByteString.Lazy as L
  - Callers should use Git.Branch.changed first, to make sure that
  - there are changes from the current branch to the branch being merged in.
  -}
-autoMergeFrom :: Git.Ref -> Maybe Git.Ref -> [Git.Merge.MergeConfig] -> Git.Branch.CommitMode -> Annex Bool
-autoMergeFrom branch currbranch mergeconfig commitmode = do
+autoMergeFrom :: Git.Ref -> Maybe Git.Ref -> [Git.Merge.MergeConfig] -> Annex Bool -> Git.Branch.CommitMode -> Annex Bool
+autoMergeFrom branch currbranch mergeconfig canresolvemerge commitmode = do
 	showOutput
 	case currbranch of
 		Nothing -> go Nothing
 		Just b -> go =<< inRepo (Git.Ref.sha b)
   where
 	go old = ifM isDirect
-		( mergeDirect currbranch old branch (resolveMerge old branch False) mergeconfig commitmode
+		( mergeDirect currbranch old branch resolvemerge mergeconfig commitmode
 		, do
 			r <- inRepo (Git.Merge.merge branch mergeconfig commitmode)
-				<||> (resolveMerge old branch False <&&> commitResolvedMerge commitmode)
+				<||> (resolvemerge <&&> commitResolvedMerge commitmode)
 			-- Merging can cause new associated files to appear
 			-- and the smudge filter will add them to the database.
 			-- To ensure that this process sees those changes,
@@ -62,6 +62,11 @@ autoMergeFrom branch currbranch mergeconfig commitmode = do
 			Database.Keys.closeDb
 			return r
 		)
+	  where
+		resolvemerge = ifM canresolvemerge
+			( resolveMerge old branch False
+			, return False 
+			)
 
 {- Resolves a conflicted merge. It's important that any conflicts be
  - resolved in a way that itself avoids later merge conflicts, since
diff --git a/Assistant/Sync.hs b/Assistant/Sync.hs
index 8f30aa4f7..e6a5bc5d5 100644
--- a/Assistant/Sync.hs
+++ b/Assistant/Sync.hs
@@ -211,7 +211,8 @@ manualPull currentbranch remotes = do
 		else return Nothing
 	haddiverged <- liftAnnex Annex.Branch.forceUpdate
 	forM_ normalremotes $ \r ->
-		liftAnnex $ Command.Sync.mergeRemote r currentbranch Command.Sync.mergeConfig
+		liftAnnex $ Command.Sync.mergeRemote r
+			currentbranch Command.Sync.mergeConfig def
 	return (catMaybes failed, haddiverged)
   where
 	wantpull gc = remoteAnnexPull gc
diff --git a/Assistant/Threads/Merger.hs b/Assistant/Threads/Merger.hs
index 0bb37e664..05341db1e 100644
--- a/Assistant/Threads/Merger.hs
+++ b/Assistant/Threads/Merger.hs
@@ -78,6 +78,7 @@ onChange file
 					]
 				void $ liftAnnex $ Command.Sync.merge
 					currbranch Command.Sync.mergeConfig
+					def
 					Git.Branch.AutomaticCommit
 					changedbranch
 	mergecurrent _ = noop
diff --git a/CHANGELOG b/CHANGELOG
index 3540b937a..d85926d70 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -12,6 +12,10 @@ git-annex (6.20170520) UNRELEASED; urgency=medium
   * metadata: When setting metadata of a file that did not exist,
     no error message was displayed, unlike getting metadata and most other
     git-annex commands. Fixed this oversight.
+  * Added annex.resolvemerge configuration, which can be set to false to 
+    disable the usual automatic merge conflict resolution done by git-annex
+    sync and the assistant.
+  * sync: Added --no-resolvemerge option.
 
  -- Joey Hess <id@joeyh.name>  Wed, 24 May 2017 14:03:40 -0400
 
diff --git a/Command/Merge.hs b/Command/Merge.hs
index 80a8227d1..4f99093ab 100644
--- a/Command/Merge.hs
+++ b/Command/Merge.hs
@@ -33,4 +33,4 @@ mergeBranch = do
 mergeSynced :: CommandStart
 mergeSynced = do
 	prepMerge
-	mergeLocal mergeConfig =<< join getCurrBranch
+	mergeLocal mergeConfig def =<< join getCurrBranch
diff --git a/Command/PostReceive.hs b/Command/PostReceive.hs
index ffb5516a2..4db775214 100644
--- a/Command/PostReceive.hs
+++ b/Command/PostReceive.hs
@@ -48,4 +48,4 @@ fixPostReceiveHookEnv = do
 updateInsteadEmulation :: CommandStart
 updateInsteadEmulation = do
 	prepMerge
-	mergeLocal mergeConfig =<< join getCurrBranch
+	mergeLocal mergeConfig def =<< join getCurrBranch
diff --git a/Command/Sync.hs b/Command/Sync.hs
index 332daca73..9ecb98620 100644
--- a/Command/Sync.hs
+++ b/Command/Sync.hs
@@ -76,8 +76,14 @@ data SyncOptions  = SyncOptions
 	, noContentOption :: Bool
 	, contentOfOption :: [FilePath]
 	, keyOptions :: Maybe KeyOptions
+	, resolveMergeOverride :: ResolveMergeOverride
 	}
 
+newtype ResolveMergeOverride = ResolveMergeOverride Bool
+
+instance Default ResolveMergeOverride where
+	def = ResolveMergeOverride False
+
 optParser :: CmdParamsDesc -> Parser SyncOptions
 optParser desc = SyncOptions
 	<$> (many $ argument str
@@ -117,6 +123,9 @@ optParser desc = SyncOptions
 		<> metavar paramPath
 		))
 	<*> optional parseAllOption
+	<*> (ResolveMergeOverride <$> invertableSwitch "resolvemerge" True
+		( help "do not automatically resolve merge conflicts"
+		))
 
 -- Since prepMerge changes the working directory, FilePath options
 -- have to be adjusted.
@@ -132,6 +141,7 @@ instance DeferredParseClass SyncOptions where
 		<*> pure (noContentOption v)
 		<*> liftIO (mapM absPath (contentOfOption v))
 		<*> pure (keyOptions v)
+		<*> pure (resolveMergeOverride v)
 
 seek :: SyncOptions -> CommandSeek
 seek o = allowConcurrentOutput $ do
@@ -150,7 +160,7 @@ seek o = allowConcurrentOutput $ do
 	-- These actions cannot be run concurrently.
 	mapM_ includeCommandAction $ concat
 		[ [ commit o ]
-		, [ withbranch (mergeLocal mergeConfig) ]
+		, [ withbranch (mergeLocal mergeConfig (resolveMergeOverride o)) ]
 		, map (withbranch . pullRemote o mergeConfig) gitremotes
 		,  [ mergeAnnex ]
 		]
@@ -219,11 +229,14 @@ mergeConfig =
 	, Git.Merge.MergeUnrelatedHistories
 	]
 
-merge :: CurrBranch -> [Git.Merge.MergeConfig] -> Git.Branch.CommitMode -> Git.Branch -> Annex Bool
-merge (Just b, Just adj) mergeconfig commitmode tomerge =
-	updateAdjustedBranch tomerge (b, adj) mergeconfig commitmode
-merge (b, _) mergeconfig commitmode tomerge =
-	autoMergeFrom tomerge b mergeconfig commitmode
+merge :: CurrBranch -> [Git.Merge.MergeConfig] -> ResolveMergeOverride -> Git.Branch.CommitMode -> Git.Branch -> Annex Bool
+merge currbranch mergeconfig resolvemergeoverride commitmode tomerge = case currbranch of
+	(Just b, Just adj) -> updateAdjustedBranch tomerge (b, adj) mergeconfig canresolvemerge commitmode
+	(b, _) -> autoMergeFrom tomerge b mergeconfig canresolvemerge commitmode
+  where
+	canresolvemerge = case resolvemergeoverride of
+		ResolveMergeOverride True -> getGitConfigVal annexResolveMerge
+		ResolveMergeOverride False -> return False
 
 syncBranch :: Git.Branch -> Git.Branch
 syncBranch = Git.Ref.underBase "refs/heads/synced" . fromDirectBranch . fromAdjustedBranch
@@ -296,15 +309,15 @@ commitStaged commitmode commitmessage = do
 	void $ inRepo $ Git.Branch.commit commitmode False commitmessage branch parents
 	return True
 
-mergeLocal :: [Git.Merge.MergeConfig] -> CurrBranch -> CommandStart
-mergeLocal mergeconfig currbranch@(Just _, _) =
+mergeLocal :: [Git.Merge.MergeConfig] -> ResolveMergeOverride -> CurrBranch -> CommandStart
+mergeLocal mergeconfig resolvemergeoverride currbranch@(Just _, _) =
 	go =<< needMerge currbranch
   where
 	go Nothing = stop
 	go (Just syncbranch) = do
 		showStart "merge" $ Git.Ref.describe syncbranch
-		next $ next $ merge currbranch mergeconfig Git.Branch.ManualCommit syncbranch
-mergeLocal _ (Nothing, madj) = do
+		next $ next $ merge currbranch mergeconfig resolvemergeoverride Git.Branch.ManualCommit syncbranch
+mergeLocal _ _ (Nothing, madj) = do
 	b <- inRepo Git.Branch.currentUnsafe
 	ifM (isJust <$> needMerge (b, madj))
 		( do
@@ -365,7 +378,7 @@ pullRemote o mergeconfig remote branch = stopUnless (pure $ pullOption o && want
 	next $ do
 		showOutput
 		stopUnless fetch $
-			next $ mergeRemote remote branch mergeconfig
+			next $ mergeRemote remote branch mergeconfig (resolveMergeOverride o)
   where
 	fetch = inRepoWithSshOptionsTo (Remote.repo remote) (Remote.gitconfig remote) $
 		Git.Command.runBool
@@ -377,8 +390,8 @@ pullRemote o mergeconfig remote branch = stopUnless (pure $ pullOption o && want
  - were committed (or pushed changes, if this is a bare remote),
  - while the synced/master may have changes that some
  - other remote synced to this remote. So, merge them both. -}
-mergeRemote :: Remote -> CurrBranch -> [Git.Merge.MergeConfig] -> CommandCleanup
-mergeRemote remote currbranch mergeconfig = ifM isBareRepo
+mergeRemote :: Remote -> CurrBranch -> [Git.Merge.MergeConfig] -> ResolveMergeOverride -> CommandCleanup
+mergeRemote remote currbranch mergeconfig resolvemergeoverride = ifM isBareRepo
 	( return True
 	, case currbranch of
 		(Nothing, _) -> do
@@ -390,7 +403,7 @@ mergeRemote remote currbranch mergeconfig = ifM isBareRepo
 	)
   where
 	mergelisted getlist = and <$> 
-		(mapM (merge currbranch mergeconfig Git.Branch.ManualCommit . remoteBranch remote) =<< getlist)
+		(mapM (merge currbranch mergeconfig resolvemergeoverride Git.Branch.ManualCommit . remoteBranch remote) =<< getlist)
 	tomerge = filterM (changed remote)
 	branchlist Nothing = []
 	branchlist (Just branch) = [branch, syncBranch branch]
diff --git a/Types/GitConfig.hs b/Types/GitConfig.hs
index f66136cb1..cec64b57a 100644
--- a/Types/GitConfig.hs
+++ b/Types/GitConfig.hs
@@ -58,6 +58,7 @@ data GitConfig = GitConfig
 	, annexHttpHeaders :: [String]
 	, annexHttpHeadersCommand :: Maybe String
 	, annexAutoCommit :: Configurable Bool
+	, annexResolveMerge :: Configurable Bool
 	, annexSyncContent :: Configurable Bool
 	, annexDebug :: Bool
 	, annexWebOptions :: [String]
@@ -115,6 +116,8 @@ extractGitConfig r = GitConfig
 	, annexHttpHeadersCommand = getmaybe (annex "http-headers-command")
 	, annexAutoCommit = configurable True $ 
 		getmaybebool (annex "autocommit")
+	, annexResolveMerge = configurable True $ 
+		getmaybebool (annex "resolvemerge")
 	, annexSyncContent = configurable False $ 
 		getmaybebool (annex "synccontent")
 	, annexDebug = getbool (annex "debug") False
diff --git a/doc/forum/controlling_how___34__git_annex_sync__34___resolves_conflicts/comment_2_c091e5a668b15aca7b2faa955beab403._comment b/doc/forum/controlling_how___34__git_annex_sync__34___resolves_conflicts/comment_2_c091e5a668b15aca7b2faa955beab403._comment
new file mode 100644
index 000000000..f254f6e7d
--- /dev/null
+++ b/doc/forum/controlling_how___34__git_annex_sync__34___resolves_conflicts/comment_2_c091e5a668b15aca7b2faa955beab403._comment
@@ -0,0 +1,8 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 2"""
+ date="2017-06-01T16:16:44Z"
+ content="""
+I've implemented the annex.automerge configuration setting, for the next
+release. There's also a `git annex sync --no-resolvemerge`
+"""]]
diff --git a/doc/git-annex-config.mdwn b/doc/git-annex-config.mdwn
index 8b505cde3..bf24251d8 100644
--- a/doc/git-annex-config.mdwn
+++ b/doc/git-annex-config.mdwn
@@ -32,6 +32,12 @@ These settings can be overridden on a per-repository basis using
   Set to false to prevent the git-annex assistant and git-annex sync
   from automatically committing changes to files in the repository.
 
+* `annex.resolvemerge`
+
+  Set to false to prevent merge conflicts being automatically resolved
+  by the git-annex assitant, git-annex sync, git-annex merge, 
+  and the git-annex post-receive hook.
+
 * `annex.synccontent`
 
   Set to true to make git-annex sync default to syncing content.
diff --git a/doc/git-annex-merge.mdwn b/doc/git-annex-merge.mdwn
index 3001e9bed..bb204d725 100644
--- a/doc/git-annex-merge.mdwn
+++ b/doc/git-annex-merge.mdwn
@@ -12,6 +12,9 @@ This performs the same merging (and merge conflict resolution)
 that is done by the sync command, but without pushing or pulling any
 data.
 
+When annex.resolvemerge is set to false, merge conflict resolution
+will not be done.
+
 # SEE ALSO
 
 [[git-annex]](1)
diff --git a/doc/git-annex-sync.mdwn b/doc/git-annex-sync.mdwn
index a27d31565..2aa009cf8 100644
--- a/doc/git-annex-sync.mdwn
+++ b/doc/git-annex-sync.mdwn
@@ -21,11 +21,6 @@ worry about the details, you can use sync.
 The content of annexed objects is not synced by default, but the --content
 option (see below) can make that also be synchronized.
 
-Merge conflicts are automatically handled 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 normally update the remote's working
 tree with changes made to the local repository. (Unless it's configured
 with receive.denyCurrentBranch=updateInstead.) However, those changes
@@ -114,6 +109,18 @@ by running "git annex sync" on the remote.
   less efficient. When --content is synced, the files are processed
   in parallel as well.
 
+* `--resolvemerge`, `--no-resolvemerge`
+
+  By default, merge conflicts are automatically handled 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.variant-A" and "foo.variant-B". (See
+  [[git-annex-resolvemerge]](1) for details.)
+
+  Use `--no-resolvemerge` to disable this automatic merge conflict
+  resolution. It can also be disabled by setting annex.resolvemerge
+  to false.
+
 # SEE ALSO
 
 [[git-annex]](1)
diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index 8a841a941..99f6c9076 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -1040,6 +1040,15 @@ Here are all the supported configuration settings.
   To configure the behavior in all clones of the repository,
   this can be set in [[git-annex-config]].
 
+* `annex.resolvemerge`
+
+  Set to false to prevent merge conflicts being automatically resolved
+  by the git-annex assitant, git-annex sync, git-annex merge,
+  and the git-annex post-receive hook.
+
+  To configure the behavior in all clones of the repository,
+  this can be set in [[git-annex-config]].
+
 * `annex.synccontent`
 
   Set to true to make git-annex sync default to syncing content.