remove direct mode remnant of merging unrelated histories

sync, merge, post-receive: Avoid merging unrelated histories, which used to
be allowed only to support direct mode repositories.

(However, sync does still merge unrelated histories when importing trees
from special remotes, and the assistant still merges unrelated histories
always.)

See 556b2ded2b for why this was added
back in 2016, for direct mode.

This is a behavior change, which might break something that was relying
on sync merging unrelated histories, but git had a good reason to
prevent it, since it's easy to foot shoot with it, and git-annex should
follow suit.

Sponsored-by: Noam Kremen on Patreon

Assistant/Sync.hs

@@ -213,7 +213,8 @@ syncAction rs a
 manualPull :: Command.Sync.CurrBranch -> [Remote] -> Assistant ([Remote], Bool)
 manualPull currentbranch remotes = do
 	g <- liftAnnex gitRepo
-	mc <- liftAnnex Command.Sync.mergeConfig
+	-- Allow merging unrelated histories.
+	mc <- liftAnnex $ Command.Sync.mergeConfig True
 	failed <- forM remotes $ \r -> if wantpull $ Remote.gitconfig r
 		then do
 			g' <- liftAnnex $ do

Assistant/Threads/Merger.hs

@@ -90,7 +90,8 @@ onChange file
 					]
 				void $ liftAnnex $ do
 					cmode <- annexCommitMode <$> Annex.getGitConfig
-					mc <- Command.Sync.mergeConfig
+					-- Allow merging unrelated histories.
+					mc <- Command.Sync.mergeConfig True
 					Command.Sync.merge
 						currbranch
 						mc

CHANGELOG

@@ -9,6 +9,11 @@ git-annex (8.20210715) UNRELEASED; urgency=medium
   * sync: When --quiet is used, run git commit, push, and pull without
     their ususual output.
   * merge: When --quiet is used, run git merge without its usual output.
+  * sync, merge, post-receive: Avoid merging unrelated histories,
+    which used to be allowed only to support direct mode repositories.
+    (However, sync does still merge unrelated histories when importing
+    trees from special remotes, and the assistant still merges unrelated
+    histories.)
 
  -- Joey Hess <id@joeyh.name>  Wed, 14 Jul 2021 14:26:36 -0400
 

Command/Merge.hs

@@ -41,14 +41,14 @@ mergeAnnexBranch = starting "merge" ai si $ do
 
 mergeSyncedBranch :: CommandStart
 mergeSyncedBranch = do
-	mc <- mergeConfig
+	mc <- mergeConfig False
 	mergeLocal mc def =<< getCurrentBranch
 
 mergeBranch :: Git.Ref -> CommandStart
 mergeBranch r = starting "merge" ai si $ do
 	currbranch <- getCurrentBranch
 	let o = def { notOnlyAnnexOption = True }
-	mc <- mergeConfig
+	mc <- mergeConfig False
 	next $ merge currbranch mc o Git.Branch.ManualCommit r
   where
 	ai = ActionItemOther (Just (Git.fromRef r))

Command/PostReceive.hs

@@ -52,5 +52,5 @@ updateInsteadEmulation :: CommandStart
 updateInsteadEmulation = do
 	prepMerge
 	let o = def { notOnlyAnnexOption = True }
-	mc <- mergeConfig
+	mc <- mergeConfig False
 	mergeLocal mc o =<< getCurrentBranch

Command/Sync.hs

@@ -218,7 +218,7 @@ seek' o = do
 			commandAction (withbranch cleanupLocal)
 			mapM_ (commandAction . withbranch . cleanupRemote) gitremotes
 		else do
-			mc <- mergeConfig
+			mc <- mergeConfig False
 
 			-- Syncing involves many actions, any of which
 			-- can independently fail, without preventing
@@ -234,7 +234,7 @@ seek' o = do
 			content <- shouldSyncContent o
 
 			forM_ (filter isImport contentremotes) $
-				withbranch . importRemote content o mc
+				withbranch . importRemote content o
 			forM_ (filter isThirdPartyPopulated contentremotes) $
 				pullThirdPartyPopulated o
 			
@@ -275,20 +275,17 @@ seek' o = do
 prepMerge :: Annex ()
 prepMerge = Annex.changeDirectory . fromRawFilePath =<< fromRepo Git.repoPath
 
-mergeConfig :: Annex [Git.Merge.MergeConfig]
-mergeConfig = do
+mergeConfig :: Bool -> Annex [Git.Merge.MergeConfig]
+mergeConfig mergeunrelated = do
 	quiet <- commandProgressDisabled
 	return $ catMaybes
 		[ Just Git.Merge.MergeNonInteractive
-		-- In several situations, unrelated histories should be
-		-- merged together. This includes pairing in the assistant,
-		-- merging from a remote into a newly created direct mode
-		-- repo, and an initial merge from an import from a special
-		-- remote. (Once direct mode is removed, this could be
-		-- changed, so only the assistant and import from special
-		-- remotes use it.)
-		, Just Git.Merge.MergeUnrelatedHistories
-		, if quiet then Just Git.Merge.MergeQuiet else Nothing
+		, if mergeunrelated 
+			then Just Git.Merge.MergeUnrelatedHistories
+			else Nothing
+		, if quiet
+			then Just Git.Merge.MergeQuiet
+			else Nothing
 		]
 
 merge :: CurrBranch -> [Git.Merge.MergeConfig] -> SyncOptions -> Git.Branch.CommitMode -> Git.Branch -> Annex Bool
@@ -483,8 +480,8 @@ pullRemote o mergeconfig remote branch = stopUnless (pure $ pullOption o && want
 	ai = ActionItemOther (Just (Remote.name remote))
 	si = SeekInput []
 
-importRemote :: Bool -> SyncOptions -> [Git.Merge.MergeConfig] -> Remote -> CurrBranch -> CommandSeek
-importRemote importcontent o mergeconfig remote currbranch
+importRemote :: Bool -> SyncOptions -> Remote -> CurrBranch -> CommandSeek
+importRemote importcontent o remote currbranch
 	| not (pullOption o) || not wantpull = noop
 	| otherwise = case remoteAnnexTrackingBranch (Remote.gitconfig remote) of
 		Nothing -> noop
@@ -497,7 +494,13 @@ importRemote importcontent o mergeconfig remote currbranch
 			if canImportKeys remote importcontent
 				then do
 					Command.Import.seekRemote remote branch subdir importcontent (CheckGitIgnore True)
-					void $ mergeRemote remote currbranch mergeconfig o
+					-- Importing generates a branch
+					-- that is not initially connected
+					-- to the current branch, so allow
+					-- merging unrelated histories when
+					-- mergeing it.
+					mc <- mergeConfig True
+					void $ mergeRemote remote currbranch mc o
 				else warning $ "Cannot import from " ++ Remote.name remote ++ " when not syncing content."
   where
 	wantpull = remoteAnnexPull (Remote.gitconfig remote)