disable journal read optimisation when alwayscommit=false

The journal read optimisation in aeca7c220 later got fixed in eedd73b84
to stage and commit any files that were left in the journal by a
previous git-annex run. That's necessary for the optimisation to work
correctly. But it also meant that alwayscommit=false started committing
the previous git-annex processes journalled changes, which defeated the
purpose of the config setting entirely.

So, disable the optimisation when alwayscommit=false, leaving the
files in the journal and not committing them. See my comments on the bug
report for why this seemed the best approach.

Also fixes a problem when annex.merge-annex-branches=false and there
are changes in the journal. That config indirectly prevents committing
the journal. (Which seems a bit odd given its name, but it always has..)
So, when there were changes in the journal, perhaps left there due to
alwayscommit=false being set before, the optimisation would prevent
git-annex from reading the journal files, and it would operate with out
of date information.

Annex/Branch.hs

@@ -1,6 +1,6 @@
 {- management of the git-annex branch
  -
- - Copyright 2011-2019 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -14,6 +14,7 @@ module Annex.Branch (
 	hasSibling,
 	siblingBranches,
 	create,
+	UpdateMade(..),
 	update,
 	forceUpdate,
 	updateTo,
@@ -125,12 +126,17 @@ getBranch = maybe (hasOrigin >>= go >>= use) return =<< branchsha
 {- Ensures that the branch and index are up-to-date; should be
  - called before data is read from it. Runs only once per git-annex run. -}
 update :: Annex BranchState
-update = runUpdateOnce $ void $ updateTo =<< siblingBranches
+update = runUpdateOnce $ journalClean <$$> updateTo =<< siblingBranches
 
 {- Forces an update even if one has already been run. -}
-forceUpdate :: Annex Bool
+forceUpdate :: Annex UpdateMade
 forceUpdate = updateTo =<< siblingBranches
 
+data UpdateMade = UpdateMade
+	{ refsWereMerged :: Bool
+	, journalClean :: Bool
+	}
+
 {- Merges the specified Refs into the index, if they have any changes not
  - already in it. The Branch names are only used in the commit message;
  - it's even possible that the provided Branches have not been updated to
@@ -149,13 +155,13 @@ forceUpdate = updateTo =<< siblingBranches
  -
  - Returns True if any refs were merged in, False otherwise.
  -}
-updateTo :: [(Git.Sha, Git.Branch)] -> Annex Bool
+updateTo :: [(Git.Sha, Git.Branch)] -> Annex UpdateMade
 updateTo pairs = ifM (annexMergeAnnexBranches <$> Annex.getGitConfig)
 	( updateTo' pairs
-	, return False
+	, return (UpdateMade False False)
 	)
 
-updateTo' :: [(Git.Sha, Git.Branch)] -> Annex Bool
+updateTo' :: [(Git.Sha, Git.Branch)] -> Annex UpdateMade
 updateTo' pairs = do
 	-- ensure branch exists, and get its current ref
 	branchref <- getBranch
@@ -167,7 +173,7 @@ updateTo' pairs = do
 		else do
 			mergedrefs <- getMergedRefs
 			filterM isnewer (excludeset mergedrefs unignoredrefs)
-	if null tomerge
+	journalclean <- if null tomerge
 		{- Even when no refs need to be merged, the index
 		 - may still be updated if the branch has gotten ahead 
 		 - of the index, or just if the journal is dirty. -}
@@ -179,11 +185,23 @@ updateTo' pairs = do
 				 - a commit needs to be done. -}
 				when dirty $
 					go branchref dirty [] jl
-			, when dirty $
-				lockJournal $ go branchref dirty []
+				return True
+			, if dirty
+				then ifM (annexAlwaysCommit <$> Annex.getGitConfig)
+					( do
+						lockJournal $ go branchref dirty []
+						return True
+					, return False
+					)
+				else return True
 			)
-		else lockJournal $ go branchref dirty tomerge
-	return $ not $ null tomerge
+		else do
+			lockJournal $ go branchref dirty tomerge
+			return True
+	return $ UpdateMade
+		{ refsWereMerged = not (null tomerge)
+		, journalClean = journalclean
+		}
   where
 	excludeset s = filter (\(r, _) -> S.notMember r s)
 	isnewer (r, _) = inRepo $ Git.Branch.changed fullname r

Annex/BranchState.hs

@@ -28,26 +28,24 @@ checkIndexOnce a = unlessM (indexChecked <$> getState) $ do
 	changeState $ \s -> s { indexChecked = True }
 
 {- Runs an action to update the branch, if it's not been updated before
- - in this run of git-annex. -}
-runUpdateOnce :: Annex () -> Annex BranchState
+ - in this run of git-annex. 
+ -
+ - The action should return True if anything that was in the journal
+ - before got staged (or if the journal was empty). That lets an opmisation
+ - be done: The journal then does not need to be checked going forward,
+ - until new information gets written to it.
+ -}
+runUpdateOnce :: Annex Bool -> Annex BranchState
 runUpdateOnce a = do
 	st <- getState
 	if branchUpdated st
 		then return st
 		else do
-			a
+			journalstaged <- a
 			let stf = \st' -> st'
 				{ branchUpdated = True
-				-- The update staged anything that was
-				-- journalled before, so the journal
-				-- does not need to be checked going
-				-- forward, unless new information
-				-- gets written to it, or unless
-				-- this run of git-annex needs to notice
-				-- changes journalled by other processes
-				-- while it's running.
-				, journalIgnorable = not $
-					journalNeverIgnorable st'
+				, journalIgnorable = journalstaged 
+					&& not (journalNeverIgnorable st')
 				}
 			changeState stf
 			return (stf st)

Assistant/Sync.hs

@@ -216,7 +216,8 @@ manualPull currentbranch remotes = do
 				, return $ Just r
 				)
 		else return Nothing
-	haddiverged <- liftAnnex Annex.Branch.forceUpdate
+	haddiverged <- Annex.Branch.refsWereMerged
+		<$> liftAnnex Annex.Branch.forceUpdate
 	forM_ remotes $ \r ->
 		liftAnnex $ Command.Sync.mergeRemote r
 			currentbranch Command.Sync.mergeConfig def

Assistant/Threads/Merger.hs

@@ -65,7 +65,8 @@ onChange file
 	| ".lock" `isSuffixOf` file = noop
 	| isAnnexBranch file = do
 		branchChanged
-		diverged <- liftAnnex Annex.Branch.forceUpdate
+		diverged <- Annex.Branch.refsWereMerged
+			<$> liftAnnex Annex.Branch.forceUpdate
 		when diverged $ do
 			updateExportTreeFromLogAll
 			queueDeferredDownloads "retrying deferred download" Later

doc/bugs/commits_created_despite_alwayscommit__61__false_as_of_recent_change.mdwn

@@ -91,3 +91,5 @@ index 712c5c10f..f248b3eb4 100644
 [[!tag projects/datalad]]
 
 [0]: https://github.com/datalad/datalad-extensions/pull/9
+
+> [[fixed|done]] --[[Joey]]