merge git-annex branch in memory in read-only repository

Improved support for using git-annex in a read-only repository, git-annex
branch information from remotes that cannot be merged into the git-annex
branch will now not crash it, but will be merged in memory.

To avoid this making git-annex behave one way in a read-only repository,
and another way when it can write, it's important that Annex.Branch.get
return the same thing (modulo log file compaction) in both cases.

This manages that mostly. There are some exceptions:

- When there is a transition in one of the remote git-annex branches
  that has not yet been applied to the local or other git-annex branches.
  Transitions are not handled.
- `git-annex log` runs git log on the git-annex branch, and so
  it will not be able to show information coming from the other, not yet
  merged branches.
- Annex.Branch.files only looks at files in the git-annex branch and not
  unmerged branches. This affects git-annex info output.
- Annex.Branch.hs.overBranchFileContents ditto. Affects --all and
  also importfeed (but importfeed cannot work in a read-only repo
  anyway).
- CmdLine.Seek.seekFilteredKeys when precaching location logs.
  Note use of Annex.Branch.fullname
- Database.ContentIdentifier.needsUpdateFromLog and updateFromLog

These warts make this not suitable to be merged yet.

This readonly code path is more expensive, since it has to query several
branches. The value does get cached, but still large queries will be
slower in a read-only repository when there are unmerged git-annex
branches.

When annex.merge-annex-branches=false, updateTo skips doing anything,
and so the read-only repository code does not get triggered. So a user who
is bothered by the extra work can set that.

Other writes to the repository can still result in permissions errors.
This includes the initial creation of the git-annex branch, and of course
any writes to the git-annex branch.

Sponsored-by: Dartmouth College's Datalad project

Annex/Branch.hs

@@ -141,17 +141,12 @@ 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 $ journalClean <$$> updateTo =<< siblingBranches
+update = runUpdateOnce $ updateTo =<< siblingBranches
 
 {- Forces an update even if one has already been run. -}
 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
@@ -167,8 +162,6 @@ data UpdateMade = UpdateMade
  -
  - Also handles performing any Transitions that have not yet been
  - performed, in either the local branch, or the Refs.
- -
- - Returns True if any refs were merged in, False otherwise.
  -}
 updateTo :: [(Git.Sha, Git.Branch)] -> Annex UpdateMade
 updateTo pairs = ifM (annexMergeAnnexBranches <$> Annex.getGitConfig)
@@ -180,7 +173,6 @@ updateTo' :: [(Git.Sha, Git.Branch)] -> Annex UpdateMade
 updateTo' pairs = do
 	-- ensure branch exists, and get its current ref
 	branchref <- getBranch
-	dirty <- journalDirty gitAnnexJournalDir
 	ignoredrefs <- getIgnoredRefs
 	let unignoredrefs = excludeset ignoredrefs pairs
 	tomerge <- if null unignoredrefs
@@ -188,42 +180,50 @@ updateTo' pairs = do
 		else do
 			mergedrefs <- getMergedRefs
 			filterM isnewer (excludeset mergedrefs unignoredrefs)
-	journalcleaned <- if null tomerge
+	{- In a read-only repository, catching permission denied lets
-		{- Even when no refs need to be merged, the index
+	 - query operations still work, although they will need to do
-		 - may still be updated if the branch has gotten ahead 
+	 - additional work since the refs are not merged. -}
-		 - of the index, or just if the journal is dirty. -}
+	catchPermissionDenied
-		then ifM (needUpdateIndex branchref)
+		(const (return (UpdateFailedPermissions (branchref : map fst tomerge))))
-			( lockJournal $ \jl -> do
+		(go branchref tomerge)
-				forceUpdateIndex jl branchref
-				{- When there are journalled changes
-				 - as well as the branch being updated,
-				 - a commit needs to be done. -}
-				when dirty $
-					go branchref dirty [] jl
-				return True
-			, if dirty
-				then ifM (annexAlwaysCommit <$> Annex.getGitConfig)
-					( do
-						lockJournal $ go branchref dirty []
-						return True
-					, return False
-					)
-				else return True
-			)
-		else do
-			lockJournal $ go branchref dirty tomerge
-			return True
-	journalclean <- if journalcleaned
-		then not <$> privateUUIDsKnown
-		else pure False
-	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
-	go branchref dirty tomerge jl = stagejournalwhen dirty jl $ do
+	go branchref tomerge = do
+		dirty <- journalDirty gitAnnexJournalDir
+		journalcleaned <- 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. -}
+			then ifM (needUpdateIndex branchref)
+				( lockJournal $ \jl -> do
+					forceUpdateIndex jl branchref
+					{- When there are journalled changes
+					 - as well as the branch being updated,
+					 - a commit needs to be done. -}
+					when dirty $
+						go' branchref dirty [] jl
+					return True
+				, if dirty
+					then ifM (annexAlwaysCommit <$> Annex.getGitConfig)
+						( lockJournal $ \jl -> do
+							go' branchref dirty [] jl
+							return True
+						, return False
+						)
+					else return True
+				)
+			else lockJournal $ \jl -> do
+				go' branchref dirty tomerge jl
+				return True
+		journalclean <- if journalcleaned
+			then not <$> privateUUIDsKnown
+			else pure False
+		return $ UpdateMade
+			{ refsWereMerged = not (null tomerge)
+			, journalClean = journalclean 
+			}
+	go' branchref dirty tomerge jl = stagejournalwhen dirty jl $ do
 		let (refs, branches) = unzip tomerge
 		merge_desc <- if null tomerge
 			then commitMessage
@@ -254,22 +254,33 @@ updateTo' pairs = do
 		| otherwise = withIndex a
 
 {- Gets the content of a file, which may be in the journal, or in the index
- - (and committed to the branch).
+ - (and committed to the branch). 
+ -
+ - Returns an empty string if the file doesn't exist yet.
  - 
  - Updates the branch if necessary, to ensure the most up-to-date available
- - content is returned.
+ - content is returned. When permissions prevent updating the branch,
- -
+ - reads the content from the journal, plus the branch, plus all unmerged
- - Returns an empty string if the file doesn't exist yet. -}
+ - refs.
+ -}
 get :: RawFilePath -> Annex L.ByteString
-get file = getCache file >>= \case
+get file = do
-	Just content -> return content
+	st <- update
-	Nothing -> do
+	case getCache file st of
-		st <- update
+		Just content -> return content
-		content <- if journalIgnorable st
+		Nothing -> do
-			then getRef fullname file
+			content <- if journalIgnorable st
-			else getLocal file
+				then getRef fullname file
-		setCache file content
+				else if null (unmergedRefs st) 
-		return content
+					then getLocal file
+					else unmergedbranchfallback (unmergedRefs st)
+			setCache file content
+			return content
+  where
+	unmergedbranchfallback refs = do
+		l <- getLocal file
+		bs <- forM refs $ \ref -> getRef ref file
+		return (l <> mconcat bs)
 
 {- Used to cache the value of a file, which has been read from the branch
  - using some optimised method. The journal has to be checked, in case
@@ -285,7 +296,7 @@ precache file branchcontent = do
 			JournalledContent journalcontent -> journalcontent
 			PossiblyStaleJournalledContent journalcontent ->
 				branchcontent <> journalcontent
-	Annex.BranchState.setCache file content
+	setCache file content
 
 {- Like get, but does not merge the branch, so the info returned may not
  - reflect changes in remotes.
@@ -452,7 +463,7 @@ commitIndex' jl branchref message basemessage retrynum parents = do
 
 {- Lists all files on the branch. including ones in the journal
  - that have not been committed yet. There may be duplicates in the list. -}
-files :: Annex ([RawFilePath], IO Bool)
+tfiles :: Annex ([RawFilePath], IO Bool)
 files = do
 	_  <- update
 	(bfs, cleanup) <- branchFiles

Annex/BranchState.hs

@@ -2,7 +2,7 @@
  -
  - Runtime state about the git-annex branch, and a small cache.
  -
- - Copyright 2011-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -13,6 +13,7 @@ import Annex.Common
 import Types.BranchState
 import qualified Annex
 import Logs
+import qualified Git
 
 import qualified Data.ByteString.Lazy as L
 
@@ -30,29 +31,47 @@ checkIndexOnce a = unlessM (indexChecked <$> getState) $ do
 	a
 	changeState $ \s -> s { indexChecked = True }
 
+data UpdateMade 
+	= UpdateMade
+		{ refsWereMerged :: Bool
+		, journalClean :: Bool
+		}
+	| UpdateFailedPermissions
+		{ refsUnmerged :: [Git.Sha]
+		}
+
 {- Runs an action to update the branch, if it's not been updated before
  - 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.
- -
  - When interactive access is enabled, the journal is always checked when
  - reading values from the branch, and so this does not need to update
  - the branch.
+ -
+ - When the action leaves the journal clean, by staging anything that
+ - was in it, an optimisation is enabled: The journal does not need to
+ - be checked going forward, until new information gets written to it.
+ -
+ - When the action is unable to update the branch due to a permissions
+ - problem, 
  -}
-runUpdateOnce :: Annex Bool -> Annex BranchState
+runUpdateOnce :: Annex UpdateMade -> Annex BranchState
-runUpdateOnce a = do
+runUpdateOnce update = do
 	st <- getState
 	if branchUpdated st || needInteractiveAccess st
 		then return st
 		else do
-			journalstaged <- a
+			um <- update
-			let stf = \st' -> st'
+			let stf = case um of
-				{ branchUpdated = True
+				UpdateMade {} -> \st' -> st'
-				, journalIgnorable = journalstaged 
+					{ branchUpdated = True
-				}
+					, journalIgnorable = journalClean um
+					}
+				UpdateFailedPermissions {} -> \st' -> st'
+					{ branchUpdated = True
+					, journalIgnorable = False
+					, unmergedRefs = refsUnmerged um
+					, cachedFileContents = []
+					}
 			changeState stf
 			return (stf st)
 
@@ -98,13 +117,13 @@ setCache file content = changeState $ \s -> s
 		| length l < logFilesToCache = (file, content) : l
 		| otherwise = (file, content) : Prelude.init l
 
-getCache :: RawFilePath -> Annex (Maybe L.ByteString)
+getCache :: RawFilePath -> BranchState -> Maybe L.ByteString
-getCache file = (\st -> go (cachedFileContents st) st) <$> getState
+getCache file state = go (cachedFileContents state)
   where
-	go [] _ = Nothing
+	go [] = Nothing
-	go ((f,c):rest) state
+	go ((f,c):rest)
 		| f == file && not (needInteractiveAccess state) = Just c
-		| otherwise = go rest state
+		| otherwise = go rest
 
 invalidateCache :: Annex ()
 invalidateCache = changeState $ \s -> s { cachedFileContents = [] }

Assistant/Sync.hs

@@ -225,8 +225,9 @@ manualPull currentbranch remotes = do
 				, return $ Just r
 				)
 		else return Nothing
-	haddiverged <- Annex.Branch.refsWereMerged
+	haddiverged <- liftAnnex Annex.Branch.forceUpdate >>= return . \case
-		<$> liftAnnex Annex.Branch.forceUpdate
+		u@(Annex.Branch.UpdateMade {}) -> Annex.Branch.refsWereMerged u
+		(Annex.Branch.UpdateFailedPermissions {}) -> True
 	forM_ remotes $ \r ->
 		liftAnnex $ Command.Sync.mergeRemote r
 			currentbranch mc def

Assistant/Threads/Merger.hs

@@ -70,8 +70,9 @@ onChange file
 	| ".lock" `isSuffixOf` file = noop
 	| isAnnexBranch file = do
 		branchChanged
-		diverged <- Annex.Branch.refsWereMerged
+		diverged <- liftAnnex Annex.Branch.forceUpdate >>= return . \case
-			<$> liftAnnex Annex.Branch.forceUpdate
+			u@(Annex.Branch.UpdateMade {}) -> Annex.Branch.refsWereMerged u
+			(Annex.Branch.UpdateFailedPermissions {}) -> True
 		when diverged $ do
 			updateExportTreeFromLogAll
 			queueDeferredDownloads "retrying deferred download" Later

CHANGELOG

@@ -17,6 +17,10 @@ git-annex (8.20211124) UNRELEASED; urgency=medium
   * sync: Better error message when unable to export to a remote because
     remote.name.annex-tracking-branch is configured to a ref that does not
     exist.
+  * Improved support for using git-annex in a read-only repository,
+    git-annex branch information from remotes that cannot be merged into
+    the git-annex branch will now not crash it, but will be merged in
+    memory.
 
  -- Joey Hess <id@joeyh.name>  Tue, 23 Nov 2021 15:58:27 -0400
 

Types/BranchState.hs

@@ -1,6 +1,6 @@
 {- git-annex BranchState data type
  -
- - Copyright 2011-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -8,17 +8,23 @@
 module Types.BranchState where
 
 import Common
+import qualified Git
 
 import qualified Data.ByteString.Lazy as L
 
 data BranchState = BranchState
 	{ branchUpdated :: Bool
-	-- ^ has the branch been updated this run?
+	-- ^ has the branch been updated this run? (Or an update tried and
+	-- failed due to permissions.)
 	, indexChecked :: Bool
 	-- ^ has the index file been checked to exist?
 	, journalIgnorable :: Bool
 	-- ^ can reading the journal be skipped, while still getting
 	-- sufficiently up-to-date information from the branch?
+	, unmergedRefs :: [Git.Sha]
+	-- ^ when the branch was not able to be updated due to permissions,
+	-- these other git refs contain unmerged information and need to be
+	-- queried, along with the index and the journal.
 	, cachedFileContents :: [(RawFilePath, L.ByteString)]
 	-- ^ contents of a few files recently read from the branch
 	, needInteractiveAccess :: Bool
@@ -29,4 +35,4 @@ data BranchState = BranchState
 	}
 
 startBranchState :: BranchState
-startBranchState = BranchState False False False [] False
+startBranchState = BranchState False False False [] [] False