error out when another branch has been manually merged into the adjusted branch

This avoids losing the merge commit when re-running git-annex adjust in the
adjusted branch.

It also makes git-annex sync error out, rather than displaying a warning
and exiting successfully.

Sponsored-by: Leon Schuermann on Patreon

Annex/AdjustedBranch.hs

@@ -524,15 +524,12 @@ propigateAdjustedCommits'
 propigateAdjustedCommits' warnwhendiverged origbranch adj _commitsprevented =
 	inRepo (Git.Ref.sha basis) >>= \case
 		Just origsha -> catCommit currbranch >>= \case
-			Just currcommit ->
-				newcommits >>= go origsha origsha False >>= \case
-					Left e -> do
-						warning (UnquotedString e)
-						return (Nothing, return ())
-					Right newparent -> return
-						( Just newparent
-						, rebase currcommit newparent
-						)
+			Just currcommit -> do
+				newparent <- newcommits >>= go origsha origsha False
+				return
+					( Just newparent
+					, rebase currcommit newparent
+					)
 			Nothing -> return (Nothing, return ())
 		Nothing -> do
 			warning $ UnquotedString $ 
@@ -553,16 +550,14 @@ propigateAdjustedCommits' warnwhendiverged origbranch adj _commitsprevented =
 					warning $ UnquotedString $ 
 						"Original branch " ++ fromRef origbranch ++ " has diverged from current adjusted branch " ++ fromRef currbranch
 			_ -> inRepo $ Git.Branch.update' origbranch parent
-		return (Right parent)
+		return parent
 	go origsha parent pastadjcommit (sha:l) = catCommit sha >>= \case
 		Just c
 			| hasAdjustedBranchCommitMessage c ->
 				go origsha parent True l
-			| pastadjcommit ->
-				reverseAdjustedCommit parent adj (sha, c) origbranch
-					>>= \case
-						Left e -> return (Left e)
-						Right commit -> go origsha commit pastadjcommit l
+			| pastadjcommit -> do
+				commit <- reverseAdjustedCommit parent adj (sha, c) origbranch
+				go origsha commit pastadjcommit l
 		_ -> go origsha parent pastadjcommit l
 	rebase currcommit newparent = do
 		-- Reuse the current adjusted tree, and reparent it
@@ -582,10 +577,10 @@ rebaseOnTopMsg = "rebasing adjusted branch on top of updated original branch"
  - The commit message, and the author and committer metadata are
  - copied over from the basiscommit. However, any gpg signature
  - will be lost, and any other headers are not copied either. -}
-reverseAdjustedCommit :: Sha -> Adjustment -> (Sha, Commit) -> OrigBranch -> Annex (Either String Sha)
+reverseAdjustedCommit :: Sha -> Adjustment -> (Sha, Commit) -> OrigBranch -> Annex Sha
 reverseAdjustedCommit commitparent adj (csha, basiscommit) origbranch
-	| length (commitParent basiscommit) > 1 = return $
-		Left $ "unable to propagate merge commit " ++ show csha ++ " back to " ++ show origbranch
+	| length (commitParent basiscommit) > 1 = giveup $
+		"unable to propagate merge commit " ++ show csha ++ " back to " ++ show origbranch
 	| otherwise = do
 		cmode <- annexCommitMode <$> Annex.getGitConfig
 		treesha <- reverseAdjustedTree commitparent adj csha
@@ -595,7 +590,7 @@ reverseAdjustedCommit commitparent adj (csha, basiscommit) origbranch
 				Git.Branch.commitTree cmode
 					[commitMessage basiscommit]
 					[commitparent] treesha
-		return (Right revadjcommit)
+		return revadjcommit
 
 {- Adjusts the tree of the basis, changing only the files that the
  - commit changed, and reverse adjusting those changes.

CHANGELOG

@@ -16,6 +16,10 @@ git-annex (10.20250722) UNRELEASED; urgency=medium
     and display.
   * Improve behavior when there are special remotes configured with
     autoenable=yes with names that conflict with other remotes.
+  * adjust: When another branch has been manually merged into the adjusted
+    branch, re-adjusting errors out, rather than losing that merge commit.
+  * sync: When another branch has been manually merged into an adjusted
+    branch, error out rather than only displaying a warning.
   * Bump aws build dependency to 0.24.1.
   * stack.yaml: Update to lts-24.2.
 

doc/bugs/Re-Adjust_Loses_Commits/comment_2_5b9c6c1966f967ff417c2acc39cfada4._comment

@@ -0,0 +1,37 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 2"""
+ date="2025-08-20T16:34:25Z"
+ content="""
+Thanks for bumping this. It was in my backlog. I've taken a look at it now.
+
+Note that you can use the reflog to get back to the missing commits.
+
+The [[git-annex-adjust]] warns about merging into an adjusted branch. And
+suggests to use `git-annex merge` to merge a branch into an adjusted
+branch. Which avoids this problem.
+
+Probably the best thing for it to do in this situation is to fail in a way
+that leaves the adjusted branch as-is. The user can then address the
+problem, eg by resetting the adjusted branch to a point before the merge
+and doing the merge some other way.
+
+It would be difficult to handle propagating a merge commit back to the
+original branch. Usually when on an adjusted branch, any commit of annexed
+files can be assumed to have the adjustment (eg unlocking) applied to the
+files. And so reversing the adjustment will yield the desired state (eg
+locked files). But a merge commit may not be of another adjusted branch,
+it could be a non-adjusted branch. Or it could be a branch with a different
+adjustment applied to it. Reversing the adjustment would then do the wrong
+thing.
+
+Consider for example, if the --unlock adjustment were used. But then a
+branch adjusted with --hide-missing were merged in. This is basically
+indistingushable from merging in a branch where some unwanted annexed file
+is removed.
+
+Also, it looks at the diff of changes made in a commit to know which
+annexed files were changed and reverse adjusts those files. In a merge
+commit, it's not clear which of the multiple parents it should diff
+against.
+"""]]

doc/git-annex-adjust.mdwn

@@ -21,7 +21,7 @@ to a public branch with commands like `git-annex unlock`.
 
 While in the adjusted branch, you can use git-annex and git commands as
 usual. Any commits that you make will initially only be made to the
-adjusted branch. 
+adjusted branch.
 
 To propagate commits from the adjusted branch back to the original branch,
 and to other repositories, as well as to merge in changes from other
@@ -31,8 +31,9 @@ made by this command.
 
 When in an adjusted branch, using `git merge otherbranch` is often not
 ideal, because merging a non-adjusted branch may lead to unnecessary
-merge conflicts, or add files in non-adjusted form. To avoid those
-problems, use `git annex merge otherbranch`.
+merge conflicts, or add files in non-adjusted form. And such merges
+cannot be propagated from the adjusted branch back to the original branch.
+To avoid those problems, use `git annex merge otherbranch`.
 
 Re-running this command with the same options
 while inside the adjusted branch will update the adjusted branch