fix master push overwrite race when updating adjusted branch, by maintaining basis ref
This commit is contained in:
Joey Hess
parent
f0ddc0a75c
commit
7d28110c68
2 changed files with 95 additions and 57 deletions
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@ -100,6 +100,17 @@ adjustTreeItem ShowMissingAdjustment ti = return (Just ti)
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type OrigBranch = Branch
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type AdjBranch = Branch
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-- This is a hidden branch ref, that's used as the basis for the AdjBranch,
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-- since pushes can overwrite the OrigBranch at any time. So, changes
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-- are propigated from the AdjBranch to the head of the BasisBranch.
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newtype BasisBranch = BasisBranch Ref
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-- The basis for refs/heads/adjusted/master(unlocked) is
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-- refs/adjusted/master(unlocked).
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basisBranch :: AdjBranch -> BasisBranch
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basisBranch adjbranch = BasisBranch $
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Ref ("refs/" ++ fromRef (Git.Ref.base adjbranch))
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adjustedBranchPrefix :: String
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adjustedBranchPrefix = "refs/heads/adjusted/"
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@ -135,7 +146,7 @@ adjustedToOriginal b
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getAdjustment :: Branch -> Maybe Adjustment
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getAdjustment = fmap fst . adjustedToOriginal
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fromAdjustedBranch :: Branch -> OrigBranch
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fromAdjustedBranch :: AdjBranch -> OrigBranch
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fromAdjustedBranch b = maybe b snd (adjustedToOriginal b)
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originalBranch :: Annex (Maybe OrigBranch)
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@ -143,7 +154,7 @@ originalBranch = fmap fromAdjustedBranch <$> inRepo Git.Branch.current
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{- Enter an adjusted version of current branch (or, if already in an
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- adjusted version of a branch, changes the adjustment of the original
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t a- branch).
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- branch).
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-
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- Can fail, if no branch is checked out, or perhaps if staged changes
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- conflict with the adjusted branch.
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@ -173,23 +184,30 @@ adjustToCrippledFileSystem = do
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]
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enterAdjustedBranch UnlockAdjustment
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updateBasisBranch :: BasisBranch -> Ref -> Annex ()
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updateBasisBranch (BasisBranch basis) new =
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inRepo $ Git.Branch.update' basis new
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adjustBranch :: Adjustment -> OrigBranch -> Annex AdjBranch
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adjustBranch adj origbranch = do
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sha <- adjust adj origbranch
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-- Start basis off with the current value of the origbranch.
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updateBasisBranch basis origbranch
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sha <- adjustCommit adj basis
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inRepo $ Git.Branch.update "entering adjusted branch" adjbranch sha
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return adjbranch
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where
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adjbranch = originalToAdjusted origbranch adj
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basis = basisBranch adjbranch
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adjust :: Adjustment -> Ref -> Annex Sha
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adjust adj orig = do
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treesha <- adjustTree adj orig
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commitAdjustedTree treesha orig
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adjustCommit :: Adjustment -> BasisBranch -> Annex Sha
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adjustCommit adj basis = do
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treesha <- adjustTree adj basis
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commitAdjustedTree treesha basis
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adjustTree :: Adjustment -> Ref -> Annex Sha
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adjustTree adj orig = do
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adjustTree :: Adjustment -> BasisBranch -> Annex Sha
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adjustTree adj (BasisBranch basis) = do
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let toadj = adjustTreeItem adj
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treesha <- Git.Tree.adjustTree toadj [] [] orig =<< Annex.gitRepo
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treesha <- Git.Tree.adjustTree toadj [] [] basis =<< Annex.gitRepo
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return treesha
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type CommitsPrevented = Git.LockFile.LockHandle
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@ -213,11 +231,13 @@ preventCommits = bracket setup cleanup
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- clones of a repo, at different times. The commit message and other
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- metadata is based on the parent.
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-}
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commitAdjustedTree :: Sha -> Ref -> Annex Sha
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commitAdjustedTree treesha parent = commitAdjustedTree' treesha parent [parent]
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commitAdjustedTree :: Sha -> BasisBranch -> Annex Sha
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commitAdjustedTree treesha parent@(BasisBranch b) =
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commitAdjustedTree' treesha parent [b]
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commitAdjustedTree' :: Sha -> Ref -> [Ref] -> Annex Sha
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commitAdjustedTree' treesha basis parents = go =<< catCommit basis
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commitAdjustedTree' :: Sha -> BasisBranch -> [Ref] -> Annex Sha
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commitAdjustedTree' treesha (BasisBranch basis) parents =
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go =<< catCommit basis
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where
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go Nothing = inRepo mkcommit
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go (Just basiscommit) = inRepo $ commitWithMetaData
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@ -238,10 +258,15 @@ updateAdjustedBranch tomerge (origbranch, adj) commitmode = catchBoolIO $
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join $ preventCommits $ \commitsprevented ->
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go commitsprevented =<< inRepo Git.Branch.current
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where
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adjbranch = originalToAdjusted origbranch adj
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basis = basisBranch adjbranch
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go commitsprevented (Just currbranch) =
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ifM (inRepo $ Git.Branch.changed currbranch tomerge)
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( do
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(updatedorig, _) <- propigateAdjustedCommits' origbranch (adj, currbranch) commitsprevented
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(updatedorig, _) <- propigateAdjustedCommits'
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origbranch (adj, currbranch)
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commitsprevented
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changestomerge updatedorig currbranch
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, nochangestomerge
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)
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@ -255,7 +280,7 @@ updateAdjustedBranch tomerge (origbranch, adj) commitmode = catchBoolIO $
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- updatedorig. The result of the merge can the be
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- adjusted to yield the final adjusted branch.
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-
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- In order to do a merge into a branch that is not checked out,
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- In order to do a merge into a ref that is not checked out,
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- set the work tree to a temp directory, and set GIT_DIR
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- to another temp directory, in which HEAD contains the
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- updatedorig sha. GIT_COMMON_DIR is set to point to the real
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@ -293,21 +318,23 @@ updateAdjustedBranch tomerge (origbranch, adj) commitmode = catchBoolIO $
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createDirectoryIfMissing True d
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cleanup _ = removeDirectoryRecursive d
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{- A merge commit has been made between the origbranch and
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- tomerge. Update origbranch to point to that commit, adjust
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- it to get the new adjusted branch, and check it out.
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{- A merge commit has been made between the basisbranch and
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- tomerge. Update the basisbranch and origbranch to point
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- to that commit, adjust it to get the new adjusted branch,
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- and check it out.
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-
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- But, there may be unstaged work tree changes that conflict,
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- so the check out is done by making a normal merge of
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- the new adjusted branch.
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-}
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postmerge currbranch (Just mergecommit) = do
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inRepo $ Git.Branch.update "updating original branch" origbranch mergecommit
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adjtree <- adjustTree adj mergecommit
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adjmergecommit <- commitAdjustedTree adjtree mergecommit
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updateBasisBranch basis mergecommit
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inRepo $ Git.Branch.update' origbranch mergecommit
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adjtree <- adjustTree adj (BasisBranch mergecommit)
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adjmergecommit <- commitAdjustedTree adjtree (BasisBranch mergecommit)
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-- Make currbranch be the parent, so that merging
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-- this commit will be a fast-forward.
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adjmergecommitff <- commitAdjustedTree' adjtree mergecommit [currbranch]
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adjmergecommitff <- commitAdjustedTree' adjtree (BasisBranch mergecommit) [currbranch]
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showAction "Merging into adjusted branch"
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ifM (autoMergeFrom adjmergecommitff (Just currbranch) commitmode)
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( reparent currbranch adjtree adjmergecommit =<< getcurrentcommit
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@ -337,25 +364,26 @@ updateAdjustedBranch tomerge (origbranch, adj) commitmode = catchBoolIO $
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Just c -> catCommit c
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{- Check for any commits present on the adjusted branch that have not yet
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- been propigated to the orig branch, and propigate them.
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- been propigated to the basis branch, and propigate them to the basis
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- branch and from there on to the orig branch.
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-
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- After propigating the commits back to the orig banch,
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- rebase the adjusted branch on top of the updated orig branch.
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- After propigating the commits back to the basis banch,
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- rebase the adjusted branch on top of the updated basis branch.
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-}
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propigateAdjustedCommits :: OrigBranch -> (Adjustment, AdjBranch) -> Annex ()
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propigateAdjustedCommits origbranch (adj, currbranch) =
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preventCommits $ \commitsprevented ->
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join $ snd <$> propigateAdjustedCommits' origbranch (adj, currbranch) commitsprevented
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{- Returns sha of updated orig branch, and action which will rebase
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- the adjusted branch on top of the updated orig branch. -}
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{- Returns sha of updated basis branch, and action which will rebase
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- the adjusted branch on top of the updated basis branch. -}
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propigateAdjustedCommits'
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:: OrigBranch
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-> (Adjustment, AdjBranch)
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-> CommitsPrevented
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-> Annex (Maybe Sha, Annex ())
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propigateAdjustedCommits' origbranch (adj, currbranch) _commitsprevented = do
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ov <- inRepo $ Git.Ref.sha (Git.Ref.under "refs/heads" origbranch)
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ov <- inRepo $ Git.Ref.sha basis
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case ov of
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Just origsha -> do
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cv <- catCommit currbranch
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@ -373,12 +401,15 @@ propigateAdjustedCommits' origbranch (adj, currbranch) _commitsprevented = do
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Nothing -> return (Nothing, return ())
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Nothing -> return (Nothing, return ())
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where
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newcommits = inRepo $ Git.Branch.changedCommits origbranch currbranch
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(BasisBranch basis) = basisBranch adjbranch
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adjbranch = originalToAdjusted origbranch adj
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newcommits = inRepo $ Git.Branch.changedCommits basis currbranch
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-- Get commits oldest first, so they can be processed
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-- in order made.
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[Param "--reverse"]
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go parent _ [] = do
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inRepo $ Git.Branch.update "updating adjusted branch" origbranch parent
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updateBasisBranch (BasisBranch basis) parent
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inRepo $ Git.Branch.update' origbranch parent
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return (Right parent)
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go parent pastadjcommit (sha:l) = do
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mc <- catCommit sha
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@ -393,10 +424,9 @@ propigateAdjustedCommits' origbranch (adj, currbranch) _commitsprevented = do
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Right commit -> go commit pastadjcommit l
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_ -> go parent pastadjcommit l
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rebase currcommit newparent = do
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-- Reuse the current adjusted tree,
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-- and reparent it on top of the new
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-- version of the origbranch.
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commitAdjustedTree (commitTree currcommit) newparent
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-- Reuse the current adjusted tree, and reparent it
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-- on top of the newparent.
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commitAdjustedTree (commitTree currcommit) (BasisBranch newparent)
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>>= inRepo . Git.Branch.update rebaseOnTopMsg currbranch
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rebaseOnTopMsg :: String
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@ -462,14 +492,18 @@ diffTreeToTreeItem dti = TreeItem
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{- Cloning a repository that has an adjusted branch checked out will
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- result in the clone having the same adjusted branch checked out -- but
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- the origbranch won't exist in the clone. Create the origbranch. -}
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- the origbranch won't exist in the clone, nor will the basis.
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- Create them. -}
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checkAdjustedClone :: Annex ()
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checkAdjustedClone = go =<< inRepo Git.Branch.current
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where
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go Nothing = return ()
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go (Just currbranch) = case adjustedToOriginal currbranch of
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Nothing -> return ()
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Just (_adj, origbranch) ->
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unlessM (inRepo $ Git.Ref.exists origbranch) $ do
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let remotebranch = Git.Ref.underBase "refs/remotes/origin" origbranch
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Just (adj, origbranch) -> do
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let remotebranch = Git.Ref.underBase "refs/remotes/origin" origbranch
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let basis@(BasisBranch bb) = basisBranch (originalToAdjusted origbranch adj)
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unlessM (inRepo $ Git.Ref.exists bb) $
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updateBasisBranch basis remotebranch
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unlessM (inRepo $ Git.Ref.exists origbranch) $
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inRepo $ Git.Branch.update' origbranch remotebranch
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@ -256,6 +256,28 @@ in [[todo/deferred_update_mode]]. Arguably, it's just as confusing for the
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file to remain visible but have its content temporarily replaced with a
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annex pointer.
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### master push overwrite race (fixed)
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There are potentially races in code that assumes a branch like
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master is not being changed by someone else.
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In particular, if propigateAdjustedCommits rebases the adjusted branch on
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top of master. That is called by sync. The assumption is that any changes
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in master have already been handled by updateAdjustedBranch. But, if
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another remote pushed a new master at just the right time, the adjusted
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branch could be rebased on top of a master that it doesn't incorporate,
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which is wrong.
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Best fix seems to be to maintain a basis ref, that is not a branch,
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like refs/adjusted/master(unlocked). Copy master's ref to it when
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entering the view branch. Then, make all adjustments via the basis
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ref, and propigate back to refs/heads/master.
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It's fine to overwrite changes that were pushed to master when
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propigating from the adjusted branch. Synced changes also go to
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synced/master so won't be lost. Pushes not made using git-annex sync
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of master are not really desired, just a possibility.
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## integration with view branches
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Entering a view from an adjusted branch should probably carry the adjusting
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@ -279,21 +301,3 @@ into adjusted view worktrees.]
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will make copies of the content of annexed files, so this would need
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to checkout the adjusted branch some other way. Maybe generalize so this
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more efficient checkout is available as a git-annex command?
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* There are potentially races in code that assumes a branch like
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master is not being changed by someone else.
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In particular, propigateAdjustedCommits rebases the adjusted branch on
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top of master. That is called by sync. The assumption is that any changes
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in master have already been handled by updateAdjustedBranch. But, if
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another remote pushed a new master at just the right time, the adjusted
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branch could be rebased on top of a master that it doesn't incorporate,
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which is wrong.
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Best fix seems to be to use a hidden ref, like refs/annex/adjusted/master
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and copy master's ref to it when entering the view branch. Then, make
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all adjustments via that ref, and propigate back to refs/heads/master.
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It's fine to overwrite changes that were pushed to master when
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propigating from the adjusted branch. Synced changes also go to
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synced/master so won't be lost. Pushes not made using git-annex sync
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of master are not really desired, just a possibility.
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