faster union merge of multiple branches into index

only write index once

Annex/Branch.hs

@@ -139,8 +139,18 @@ update = do
 			 - from the branches.
 			 -}
 			unless (null fs) $ stageJournalFiles fs
-			mapM_ mergeref refs
 			g <- gitRepo
+			unless (null refs) $ do
+				showSideAction $ "merging " ++
+					(unwords $ map Git.refDescribe refs) ++
+					" into " ++ name
+				{- Note: This merges the branches into the index.
+				 - Any unstaged changes in the git-annex branch
+				 - (if it's checked out) will be removed. So,
+				 - documentation advises users not to directly
+				 - modify the branch.
+				 -}
+				liftIO $ Git.UnionMerge.merge_index g refs
 			liftIO $ Git.commit g "update" fullname (fullname:refs)
 			Annex.changeState $ \s -> s { Annex.branchstate = state { branchUpdated = True } }
 			invalidateCache
@@ -155,22 +165,6 @@ update = do
 				Params "--oneline -n1"
 				]
 			return $ not $ L.null diffs
-		mergeref ref = do
-			showSideAction $ "merging " ++
-				Git.refDescribe ref ++ " into " ++ name
-			{- By passing only one ref, it is actually
-			 - merged into the index, preserving any
-			 - changes that may already be staged.
-			 -
-			 - However, any changes in the git-annex
-			 - branch that are *not* reflected in the
-			 - index will be removed. So, documentation
-			 - advises users not to directly modify the
-			 - branch.
-			 -}
-			g <- gitRepo
-			liftIO $ Git.UnionMerge.merge g [ref]
-			return $ Just ref
 
 {- Checks if a git ref exists. -}
 refExists :: GitRef -> Annex Bool

Git/UnionMerge.hs

@@ -7,6 +7,7 @@
 
 module Git.UnionMerge (
 	merge,
+	merge_index,
 	update_index,
 	update_index_line,
 	ls_tree
@@ -18,24 +19,24 @@ import Data.Maybe
 import Data.String.Utils
 import qualified Data.ByteString.Lazy.Char8 as L
 
+import Common
 import Git
-import Utility.SafeCommand
 
 {- Performs a union merge between two branches, staging it in the index.
  - Any previously staged changes in the index will be lost.
  -
- - When only one branch is specified, it is merged into the index.
- - In this case, previously staged changes in the index are preserved.
- -
  - Should be run with a temporary index file configured by Git.useIndex.
  -}
-merge :: Repo -> [String] -> IO ()
-merge g (x:y:[]) = do
+merge :: Repo -> String -> String -> IO ()
+merge g x y = do
 	a <- ls_tree g x
 	b <- merge_trees g x y
 	update_index g (a++b)
-merge g [x] = merge_tree_index g x >>= update_index g
-merge _ _ = error "wrong number of branches to merge"
+
+{- Merges a list of branches into the index. Previously staged changed in
+ - the index are preserved (and participate in the merge). -}
+merge_index :: Repo -> [String] -> IO ()
+merge_index g bs = update_index g =<< concat <$> mapM (merge_tree_index g) bs
 
 {- Feeds a list into update-index. Later items in the list can override
  - earlier ones, so the list can be generated from any combination of

git-union-merge.hs

@@ -41,6 +41,6 @@ main = do
 	g <- Git.configRead =<< Git.repoFromCwd
 	_ <- Git.useIndex (tmpIndex g)
 	setup g
-	Git.UnionMerge.merge g [aref, bref]
+	Git.UnionMerge.merge g aref bref
 	Git.commit g "union merge" newref [aref, bref]
 	cleanup g