Avoid using git commit in direct mode, since in some situations it will read the full contents of files in the tree.

The assistant's commit code also always avoids git commit, for simplicity.
Indirect mode sync still does a git commit -a to catch unstaged changes.

Note that this means that direct mode sync no longer runs the pre-commit
hook or any other hooks git commit might call. The git annex pre-commit
hook action for direct mode is however explicitly run. (The assistant
already ran git commit with hooks disabled, so no change there.)

2 files changed, 34 insertions, 8 deletions

diff --git a/Git/Branch.hs b/Git/Branch.hs
index 7b3297d74..405fa108f 100644
--- a/Git/Branch.hs
+++ b/Git/Branch.hs
@@ -89,18 +89,38 @@ fastForward branch (first:rest) repo =
 			(False, False) -> findbest c rs -- same
 
 {- Commits the index into the specified branch (or other ref), 
- - with the specified parent refs, and returns the committed sha -}
-commit :: String -> Branch -> [Ref] -> Repo -> IO Sha
-commit message branch parentrefs repo = do
+ - with the specified parent refs, and returns the committed sha.
+ -
+ - Without allowempy set, avoids making a commit if there is exactly
+ - one parent, and it has the same tree that would be committed.
+ -
+ - Unlike git-commit, does not run any hooks, or examine the work tree
+ - in any way.
+ -}
+commit :: Bool -> String -> Branch -> [Ref] -> Repo -> IO (Maybe Sha)
+commit allowempty message branch parentrefs repo = do
 	tree <- getSha "write-tree" $
 		pipeReadStrict [Param "write-tree"] repo
-	sha <- getSha "commit-tree" $ pipeWriteRead
-		(map Param $ ["commit-tree", show tree] ++ ps)
-		(Just $ flip hPutStr message) repo
-	update branch sha repo
-	return sha
+	ifM (cancommit tree)
+		( do
+			sha <- getSha "commit-tree" $ pipeWriteRead
+				(map Param $ ["commit-tree", show tree] ++ ps)
+				(Just $ flip hPutStr message) repo
+			update branch sha repo
+			return $ Just sha
+		, return Nothing
+		)
   where
 	ps = concatMap (\r -> ["-p", show r]) parentrefs
+	cancommit tree
+		| allowempty = return True
+		| otherwise = case parentrefs of
+			[p] -> maybe False (tree /=) <$> Git.Ref.tree p repo
+			_ -> return True
+
+commitAlways :: String -> Branch -> [Ref] -> Repo -> IO Sha
+commitAlways message branch parentrefs repo = fromJust
+	<$> commit True message branch parentrefs repo
 
 {- A leading + makes git-push force pushing a branch. -}
 forcePush :: String -> String
diff --git a/Git/Ref.hs b/Git/Ref.hs
index 6ce1b8784..09472930f 100644
--- a/Git/Ref.hs
+++ b/Git/Ref.hs
@@ -10,6 +10,7 @@ module Git.Ref where
 import Common
 import Git
 import Git.Command
+import Git.Sha
 
 import Data.Char (chr)
 
@@ -105,6 +106,11 @@ matchingUniq refs repo = nubBy uniqref <$> matching refs repo
   where
 	uniqref (a, _) (b, _) = a == b
 
+{- Gets the sha of the tree a ref uses. -}
+tree :: Ref -> Repo -> IO (Maybe Sha)
+tree ref = extractSha <$$> pipeReadStrict
+	[ Param "rev-parse", Param (show ref ++ ":") ]
+
 {- Checks if a String is a legal git ref name.
  -
  - The rules for this are complex; see git-check-ref-format(1) -}