multiple -m

sync, assist, import: Allow -m option to be specified multiple times, to
provide additional paragraphs for the commit message.

The option parser didn't allow multiple -m before, so there is no risk of
behavior change breaking something that was for some reason using multiple
-m already.

Pass through to git commands, so that the method used to assemble the
paragrahs is whatever git does. Which might conceivably change in the
future.

Note that git commit-tree has supported -m since git 1.7.7. commitTree
was probably not using it since it predates that version. Since the
configure script prevents building git-annex with git older than 2.1,
there is no risk that it's not supported now.

Sponsored-by: Nicholas Golder-Manning on Patreon

Git/Branch.hs

@@ -178,7 +178,7 @@ commit commitmode allowempty message branch parentrefs repo = do
 	tree <- writeTree repo
 	ifM (cancommit tree)
 		( do
-			sha <- commitTree commitmode message parentrefs tree repo
+			sha <- commitTree commitmode [message] parentrefs tree repo
 			update' branch sha repo
 			return $ Just sha
 		, return Nothing
@@ -207,15 +207,15 @@ writeTreeQuiet repo = extractSha <$> withNullHandle go
 	go nullh = pipeReadStrict' (\p -> p { std_err = UseHandle nullh }) 
 		[Param "write-tree"] repo
 
-commitTree :: CommitMode -> String -> [Ref] -> Ref -> Repo -> IO Sha
-commitTree commitmode message parentrefs tree repo =
-	getSha "commit-tree" $
-		pipeWriteRead ([Param "commit-tree", Param (fromRef tree)] ++ ps)
-			sendmsg repo
+commitTree :: CommitMode -> [String] -> [Ref] -> Ref -> Repo -> IO Sha
+commitTree commitmode messages parentrefs tree repo =
+	getSha "commit-tree" $ pipeReadStrict ps repo
   where
-	sendmsg = Just $ flip hPutStr message
-	ps = applyCommitModeForCommitTree commitmode parentparams repo
-	parentparams = map Param $ concatMap (\r -> ["-p", fromRef r]) parentrefs
+	ps = [Param "commit-tree", Param (fromRef tree)]
+		++ applyCommitModeForCommitTree commitmode baseparams repo
+	baseparams = map Param $
+		concatMap (\r -> ["-p", fromRef r]) parentrefs
+			++ concatMap (\msg -> ["-m", msg]) messages
 
 {- A leading + makes git-push force pushing a branch. -}
 forcePush :: String -> String