fix test suite when git is too old to understand --allow-unrelated-histories

Git/Merge.hs

@@ -10,6 +10,7 @@ module Git.Merge (
 	CommitMode(..),
 	merge,
 	merge',
+	mergeUnrelatedHistoriesParam,
 	stageMerge,
 ) where
 
@@ -44,15 +45,21 @@ merge' extraparams branch mergeconfig commitmode r
 
 merge'' :: [CommandParam] -> [MergeConfig] -> Repo -> IO Bool
 merge'' ps mergeconfig r
-	| MergeUnrelatedHistories `elem` mergeconfig =
-		ifM (Git.Version.older "2.9.0")
-			( go ps
-			, go (ps ++ [Param "--allow-unrelated-histories"])
-			)
+	| MergeUnrelatedHistories `elem` mergeconfig = do
+		up <- mergeUnrelatedHistoriesParam
+		go (ps ++ maybeToList up)
 	| otherwise = go ps
   where
 	go ps' = runBool ps' r
 
+{- Git used to default to merging unrelated histories; newer versions need
+ - an option. -}
+mergeUnrelatedHistoriesParam :: IO (Maybe CommandParam)
+mergeUnrelatedHistoriesParam = ifM (Git.Version.older "2.9.0")
+	( return Nothing
+	, return (Just (Param "--allow-unrelated-histories"))
+	)
+
 {- Stage the merge into the index, but do not commit it.-}
 stageMerge :: Ref -> [MergeConfig] -> Repo -> IO Bool
 stageMerge branch = merge''

Test.hs

@@ -36,6 +36,7 @@ import qualified Git.Types
 import qualified Git.Ref
 import qualified Git.LsTree
 import qualified Git.FilePath
+import qualified Git.Merge
 import qualified Annex.Locations
 #ifndef mingw32_HOST_OS
 import qualified Types.GitConfig
@@ -1739,7 +1740,9 @@ test_export_import = intmpclonerepoInDirect $ do
 
 	writedir "import" (content "import")
 	git_annex "import" ["master", "--from", "foo"] @? "import from dir failed"
-	boolSystem "git" [Param "merge", Param "foo/master", Param "-mmerge", Param "--allow-unrelated-histories"] @? "git merge foo/master failed"
+	up <- Git.Merge.mergeUnrelatedHistoriesParam
+	let mergeps = [Param "merge", Param "foo/master", Param "-mmerge"] ++ maybeToList up
+	boolSystem "git" mergeps @? "git merge foo/master failed"
 	-- FIXME fails when in an adjusted unlocked branch because
 	-- it's imported locked
 	--annexed_present "import"