improved git-annex branch changing

All changes to files in the branch are now made via pure functions that
transform the old file into the new. This will allow adding locking
to prevent read/write races. It also makes the code nicer, and purer.

I noticed a behavior change, really a sort of bug fix. Before,
'git annex untrust foo --trust bar' would change both trust levels
permanantly, now the --trust doesn't get stored.

1 files changed, 3 insertions, 5 deletions

diff --git a/Trust.hs b/Trust.hs
index 232eea6a5..0c8836c85 100644
--- a/Trust.hs
+++ b/Trust.hs
@@ -64,11 +64,9 @@ trustSet :: UUID -> TrustLevel -> Annex ()
 trustSet uuid level = do
 	when (null uuid) $
 		error "unknown UUID; cannot modify trust level"
-        m <- trustMap
-	when (M.lookup uuid m /= Just level) $ do
-		let m' = M.insert uuid level m
-		Branch.change trustLog (serialize m')
-		Annex.changeState $ \s -> s { Annex.trustmap = Just m' }
+	Branch.change trustLog $
+		serialize . M.insert uuid level . M.fromList . trustMapParse
+	Annex.changeState $ \s -> s { Annex.trustmap = Nothing }
         where
                 serialize m = unlines $ map showpair $ M.toList m
 		showpair (u, t) = u ++ " " ++ show t