type based git config handling

Now there's a Config type, that's extracted from the git config at startup.
Note that laziness means that individual config values are only looked up
and parsed on demand, and so we get implicit memoization for all of them.
So this is not only prettier and more type safe, it optimises several
places that didn't have explicit memoization before. As well as getting rid
of the ugly explicit memoization code.

Not yet done for annex.<remote>.* configuration settings.

Annex.hs

@@ -1,6 +1,6 @@
 {- git-annex monad
  -
- - Copyright 2010-2011 Joey Hess <joey@kitenet.net>
+ - Copyright 2010-2012 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -28,6 +28,9 @@ module Annex (
 	gitRepo,
 	inRepo,
 	fromRepo,
+	getConfig,
+	changeConfig,
+	changeGitRepo,
 ) where
 
 import "mtl" Control.Monad.State.Strict
@@ -43,6 +46,7 @@ import Git.CheckAttr
 import Git.SharedRepository
 import qualified Git.Queue
 import Types.Backend
+import Types.Config
 import qualified Types.Remote
 import Types.Crypto
 import Types.BranchState
@@ -88,6 +92,7 @@ type PreferredContentMap = M.Map UUID (Utility.Matcher.Matcher (S.Set UUID -> Fi
 -- internal state storage
 data AnnexState = AnnexState
 	{ repo :: Git.Repo
+	, config :: Config
 	, backends :: [BackendA Annex]
 	, remotes :: [Types.Remote.RemoteA Annex]
 	, output :: MessageState
@@ -99,7 +104,6 @@ data AnnexState = AnnexState
 	, catfilehandle :: Maybe CatFileHandle
 	, checkattrhandle :: Maybe CheckAttrHandle
 	, forcebackend :: Maybe String
-	, forcenumcopies :: Maybe Int
 	, limit :: Matcher (FileInfo -> Annex Bool)
 	, uuidmap :: Maybe UUIDMap
 	, preferredcontentmap :: Maybe PreferredContentMap
@@ -118,6 +122,7 @@ data AnnexState = AnnexState
 newState :: Git.Repo -> AnnexState
 newState gitrepo = AnnexState
 	{ repo = gitrepo
+	, config = extractConfig gitrepo
 	, backends = []
 	, remotes = []
 	, output = defaultMessageState
@@ -129,7 +134,6 @@ newState gitrepo = AnnexState
 	, catfilehandle = Nothing
 	, checkattrhandle = Nothing
 	, forcebackend = Nothing
-	, forcenumcopies = Nothing
 	, limit = Left []
 	, uuidmap = Nothing
 	, preferredcontentmap = Nothing
@@ -197,3 +201,18 @@ inRepo a = liftIO . a =<< gitRepo
 {- Extracts a value from the annex's git repisitory. -}
 fromRepo :: (Git.Repo -> a) -> Annex a
 fromRepo a = a <$> gitRepo
+
+{- Gets the Config settings. -}
+getConfig :: Annex Config
+getConfig = getState config
+
+{- Modifies a Config setting. -}
+changeConfig :: (Config -> Config) -> Annex ()
+changeConfig a = changeState $ \s -> s { config = a (config s) }
+
+{- Changing the git Repo data also involves re-extracting its Config. -}
+changeGitRepo :: Git.Repo -> Annex ()
+changeGitRepo r = changeState $ \s -> s
+	{ repo = r
+	, config = extractConfig r
+	}