Clean up handling of git directory and git worktree.

Baked into the code was an assumption that a repository's git directory
could be determined by adding ".git" to its work tree (or nothing for bare
repos). That fails when core.worktree, or GIT_DIR and GIT_WORK_TREE are
used to separate the two.

This was attacked at the type level, by storing the gitdir and worktree
separately, so Nothing for the worktree means a bare repo.

A complication arose because we don't learn where a repository is bare
until its configuration is read. So another Location type handles
repositories that have not had their config read yet. I am not entirely
happy with this being a Location type, rather than representing them
entirely separate from the Git type. The new code is not worse than the
old, but better types could enforce more safety.

Added support for core.worktree. Overriding it with -c isn't supported
because it's not really clear what to do if a git repo's config is read, is
not bare, and is then overridden to bare. What is the right git directory
in this case? I will worry about this if/when someone has a use case for
overriding core.worktree with -c. (See Git.Config.updateLocation)

Also removed and renamed some functions like gitDir and workTree that
misused git's terminology.

One minor regression is known: git annex add in a bare repository does not
print a nice error message, but runs git ls-files in a way that fails
earlier with a less nice error message. This is because before --work-tree
was always passed to git commands, even in a bare repo, while now it's not.

Git.hs

@@ -3,7 +3,7 @@
  - This is written to be completely independant of git-annex and should be
  - suitable for other uses.
  -
- - 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.
  -}
@@ -17,19 +17,17 @@ module Git (
 	repoIsUrl,
 	repoIsSsh,
 	repoIsHttp,
+	repoIsLocal,
 	repoIsLocalBare,
 	repoDescribe,
 	repoLocation,
-	workTree,
-	gitDir,
-	configTrue,
+	repoPath,
+	localGitDir,
 	attributes,
 	hookPath,
 	assertLocal,
 ) where
 
-import qualified Data.Map as M
-import Data.Char
 import Network.URI (uriPath, uriScheme, unEscapeString)
 import System.Posix.Files
 
@@ -41,15 +39,34 @@ import Utility.FileMode
 repoDescribe :: Repo -> String
 repoDescribe Repo { remoteName = Just name } = name
 repoDescribe Repo { location = Url url } = show url
-repoDescribe Repo { location = Dir dir } = dir
+repoDescribe Repo { location = Local { worktree = Just dir } } = dir
+repoDescribe Repo { location = Local { gitdir = dir } } = dir
+repoDescribe Repo { location = LocalUnknown dir } = dir
 repoDescribe Repo { location = Unknown } = "UNKNOWN"
 
 {- Location of the repo, either as a path or url. -}
 repoLocation :: Repo -> String
 repoLocation Repo { location = Url url } = show url
-repoLocation Repo { location = Dir dir } = dir
+repoLocation Repo { location = Local { worktree = Just dir } } = dir
+repoLocation Repo { location = Local { gitdir = dir } } = dir
+repoLocation Repo { location = LocalUnknown dir } = dir
 repoLocation Repo { location = Unknown } = undefined
 
+{- Path to a repository. For non-bare, this is the worktree, for bare, 
+ - it's the gitdir, and for URL repositories, is the path on the remote
+ - host. -}
+repoPath :: Repo -> FilePath
+repoPath Repo { location = Url u } = unEscapeString $ uriPath u
+repoPath Repo { location = Local { worktree = Just d } } = d
+repoPath Repo { location = Local { gitdir = d } } = d
+repoPath Repo { location = LocalUnknown dir } = dir
+repoPath Repo { location = Unknown } = undefined
+
+{- Path to a local repository's .git directory. -}
+localGitDir :: Repo -> FilePath
+localGitDir Repo { location = Local { gitdir = d } } = d
+localGitDir _ = undefined
+
 {- Some code needs to vary between URL and normal repos,
  - or bare and non-bare, these functions help with that. -}
 repoIsUrl :: Repo -> Bool
@@ -74,11 +91,12 @@ repoIsHttp Repo { location = Url url }
 	| otherwise = False
 repoIsHttp _ = False
 
-configAvail ::Repo -> Bool
-configAvail Repo { config = c } = c /= M.empty
+repoIsLocal :: Repo -> Bool
+repoIsLocal Repo { location = Local { } } = True
+repoIsLocal _ = False
 
 repoIsLocalBare :: Repo -> Bool
-repoIsLocalBare r@(Repo { location = Dir _ }) = configAvail r && configBare r
+repoIsLocalBare Repo { location = Local { worktree = Nothing } } = True
 repoIsLocalBare _ = False
 
 assertLocal :: Repo -> a -> a
@@ -90,49 +108,18 @@ assertLocal repo action
 		]
 	| otherwise = action
 
-configBare :: Repo -> Bool
-configBare repo = maybe unknown (fromMaybe False . configTrue) $
-	M.lookup "core.bare" $ config repo
-	where
-		unknown = error $ "it is not known if git repo " ++
-			repoDescribe repo ++
-			" is a bare repository; config not read"
-
 {- Path to a repository's gitattributes file. -}
 attributes :: Repo -> FilePath
 attributes repo
-	| configBare repo = workTree repo ++ "/info/.gitattributes"
-	| otherwise = workTree repo ++ "/.gitattributes"
-
-{- Path to a repository's .git directory. -}
-gitDir :: Repo -> FilePath
-gitDir repo
-	| configBare repo = workTree repo
-	| otherwise = workTree repo </> ".git"
+	| repoIsLocalBare repo = repoPath repo ++ "/info/.gitattributes"
+	| otherwise = repoPath repo ++ "/.gitattributes"
 
 {- Path to a given hook script in a repository, only if the hook exists
  - and is executable. -}
 hookPath :: String -> Repo -> IO (Maybe FilePath)
 hookPath script repo = do
-	let hook = gitDir repo </> "hooks" </> script
+	let hook = localGitDir repo </> "hooks" </> script
 	ifM (catchBoolIO $ isexecutable hook)
 		( return $ Just hook , return Nothing )
 	where
 		isexecutable f = isExecutable . fileMode <$> getFileStatus f
-
-{- Path to a repository's --work-tree, that is, its top.
- -
- - Note that for URL repositories, this is the path on the remote host. -}
-workTree :: Repo -> FilePath
-workTree Repo { location = Url u } = unEscapeString $ uriPath u
-workTree Repo { location = Dir d } = d
-workTree Repo { location = Unknown } = undefined
-
-{- Checks if a string from git config is a true value. -}
-configTrue :: String -> Maybe Bool
-configTrue s
-	| s' == "true" = Just True
-	| s' == "false" = Just False
-	| otherwise = Nothing
-	where
-		s' = map toLower s