Support git's core.sharedRepository configuration

This is incomplete, it does not honor it yet for hash directories
and other annex bookkeeping files. Some of that is not needed for a bare
repo; some of it may be.

Utility/FileMode.hs

@@ -1,6 +1,6 @@
 {- File mode utilities.
  -
- - Copyright 2010 Joey Hess <joey@kitenet.net>
+ - Copyright 2010-2012 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -9,16 +9,36 @@ module Utility.FileMode where
 
 import Common
 
+import Control.Exception (bracket)
 import System.Posix.Types
 import Foreign (complement)
 
+combineModes :: [FileMode] -> FileMode
+combineModes [] = undefined
+combineModes [m] = m
+combineModes (m:ms) = foldl unionFileModes m ms
+
+{- Applies a conversion function to a file's mode. -}
 modifyFileMode :: FilePath -> (FileMode -> FileMode) -> IO ()
 modifyFileMode f convert = do
+	_ <- modifyFileMode' f convert
+	return ()
+modifyFileMode' :: FilePath -> (FileMode -> FileMode) -> IO FileMode
+modifyFileMode' f convert = do
 	s <- getFileStatus f
-	let cur = fileMode s
-	let new = convert cur
-	when (new /= cur) $
+	let old = fileMode s
+	let new = convert old
+	when (new /= old) $
 		setFileMode f new
+	return old
+
+{- Runs an action after changing a file's mode, then restores the old mode. -}
+withModifiedFileMode :: FilePath -> (FileMode -> FileMode) -> IO a -> IO a
+withModifiedFileMode file convert a = bracket setup cleanup go
+	where
+		setup = modifyFileMode' file convert
+		cleanup oldmode = modifyFileMode file (const oldmode)
+		go _ = a
 
 {- Removes a FileMode from a file.
  - For example, call with otherWriteMode to chmod o-w -}
@@ -28,23 +48,43 @@ unsetFileMode f m = modifyFileMode f $
 
 {- Removes the write bits from a file. -}
 preventWrite :: FilePath -> IO ()
-preventWrite f = unsetFileMode f writebits
+preventWrite f = unsetFileMode f $ combineModes writebits
 	where
-		writebits = foldl unionFileModes ownerWriteMode
-					[groupWriteMode, otherWriteMode]
+		writebits = [ownerWriteMode, groupWriteMode, otherWriteMode]
 
 {- Turns a file's write bit back on. -}
 allowWrite :: FilePath -> IO ()
 allowWrite f = modifyFileMode f $
 	\cur -> cur `unionFileModes` ownerWriteMode
 
+{- Allows owner and group to read and write to a file. -}
+groupWriteRead :: FilePath -> IO ()
+groupWriteRead f = modifyFileMode f $ \cur -> combineModes
+	[ cur
+	, ownerWriteMode, groupWriteMode
+	, ownerReadMode, groupReadMode
+	]
+
+{- Allows group to read a file. -}
+groupRead :: FilePath -> IO ()
+groupRead f = modifyFileMode f $ \cur -> combineModes
+	[ cur
+	, ownerReadMode, groupReadMode
+	]
+
+{- Allows all to read a file. -}
+allRead :: FilePath -> IO ()
+allRead f = modifyFileMode f $ \cur -> combineModes
+	[ cur
+	, ownerReadMode, groupReadMode, otherReadMode
+	]
+
 {- Checks if a file mode indicates it's a symlink. -}
 isSymLink :: FileMode -> Bool
 isSymLink mode = symbolicLinkMode `intersectFileModes` mode == symbolicLinkMode
 
 {- Checks if a file has any executable bits set. -}
 isExecutable :: FileMode -> Bool
-isExecutable mode = ebits `intersectFileModes` mode /= 0
+isExecutable mode = combineModes ebits `intersectFileModes` mode /= 0
 	where
-		ebits = ownerExecuteMode `unionFileModes`
-			groupExecuteMode `unionFileModes` otherExecuteMode
+		ebits = [ownerExecuteMode, groupExecuteMode, otherExecuteMode]