git-annex/Annex/VariantFile.hs
2015-01-21 12:50:09 -04:00

45 lines
1.4 KiB
Haskell

{- git-annex .variant files for automatic merge conflict resolution
-
- Copyright 2014 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Annex.VariantFile where
import Common.Annex
import Types.Key
import Data.Hash.MD5
variantMarker :: String
variantMarker = ".variant-"
mkVariant :: FilePath -> String -> FilePath
mkVariant file variant = takeDirectory file
</> dropExtension (takeFileName file)
++ variantMarker ++ variant
++ takeExtension file
{- The filename to use when resolving a conflicted merge of a file,
- that points to a key.
-
- Something derived from the key needs to be included in the filename,
- but rather than exposing the whole key to the user, a very weak hash
- is used. There is a very real, although still unlikely, chance of
- conflicts using this hash.
-
- In the event that there is a conflict with the filename generated
- for some other key, that conflict will itself be handled by the
- conflicted merge resolution code. That case is detected, and the full
- key is used in the filename.
-}
variantFile :: FilePath -> Key -> FilePath
variantFile file key
| doubleconflict = mkVariant file (key2file key)
| otherwise = mkVariant file (shortHash $ key2file key)
where
doubleconflict = variantMarker `isInfixOf` file
shortHash :: String -> String
shortHash = take 4 . md5s . md5FilePath