git-annex/Git/Version.hs

{- git version checking
 -
 - Copyright 2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Git.Version where

import Common
import qualified Build.SysConfig

{- Using the version it was configured for avoids running git to check its
 - version, at the cost that upgrading git won't be noticed.
 - This is only acceptable because it's rare that git's version influences
 - code's behavior. -}
version :: String
version = Build.SysConfig.gitversion

older :: String -> Bool
older v = normalize version < normalize v

{- To compare dotted versions like 1.7.7 and 1.8, they are normalized to
 - a somewhat arbitrary integer representation. -}
normalize :: String -> Integer
normalize = sum . mult 1 . reverse .
		extend precision . take precision .
		map readi . split "."
  where
	extend n l = l ++ replicate (n - length l) 0
	mult _ [] = []
	mult n (x:xs) = (n*x) : mult (n*10^width) xs
	readi :: String -> Integer
	readi s = case reads s of
		((x,_):_) -> x
		_ -> 0
	precision = 10 -- number of segments of the version to compare
	width = length "yyyymmddhhmmss" -- maximum width of a segment