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|
{- git branch stuff
-
- Copyright 2011 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Git.Branch where
import qualified Data.ByteString.Lazy.Char8 as L
import Common
import Git
{- Checks if the second branch has any commits not present on the first
- branch. -}
changed :: Branch -> Branch -> Repo -> IO Bool
changed origbranch newbranch repo
| origbranch == newbranch = return False
| otherwise = not . L.null <$> diffs
where
diffs = Git.pipeRead
[ Param "log"
, Param (show origbranch ++ ".." ++ show newbranch)
, Params "--oneline -n1"
] repo
{- Given a set of refs that are all known to have commits not
- on the branch, tries to update the branch by a fast-forward.
-
- In order for that to be possible, one of the refs must contain
- every commit present in all the other refs.
-}
fastForward :: Branch -> [Ref] -> Repo -> IO Bool
fastForward _ [] _ = return True
fastForward branch (first:rest) repo = do
-- First, check that the branch does not contain any
-- new commits that are not in the first ref. If it does,
-- cannot fast-forward.
diverged <- changed first branch repo
if diverged
then no_ff
else maybe no_ff do_ff =<< findbest first rest
where
no_ff = return False
do_ff to = do
Git.run "update-ref"
[Param $ show branch, Param $ show to] repo
return True
findbest c [] = return $ Just c
findbest c (r:rs)
| c == r = findbest c rs
| otherwise = do
better <- changed c r repo
worse <- changed r c repo
case (better, worse) of
(True, True) -> return Nothing -- divergent fail
(True, False) -> findbest r rs -- better
(False, True) -> findbest c rs -- worse
(False, False) -> findbest c rs -- same
|
