Refuse to build with git older than 1.7.1.1, which is needed for git checkout -B

Build/Configure.hs

@@ -10,6 +10,7 @@ import System.FilePath
 import System.Environment (getArgs)
 import Data.Maybe
 import Control.Monad.IfElse
+import Control.Monad
 import Data.Char
 
 import Build.TestConfig
@@ -95,8 +96,12 @@ getUpgradeLocation = do
 	return $ Config "upgradelocation" $ MaybeStringConfig e
 
 getGitVersion :: Test
-getGitVersion = Config "gitversion" . StringConfig . show
-	<$> Git.Version.installed
+getGitVersion = do
+	v <- Git.Version.installed
+	let oldestallowed = Git.Version.normalize "1.7.1.0"
+	when (v < oldestallowed) $
+		error $ "installed git version " ++ show v ++ " is too old! (Need " ++ show oldestallowed ++ " or newer)"
+	return $ Config "gitversion" $ StringConfig $ show v
 
 getSshConnectionCaching :: Test
 getSshConnectionCaching = Config "sshconnectioncaching" . BoolConfig <$>

debian/changelog

@@ -3,6 +3,8 @@ git-annex (5.20140108) UNRELEASED; urgency=medium
   * Added tahoe special remote.
   * external special remote protocol: Added GETGITDIR, and GETAVAILABILITY.
   * Android: Avoid passing --clobber to busybox wget.
+  * Refuse to build with git older than 1.7.1.1, which is needed for
+    git checkout -B
 
  -- Joey Hess <joeyh@debian.org>  Wed, 08 Jan 2014 13:13:54 -0400
 

doc/bugs/Check_for_minimum_Git_version.mdwn

@@ -26,3 +26,16 @@ usage: git checkout [options] <branch>
 
 # End of transcript or log.
 """]]
+
+> git-annex checks the git version at compile time and arranges to use
+> commands that will work with that version of git at run time.
+> 
+> Adding a runtime check for a minimum git version would slow every git-annex
+> command down and so I don't want to do it. It's up to the user to not
+> built git-annex with a new version of git and then try to use it with an
+> old version of git.
+> 
+> `git checkout -B` seems to have been added to git quite a long time ago
+> (2010), in version 1.7.1.1. I've made git-annex check at compile
+> time if being built with such an old version and refuse to build.
+> [[done]]. --[[Joey]]