Fix a bug in symlink calculation code, that triggered in rare cases where an annexed file is in a subdirectory that nearly matched to the .git/annex/object/xx/yy subdirectories.

This is a straight up pure-code stinker. The relative path calculation
looked for common subdirectories in the two paths, but failed to stop
after the paths diverged. When a later pair of subdirectories were the
same, the resulting relative path was wrong.

Added regression test for this.

Utility/Path.hs

@@ -82,7 +82,7 @@ relPathDirToFile from to = join s $ dotdots ++ uncommon
 		s = [pathSeparator]
 		pfrom = split s from
 		pto = split s to
-		common = map fst $ filter same $ zip pfrom pto
+		common = map fst $ takeWhile same $ zip pfrom pto
 		same (c,d) = c == d
 		uncommon = drop numcommon pto
 		dotdots = replicate (length pfrom - numcommon) ".."
@@ -95,6 +95,15 @@ prop_relPathDirToFile_basics from to
 	where
 		r = relPathDirToFile from to 
 
+prop_relPathDirToFile_regressionTest :: Bool
+prop_relPathDirToFile_regressionTest = same_dir_shortcurcuits_at_difference
+	where
+		{- Two paths have the same directory component at the same
+		 - location, but it's not really the same directory.
+		 - Code used to get this wrong. -}
+		same_dir_shortcurcuits_at_difference =
+			relPathDirToFile "/tmp/r/lll/xxx/yyy/18" "/tmp/r/.git/annex/objects/18/gk/SHA256-foo/SHA256-foo" == "../../../../.git/annex/objects/18/gk/SHA256-foo/SHA256-foo"
+
 {- Given an original list of files, and an expanded list derived from it,
  - ensures that the original list's ordering is preserved. 
  -

debian/changelog

@@ -8,6 +8,9 @@ git-annex (3.20120230) UNRELEASED; urgency=low
   * Add configurable hooks that are run when git-annex starts and stops
     using a remote: remote.name.annex-start-command and
     remote.name.annex-stop-command
+  * Fix a bug in symlink calculation code, that triggered in rare
+    cases where an annexed file is in a subdirectory that nearly
+    matched to the .git/annex/object/xx/yy subdirectories.
 
  -- Joey Hess <joeyh@debian.org>  Thu, 01 Mar 2012 22:34:27 -0400
 

test.hs

@@ -82,6 +82,7 @@ quickcheck = TestLabel "quickcheck" $ TestList
 	, qctest "prop_parentDir_basics" Utility.Path.prop_parentDir_basics
 
 	, qctest "prop_relPathDirToFile_basics" Utility.Path.prop_relPathDirToFile_basics
+	, qctest "prop_relPathDirToFile_regressionTest" Utility.Path.prop_relPathDirToFile_regressionTest
 	, qctest "prop_cost_sane" Config.prop_cost_sane
 	, qctest "prop_hmacWithCipher_sane" Crypto.prop_hmacWithCipher_sane
 	, qctest "prop_TimeStamp_sane" Logs.UUIDBased.prop_TimeStamp_sane