Allowed track only if we're in a working dir

See `git add`; Exit status and message are taken from there.

Fixes github/git-lfs#353

commands/command_track.go

@@ -25,6 +25,10 @@ func trackCommand(cmd *cobra.Command, args []string) {
 		Print("Not a git repository.")
 		os.Exit(128)
 	}
+	if lfs.LocalWorkingDir == "" {
+		Print("This operation must be run in a work tree.")
+		os.Exit(128)
+	}
 
 	lfs.InstallHooks(false)
 	knownPaths := findPaths()

lfs/lfs.go

@@ -128,7 +128,8 @@ func recursiveResolveGitDir(dir string) (string, string, error) {
 	}
 
 	if filepath.Base(dir) == gitExt {
-		return filepath.Dir(dir), dir, nil
+		// We're in the `.git` directory.  Make no assumptions about the working directory.
+		return "", dir, nil
 	}
 
 	gitDir := filepath.Join(dir, gitExt)

test/test-submodule.sh

@@ -51,7 +51,7 @@ begin_test "submodule env"
   echo "./.git"
   git lfs env | tee env.log
   grep "Endpoint=$GITSERVER/$reponame.git/info/lfs$" env.log
-  grep "LocalWorkingDir=$TRASHDIR/repo$" env.log
+  grep "LocalWorkingDir=$" env.log
   grep "LocalGitDir=$TRASHDIR/repo/.git$" env.log
   grep "LocalMediaDir=$TRASHDIR/repo/.git/lfs/objects$" env.log
   grep "TempDir=$TRASHDIR/repo/.git/lfs/tmp$" env.log