is_fast_forward: make sure git interprets arguments as revisions

so git prints a clearer error message on configuration errors in
.git/config

1 files changed, 2 insertions, 1 deletions

diff --git a/gbp/git.py b/gbp/git.py
index 1ecab9f1..cf85f0a0 100644
--- a/gbp/git.py
+++ b/gbp/git.py
@@ -175,7 +175,8 @@ class GitRepository(object):
         has_local = False       # local repo has new commits
         has_remote = False      # remote repo has new commits
         out = self.__git_getoutput('rev-list', ["--left-right",
-                                   "%s...%s" % (from_branch, to_branch)])[0]
+                                   "%s...%s" % (from_branch, to_branch),
+                                   "--"])[0]
 
         if not out: # both branches have the same commits
             return True, True