-def update_ref(refname, newval, oldval, repo_dir=None):
- """Update a repository reference."""
- if not oldval:
- oldval = b''
+def update_ref(refname, newval, oldval, repo_dir=None, force=False):
+ """Update a repository reference.
+
+ With force=True, don't care about the previous ref (oldval);
+ with force=False oldval must be either a sha1 or None (for an
+ entirely new branch)
+ """
+ if force:
+ assert oldval is None
+ oldarg = []
+ elif not oldval:
+ oldarg = [b'']
+ else:
+ oldarg = [hexlify(oldval)]