morph branch: Check if the ref already exists before anything else

This was done to ensure tests.branching/branch-fails-if-branch-exists
always passes, but also seems like the right approach in general.

1 files changed, 9 insertions, 0 deletions

diff --git a/morphlib/cachedrepo.py b/morphlib/cachedrepo.py
index 312f580f..0a085bb2 100644
--- a/morphlib/cachedrepo.py
+++ b/morphlib/cachedrepo.py
@@ -104,6 +104,15 @@ class CachedRepo(object):
         self.path = path
         self.is_mirror = not url.startswith('file://')
 
+    def ref_exists(self, ref):
+        '''Returns True if the given ref exists in the repo'''
+
+        try:
+            self._rev_parse(ref)
+        except cliapp.AppException:
+            return False
+        return True
+
     def resolve_ref(self, ref):
         '''Attempts to resolve a ref into its SHA1 and tree SHA1.