Detach head before reset

During repo reset we currently try to reset the head to the HEAD of
the remote repo. In some cases this doesn't work so simply reset
the current HEAD revision as a commit to detach the head upfront.

Change-Id: I167e6ce92680c40d2067939cedaa5ed98b950515

1 files changed, 13 insertions, 13 deletions

diff --git a/zuul/merger/merger.py b/zuul/merger/merger.py
index 0dc7264c8..3ff8e7b2a 100644
--- a/zuul/merger/merger.py
+++ b/zuul/merger/merger.py
@@ -287,20 +287,20 @@ class Repo(object):
         repo = Repo._createRepoObject(local_path, env)
         origin = repo.remotes.origin
 
-        # Reset the working directory to the default remote branch.
+        # Detach HEAD so we can work with references without interfering
+        # with any active branch. Any remote ref will do as long as it can
+        # be dereferenced to an existing commit.
         for ref in origin.refs:
-            if ref.remote_head != "HEAD":
-                continue
-            # Use the ref the remote HEAD is pointing to
-            head_ref = ref.ref
-            head = head_ref.remote_head
-            repo.create_head(head, head_ref, force=True)
-            if log:
-                log.debug("Reset to %s", head)
-            else:
-                messages.append("Reset to %s" % head)
-            repo.head.reference = head
-            break
+            try:
+                repo.head.reference = ref.commit
+                break
+            except Exception:
+                if log:
+                    log.debug("Unable to detach HEAD to %s", ref)
+                else:
+                    messages.append("Unable to detach HEAD to %s" % ref)
+        else:
+            raise Exception("Couldn't detach HEAD to any existing commit")
 
         # Delete local heads that no longer exist on the remote end
         remote_heads = {r.remote_head for r in origin.refs}