owners: Set correct branch to compute diff.

We have to use refs/remotes/origin/foo instead of refs/heads/foo,
as refs/heads/foo might not be defined.

https://logs.chromium.org/logs/infra-internal/buildbucket/cr-buildbucket.appspot.com/8853851694141987488/+/u/build/git_cl_upload/stdout

Change-Id: Ic729510d7beca63c25ea84394758cb62f76c572f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2729615
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>

owners_client.py

@@ -176,9 +176,12 @@ class DepotToolsClient(OwnersClient):
     self._db.override_files = self._GetOriginalOwnersFiles()
 
   def _GetOriginalOwnersFiles(self):
+    remote, _ = scm.GIT.FetchUpstreamTuple(self._root)
+    branch = ''.join(scm.GIT.RefToRemoteRef(self._branch, remote))
+
     return {
-      f: scm.GIT.GetOldContents(self._root, f, self._branch).splitlines()
-      for _, f in scm.GIT.CaptureStatus(self._root, self._branch)
+      f: scm.GIT.GetOldContents(self._root, f, branch).splitlines()
+      for _, f in scm.GIT.CaptureStatus(self._root, branch)
       if os.path.basename(f) == 'OWNERS'
     }
 

tests/owners_client_test.py

@@ -42,17 +42,27 @@ class DepotToolsClientTest(unittest.TestCase):
     })
     self.root = '/'
     self.fopen = self.repo.open_for_reading
-    mock.patch(
-        'owners_client.DepotToolsClient._GetOriginalOwnersFiles',
-        return_value={}).start()
     self.addCleanup(mock.patch.stopall)
     self.client = owners_client.DepotToolsClient(
-        '/', 'branch', self.fopen, self.repo)
+        '/', 'refs/heads/main', self.fopen, self.repo)
+
+  @mock.patch('scm.GIT.CaptureStatus')
+  @mock.patch('scm.GIT.GetOldContents')
+  @mock.patch('scm.GIT.FetchUpstreamTuple')
+  def testListOwners(
+      self, mockFetchUpstreamTuple, mockGetOldContents, mockCaptureStatus):
+    mockFetchUpstreamTuple.return_value = ('remote', 'refs/heads/blah')
+    mockGetOldContents.side_effect = lambda r, f, _b: self.repo.files[r + f]
+    mockCaptureStatus.return_value = [
+        ('M', 'bar/everyone/foo.txt'),
+        ('M', 'OWNERS'),
+    ]
 
-  def testListOwners(self):
     self.assertEqual(
         ['*', 'missing@example.com'],
         self.client.ListOwners('bar/everyone/foo.txt'))
+    mockCaptureStatus.assert_called_once_with(
+        '/', 'refs/remotes/remote/main')
 
 
 class GerritClientTest(unittest.TestCase):