gitdir: add HEAD property to find the current branch

This is needed for status to tell if a repo is checked out in an
unexpected branch.

2 files changed, 15 insertions, 0 deletions

diff --git a/morphlib/gitdir.py b/morphlib/gitdir.py
index cb247303..c075f456 100644
--- a/morphlib/gitdir.py
+++ b/morphlib/gitdir.py
@@ -195,6 +195,11 @@ class GitDirectory(object):
         tree = self._rev_parse_tree(ref)
         return self.cat_file('blob', tree, filename)
 
+    @property
+    def HEAD(self):
+        output = self._runcmd(['git', 'rev-parse', '--abbrev-ref', 'HEAD'])
+        return output.strip()
+
 
 def init(dirname):
     '''Initialise a new git repository.'''
diff --git a/morphlib/gitdir_tests.py b/morphlib/gitdir_tests.py
index 175b8ee7..84b8787a 100644
--- a/morphlib/gitdir_tests.py
+++ b/morphlib/gitdir_tests.py
@@ -137,3 +137,13 @@ class GitDirectoryContentsTests(unittest.TestCase):
         gd = morphlib.gitdir.GitDirectory(self.dirname)
         self.assertRaises(morphlib.gitdir.InvalidRefError,
                           gd.read_file, 'bar', 'no-such-ref')
+
+    def test_HEAD(self):
+        gd = morphlib.gitdir.GitDirectory(self.dirname)
+        self.assertEqual(gd.HEAD, 'master')
+
+        gd.branch('foo', 'master')
+        self.assertEqual(gd.HEAD, 'master')
+
+        gd.checkout('foo')
+        self.assertEqual(gd.HEAD, 'foo')