util: Resolve HEAD in repos that have a remote

JIRA: COMPOSE-3597
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/util.py

@@ -265,7 +265,10 @@ def resolve_git_ref(repourl, ref):
 
     lines = []
     for line in output.split("\n"):
-        if line and ("refs/heads/" in line or "refs/tags/" in line or "HEAD" in line):
+        # Keep only lines that represent branches and tags, and also a line for
+        # currently checked out HEAD. The leading tab is required to
+        # distinguish it from HEADs that could exist in remotes.
+        if line and ("refs/heads/" in line or "refs/tags/" in line or "\tHEAD" in line):
             lines.append(line)
     if len(lines) == 0:
         # Branch does not exist in remote repo

tests/test_util.py

@@ -61,6 +61,20 @@ class TestGitRefResolver(unittest.TestCase):
             universal_newlines=True,
         )
 
+    @mock.patch('pungi.util.run')
+    def test_resolve_ref_with_remote_head(self, run):
+        run.return_value = (
+            0, "CAFEBABE\tHEAD\nBABECAFE\trefs/remotes/origin/HEAD"
+        )
+
+        ref = util.resolve_git_ref("https://git.example.com/repo.git", "HEAD")
+
+        self.assertEqual(ref, "CAFEBABE")
+        run.assert_called_once_with(
+            ["git", "ls-remote", "https://git.example.com/repo.git", "HEAD"],
+            universal_newlines=True,
+        )
+
     @mock.patch('pungi.util.run')
     def test_resolve_missing_spec(self, run):
         url = util.resolve_git_url('https://git.example.com/repo.git')