[scm] Handle empty .gitmodules file

R=yiwzhang@google.com

Bug: 372697507
Change-Id: I6ac59b762fedd328d23dcfb4f8ef328f96eb36a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5923135
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>

scm.py

@@ -1113,9 +1113,13 @@ class GIT(object):
         """
         if not os.path.exists(os.path.join(repo_root, '.gitmodules')):
             return []
-        config_output = GIT.Capture(
-            ['config', '--file', '.gitmodules', '--get-regexp', 'path'],
-            cwd=repo_root)
+        try:
+            config_output = GIT.Capture(
+                ['config', '--file', '.gitmodules', '--get-regexp', 'path'],
+                cwd=repo_root)
+        except subprocess2.CalledProcessError:
+            # Git exits with 1 if no config matches are found.
+            return []
         assert isinstance(config_output, str)
         return [
             line.split()[-1].replace('/', os.path.sep)

tests/scm_unittest.py

@@ -149,6 +149,15 @@ class GitWrapperTestCase(unittest.TestCase):
     def testListSubmodules_missing(self):
         self.assertEqual(scm.GIT.ListSubmodules('root'), [])
 
+    @mock.patch('os.path.exists', return_value=True)
+    @mock.patch('scm.GIT.Capture')
+    def testListSubmodules_empty(self, mockCapture, *_mock):
+        mockCapture.side_effect = [
+            subprocess2.CalledProcessError(1, '', '', '', ''),
+        ]
+        self.assertEqual(scm.GIT.ListSubmodules('root'), [])
+
+
 
 class RealGitTest(fake_repos.FakeReposTestBase):
     def setUp(self):