Use real default branch in gclient

Currently, gclient sync assumes the default branch is master, and
it doesn't work at all if such branch doesn't exist. This change queries
local git copy to get remote HEAD. If local git version is not
available, it queries remote git server using ls-remote.

This change requires git version 2.28 (depot_tools comes with 2.29).

R=ehmaldonado@chromium.org

Bug: 1156318
Change-Id: Id348e0f1004093f395139e8f4d62adb66b94ca9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2628359
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

gclient_scm.py

@@ -473,8 +473,6 @@ class GitWrapper(SCMWrapper):
 
     self._CheckMinVersion("1.6.6")
 
-    # If a dependency is not pinned, track the default remote branch.
-    default_rev = 'refs/remotes/%s/master' % self.remote
     url, deps_revision = gclient_utils.SplitUrlRevision(self.url)
     revision = deps_revision
     managed = True
@@ -487,7 +485,9 @@ class GitWrapper(SCMWrapper):
       revision = deps_revision
       managed = False
     if not revision:
-      revision = default_rev
+      # If a dependency is not pinned, track the default remote branch.
+      revision = scm.GIT.GetRemoteHeadRef(self.checkout_path, self.url,
+                                          self.remote)
 
     if managed:
       self._DisableHooks()

scm.py

@@ -111,7 +111,7 @@ class GIT(object):
     return env
 
   @staticmethod
-  def Capture(args, cwd, strip_out=True, **kwargs):
+  def Capture(args, cwd=None, strip_out=True, **kwargs):
     env = GIT.ApplyEnvVars(kwargs)
     output = subprocess2.check_output(
         ['git'] + args, cwd=cwd, stderr=subprocess2.PIPE, env=env, **kwargs)
@@ -193,6 +193,31 @@ class GIT(object):
     except subprocess2.CalledProcessError:
       return None
 
+  @staticmethod
+  def GetRemoteHeadRef(cwd, url, remote):
+    """Returns the full default remote branch reference, e.g.
+    'refs/remotes/origin/main'."""
+    if os.path.exists(cwd):
+      try:
+        # Try using local git copy first
+        ref = 'refs/remotes/%s/HEAD' % remote
+        return GIT.Capture(['symbolic-ref', ref], cwd=cwd)
+      except subprocess2.CalledProcessError:
+        pass
+
+    try:
+      # Fetch information from git server
+      resp = GIT.Capture(['ls-remote', '--symref', url, 'HEAD'])
+      regex = r'^ref: (.*)\tHEAD$'
+      for line in resp.split('\n'):
+        m = re.match(regex, line)
+        if m:
+          return ''.join(GIT.RefToRemoteRef(m.group(1), remote))
+    except subprocess2.CalledProcessError:
+      pass
+    # Return default branch
+    return 'refs/remotes/%s/master' % remote
+
   @staticmethod
   def GetBranch(cwd):
     """Returns the short branch name, e.g. 'main'."""

tests/gclient_scm_test.py

@@ -196,6 +196,11 @@ from :3
         stderr=STDOUT, cwd=path).communicate()
     Popen([GIT, 'config', 'user.name', 'Some User'], stdout=PIPE,
         stderr=STDOUT, cwd=path).communicate()
+    # Set HEAD back to master
+    Popen([GIT, 'checkout', 'master', '-q'],
+          stdout=PIPE,
+          stderr=STDOUT,
+          cwd=path).communicate()
     return True
 
   def _GetAskForDataCallback(self, expected_prompt, return_value):
@@ -640,7 +645,7 @@ class ManagedGitWrapperTestCaseMock(unittest.TestCase):
       self, mockCheckOutput, mockExists, mockIsdir, mockClone):
     mockIsdir.side_effect = lambda path: path == self.base_path
     mockExists.side_effect = lambda path: path == self.base_path
-    mockCheckOutput.return_value = b''
+    mockCheckOutput.side_effect = [b'refs/remotes/origin/main', b'', b'']
 
     options = self.Options()
     scm = gclient_scm.GitWrapper(
@@ -648,18 +653,21 @@ class ManagedGitWrapperTestCaseMock(unittest.TestCase):
     scm.update(options, None, [])
 
     env = gclient_scm.scm.GIT.ApplyEnvVars({})
-    self.assertEqual(
-        mockCheckOutput.mock_calls,
-        [
-            mock.call(
-                ['git', '-c', 'core.quotePath=false', 'ls-files'],
-                cwd=self.base_path, env=env, stderr=-1),
-            mock.call(
-                ['git', 'rev-parse', '--verify', 'HEAD'],
-                cwd=self.base_path, env=env, stderr=-1),
+    self.assertEqual(mockCheckOutput.mock_calls, [
+        mock.call(['git', 'symbolic-ref', 'refs/remotes/origin/HEAD'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
+        mock.call(['git', '-c', 'core.quotePath=false', 'ls-files'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
+        mock.call(['git', 'rev-parse', '--verify', 'HEAD'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
     ])
-    mockClone.assert_called_with(
-        'refs/remotes/origin/master', self.url, options)
+    mockClone.assert_called_with('refs/remotes/origin/main', self.url, options)
     self.checkstdout('\n')
 
   @mock.patch('gclient_scm.GitWrapper._Clone')
@@ -670,7 +678,7 @@ class ManagedGitWrapperTestCaseMock(unittest.TestCase):
       self, mockCheckOutput, mockExists, mockIsdir, mockClone):
     mockIsdir.side_effect = lambda path: path == self.base_path
     mockExists.side_effect = lambda path: path == self.base_path
-    mockCheckOutput.return_value = b''
+    mockCheckOutput.side_effect = [b'refs/remotes/origin/main', b'', b'']
     mockClone.side_effect = [
         gclient_scm.subprocess2.CalledProcessError(
             None, None, None, None, None),
@@ -683,18 +691,21 @@ class ManagedGitWrapperTestCaseMock(unittest.TestCase):
     scm.update(options, None, [])
 
     env = gclient_scm.scm.GIT.ApplyEnvVars({})
-    self.assertEqual(
-        mockCheckOutput.mock_calls,
-        [
-            mock.call(
-                ['git', '-c', 'core.quotePath=false', 'ls-files'],
-                cwd=self.base_path, env=env, stderr=-1),
-            mock.call(
-                ['git', 'rev-parse', '--verify', 'HEAD'],
-                cwd=self.base_path, env=env, stderr=-1),
+    self.assertEqual(mockCheckOutput.mock_calls, [
+        mock.call(['git', 'symbolic-ref', 'refs/remotes/origin/HEAD'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
+        mock.call(['git', '-c', 'core.quotePath=false', 'ls-files'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
+        mock.call(['git', 'rev-parse', '--verify', 'HEAD'],
+                  cwd=self.base_path,
+                  env=env,
+                  stderr=-1),
     ])
-    mockClone.assert_called_with(
-        'refs/remotes/origin/master', self.url, options)
+    mockClone.assert_called_with('refs/remotes/origin/main', self.url, options)
     self.checkstdout('\n')
 
 

tests/scm_unittest.py

@@ -99,6 +99,26 @@ class GitWrapperTestCase(unittest.TestCase):
       r = scm.GIT.RemoteRefToRef(k, remote)
       self.assertEqual(r, v, msg='%s -> %s, expected %s' % (k, r, v))
 
+  @mock.patch('scm.GIT.Capture')
+  @mock.patch('os.path.exists', lambda _:True)
+  def testGetRemoteHeadRefLocal(self, mockCapture):
+    mockCapture.side_effect = ['refs/remotes/origin/main']
+    self.assertEqual('refs/remotes/origin/main',
+                     scm.GIT.GetRemoteHeadRef('foo', 'proto://url', 'origin'))
+    self.assertEqual(mockCapture.call_count, 1)
+
+  @mock.patch('scm.GIT.Capture')
+  @mock.patch('os.path.exists', lambda _:True)
+  def testGetRemoteHeadRefRemote(self, mockCapture):
+    mockCapture.side_effect = [
+        subprocess2.CalledProcessError(1, '', '', '', ''),
+        'ref: refs/heads/main\tHEAD\n' +
+        '0000000000000000000000000000000000000000\tHEAD',
+    ]
+    self.assertEqual('refs/remotes/origin/main',
+                     scm.GIT.GetRemoteHeadRef('foo', 'proto://url', 'origin'))
+    self.assertEqual(mockCapture.call_count, 2)
+
 
 class RealGitTest(fake_repos.FakeReposTestBase):
   def setUp(self):
@@ -180,10 +200,10 @@ class RealGitTest(fake_repos.FakeReposTestBase):
     self.assertEqual(
         (None, None), scm.GIT.FetchUpstreamTuple(self.cwd))
 
-  @mock.patch('scm.GIT.GetRemoteBranches', return_value=['origin/master'])
+  @mock.patch('scm.GIT.GetRemoteBranches', return_value=['origin/main'])
   def testFetchUpstreamTuple_GuessOriginMaster(self, _mockGetRemoteBranches):
-    self.assertEqual(
-        ('origin', 'refs/heads/master'), scm.GIT.FetchUpstreamTuple(self.cwd))
+    self.assertEqual(('origin', 'refs/heads/main'),
+                     scm.GIT.FetchUpstreamTuple(self.cwd))
 
   @mock.patch('scm.GIT.GetRemoteBranches',
               return_value=['origin/master', 'origin/main'])