sync: superproject - support for switching hosts and switching branches.

+ superproject will be fetched into a directory with the name
  “<remote name>-superproject.git” instead of the current
  “superproject.git” folder.

+ Deleted  _Clone method and added _Init method.

+ _Init method will do “git init --bare <remote>-superproject.git”.
  It will create the folder and set up a bare repository in
  <remote>-superproject.git folder.

+ _Fetch method, will pass <remote url>, <branch> arguments.
  Moved the --filter argument from “git clone” to “git fetch”.
  _Fetch method will execute the following command to fetch
  superproject. Added --no-tags argument.

  master:  git fetch <remote url> --force --no-tags --filter blob:none
  branch:  git fetch <remote url> --force --no-tags --filter blob:none \
           <branch>:<branch>

+ Performance improvements for aosp-master
  ++ repo init performance improved from 35 seconds to 17 seconds.
  ++ repo init --use-superproject is around 5 to 7 secsonds slower.
  ++ repo sync --use-superproject is around 3 to 4 minutes faster.

Tested the code with the following commands.

$ ./run_tests -v

Tested the sync code by using repo_dev alias and pointing to this CL.

$ time repo_dev init -u sso://android.git.corp.google.com/platform/manifest -b master --partial-clone --clone-filter=blob:limit=10M --repo-rev=main --use-superproject
...
  real	0m20.648s
  user	0m8.046s
  sys	0m3.271s

+ Without superproject
$ time repo init -u sso://android.git.corp.google.com/platform/manifest -b master --partial-clone --clone-filter=blob:limit=10M --repo-rev=main
  real	0m13.078s
  user	0m9.783s
  sys	0m2.528s

$ time repo_dev sync -c -j32 --use-superproject
...
  real	15m7.072s
  user	110m7.216s
  sys	20m17.559s

+ Without superproject
$ time repo sync -c -j32
...
  real	19m25.644s
  user	91m56.331s
  sys	20m59.170s

Bug: [google internal] b/180492484
Bug: [google internal] b/179470886
Bug: [google internal] b/180124069
Bug: https://crbug.com/gerrit/13709
Bug: https://crbug.com/gerrit/13707

Change-Id: Ib04bd7f1e25ceb75532643e58ad0129300ba3299
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/297702
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Raman Tenneti <rtenneti@google.com>

tests/test_git_superproject.py

@@ -97,17 +97,17 @@ class SuperprojectTestCase(unittest.TestCase):
     with mock.patch.object(self._superproject, '_GetBranch', return_value='junk'):
       self.assertFalse(superproject.Sync())
 
-  def test_superproject_get_superproject_mock_clone(self):
-    """Test with _Clone failing."""
-    with mock.patch.object(self._superproject, '_Clone', return_value=False):
+  def test_superproject_get_superproject_mock_init(self):
+    """Test with _Init failing."""
+    with mock.patch.object(self._superproject, '_Init', return_value=False):
       self.assertFalse(self._superproject.Sync())
 
   def test_superproject_get_superproject_mock_fetch(self):
-    """Test with _Fetch failing and _clone being called."""
-    with mock.patch.object(self._superproject, '_Clone', return_value=True):
+    """Test with _Fetch failing."""
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
       os.mkdir(self._superproject._superproject_path)
       with mock.patch.object(self._superproject, '_Fetch', return_value=False):
-        self.assertTrue(self._superproject.Sync())
+        self.assertFalse(self._superproject.Sync())
 
   def test_superproject_get_all_project_commit_ids_mock_ls_tree(self):
     """Test with LsTree being a mock."""
@@ -116,14 +116,15 @@ class SuperprojectTestCase(unittest.TestCase):
             '160000 commit e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06\tbootable/recovery\x00'
             '120000 blob acc2cbdf438f9d2141f0ae424cec1d8fc4b5d97f\tbootstrap.bash\x00'
             '160000 commit ade9b7a0d874e25fff4bf2552488825c6f111928\tbuild/bazel\x00')
-    with mock.patch.object(self._superproject, '_Clone', return_value=True):
-      with mock.patch.object(self._superproject, '_LsTree', return_value=data):
-        commit_ids = self._superproject._GetAllProjectsCommitIds()
-        self.assertEqual(commit_ids, {
-            'art': '2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea',
-            'bootable/recovery': 'e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06',
-            'build/bazel': 'ade9b7a0d874e25fff4bf2552488825c6f111928'
-        })
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      with mock.patch.object(self._superproject, '_Fetch', return_value=True):
+        with mock.patch.object(self._superproject, '_LsTree', return_value=data):
+          commit_ids = self._superproject._GetAllProjectsCommitIds()
+          self.assertEqual(commit_ids, {
+              'art': '2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea',
+              'bootable/recovery': 'e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06',
+              'build/bazel': 'ade9b7a0d874e25fff4bf2552488825c6f111928'
+          })
 
   def test_superproject_write_manifest_file(self):
     """Test with writing manifest to a file after setting revisionId."""
@@ -151,7 +152,7 @@ class SuperprojectTestCase(unittest.TestCase):
     projects = self._superproject._manifest.projects
     data = ('160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00'
             '160000 commit e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06\tbootable/recovery\x00')
-    with mock.patch.object(self._superproject, '_Clone', return_value=True):
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
       with mock.patch.object(self._superproject, '_Fetch', return_value=True):
         with mock.patch.object(self._superproject,
                                '_LsTree',