gitclone: add support for submodules, enabled by default

An unrelated change is about develop mode: the behaviour was simplified to do nothing if a working copy already exists.

TODO: handle removal of submodules

/reviewed-on !7

README.rst

@@ -121,7 +121,7 @@ try to redownload resource with wrong md5sum.
  slapos.recipe.build:gitclone
 ==============================
 
-Checkout a git repository.
+Checkout a git repository and its submodules by default.
 Supports slapos.libnetworkcache if present, and if boolean 'use-cache' option
 is true.
 
@@ -236,6 +236,7 @@ Then let's run the buildout::
   Running uninstall recipe.
   Installing git-clone.
   Cloning into '/sample-buildout/parts/git-clone'...
+  HEAD is now at 2566127 ...
 
 Let's take a look at the buildout parts directory now::
 
@@ -249,15 +250,12 @@ And let's see that current revision is "2566127"::
   >>> print(subprocess.check_output(['git', 'rev-parse', '--short', 'HEAD'], universal_newlines=True))
   2566127
 
-When updating, it will do a "git fetch; git reset revision"::
+When updating, it shouldn't do anything as revision is mentioned::
 
   >>> cd(sample_buildout)
   >>> print(system(buildout))
   Updating git-clone.
   ...
-  HEAD is now at 2566127 ... 
-  ...
-  <BLANKLINE>
 
 Empty revision/branch
 ~~~~~~~~~~~~~~~~~~~~~
@@ -327,7 +325,7 @@ and branch parameter is ignored::
 Setup a "develop" repository
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-If you need to setup a repository that will be manually alterated over time for
+If you need to setup a repository that will be manually altered over time for
 development purposes, you need to make sure buildout will NOT alter it and NOT
 erase your local modifications by specifying the "develop" flag::
 
@@ -366,7 +364,6 @@ repository::
   >>> cd(sample_buildout)
   >>> print(system(buildout))
   Updating git-clone.
-  Fetching origin
   ...
   <BLANKLINE>
 
@@ -386,17 +383,7 @@ Then, when update occurs, nothing is done::
   >>> cd(sample_buildout)
   >>> print(system(buildout))
   Updating git-clone.
-  Fetching origin
-  Fetching broken
-  Unable to update:
-  Traceback (most recent call last):
-  ...
-  ...CalledProcessError: Command '['git', 'fetch', '--all']' returned non-zero exit status 1
-  <BLANKLINE>
   ...
-  fatal: unable to access 'http://git.erp5.org/repos/nowhere/': The requested URL returned error: 500
-  error: Could not fetch broken
-  <BLANKLINE> 
 
   >>> cd(sample_buildout, 'parts', 'git-clone')
   >>> print(system('cat local_change'))
@@ -450,6 +437,21 @@ boolean option::
   repository = https://example.net/example.git/
   ignore-ssl-certificate = true
 
+Ignore cloning submodules
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+By default, cloning the repository will clone its submodules also. You can force
+git to ignore cloning submodules by defining `ignore-cloning-submodules` boolean
+option to 'true'::
+
+  [buildout]
+  parts = git-clone
+
+  [git-clone]
+  recipe = slapos.recipe.build:gitclone
+  repository = https://lab.nexedi.com/tiwariayush/test_erp5
+  ignore-cloning-submodules = true
+
 Other options
 ~~~~~~~~~~~~~
 

slapos/recipe/build/tests.py

@@ -4,10 +4,13 @@ from zope.testing import renormalizing
 import os
 import re
 import shutil
-import stat
 import tempfile
 import unittest
 import zc.buildout.testing
+from zc.buildout.testing import buildoutTearDown
+from contextlib import contextmanager
+from functools import wraps
+from subprocess import check_call, check_output, CalledProcessError
 from slapos.recipe.gitclone import GIT_CLONE_ERROR_MESSAGE, \
     GIT_CLONE_CACHE_ERROR_MESSAGE
 
@@ -26,25 +29,134 @@ def setUp(test):
   zc.buildout.testing.buildoutSetUp(test)
   zc.buildout.testing.install_develop('slapos.recipe.build', test)
 
+@contextmanager
+def chdir(path):
+  old = os.getcwd()
+  try:
+    os.chdir(path)
+    yield old
+  finally:
+    os.chdir(old)
+
+def with_buildout(wrapped):
+  def wrapper(self):
+    self.globs = {}
+    setUp(self)
+    try:
+      wrapped(self, **self.globs)
+    finally:
+      buildoutTearDown(self)
+  return wraps(wrapped)(wrapper)
+
 class GitCloneNonInformativeTests(unittest.TestCase):
 
   def setUp(self):
     self.dir = os.path.realpath(tempfile.mkdtemp())
     self.parts_directory_path = os.path.join(self.dir, 'test_parts')
 
+  def setUpParentRepository(self):
+    """
+    This function sets ups repositories for parent repo and adds file and commit
+    to it.
+    """
+    # Create parent and submodule directory
+    self.project_dir = os.path.join(self.dir, 'main_repo')
+    os.mkdir(self.project_dir)
+
+    # Add files and folder in parent repo and initialize git in it
+    check_call(['git', 'init'], cwd=self.project_dir)
+    self.setUpGitConfig(self.project_dir)
+    os.mkdir(os.path.join(self.project_dir, 'dir1'))
+    self.touch(self.project_dir, 'file1.py')
+    self.gitAdd(self.project_dir)
+    self.gitCommit(self.project_dir, msg='Add file and folder in main repo')
+
+  def setUpSubmoduleRepository(self):
+    """
+    This function sets up repositories and config for parent repo and a
+    submodule repo and create small commits as well as links the 2 repos.
+    """
+    # Create parent and submodule directory
+    self.submodule_dir = os.path.join(self.dir ,'submodule_repo')
+    os.mkdir(self.submodule_dir)
+
+    # Add files in submodule repo and initialize git in it
+    check_call(['git', 'init'], cwd=self.submodule_dir)
+    self.setUpGitConfig(self.submodule_dir)
+    self.touch(self.submodule_dir, 'file1.py')
+    self.gitAdd(self.submodule_dir)
+    self.gitCommit(self.submodule_dir, msg='Add file1 in submodule repo')
+
+  def attachSubmoduleToParent(self):
+    """
+    Adds the submodule repo to parent repo and creates a commit in parent if
+    parent and submodule repo are present.
+    """
+    assert hasattr(self, 'project_dir') and hasattr(self, 'submodule_dir'), (
+      "Make sure parent repo and submodule repo are present")
+    submodule_dir_main_repo = os.path.join(self.project_dir, 'dir1')
+    # Add submodule to main repo and commit
+    check_call(['git', 'submodule', 'add', self.submodule_dir],
+                cwd=submodule_dir_main_repo)
+    self.gitCommit(self.project_dir, msg='Add submodule repo')
+
+  def createRepositoriesAndConnect(self):
+    """
+    Creates parent and submodule repository and then adds the submodule repo to
+    parent repo and creates a commit in parent.
+    """
+    self.setUpParentRepository()
+    self.setUpSubmoduleRepository()
+    self.attachSubmoduleToParent()
+
   def tearDown(self):
     shutil.rmtree(self.dir)
     for var in list(os.environ):
       if var.startswith('SRB_'):
         del os.environ[var]
 
-  def write_file(self, filename, contents, mode=stat.S_IREAD | stat.S_IWUSR):
-    path = os.path.join(self.dir, filename)
-    fh = open(path, 'w')
-    fh.write(contents)
-    fh.close()
-    os.chmod(path, mode)
-    return path
+  def setUpGitConfig(self, proj_dir):
+    """
+    Setup user and email for given git repository
+    """
+    check_call(['git', 'config', 'user.email', 'test@example.com'], cwd=proj_dir)
+    check_call(['git', 'config', 'user.name', 'Test'], cwd=proj_dir)
+
+  def gitOutput(self, *args, **kw):
+    return check_output(('git',) + args, universal_newlines=True, **kw)
+
+  def gitAdd(self, proj_dir):
+    """runs a 'git add .' in the provided git repo
+    :param proj_dir:    path to a git repo
+    """
+    check_call(['git', 'add', '.'], cwd=proj_dir)
+
+  def gitCommit(self, proj_dir, msg):
+    """runs a 'git commit -m msg' in the provided git repo
+    :param proj_dir:  path to a git repo
+    """
+    check_call(['git', 'commit', '-m', msg], cwd=proj_dir)
+
+  def getRepositoryHeadCommit(self, proj_dir):
+    """
+    Returns the sha of HEAD of a git repo
+    """
+    return self.gitOutput('rev-parse', 'HEAD', cwd=proj_dir).rstrip()
+
+  def touch(self, *parts):
+    os.close(os.open(os.path.join(*parts), os.O_CREAT, 0o666))
+
+  def readFile(self, *parts):
+    with open(os.path.join(*parts), 'r') as f:
+      return f.read()
+
+  def checkLocalChanges(self, parent_local_change_path,
+                        submodule_local_change_path):
+    # Check if the file are created at the expected position and check contents
+    self.assertTrue(os.path.exists(parent_local_change_path))
+    self.assertTrue(os.path.exists(submodule_local_change_path))
+    self.assertEqual(self.readFile(parent_local_change_path), 'foo')
+    self.assertEqual(self.readFile(submodule_local_change_path), 'bar')
 
   def makeGitCloneRecipe(self, options):
     from slapos.recipe.gitclone import Recipe
@@ -63,15 +175,15 @@ class GitCloneNonInformativeTests(unittest.TestCase):
   def test_using_download_cache_if_git_fails(self):
     recipe = self.makeGitCloneRecipe({"use-cache": "true",
                                       "repository": BAD_GIT_REPOSITORY})
-    os.chdir(self.dir)
-    with self.assertRaises(zc.buildout.UserError) as cm:
+    with chdir(self.dir), \
+         self.assertRaises(zc.buildout.UserError) as cm:
       recipe.install()
     self.assertEqual(str(cm.exception), GIT_CLONE_CACHE_ERROR_MESSAGE)
 
   def test_not_using_download_cache_if_forbidden(self):
     recipe = self.makeGitCloneRecipe({"repository": BAD_GIT_REPOSITORY})
-    os.chdir(self.dir)
-    with self.assertRaises(zc.buildout.UserError) as cm:
+    with chdir(self.dir), \
+         self.assertRaises(zc.buildout.UserError) as cm:
       recipe.install()
     self.assertEqual(str(cm.exception), GIT_CLONE_ERROR_MESSAGE)
 
@@ -90,6 +202,239 @@ class GitCloneNonInformativeTests(unittest.TestCase):
     self.assertTrue(os.path.exists(git_repository_path))
     self.assertFalse(os.path.exists(bad_file_path), "pyc file not removed")
 
+  @with_buildout
+  def test_clone_and_update_submodule(self, buildout, write,
+                                      sample_buildout, **kw):
+    """
+    Remote:
+      Repositories status:  Parent repo(M1) and Submodule repo (S1)
+      Parent repo (M1) ---references---> Submodule(S1)
+    Local:
+      Buildout should install(using branch) at M1+S1
+
+    Remote:
+      Repositories status:  Parent repo(M2) and Submodule repo (S2)
+      Parent repo (M2) ---references---> Submodule(S1)
+    Local:
+      Buildout should update to at M2+S1
+
+    Remote:
+      Repositories status:  Parent repo(M3) and Submodule repo (S2)
+      Parent repo (M3) ---references---> Submodule(S2)
+    Local:
+      Buildout should update to M3+S2
+    """
+    self.createRepositoriesAndConnect()
+
+    # Clone repositories in status M1 and S1 (M1---->S1)
+    write(sample_buildout, 'buildout.cfg',
+"""
+[buildout]
+parts = git-clone
+
+[git-clone]
+recipe = slapos.recipe.build:gitclone
+repository = %s
+""" % self.project_dir)
+    check_call([buildout])
+
+    main_repo_path = os.path.join(sample_buildout, 'parts', 'git-clone')
+    self.assertTrue(os.path.exists(main_repo_path))
+    submodule_repo_path = os.path.join(main_repo_path, 'dir1',
+                                       'submodule_repo')
+    # Check if the submodule is not empty
+    self.assertTrue(os.listdir(submodule_repo_path))
+
+    # Get the head commit of the submodule repo
+    head_commit_submodule_after_clone = self.getRepositoryHeadCommit(
+                                              submodule_repo_path)
+
+    # Add untracked files as markers to check that the part
+    # was updated rather than removed+reinstalled.
+    write(main_repo_path, 'local_change_main', 'foo')
+    write(submodule_repo_path, 'local_change_submodule', 'bar')
+    parent_local_change_path = os.path.join(main_repo_path,
+                                            'local_change_main')
+    submodule_local_change_path = os.path.join(submodule_repo_path,
+                                               'local_change_submodule')
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+    # Trigger `update` method call for gitclone recipe
+    check_call([buildout])
+
+    # The local changes should be still there after update
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+    # On REMOTE, update submodule repository and parent repo with new commit,
+    # but do not update the pointer to submodule on parent repo
+    self.touch(self.project_dir, 'file2.py')
+    self.gitAdd(self.project_dir)
+    self.gitCommit(self.project_dir, msg='Add file2 in main repo')
+    self.touch(self.submodule_dir, 'file2.py')
+    self.gitAdd(self.submodule_dir)
+    self.gitCommit(self.submodule_dir, msg='Add file2 in submodule repo')
+
+    # Trigger update on the same branch. Remember the state at remote is
+    # M2 and S2 (M2---->S1)
+    check_call([buildout])
+    head_commit_submodule_after_first_update = self.getRepositoryHeadCommit(
+                                                      submodule_repo_path)
+    # The local changes should be still there after update
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+    # On REMOTE, add new commit to submodule and then update the submodule
+    # pointer on parent repo and commit it
+    submodule_dir_main_repo = os.path.join(self.project_dir, 'dir1',
+                                           'submodule_repo')
+    check_call(['git', 'checkout', 'master'], cwd=submodule_dir_main_repo)
+    check_call(['git', 'pull', '--ff'], cwd=submodule_dir_main_repo)
+    self.gitAdd(self.project_dir)
+    self.gitCommit(self.project_dir, msg='Update submodule version')
+
+    # Trigger update again on the same branch. Remember the state at remote is
+    # M3 and S2(M3---->S2)
+    check_call([buildout])
+    head_commit_submodule_after_second_update = self.getRepositoryHeadCommit(
+                                                      submodule_repo_path)
+    # The local changes should be still there after update
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+
+    # Check the HEAD of the submodule
+    submodule_head_commit = self.getRepositoryHeadCommit(self.submodule_dir)
+    self.assertEqual(head_commit_submodule_after_clone,
+                     head_commit_submodule_after_first_update)
+
+    self.assertNotEqual(head_commit_submodule_after_first_update,
+                        head_commit_submodule_after_second_update)
+
+    self.assertEqual(head_commit_submodule_after_second_update,
+                     submodule_head_commit)
+
+    # Update the recipe with new revision for parent and trigger uninstall/
+    # install
+    write(sample_buildout, 'buildout.cfg',
+"""
+[buildout]
+parts = git-clone
+
+[git-clone]
+recipe = slapos.recipe.build:gitclone
+repository = %s
+revision = %s
+""" % (self.project_dir, str(self.getRepositoryHeadCommit(self.project_dir))))
+    check_call([buildout])
+
+    self.assertTrue(os.path.exists(main_repo_path))
+    # Check if the submodule is not empty
+    self.assertTrue(os.listdir(submodule_repo_path))
+
+    # Since calling buildout should've reinstalled, we expect the local changes
+    # to be gone
+    self.assertFalse(os.path.exists(parent_local_change_path))
+    self.assertFalse(os.path.exists(submodule_local_change_path))
+
+    # Get the head commit of the submodule repo
+    head_commit_submodule_with_revision = self.getRepositoryHeadCommit(
+                                                      submodule_repo_path)
+
+    self.assertEqual(head_commit_submodule_with_revision,
+                     submodule_head_commit)
+
+  @with_buildout
+  def test_clone_install_and_udpate_develop_mode(self, buildout, write,
+                                                 sample_buildout, **kw):
+    """
+    Test to verify the result of development mode, i.e., develop = True.
+    In this case, we expect local changes to be untouched
+    """
+    self.createRepositoriesAndConnect()
+
+    # Clone repositories in status M1 and S1 (M1---->S1)
+    write(sample_buildout, 'buildout.cfg',
+"""
+[buildout]
+parts = git-clone
+
+[git-clone]
+recipe = slapos.recipe.build:gitclone
+repository = %s
+develop=True
+""" % self.project_dir)
+    check_call([buildout])
+
+    main_repo_path = os.path.join(sample_buildout, 'parts', 'git-clone')
+    self.assertTrue(os.path.exists(main_repo_path))
+    submodule_repo_path = os.path.join(main_repo_path, 'dir1',
+                                       'submodule_repo')
+    # Check if the submodule is not empty
+    self.assertTrue(os.listdir(submodule_repo_path))
+
+    # Add untracked files as markers to check that the part
+    # was updated rather than removed+reinstalled.
+    write(main_repo_path, 'local_change_main', 'foo')
+    write(submodule_repo_path, 'local_change_submodule', 'bar')
+    parent_local_change_path = os.path.join(main_repo_path,
+                                            'local_change_main')
+    submodule_local_change_path = os.path.join(submodule_repo_path,
+                                               'local_change_submodule')
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+    # Trigger `update` method call for gitclone recipe
+    check_call([buildout])
+
+    # The local changes should be still there after update as it is develop mode
+    self.checkLocalChanges(parent_local_change_path, submodule_local_change_path)
+
+  @with_buildout
+  def test_git_add_for_submodule_changes(self, buildout, write,
+                                         sample_buildout, **kw):
+    """
+    Test to verify the result of `git status` being executed from parent as well
+    as submodule repository after making some local changes in submodule repo
+    """
+    # Create a parent repo
+    self.setUpParentRepository()
+    # Create submodule repository
+    self.setUpSubmoduleRepository()
+    # Attach the submodule repository to the parent repo on remote
+    self.attachSubmoduleToParent()
+
+    write(sample_buildout, 'buildout.cfg',
+"""
+[buildout]
+parts = git-clone
+
+[git-clone]
+recipe = slapos.recipe.build:gitclone
+repository = %s
+""" % self.project_dir)
+    check_call([buildout])
+
+    local_parent_dir = os.path.join(sample_buildout, 'parts', 'git-clone')
+    local_submodule_dir = os.path.join(local_parent_dir, 'dir1',
+                                       'submodule_repo')
+
+    # Now so some change manually in submodule repo, but don't commit
+    self.touch(local_submodule_dir, 'file2.py')
+    self.gitAdd(local_submodule_dir)
+
+    # Do `git status` to check if the changes are shown for the repo in parent
+    # This should the changes been done in the main as well as submodule repo
+    files_changed = self.gitOutput('status', '--porcelain',
+                                    cwd=local_parent_dir)
+    file_changed, = files_changed.splitlines()
+    # Check if submodule directory is part of modified list
+    self.assertEqual(file_changed, ' M dir1/submodule_repo')
+
+    # Now that `git status` in parent repo shows changes in the submodule repo,
+    # do `git status` in the submodule repo to re-confirm the exact file change
+    files_changed = self.gitOutput('status', '--porcelain',
+                                    cwd=local_submodule_dir)
+    file_changed, = files_changed.splitlines()
+    # Check if submodule directory is part of modified list
+    self.assertEqual(file_changed, 'A  file2.py')
+
   def test_ignore_ssl_certificate(self, ignore_ssl_certificate=True):
     import slapos.recipe.gitclone
 
@@ -117,7 +462,6 @@ class GitCloneNonInformativeTests(unittest.TestCase):
 
     # Check git clone parameters
     _ = self.assertIn if ignore_ssl_certificate else self.assertNotIn
-    _("--config", check_call_parameter_list[0][0])
     _("http.sslVerify=false", check_call_parameter_list[0][0])
 
     # Restore original check_call method
@@ -126,6 +470,26 @@ class GitCloneNonInformativeTests(unittest.TestCase):
   def test_ignore_ssl_certificate_false(self):
     self.test_ignore_ssl_certificate(ignore_ssl_certificate=False)
 
+  def test_clone_submodules_by_default(self, ignore_cloning_submodules=False):
+    self.createRepositoriesAndConnect()
+    recipe = self.makeGitCloneRecipe(
+      {'repository': self.project_dir,
+        'ignore-cloning-submodules': str(ignore_cloning_submodules).lower()}
+    )
+    recipe.install()
+    main_repo_path = os.path.join(self.parts_directory_path, "test")
+    self.assertTrue(os.path.exists(main_repo_path))
+    submodule_repo_path = os.path.join(main_repo_path, 'dir1',
+                                       'submodule_repo')
+    # Check if the folder exists
+    self.assertTrue(os.path.exists(main_repo_path))
+    # Check is there is anything in submodule repository path
+    self.assertNotEqual(bool(ignore_cloning_submodules),
+                        bool(os.listdir(submodule_repo_path)))
+
+  def test_ignore_cloning_submodules(self):
+    self.test_clone_submodules_by_default(ignore_cloning_submodules=True)
+
 def test_suite():
   suite = unittest.TestSuite((
       doctest.DocFileSuite(

slapos/recipe/gitclone.py

@@ -34,7 +34,7 @@ import time
 import traceback
 
 from zc.buildout import UserError
-from subprocess import call, check_call, CalledProcessError
+from subprocess import check_call, CalledProcessError
 import subprocess
 
 try:
@@ -145,7 +145,8 @@ class Recipe(object):
       self.git_command = 'git'
     self.sparse = options.get('sparse-checkout', '').strip()
     # Set boolean values
-    for key in ('develop', 'shared', 'use-cache', 'ignore-ssl-certificate'):
+    for key in ('develop', 'shared', 'use-cache', 'ignore-ssl-certificate',
+                'ignore-cloning-submodules'):
       setattr(self, key.replace('-', '_'), options.get(key, '').lower() in TRUE_VALUES)
     if self.shared:
       self.use_cache = False
@@ -171,7 +172,6 @@ class Recipe(object):
       command.append(revision)
     check_call(command, cwd=self.location)
 
-
   def install(self):
     """
     Do a git clone.
@@ -213,6 +213,13 @@ class Recipe(object):
 
     if config and self.use_cache:
       raise NotImplementedError
+
+    if not self.ignore_cloning_submodules:
+      # `--recurse-submodules` to the git clone command will automatically
+      # initialize and update each submodule in the repository.
+      config.append('submodule.recurse=true')
+      git_clone_command.append('--recurse-submodules')
+
     for config in config:
       git_clone_command += '--config', config
 
@@ -230,6 +237,11 @@ class Recipe(object):
       if self.use_cache:
         upload_network_cached(os.path.join(self.location, '.git'),
                               self.repository, self.revision, self.networkcache)
+      if not self.ignore_cloning_submodules:
+        # Update submodule repository to the commit which is being pointed to
+        # in main repo
+        check_call([self.git_command, 'submodule', 'update', '--init',
+                    '--recursive'], cwd=self.location)
     except CalledProcessError:
       print("Unable to download from git repository."
             " Trying from network cache...")
@@ -260,32 +272,35 @@ class Recipe(object):
   def update(self):
     """
     Do a git fetch.
-    If user doesn't develop, reset to remote revision (or branch if revision is
-    not specified).
+    If user doesn't develop, reset to upstream of the branch.
+    With support for submodules, we also update the submodule repository if
+    there has been update to the pointer of the submodules in the parent repo.
+    This however puts the updated submodules in a DETACHED state.
     """
+    # If develop or revision parameter, no need to update
+    if self.develop or self.revision:
+      return
     try:
       # first cleanup pyc files
       self.deletePycFiles(self.location)
 
-      # then update,
-      # but, to save time, only if we don't have the revision already
-      revision_already_fetched = \
-            self.revision and   \
-            call([self.git_command, 'rev-parse', '--verify', self.revision],
-                    cwd=self.location) == 0
-      if not revision_already_fetched:
+      # Fetch and reset to the upstream
       check_call([self.git_command, 'fetch', '--all'], cwd=self.location)
-
-      # If develop parameter is set, don't reset/update.
-      # Otherwise, reset --hard
-      if not self.develop:
-        if self.revision:
-          self.gitReset(self.revision)
-        else:
       self.gitReset('@{upstream}')
+
+      if not self.ignore_cloning_submodules:
+        # Update the submodule to the commit which parent repo points to if
+        # there has been revision is present for the parent repo.
+        # According to man-page of submodule, update also clones missing
+        # submodules and updating the working tree of the submodules. This is
+        # why we do update here only after we are ok with revision of parent
+        # repo being checked out to the desired one.
+        # It will also init a submodule if required
+        # NOTE: This will put the submodule repo in a `Detached` state.
+        check_call([self.git_command, 'submodule', 'update', '--init', '-f',
+                    '--recursive'], cwd=self.location)
+
     except:
-      if not self.develop:
-        raise
       # Buildout will remove the installed location and mark the part as not
       # installed if an error occurs during update. If we are developping this
       # repository we do not want this to happen.