Issue 4503 - ensure_dependencies.py fails for git submodule

ensure_dependencies.py

 #!/usr/bin/env python
 
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import sys
 import os
 import posixpath
 import re
@@ skipping 106 matching lines @@
                 if subprocess.call(['git', 'branch', '--track', local, remote],
                                    cwd=repo, stdout=devnull, stderr=devnull) == 0:
                     newly_tracked = True
         # Finally fetch any newly tracked remote branches
         if newly_tracked:
             subprocess.check_call(['git', 'fetch', '--quiet', 'origin'], cwd=repo)
 
     def update(self, repo, rev, revname):
         subprocess.check_call(['git', 'checkout', '--quiet', revname], cwd=repo)
 
+    def parse_repo_path(self, dot_git_path):
+      # .git for submodule is a file with actual repo path like so:
+      # gitdir: ../.git/some_path/some_other_path
+      with open(dot_git_path, 'r') as f:
+        return f.read().replace('\n', '')[8:] # skip 'gitdir: ' (8 first characters)
+
     def ignore(self, target, repo):
-        module = os.path.sep + os.path.relpath(target, repo)
-        exclude_file = os.path.join(repo, '.git', 'info', 'exclude')
-        _ensure_line_exists(exclude_file, module)
+      module = os.path.relpath(target, repo)
+      dot_git_path = os.path.join(repo, ".git")
+      exclude_file = os.path.join(dot_git_path, "info", "exclude")
+      if os.path.isfile(dot_git_path):
+        logging.warning("%s seems to be Git submodule" % dot_git_path)
+        new_repo = self.parse_repo_path(dot_git_path)
+        logging.warning('actual repo path is %s' % new_repo)
+        exclude_file = os.path.join(new_repo, "info", "exclude")
+      _ensure_line_exists(exclude_file, module)
 
     def postprocess_url(self, url):
         # Handle alternative syntax of SSH URLS
         if '@' in url and ':' in url and not urlparse.urlsplit(url).scheme:
             return 'ssh://' + url.replace(':', '/', 1)
         return url
 
 repo_types = OrderedDict((
     ('hg', Mercurial()),
     ('git', Git()),
@@ skipping 230 matching lines @@
     args = parser.parse_args()
 
     if args.quiet:
         logging.disable(logging.INFO)
 
     repos = args.repos
     if not len(repos):
         repos = [os.path.dirname(__file__)]
     for repo in repos:
         resolve_deps(repo)