git-sync-deps verifies that directory is a top-level git directory.

tools/git-sync-deps

 #!/usr/bin/python
 # Copyright 2014 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 """Parse a DEPS file and git checkout all of the dependencies.
 
 Args:
@@ skipping 46 matching lines @@
 
 def git_repository_sync_is_disabled(git, directory):
   try:
     disable = subprocess.check_output(
       [git, 'config', 'sync-deps.disable'], cwd=directory)
     return disable.lower().strip() in ['true', '1', 'yes', 'on']
   except subprocess.CalledProcessError:
     return False
 
 
+def is_git_toplevel(git, directory):
+  """Return true iff the directory is the top level of a Git repository.
+
+  Args:
+    git (string) the git executable
+
+    directory (string) the path into which the repository
+              is expected to be checked out.
+  """
+  try:
+    toplevel = subprocess.check_output(
+      [git, 'rev-parse', '--show-toplevel'], cwd=directory).strip()
+    return os.path.abspath(directory) == os.path.abspath(toplevel)
+  except subprocess.CalledProcessError:
+    return False
+
+
 def git_checkout_to_directory(git, repo, checkoutable, directory, verbose):
   """Checkout (and clone if needed) a Git repository.
 
   Args:
     git (string) the git executable
 
     repo (string) the location of the repository, suitable
          for passing to `git clone`.
 
     checkoutable (string) a tag, branch, or commit, suitable for
                  passing to `git checkout`
 
     directory (string) the path into which the repository
               should be checked out.
 
     verbose (boolean)
 
   Raises an exception if any calls to git fail.
   """
   if not os.path.isdir(directory):
     subprocess.check_call(
       [git, 'clone', '--quiet', repo, directory])
 
+  if not is_git_toplevel(git, directory):
+    # if the directory exists, but isn't a git repo, you will modify
+    # the parent repostory, which isn't what you want.
+    sys.stdout.write('%s\n  IS NOT TOP-LEVEL GIT DIRECTORY.\n' % directory)
+    return
+
   # Check to see if this repo is disabled.  Quick return.
   if git_repository_sync_is_disabled(git, directory):
     sys.stdout.write('%s\n  SYNC IS DISABLED.\n' % directory)
     return
 
   subprocess.check_call([git, 'fetch', '--quiet'], cwd=directory)
 
   subprocess.check_call(
     [git, 'checkout', '--quiet', checkoutable], cwd=directory)
 
@@ skipping 73 matching lines @@
   try:
     git_sync_deps(deps_file_path, argv, verbose)
     return 0
   except DepsError:
     usage(deps_file_path)
     return 1
 
 
 if __name__ == '__main__':
   exit(main(sys.argv[1:]))