Pull Chromium dependencies to Pipa checkout via DEPS and GITDEPS.

pipa/build/gitdeps.py

Index: pipa/build/gitdeps.py
diff --git a/pipa/build/gitdeps.py b/pipa/build/gitdeps.py
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+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# This file was originally copied from syzygy project available at
+# https://github.com/google/syzygy.
+"""A utility script for checking out subdirectories of many GIT repositories
+to specified locations, like is possible with SVN and gclient. This uses a
+combination of GIT, sparse-checkout, shallow-clone and filesystem junctions.
+
+For each dependency in a 'gitdeps' file this script will checkout one
+subdirectory of one repository into a specified location. The input is as
+follows:
+
+- The user specifies a local destination for the checkout.
+- The user specifies a source repository.
+- The user specifies a list of subdirectories of the repository to get.
+- The user specifies a revision.
+
+The checkout works as follows:
+
+- An empty git checkout is initialized in the cache directory. This will be
+  in a subfolder with an essentially random name.
+- The specified repository is added as a remote to that repo.
+- A sparse-checkout directive is added to select only the desired
+  subdirectories.
+- The repository is cloned using a depth of 1 (no history, only the actual
+  contents of the desired revision).
+- The destination directories are created as junctions pointing to the
+  desired subdirectory of the checkout in the cache directory.
+
+The script maintains its state in the root of the cache directory, allowing it
+to reuse checkout directories when possible.
+"""
+
+import ast
+import glob
+import hashlib
+import logging
+import optparse
+import os
+import random
+import re
+import subprocess
+import threading
+
+
+_LOGGER = logging.getLogger(os.path.basename(__file__))
+
+
+# Matches a SHA1 hash used as a git revision.
+_GIT_SHA1_RE = re.compile('^[A-Fa-f0-9]{40}$')
+
+
+def _ParseCommandLine():
+  """Parses the command-line and returns an options structure."""
+  option_parser = optparse.OptionParser()
+  option_parser.add_option('--cache-dir', type='string',
+      default='.gitdeps-cache',
+      help='The directory to be used for storing cache files. Defaults to '
+           '.gitdeps-cache in the current working directory.')
+  option_parser.add_option('--output-dir', type='string', default='.',
+      help='The directory to be used as the root of all output. Defaults to '
+           'the current working directory.')
+  option_parser.add_option('--dry-run', action='store_true', default=False,
+      help='If true then will simply list actions that would be performed.')
+  option_parser.add_option('--force', action='store_true', default=False,
+      help='If true then will force the checkout to be completely rebuilt.')
+  option_parser.add_option('--verbose', dest='log_level', action='store_const',
+      default=logging.INFO, const=logging.DEBUG,
+      help='Enables verbose logging.')
+  option_parser.add_option('--quiet', dest='log_level', action='store_const',
+      default=logging.INFO, const=logging.ERROR,
+      help='Disables all output except for errors.')
+
+  options, args = option_parser.parse_args()
+
+  # Configure logging.
+  logging.basicConfig(level=options.log_level)
+
+  # Set default values.
+  if not args:
+    # Default to checking for a file in the current working directory.
+    _LOGGER.info('Defaulting to using GITDEPS in current working directory.')
+    args = ['GITDEPS']
+
+  # Validate arguments and options.
+  if not os.path.isdir(options.output_dir):
+    option_parser.error('Output directory does not exist: %s' %
+        options.output_dir)
+  for path in args:
+    if not os.path.exists(path):
+      option_parser.error('Missing dependency file: %s' % path)
+
+  # Normalize local paths for prettier output.
+  options.cache_dir = os.path.normpath(os.path.abspath(options.cache_dir))
+  options.output_dir = os.path.normpath(os.path.abspath(options.output_dir))
+
+  return options, args
+
+
+class RepoOptions(object):
+  """Light object used for shuttling around information about a dependency."""
+
+  def __init__(self):
+    self.repository = None
+    self.revision = None
+    self.output_dir = None
+    self.remote_dirs = []
+    self.deps_file = None
+    self.checkout_dir = None
+    self.recurse = False
+
+  def __str__(self):
+    """Stringifies this object for debugging."""
+    return ('RepoOptions(repository=%s, revision=%s, output_dir=%s, '
+            'remote_dirs=%s, deps_file=%s, checkout_dir=%s, recurse=%s)') % (
+                self.repository.__repr__(),
+                self.revision.__repr__(),
+                self.output_dir.__repr__(),
+                self.remote_dirs.__repr__(),
+                self.deps_file.__repr__(),
+                self.checkout_dir.__repr__(),
+                self.recurse.__repr__())
+
+
+def _ParseRepoOptions(cache_dir, root_output_dir, deps_file_path, key, value):
+  """Given the |root_output_dir| specified on the command line, a |key| and
+  |value| pair from a GITDEPS file, and the path of the deps file, generates
+  a corresponding RepoOptions object. The |key| is the output path of the
+  checkout relative to |root_output_dir|, and |value| consists of a
+  (repository URL, remote directory, revision hash) tuple. This can raise an
+  Exception on failure.
+  """
+  bad = False
+  if ((type(value) != list and type(value) != tuple) or len(value) < 3 or
+      len(value) > 4 or (type(value[1]) != list and type(value[1]) != tuple)):
+    bad = True
+  if len(value) == 4 and type(value[3]) != dict:
+    bad = True
+  if bad:
+    _LOGGER.error('Invalid dependency tuple: %s', value)
+    raise Exception()
+
+  # Always use lowercase SHA1 hashes for consistency.
+  refspec = value[2]
+  if _GIT_SHA1_RE.match(refspec):
+    refspec = refspec.lower()
+
+  repo_options = RepoOptions()
+  repo_options.output_dir = os.path.normpath(os.path.abspath(os.path.join(
+      root_output_dir, key)))
+  repo_options.repository = value[0]
+  repo_options.remote_dirs = value[1]
+  repo_options.revision = refspec
+  repo_options.deps_file = deps_file_path
+
+  # Parse additional options.
+  if len(value) > 3:
+    repo_options.recurse = value[3].get('recurse', False) == True
+
+  # Create a unique name for the checkout in the cache directory. Make the
+  # output directory relative to the cache directory so that they can be
+  # moved around together.
+  output_dir_rel = os.path.relpath(repo_options.output_dir,
+                                   root_output_dir).lower()
+  if output_dir_rel.startswith('..'):
+    raise Exception('Invalid output directory: %s' % key)
+  n = hashlib.md5(output_dir_rel).hexdigest()
+  repo_options.checkout_dir = os.path.abspath(os.path.join(cache_dir, n, 'src'))
+
+  return repo_options
+
+
+def _EnsureDirectoryExists(path, comment_name, dry_run):
+  """Ensures that the given |path| exists. Only actually creates the directory
+  if |dry_run| is False. |comment_name| is used during logging of this
+  operation.
+  """
+  if not comment_name:
+    comment_name += ' '
+  else:
+    comment_name = ''
+  if not os.path.exists(path):
+    _LOGGER.debug('Creating %sdirectory: %s', comment_name, path)
+    if not dry_run:
+      os.makedirs(path)
+
+
+def _GetCasedFilename(filename):
+  """Returns the full case-sensitive filename for the given |filename|. If the
+  path does not exist, returns the original |filename| as is.
+  """
+  pattern = '%s[%s]' % (filename[:-1], filename[-1])
+  filenames = glob.glob(pattern)
+  if not filenames:
+    return filename
+  return filenames[0]
+
+
+def _Shell(*cmd, **kw):
+  """Runs |cmd|, returns the results from Popen(cmd).communicate(). Additional
+  keyword arguments are passed on to subprocess.Popen. If |stdout| and |stderr|
+  are not specified, they default to subprocess.PIPE. If |dry_run| is not
+  specified it defaults to True. The command is only actually run if |dry_run|
+  is False. This can raise a RuntimeError on failure.
+  """
+  if 'cwd' in kw:
+    _LOGGER.debug('Executing %s in "%s".', cmd, kw['cwd'])
+  else:
+    _LOGGER.debug('Executing %s.', cmd)
+  if kw.get('dry_run', True):
+    return ('', '')
+  kw.pop('dry_run', None)
+  dump_on_error = kw.pop('dump_on_error', False)
+
+  kw['shell'] = True
+  kw.setdefault('stdout', subprocess.PIPE)
+  kw.setdefault('stderr', subprocess.PIPE)
+  prog = subprocess.Popen(cmd, **kw)
+
+  stdout, stderr = prog.communicate()
+  if prog.returncode != 0:
+    if dump_on_error:
+      print stdout
+      print stderr
+    raise RuntimeError('Command "%s" returned %d.' % (cmd, prog.returncode))
+  return (stdout, stderr)
+
+
+def _IsGitCheckoutRoot(path):
+  """Return true if the given |path| is the root of a git checkout."""
+  return os.path.exists(os.path.join(path, '.git'))
+
+
+# Matches a GIT config file section header, and grabs the name of the section
+# in the first group. Used by _GetGitOrigin.
+_GIT_CONFIG_SECTION_RE = re.compile(r'^\s*\[(.*?)\]\s*$')
+# Matches the URL line from a 'remote' section of a GIT config. Used by
+# _GetGitOrigin.
+_GIT_CONFIG_REMOTE_URL_RE = re.compile(r'^\s*url\s*=\s*(.*?)\s*$')
+
+
+def _GetGitOrigin(path):
+  """Returns the URL of the 'origin' remote for the git repo in |path|. Returns
+  None if the 'origin' remote doesn't exist. Raises an IOError if |path| doesn't
+  exist or is not a git repo.
+  """
+  section = None
+  for line in open(os.path.join(path, '.git', 'config'), 'rb'):
+    m = _GIT_CONFIG_SECTION_RE.match(line)
+    if m:
+      section = m.group(1)
+      continue
+
+    # We only care about the 'origin' configuration.
+    if section != 'remote "origin"':
+      continue
+
+    m = _GIT_CONFIG_REMOTE_URL_RE.match(line)
+    if m:
+      return m.group(1).strip()
+
+  return None
+
+
+def _GetGitHead(path):
+  """Returns the hash of the head of the git repo in |path|. Raises an IOError
+  if |path| doesn't exist or is not a git repo.
+  """
+  return open(os.path.join(path, '.git', 'HEAD'), 'rb').read().strip()
+
+
+def _NormalizeGitPath(path):
+  """Given a |path| in a GIT repository (relative to its root), normalizes it so
+  it will match only that exact path in a sparse checkout.
+  """
+  path = path.strip()
+  if not path.startswith('/'):
+    path = '/' + path
+  if not path.endswith('/'):
+    path += '/'
+  return path
+
+
+def _RenameCheckout(path, dry_run):
+  """Renames the checkout in |path| so that it can be subsequently deleted.
+  Only actually does the work if |dry_run| is False. Returns the path of the
+  renamed checkout directory. Raises an Exception on failure.
+  """
+
+  def _RenameCheckoutImpl(path, dry_run):
+    if dry_run:
+      return path + '-old-dryrun'
+    attempts = 0
+    while attempts < 10:
+      newpath = '%s-old-%04d' % (path, random.randint(0, 999))
+      try:
+        os.rename(path, newpath)
+        return newpath
+      except WindowsError:
+        attempts += 1
+    raise Exception('Unable to rename checkout directory: %s' % path)
+
+  newpath = _RenameCheckoutImpl(path, dry_run)
+  _LOGGER.debug('Renamed checkout directory: %s', newpath)
+  return newpath
+
+
+def _DeleteCheckout(path, dry_run):
+  """Deletes the checkout in |path|. Only actually deletes the checkout if
+  |dry_run| is False.
+  """
+  _LOGGER.info('Deleting checkout directory: %s', path)
+  if dry_run:
+    return
+  _Shell('rmdir', '/S', '/Q', path, dry_run=False)
+
+
+def _GenerateSparseCheckoutPathAndContents(repo):
+  """Generates the path to the sparse checkout file, and the desired
+  contents. Returns a tuple of (path, contents). |repo| is a RepoOptions object.
+  """
+  sparse_file = os.path.join(repo.checkout_dir, '.git', 'info',
+                             'sparse-checkout')
+  if not repo.remote_dirs:
+    contents = '*\n'
+  else:
+    contents = ''.join(_NormalizeGitPath(dir) + '\n'
+                       for dir in repo.remote_dirs)
+  return (sparse_file, contents)
+
+
+def _HasValidSparseCheckoutConfig(repo):
+  """Determines if the GIT repo in |path| has a valid sparse-checkout
+  configuration as configured by the RepoOptions |repo|. Returns True or False.
+  """
+  (sparse_file, contents) = _GenerateSparseCheckoutPathAndContents(repo)
+  try:
+    if open(sparse_file, 'rb').read() == contents:
+      return True
+    return False
+  except IOError:
+    return False
+
+
+def _CreateCheckout(path, repo, dry_run):
+  """Creates a checkout in the provided |path|. The |path| must not already
+  exist. Uses the repository configuration from the provided |repo| RepoOptions
+  object. Only actually creates the checkout if |dry_run| is false.
+  """
+  # We expect the directory not to exist, as this is a fresh checkout we are
+  # creating.
+  if not dry_run:
+    if os.path.exists(path):
+      raise Exception('Checkout directory already exists: %s' % path)
+
+  _LOGGER.info('Creating checkout directory: %s', path)
+  if not dry_run:
+    os.makedirs(path)
+
+  _LOGGER.debug('Initializing the checkout.')
+  _Shell('git', 'init', cwd=path, dry_run=dry_run)
+  _Shell('git', 'remote', 'add', 'origin', repo.repository, cwd=path,
+         dry_run=dry_run)
+  _Shell('git', 'config', 'core.sparsecheckout', 'true', cwd=path,
+         dry_run=dry_run)
+  if not dry_run:
+    _LOGGER.debug('Creating sparse checkout configuration file for '
+                  'directory: %s', repo.remote_dirs)
+    if not dry_run:
+      (path, contents) = _GenerateSparseCheckoutPathAndContents(repo)
+      with open(path, 'wb') as io:
+        io.write(contents)
+
+
+def _UpdateCheckout(path, repo, dry_run):
+  """Updates a GIT checkout in |path| by pulling down a specific revision
+  from it, as configured by RepoOptions |repo|. Only actually runs if
+  |dry_run| is False.
+  """
+  try:
+    # Try a checkout first. If this fails then we'll actually need to fetch
+    # the revision.
+    _LOGGER.info('Trying to checkout revision %s.', repo.revision)
+    _Shell('git', 'checkout', repo.revision, cwd=path,
+          dry_run=dry_run)
+    return
+  except RuntimeError:
+    pass
+
+  # Fetch the revision and then check it out. Let output go to screen rather
+  # than be buffered.
+  _LOGGER.info('Fetching and checking out revision %s.', repo.revision)
+  _Shell('git', 'fetch', '--depth=1', 'origin', repo.revision,
+         cwd=path, dry_run=dry_run, stdout=None, stderr=None)
+  _Shell('git', 'checkout', repo.revision, cwd=path,
+         dry_run=dry_run, stdout=None, stderr=None)
+
+
+# Used by _GetJunctionInfo to extract information about junctions.
+_DIR_JUNCTION_RE = re.compile(r'^.*<JUNCTION>\s+(.+)\s+\[(.+)\]$')
+
+
+# TODO(chrisha): This is ugly, and there has to be a better way!
+def _GetJunctionInfo(junction):
+  """Returns the target of a junction, if it exists, None otherwise."""
+  dirname = os.path.dirname(junction)
+  basename = os.path.basename(junction)
+  try:
+    stdout, dummy_stderr = _Shell('dir', '/AL', '/N', dirname, dry_run=False)
+  except RuntimeError:
+    return
+
+  lines = stdout.splitlines(False)
+  for line in stdout.splitlines(False):
+    m = _DIR_JUNCTION_RE.match(line)
+    if not m:
+      continue
+    if m.group(1).lower() == basename.lower():
+      return m.group(2)
+
+  return None
+
+
+def _EnsureJunction(cache_dir, target_dir, options, repo):
+  """Ensures that the appropriate junction exists from the configured output
+  directory to the specified sub-directory of the GIT checkout.
+  """
+  # Ensure that the target directory was created.
+  target_cache_dir = _GetCasedFilename(os.path.normpath(
+      os.path.join(cache_dir, target_dir)))
+  if not options.dry_run and not os.path.isdir(target_cache_dir):
+    raise Exception('Checkout does not contain the desired remote folder.')
+
+  # Ensure the parent directory exists before checking if the junction needs to
+  # be created.
+  output_dir = os.path.normpath(os.path.join(repo.output_dir, target_dir))
+  _EnsureDirectoryExists(
+      os.path.dirname(output_dir), 'junction', options.dry_run)
+
+  # Determine if the link needs to be created.
+  create_link = True
+  if os.path.exists(output_dir):
+    dest = _GetJunctionInfo(output_dir)
+
+    # If the junction is valid nothing needs to be done. If it points to the
+    # wrong place or isn't a junction then delete it and let it be remade.
+    if dest == target_cache_dir:
+      _LOGGER.debug('Junction is up to date.')
+      create_link = False
+    else:
+      if dest:
+        _LOGGER.info('Erasing existing junction: %s', output_dir)
+      else:
+        _LOGGER.info('Deleting existing directory: %s', output_dir)
+      _Shell('rmdir', '/S', '/Q', output_dir, dry_run=options.dry_run)
+
+  if create_link:
+    _LOGGER.info('Creating output junction: %s', output_dir)
+    _Shell('mklink', '/J', output_dir, target_cache_dir,
+           dry_run=options.dry_run)
+
+
+def _InstallRepository(options, repo):
+  """Installs a repository as configured by the options. Assumes that the
+  specified cache directory already exists.
+
+  Returns True if the checkout was modified, False otherwise.
+  """
+
+  _LOGGER.debug('Processing directories "%s" from repository "%s".',
+                repo.remote_dirs, repo.repository)
+
+  # Ensure the output directory's *parent* exists.
+  output_dirname = os.path.dirname(repo.output_dir)
+  output_basename = os.path.basename(repo.output_dir)
+  _EnsureDirectoryExists(output_dirname, 'output', options.dry_run)
+
+  # Get the properly cased names for the output directories.
+  output_dirname = _GetCasedFilename(output_dirname)
+  repo.output_dir = os.path.join(output_dirname, output_basename)
+
+  # These are the 3 basic steps that need to occur. Depending on the state of
+  # the checkout we may not need to perform all of them. We assume initially
+  # that everything needs to be done, unless proven otherwise.
+  create_checkout = True
+  update_checkout = True
+
+  # If the cache directory exists then lookup the repo and the revision and see
+  # what needs to be updated.
+  threads = []
+  if os.path.exists(repo.checkout_dir):
+    keep_cache_dir = False
+
+    # Only run these checks if we're not in 'force' mode. Otherwise, we
+    # deliberately turf the cache directory and start from scratch.
+    if not options.force and _IsGitCheckoutRoot(repo.checkout_dir):
+      # Get the repo origin.
+      repo_url = _GetGitOrigin(repo.checkout_dir)
+      if (repo_url == repo.repository and
+          _HasValidSparseCheckoutConfig(repo)):
+        _LOGGER.debug('Checkout is for correct repository and subdirectory.')
+        keep_cache_dir = True
+        create_checkout = False
+
+        # Get the checked out revision.
+        revhash = _GetGitHead(repo.checkout_dir)
+        if revhash == repo.revision:
+          _LOGGER.debug('Checkout is already up to date.')
+          update_checkout = False
+
+    if not keep_cache_dir:
+      # The old checkout directory is renamed and erased in a separate thread
+      # so that the new checkout can start immediately.
+      _LOGGER.info('Erasing stale checkout directory: %s', repo.checkout_dir)
+
+      # Any existing junctions to this repo must be removed otherwise the
+      # rename may fail.
+      for d in repo.remote_dirs:
+        j = os.path.abspath(os.path.join(repo.output_dir, d))
+        _RemoveOrphanedJunction(options, j)
+
+      newpath = _RenameCheckout(repo.checkout_dir, options.dry_run)
+      thread = threading.Thread(target=_DeleteCheckout,
+                                args=(newpath, options.dry_run))
+      threads.append(thread)
+      thread.start()
+
+  # Create and update the checkout as necessary.
+  if create_checkout:
+    _CreateCheckout(repo.checkout_dir, repo, options.dry_run)
+  else:
+    _LOGGER.debug('Reusing checkout directory: %s', repo.checkout_dir)
+  if update_checkout:
+    _UpdateCheckout(repo.checkout_dir, repo, options.dry_run)
+
+  # Ensure the junctions exists.
+  if repo.remote_dirs:
+    for remote_dir in repo.remote_dirs:
+      _EnsureJunction(repo.checkout_dir, remote_dir, options, repo)
+  else:
+    _EnsureJunction(repo.checkout_dir, '', options, repo)
+
+  # Join any worker threads that are ongoing.
+  for thread in threads:
+    thread.join()
+
+  # Return True if any modifications were made.
+  return create_checkout or update_checkout
+
+
+def _WriteIfChanged(path, contents, dry_run):
+  if os.path.exists(path):
+    d = open(path, 'rb').read()
+    if d == contents:
+      _LOGGER.debug('Contents unchanged, not writing file: %s', path)
+      return
+
+  _LOGGER.info('Writing file: %s', path)
+  if not dry_run:
+    open(path, 'wb').write(contents)
+
+
+def _RecurseRepository(options, repo):
+  """Recursively follows dependencies in the given repository."""
+  # Only run if there's an appropriate DEPS file.
+  deps = os.path.isfile(os.path.join(repo.checkout_dir, 'DEPS'))
+  gitdeps = os.path.isfile(os.path.join(repo.checkout_dir, '.DEPS.git'))
+  if not deps and not gitdeps:
+    _LOGGER.debug('No deps file found in repository: %s', repo.repository)
+    return
+
+  # Generate the .gclient solution file.
+  cache_dir = os.path.dirname(os.path.abspath(repo.checkout_dir))
+  gclient_file = os.path.join(cache_dir, '.gclient')
+  deps_file = 'DEPS'
+  if gitdeps:
+    deps_file = '.DEPS.git'
+  solutions = [
+    {
+      'name': 'src',
+      'url': repo.repository,
+      'managed': False,
+      'custom_deps': [],
+      'deps_file': deps_file,
+      'safesync_url': '',
+    }
+  ]
+  solutions = 'solutions=%s' % solutions.__repr__()
+  _WriteIfChanged(gclient_file, solutions, options.dry_run)
+
+  # Invoke 'gclient' on the sub-repository.
+  _Shell('gclient', 'sync', cwd=repo.checkout_dir, dry_run=options.dry_run)
+
+
+def _FindGlobalVariableInAstTree(tree, name, functions=None):
+  """Finds and evaluates to global assignment of the variables |name| in the
+  AST |tree|. Will allow the evaluations of some functions as defined in
+  |functions|.
+  """
+  if functions is None:
+    functions = {}
+
+  class FunctionEvaluator(ast.NodeTransformer):
+    """A tree transformer that evaluates permitted functions."""
+
+    def visit_BinOp(self, binop_node):
+      """Is called for BinOp nodes. We only support string additions."""
+      if type(binop_node.op) != ast.Add:
+        return binop_node
+      left = ast.literal_eval(self.visit(binop_node.left))
+      right = ast.literal_eval(self.visit(binop_node.right))
+      value = left + right
+      new_node = ast.Str(s=value)
+      new_node = ast.copy_location(new_node, binop_node)
+      return new_node
+
+    def visit_Call(self, call_node):
+      """Evaluates function calls that return a single string as output."""
+      func_name = call_node.func.id
+      if func_name not in functions:
+        return call_node
+      func = functions[func_name]
+
+      # Evaluate the arguments. We don't care about starargs, keywords or
+      # kwargs.
+      args = [ast.literal_eval(self.visit(arg)) for arg in
+                  call_node.args]
+
+      # Now evaluate the function.
+      value = func(*args)
+      new_node = ast.Str(s=value)
+      new_node = ast.copy_location(new_node, call_node)
+      return new_node
+
+  # Look for assignment nodes.
+  for node in tree.body:
+    if type(node) != ast.Assign:
+      continue
+    # Look for assignment in the 'store' context, to a variable with
+    # the given name.
+    for target in node.targets:
+      if type(target) != ast.Name:
+        continue
+      if type(target.ctx) != ast.Store:
+        continue
+      if target.id == name:
+        value = FunctionEvaluator().visit(node.value)
+        value = ast.fix_missing_locations(value)
+        value = ast.literal_eval(value)
+        return value
+
+
+def _ParseDepsFile(path):
+  """Parsed a DEPS-like file at the given |path|."""
+  # Utility function for performing variable expansions.
+  vars_dict = {}
+  def _Var(s):
+    return vars_dict[s]
+
+  contents = open(path, 'rb').read()
+  tree = ast.parse(contents, path)
+  vars_dict = _FindGlobalVariableInAstTree(tree, 'vars')
+  deps_dict = _FindGlobalVariableInAstTree(
+      tree, 'deps', functions={'Var': _Var})
+  return deps_dict
+
+
+def _RemoveFile(options, path):
+  """Removes the provided file. If it doesn't exist, raises an Exception."""
+  _LOGGER.debug('Removing file: %s', path)
+  if not os.path.isfile(path):
+    raise Exception('Path does not exist: %s' % path)
+
+  if not options.dry_run:
+    os.remove(path)
+
+
+def _RemoveOrphanedJunction(options, junction):
+  """Removes an orphaned junction at the path |junction|. If the path doesn't
+  exist or is not a junction, raises an Exception.
+  """
+  _LOGGER.debug('Removing orphaned junction: %s', junction)
+  absdir = os.path.join(options.output_dir, junction)
+  if not os.path.exists(absdir):
+    _LOGGER.debug('Junction path does not exist, ignoring.')
+    return
+  if not _GetJunctionInfo(absdir):
+    _LOGGER.error('Path is not a junction: %s', absdir)
+    raise Exception()
+  _Shell('rmdir', '/S', '/Q', absdir, dry_run=options.dry_run)
+
+  reldir = os.path.dirname(junction)
+  while reldir:
+    absdir = os.path.join(options.output_dir, reldir)
+    if os.listdir(absdir):
+      return
+    _LOGGER.debug('Removing empty parent directory of junction: %s', absdir)
+    _Shell('rmdir', '/S', '/Q', absdir, dry_run=options.dry_run)
+    reldir = os.path.dirname(reldir)
+
+
+def _GetCacheDirEntryVersion(path):
+  """Returns the version of the cache directory entry, -1 if invalid."""
+
+  git = os.path.join(path, '.git')
+  src = os.path.join(path, 'src')
+  gclient = os.path.join(path, '.gclient')
+
+  # Version 0 contains a '.git' directory and no '.gclient' entry.
+  if os.path.isdir(git):
+    if os.path.exists(gclient):
+      return -1
+    return 0
+
+  # Version 1 contains a 'src' directory and no '.git' entry.
+  if os.path.isdir(src):
+    if os.path.exists(git):
+      return -1
+    return 1
+
+
+def _GetCacheDirEntries(cache_dir):
+  """Returns the list of entries in the given |cache_dir|."""
+  entries = []
+  for path in os.listdir(cache_dir):
+    if not re.match('^[a-z0-9]{32}$', path):
+      continue
+    entries.append(path)
+  return entries
+
+
+def _GetCacheDirVersion(cache_dir):
+  """Returns the version of the cache directory."""
+  # If it doesn't exist then it's clearly the latest version.
+  if not os.path.exists(cache_dir):
+    return 1
+
+  cache_version = None
+  for path in _GetCacheDirEntries(cache_dir):
+    repo = os.path.join(cache_dir, path)
+    if not os.path.isdir(repo):
+      return -1
+
+    entry_version = _GetCacheDirEntryVersion(repo)
+    if entry_version == -1:
+      return -1
+
+    if cache_version == None:
+      cache_version = entry_version
+    else:
+      if cache_version != entry_version:
+        return -1
+
+  # If there are no entries in the cache it may as well be the latest version.
+  if cache_version is None:
+    return 1
+
+  return cache_version
+
+
+def _GetJunctionStatePath(options):
+  """Returns the junction state file path."""
+  return os.path.join(options.cache_dir, '.gitdeps_junctions')
+
+
+def _ReadJunctions(options):
+  """Reads the list of junctions as a dictionary."""
+  state_path = _GetJunctionStatePath(options)
+  old_junctions = {}
+  if os.path.exists(state_path):
+    _LOGGER.debug('Loading list of existing junctions.')
+    for j in open(state_path, 'rb'):
+      old_junctions[j.strip()] = True
+
+  return old_junctions
+
+
+def _Rename(src, dst, dry_run):
+  _LOGGER.debug('Renaming "%s" to "%s".', src, dst)
+  if not dry_run:
+    os.rename(src, dst)
+
+
+def _UpgradeCacheDir(options):
+  """Upgrades the cache directory format to the most modern layout.
+
+  Returns true on success, false otherwise.
+  """
+  cache_version = _GetCacheDirVersion(options.cache_dir)
+  if cache_version == 1:
+    _LOGGER.debug('No cache directory upgrade required.')
+    return
+
+  _LOGGER.debug('Upgrading cache directory from version 0 to 1.')
+
+  _LOGGER.debug('Removing all junctions.')
+  junctions = _ReadJunctions(options).keys()
+  junctions = sorted(junctions, key=lambda j: len(j), reverse=True)
+  for junction in junctions:
+    _RemoveOrphanedJunction(options, junction)
+  _RemoveFile(options, _GetJunctionStatePath(options))
+
+  for entry in _GetCacheDirEntries(options.cache_dir):
+    _LOGGER.debug('Upgrading cache entry "%s".', entry)
+    tmp_entry = os.path.abspath(os.path.join(
+        options.cache_dir,
+        'TMP%d-%04d' % (os.getpid(), random.randint(0, 999))))
+    abs_entry = os.path.abspath(os.path.join(options.cache_dir, entry))
+    src = os.path.join(abs_entry, 'src')
+    _Rename(abs_entry, tmp_entry, options.dry_run)
+    _EnsureDirectoryExists(abs_entry, 'cache entry', options.dry_run)
+    _Rename(tmp_entry, src, options.dry_run)
+
+  if options.dry_run:
+    _LOGGER.debug('Cache needs upgrading, unable to further simulate dry-run.')
+    raise Exception("")
+
+
+def main():
+  options, args = _ParseCommandLine()
+
+  # Upgrade the cache directory if necessary.
+  _UpgradeCacheDir(options)
+
+  # Ensure the cache directory exists and get the full properly cased path to
+  # it.
+  _EnsureDirectoryExists(options.cache_dir, 'cache', options.dry_run)
+  options.cache_dir = _GetCasedFilename(options.cache_dir)
+
+  # Read junctions that have been written in previous runs.
+  state_path = _GetJunctionStatePath(options)
+  old_junctions = _ReadJunctions(options)
+
+  # Parse each deps file in order, and extract the dependencies, looking for
+  # conflicts in the output directories.
+  output_dirs = {}
+  all_deps = []
+  for deps_file in args:
+    deps = _ParseDepsFile(deps_file)
+    for key, value in deps.iteritems():
+      repo_options = _ParseRepoOptions(
+          options.cache_dir, options.output_dir, deps_file, key, value)
+      if repo_options.output_dir in output_dirs:
+        other_repo_options = output_dirs[repo_options.output_dir]
+        _LOGGER.error('Conflicting output directory: %s',
+                      repo_options.output_dir)
+        _LOGGER.error('First specified in file: %s',
+                      other_repo_options.deps_file)
+        _LOGGER.error('And then specified in file: %s', repo_options.deps_file)
+      output_dirs[repo_options.output_dir] = repo_options
+      all_deps.append(repo_options)
+  output_dirs = {}
+
+  # Handle each dependency, in order of shortest path names first. This ensures
+  # that nested dependencies are handled properly.
+  checkout_dirs = {}
+  deps = sorted(all_deps, key=lambda x: len(x.deps_file))
+  junctions = []
+  for repo in all_deps:
+    changes_made = _InstallRepository(options, repo)
+    checkout_dirs[repo.checkout_dir] = changes_made
+
+    new_junction_dirs = repo.remote_dirs if repo.remote_dirs else ['']
+    for new_junction_dir in new_junction_dirs:
+      junction = os.path.relpath(
+          os.path.join(repo.output_dir, new_junction_dir),
+          options.output_dir)
+      old_junctions.pop(junction, None)
+      # Write each junction as we create it. This allows for recovery from
+      # partial runs.
+      if not options.dry_run:
+        open(state_path, 'ab').write(junction + '\n')
+        junctions.append(junction)
+
+  # Clean up orphaned junctions if there are any.
+  if old_junctions:
+    _LOGGER.debug('Removing orphaned junctions.')
+    for j in old_junctions.iterkeys():
+      _RemoveOrphanedJunction(options, j)
+
+  # Output the final list of junctions.
+  _LOGGER.debug('Writing final list of junctions.')
+  if not options.dry_run:
+    with open(state_path, 'wb') as io:
+      for j in sorted(junctions):
+        io.write(j)
+        io.write('\n')
+
+  # Iterate all directories in the cache directory. Any that we didn't
+  # specifically create or update should be cleaned up. Do this in parallel
+  # so things are cleaned up as soon as possible.
+  threads = []
+  for path in glob.glob(os.path.join(options.cache_dir, '*')):
+    if os.path.join(path, 'src') not in checkout_dirs:
+      _LOGGER.debug('Erasing orphaned checkout directory: %s', path)
+      thread = threading.Thread(target=_DeleteCheckout,
+                                args=(path, options.dry_run))
+      threads.append(thread)
+      thread.start()
+  for thread in threads:
+    thread.join()
+
+  # Recursively process other dependencies.
+  for repo in all_deps:
+    if not repo.recurse:
+      continue
+    if not checkout_dirs[repo.checkout_dir] and not options.force:
+      continue
+    _RecurseRepository(options, repo)
+
+  return
+
+
+if __name__ == '__main__':
+  main()