Reland: Add --no-history option to fetch and gclient for shallow clones.

gclient_scm.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Gclient-specific SCM-specific operations."""
 
 from __future__ import print_function
 
 import errno
 import logging
@@ skipping 807 matching lines @@
     clone_cmd = cfg + ['clone', '--no-checkout', '--progress']
     if self.cache_dir:
       clone_cmd.append('--shared')
     if options.verbose:
       clone_cmd.append('--verbose')
     clone_cmd.append(url)
     # If the parent directory does not exist, Git clone on Windows will not
     # create it, so we need to do it manually.
     parent_dir = os.path.dirname(self.checkout_path)
     gclient_utils.safe_makedirs(parent_dir)
+
+    template_dir = None
+    if hasattr(options, 'no_history') and options.no_history:
+      if gclient_utils.IsGitSha(revision):
+        # In the case of a subproject, the pinned sha is not necessarily the
+        # head of the remote branch (so we can't just use --depth=N). Instead,
+        # we tell git to fetch all the remote objects from SHA..HEAD by means of
+        # a template git dir which has a 'shallow' file pointing to the sha.
+        template_dir = tempfile.mkdtemp(
+            prefix='_gclient_gittmp_%s' % os.path.basename(self.checkout_path),
+            dir=parent_dir)
+        self._Run(['init', '--bare', template_dir], options, cwd=self._root_dir)
+        with open(os.path.join(template_dir, 'shallow'), 'w') as template_file:
+          template_file.write(revision)
+        clone_cmd.append('--template=' + template_dir)
+      else:
+        # Otherwise, we're just interested in the HEAD. Just use --depth.
+        clone_cmd.append('--depth=1')
+
     tmp_dir = tempfile.mkdtemp(
         prefix='_gclient_%s_' % os.path.basename(self.checkout_path),
         dir=parent_dir)
     try:
       clone_cmd.append(tmp_dir)
       self._Run(clone_cmd, options, cwd=self._root_dir, retry=True)
       gclient_utils.safe_makedirs(self.checkout_path)
       gclient_utils.safe_rename(os.path.join(tmp_dir, '.git'),
                                 os.path.join(self.checkout_path, '.git'))
     except:
       traceback.print_exc(file=self.out_fh)
       raise
     finally:
       if os.listdir(tmp_dir):
         self.Print('_____ removing non-empty tmp dir %s' % tmp_dir)
       gclient_utils.rmtree(tmp_dir)
+      if template_dir:
+        gclient_utils.rmtree(template_dir)
     self._UpdateBranchHeads(options, fetch=True)
     self._Checkout(options, revision.replace('refs/heads/', ''), quiet=True)
     if self._GetCurrentBranch() is None:
       # Squelch git's very verbose detached HEAD warning and use our own
       self.Print(
         ('Checked out %s to a detached HEAD. Before making any commits\n'
          'in this repo, you should use \'git checkout <branch>\' to switch to\n'
          'an existing branch or use \'git checkout %s -b <branch>\' to\n'
          'create a new branch for your work.') % (revision, self.remote))
 
@@ skipping 685 matching lines @@
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'theirs-conflict'))
     elif options.manually_grab_svn_rev:
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'postpone'))
     elif command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
       new_command.extend(('--accept', 'postpone'))
     return new_command