Issue 2311 - Track remote Git branches when required

ensure_dependencies.py

 #!/usr/bin/env python
 # coding: utf-8
 
 # 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
@@ skipping 79 matching lines @@
     source = source.rstrip("/")
     if not source.endswith(".git"):
       source += ".git"
     subprocess.check_call(["git", "clone", "--quiet", source, target])
 
   def get_revision_id(self, repo, rev="HEAD"):
     command = ["git", "rev-parse", "--revs-only", rev + '^{commit}']
     return subprocess.check_output(command, cwd=repo).strip()
 
   def pull(self, repo):
+    # Fetch tracked branches, new tags and the list of available remote branches
     subprocess.check_call(["git", "fetch", "--quiet", "--all", "--tags"], cwd=repo)
+    # Next we need to ensure all remote branches are tracked
+    newly_tracked = False
+    remotes = subprocess.check_output(["git", "branch", "--remotes"], cwd=repo)
+    for match in re.finditer(r"(?:^|\s)(origin/(\S+))", remotes):

[Sebastian Noack, 2015/05/06 14:45:12]

I just realized that this regexp will find the branch checkout in the remote
repository twice, e.g:

  origin/HEAD -> origin/master
  origin/master

Not a big deal, but you can simply avoid that without adding any complexity:

  re.finditer(r"^\s*(origin/(\S+))", remotes, re.M)

[kzar, 2015/05/06 15:11:13]

Oh yea, also I realised if we check for the end of the line too we actually can
skip HEAD while we're at it :)

[Sebastian Noack, 2015/05/06 15:17:56]

Yeah, realized that as well, but slightly preferred to not check for end of line
to keep assumptions as small as possible, in case the output changes in future
versions or dependent on configuration. However, it doesn't matter much. So LGTM
either with or without matching end of line.

+      remote, local = match.groups()
+      with open(os.devnull, "wb") as devnull:
+        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):
     subprocess.check_call(["git", "checkout", "--quiet", rev], cwd=repo)
 
   def ignore(self, target, repo):
     module = os.path.relpath(target, repo)
     exclude_file = os.path.join(repo, ".git", "info", "exclude")
     _ensure_line_exists(exclude_file, module)
 
   def postprocess_url(self, url):
@@ skipping 193 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)