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):
-    # First perform a fetch so we have a list of remote branch names
-    subprocess.check_call(["git", "fetch", "--quiet"], cwd=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"origin/(\S+)", remotes):
-      remote, local = match.group(0), match.group(1)
-      if local != "HEAD":
-        with open(os.devnull, "w") as devnull:
-          subprocess.call(["git", "branch", "--track", local, remote],
-                          cwd=repo, stdout=devnull, stderr=devnull)
-    # Finally we need to actually fetch all the remote branches and tags
-    subprocess.check_call(["git", "fetch", "--quiet", "--all", "--tags"], cwd=repo)
+    for match in re.finditer(r"^\s*(origin/(\S+))$", remotes, re.M):
+      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)