2 files changed, 104 insertions, 26 deletions

diff --git a/git_config.py b/git_config.py
index 78069c5d..7aad80d2 100644
--- a/git_config.py
+++ b/git_config.py
@@ -57,6 +57,7 @@ class GitConfig(object):
     self.file = file
     self.defaults = defaults
     self._cache_dict = None
+    self._section_dict = None
     self._remotes = {}
     self._branches = {}
     self._pickle = os.path.join(
@@ -168,6 +169,33 @@ class GitConfig(object):
       self._branches[b.name] = b
     return b
 
+  def HasSection(self, section, subsection = ''):
+    """Does at least one key in section.subsection exist?
+    """
+    try:
+      return subsection in self._sections[section]
+    except KeyError:
+      return False
+
+  @property
+  def _sections(self):
+    d = self._section_dict
+    if d is None:
+      d = {}
+      for name in self._cache.keys():
+        p = name.split('.')
+        if 2 == len(p):
+          section = p[0]
+          subsect = ''
+        else:
+          section = p[0]
+          subsect = '.'.join(p[1:-1])
+        if section not in d:
+          d[section] = set()
+        d[section].add(subsect)
+        self._section_dict = d
+    return d
+
   @property
   def _cache(self):
     if self._cache_dict is None:
@@ -443,11 +471,23 @@ class Branch(object):
   def Save(self):
     """Save this branch back into the configuration.
     """
-    self._Set('merge', self.merge)
-    if self.remote:
-      self._Set('remote', self.remote.name)
+    if self._config.HasSection('branch', self.name):
+      if self.remote:
+        self._Set('remote', self.remote.name)
+      else:
+        self._Set('remote', None)
+      self._Set('merge', self.merge)
+
     else:
-      self._Set('remote', None)
+      fd = open(self._config.file, 'ab')
+      try:
+        fd.write('[branch "%s"]\n' % self.name)
+        if self.remote:
+          fd.write('\tremote = %s\n' % self.remote.name)
+        if self.merge:
+          fd.write('\tmerge = %s\n' % self.merge)
+      finally:
+        fd.close()
 
   def _Set(self, key, value):
     key = 'branch.%s.%s' % (self.name, key)
diff --git a/project.py b/project.py
index 79ade3b6..8d6e4b6c 100644
--- a/project.py
+++ b/project.py
@@ -30,6 +30,21 @@ from remote import Remote
 
 from git_refs import GitRefs, HEAD, R_HEADS, R_TAGS, R_PUB, R_M
 
+def _lwrite(path, content):
+  lock = '%s.lock' % path
+
+  fd = open(lock, 'wb')
+  try:
+    fd.write(content)
+  finally:
+    fd.close()
+
+  try:
+    os.rename(lock, path)
+  except OSError:
+    os.remove(lock)
+    raise
+
 def _error(fmt, *args):
   msg = fmt % args
   print >>sys.stderr, 'error: %s' % msg
@@ -758,31 +773,54 @@ class Project(object):
   def StartBranch(self, name):
     """Create a new branch off the manifest's revision.
     """
-    try:
-      self.bare_git.rev_parse(R_HEADS + name)
-      exists = True
-    except GitError:
-      exists = False;
+    head = self.work_git.GetHead()
+    if head == (R_HEADS + name):
+      return True
 
-    if exists:
-      if name == self.CurrentBranch:
-        return True
-      else:
-        cmd = ['checkout', name, '--']
-        return GitCommand(self, cmd).Wait() == 0
+    all = self.bare_ref.all
+    if (R_HEADS + name) in all:
+      cmd = ['checkout', name, '--']
+      return GitCommand(self,
+                        cmd,
+                        capture_stdout = True).Wait() == 0
+
+    branch = self.GetBranch(name)
+    branch.remote = self.GetRemote(self.remote.name)
+    branch.merge = self.revision
 
+    rev = branch.LocalMerge
+    if rev in all:
+      revid = all[rev]
+    elif IsId(rev):
+      revid = rev
     else:
-      branch = self.GetBranch(name)
-      branch.remote = self.GetRemote(self.remote.name)
-      branch.merge = self.revision
-
-      rev = branch.LocalMerge
-      cmd = ['checkout', '-b', branch.name, rev]
-      if GitCommand(self, cmd).Wait() == 0:
-        branch.Save()
-        return True
-      else:
-        return False
+      revid = None
+
+    if head.startswith(R_HEADS):
+      try:
+        head = all[head]
+      except KeyError:
+        head = None
+
+    if revid and head and revid == head:
+      ref = os.path.join(self.gitdir, R_HEADS + name)
+      try:
+        os.makedirs(os.path.dirname(ref))
+      except OSError:
+        pass
+      _lwrite(ref, '%s\n' % revid)
+      _lwrite(os.path.join(self.worktree, '.git', HEAD),
+              'ref: %s%s\n' % (R_HEADS, name))
+      branch.Save()
+      return True
+
+    cmd = ['checkout', '-b', branch.name, rev]
+    if GitCommand(self,
+                  cmd,
+                  capture_stdout = True).Wait() == 0:
+      branch.Save()
+      return True
+    return False
 
   def CheckoutBranch(self, name):
     """Checkout a local topic branch.