--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/hg/hggit_sync.py	Thu Apr 02 08:00:57 2015 -0700
@@ -0,0 +1,94 @@
+import os
+import os.path
+import sys
+import subprocess
+
+
+class CommitInfo(object):
+    def __init__(self):
+        self.nodeid = None
+        self.timestamp = None
+        self.description = None
+
+
+def parse_commits(text):
+    commits = []
+    cur_commit = None
+    for line in text.split('\n'):
+        if line == '':
+            if cur_commit:
+                commits.append(cur_commit)
+                cur_commit = None
+            continue
+        if cur_commit is None:
+            cur_commit = CommitInfo()
+        if cur_commit.nodeid is None:
+            id_and_date = line.split(' ', 1)
+            cur_commit.nodeid = id_and_date[0]
+            cur_commit.timestamp = int(id_and_date[1].split('.')[0])
+        else:
+            cur_commit.description = line
+    return commits
+
+
+def build_commit_map(commits1, commits2):
+    commits1 = sorted(commits1, key=lambda c: c.timestamp)
+    commits2 = sorted(commits2, key=lambda c: c.timestamp)
+    commit_map = dict(map(lambda c: (c.timestamp, (c, None)), commits1))
+    for c in commits2:
+        entry = commit_map.get(c.timestamp, (None, None))
+        entry = (entry[0], c)
+        commit_map[c.timestamp] = entry
+    return commit_map
+
+
+def main():
+    hg_repo = os.getcwd()
+    if not os.path.exists(os.path.join(hg_repo, '.hg')):
+        print "You must run this in the root of a Mercurial repository."
+        return 1
+
+    git_repo = os.path.join(hg_repo, '.hg', 'git')
+    if not os.path.exists(git_repo):
+        print ("This Mercurial repository doesn't seem to have any Git mirror "
+               "to sync with.")
+        return 1
+
+    hg_output = subprocess.check_output([
+        'hg', 'log',
+        '--template', "{node} {date}\n{firstline(desc)}\n\n"])
+    hg_commits = parse_commits(hg_output)
+
+    os.chdir(git_repo)
+    git_output = subprocess.check_output([
+        'git', 'log', '--format=%H %ct%n%s%n%n'])
+    git_commits = parse_commits(git_output)
+    os.chdir(hg_repo)
+
+    commit_map = build_commit_map(git_commits, hg_commits)
+    for key, val in commit_map.iteritems():
+        if val[0] is None:
+            print ("Mercurial commit '%s' (%s) has no Git mirror yet: %s" %
+                   (val[1].nodeid, val[1].timestamp, val[1].description))
+        if val[1] is None:
+            print ("Git commit '%s' (%s) is new: %s" %
+                   (val[0].nodeid, val[0].timestamp, val[0].description))
+
+    map_file = os.path.join(hg_repo, '.hg', 'git-mapfile')
+    if len(sys.argv) > 1:
+        map_file = sys.argv[1]
+    print "Saving map file: %s" % map_file
+    with open(map_file, 'w') as fp:
+        for key, val in commit_map.iteritems():
+            if val[0] is None or val[1] is None:
+                continue
+            fp.write(val[0].nodeid)
+            fp.write(' ')
+            fp.write(val[1].nodeid)
+            fp.write('\n')
+
+
+if __name__ == '__main__':
+    res = main()
+    sys.exit(res)
+