Add notes based on current notes ref

See felipec/git-remote-hg#58

git-remote-hg

@@ -110,6 +110,12 @@ def get_config_bool(config, default=False):
     else:
         return default
 
+def rev_parse(rev):
+    cmd = ['git', 'rev-parse', '--verify', '-q', rev]
+    process = subprocess.Popen(cmd, stdout=subprocess.PIPE)
+    output, _ = process.communicate()
+    return output
+
 class Marks:
 
     def __init__(self, path, repo):
@@ -373,10 +379,23 @@ def updatebookmarks(repo, peer):
     for k, v in remotemarks.iteritems():
         localmarks[k] = hgbin(v)
 
-    if hasattr(localmarks, 'write'):
-        localmarks.write()
+    if check_version(3, 6):
+        lock = tr = None
+        try:
+            lock = repo.lock()
+            tr = repo.transaction('bookmark')
+            localmarks.recordchange(tr)
+            tr.close()
+        finally:
+            if tr is not None:
+                tr.release()
+            if lock is not None:
+                lock.release()
     else:
-        bookmarks.write(repo)
+        if hasattr(localmarks, 'write'):
+            localmarks.write()
+        else:
+            bookmarks.write(repo)
 
 def get_repo(url, alias):
     global peer
@@ -589,8 +608,11 @@ def export_ref(repo, name, kind, head):
         desc = "Notes for %s\n" % (name)
         print "data %d" % (len(desc))
         print desc
-        if marks.last_note:
-            print "from :%u" % marks.last_note
+        # continue incrementally on current notes branch (whenever possible)
+        # to avoid wiping out present content upon fetch of new repo
+        current_note = rev_parse(ref)
+        if current_note:
+            print 'from %s^0' % (ref)
 
         for rev in pending_revs:
             notes.add(rev)