--- a/src/topic/discovery.py	Sat Mar 12 18:19:27 2016 +0000
+++ b/src/topic/discovery.py	Sat Mar 12 18:42:16 2016 +0000
@@ -1,4 +1,8 @@
+import weakref
 from mercurial import branchmap
+from mercurial import error
+from mercurial import exchange
+from mercurial.i18n import _
 from . import topicmap
 
 def _headssummary(orig, repo, remote, outgoing):
@@ -49,3 +53,55 @@
         return orig(repo, proto)
     finally:
         repo.__class__ = oldrepo
+
+
+# Discovery have deficiency around phases, branch can get new heads with pure
+# phases change. This happened with a changeset was allowed to be pushed
+# because it had a topic, but it later become public and create a new branch
+# head.
+#
+# Handle this by doing an extra check for new head creation server side
+def _nbheads(repo):
+    data = {}
+    for b in repo.branchmap().iterbranches():
+        if ':' in b[0]:
+            continue
+        data[b[0]] = len(b[1])
+    return data
+
+def handlecheckheads(orig, op, inpart):
+    orig(op, inpart)
+    if op.repo.publishing():
+        return
+    tr = op.gettransaction()
+    if tr.hookargs['source'] not in ('push', 'serve'): # not a push
+        return
+    tr._prepushheads = _nbheads(op.repo)
+    reporef = weakref.ref(op.repo)
+    oldvalidator = tr.validator
+    def validator(tr):
+        repo = reporef()
+        if repo is not None:
+            repo.invalidatecaches()
+            finalheads = _nbheads(repo)
+            for branch, oldnb in tr._prepushheads.iteritems():
+                newnb = finalheads.pop(branch, 0)
+                if oldnb < newnb:
+                    msg = _('push create a new head on branch "%s"' % branch)
+                    raise error.Abort(msg)
+            for branch, newnb in finalheads.iteritems():
+                if 1 < newnb:
+                    msg = _('push create more than 1 head on new branch "%s"' % branch)
+                    raise error.Abort(msg)
+        return oldvalidator(tr)
+    tr.validator = validator
+handlecheckheads.params = frozenset()
+
+def _pushb2phases(orig, pushop, bundler):
+    hascheck =  any(p.type == 'check:heads' for p in  bundler._parts)
+    if pushop.outdatedphases and not hascheck:
+        exchange._pushb2ctxcheckheads(pushop, bundler)
+    return orig(pushop, bundler)
+
+
+