--- a/hgext3rd/topic/__init__.py	Sun Oct 15 00:07:21 2017 +0530
+++ b/hgext3rd/topic/__init__.py	Mon Oct 30 19:24:14 2017 +0100
@@ -63,6 +63,15 @@
     topic-mode = enforce-all # abort the commit (even for merge)
     topic-mode = random # use a randomized generated topic (except for merge)
     topic-mode = random-all # use a randomized generated topic (even for merge)
+
+Single head enforcing
+=====================
+
+The extensions come with an option to enforce that there is only one heads for
+each name in the repository at any time.
+
+    [experimental]
+    enforce-single-head = yes
 """
 
 from __future__ import absolute_import
@@ -99,6 +108,7 @@
 from . import (
     compat,
     constants,
+    flow,
     revset as topicrevset,
     destination,
     stack,
@@ -152,6 +162,9 @@
     configitem('experimental', 'enforce-topic',
                default=False,
     )
+    configitem('experimental', 'enforce-single-head',
+               default=False,
+    )
     configitem('experimental', 'topic-mode',
                default=None,
     )
@@ -368,6 +381,16 @@
             if desc in ('strip', 'repair') or ctr is not None:
                 return tr
 
+            if repo.ui.configbool('experimental', 'enforce-single-head'):
+                reporef = weakref.ref(self)
+                origvalidator = tr.validator
+
+                def validator(tr2):
+                    repo = reporef()
+                    flow.enforcesinglehead(repo, tr2)
+                    origvalidator(tr2)
+                tr.validator = validator
+
             # real transaction start
             ct = self.currenttopic
             if not ct: