--- a/CHANGELOG	Mon Dec 11 23:33:50 2017 +0530
+++ b/CHANGELOG	Mon Dec 11 23:47:25 2017 +0530
@@ -9,6 +9,7 @@
 Topic (0.5.2)
 
   * makes code more resilient to partiel initialization
+  * fix behavior of `hg stack` in cases of split
 
 7.0.1 -- 2017-11-14
 -------------------

--- a/hgext3rd/topic/stack.py	Mon Dec 11 23:33:50 2017 +0530
+++ b/hgext3rd/topic/stack.py	Mon Dec 11 23:47:25 2017 +0530
@@ -12,7 +12,11 @@
     obsolete,
     util,
 )
-from .evolvebits import builddependencies, _singlesuccessor
+from .evolvebits import (
+    _singlesuccessor,
+    MultipleSuccessorsError,
+    builddependencies,
+)
 
 short = node.short
 
@@ -285,7 +289,15 @@
         p1 = ctx.p1()
         p2 = ctx.p2()
         if p1.obsolete():
-            p1 = repo[_singlesuccessor(repo, p1)]
+            try:
+                p1 = repo[_singlesuccessor(repo, p1)]
+            except MultipleSuccessorsError as e:
+                successors = e.successorssets
+                if len(successors) > 1:
+                    # case of divergence which we don't handle yet
+                    raise
+                p1 = repo[successors[0][-1]]
+
         if p2.node() != node.nullid:
             entries.append((idxmap.get(p1.rev()), False, p1))
             entries.append((idxmap.get(p2.rev()), False, p2))

--- a/tests/test-topic-stack-complex.t	Mon Dec 11 23:33:50 2017 +0530
+++ b/tests/test-topic-stack-complex.t	Mon Dec 11 23:47:25 2017 +0530
@@ -128,41 +128,8 @@
   $ hg stack
   ### topic: foo (2 heads)
   ### target: default (branch), 2 behind
-  ** unknown exception encountered, please report by visiting
-  ** https://mercurial-scm.org/wiki/BugTracker
-  ** Python 2.7.12 (default, Jul 18 2016, 15:04:44) [GCC 4.8.4]
-  ** Mercurial Distributed SCM (version 4.4.2+379-6812f5c492c7)
-  ** Extensions loaded: rebase, topic, show, evolve
-  Traceback (most recent call last):
-    File "/tmp/hgtests.d2IKdr/install/bin/hg", line 41, in <module>
-      dispatch.run()
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 88, in run
-      status = (dispatch(req) or 0) & 255
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 177, in dispatch
-      ret = _runcatch(req)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 318, in _runcatch
-      return _callcatch(ui, _runcatchfunc)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 326, in _callcatch
-      return scmutil.callcatch(ui, func)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/scmutil.py", line 154, in callcatch
-      return func()
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 308, in _runcatchfunc
-      return _dispatch(req)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 912, in _dispatch
-      cmdpats, cmdoptions)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 667, in runcommand
-      ret = _runcommand(ui, options, cmd, d)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 920, in _runcommand
-      return cmdfunc()
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/dispatch.py", line 909, in <lambda>
-      d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
-    File "/tmp/hgtests.d2IKdr/install/lib/python/mercurial/util.py", line 1188, in check
-      return func(*args, **kwargs)
-    File "/home/pulkit/repo/mutable-history/hgext3rd/topic/__init__.py", line 663, in cmdstack
-      return stack.showstack(ui, repo, branch=branch, topic=topic, opts=opts)
-    File "/home/pulkit/repo/mutable-history/hgext3rd/topic/stack.py", line 288, in showstack
-      p1 = repo[_singlesuccessor(repo, p1)]
-    File "/home/pulkit/repo/mutable-history/hgext3rd/topic/evolvebits.py", line 92, in _singlesuccessor
-      raise MultipleSuccessorsError(newer)
-  hgext3rd.topic.evolvebits.MultipleSuccessorsError
-  [1]
+  t4$ Added e and f (unstable)
+  t3$ split2 (unstable)
+  t2@ split1 (current)
+  t1: Added a and b
+  t0^ Added foo (base)