--- a/hgext3rd/topic/__init__.py	Tue Jun 27 09:49:35 2017 +0200
+++ b/hgext3rd/topic/__init__.py	Tue Jun 27 15:21:38 2017 +0200
@@ -163,6 +163,13 @@
 
     extensions.wrapfunction(cmdutil, 'buildcommittext', committextwrap)
     extensions.wrapfunction(merge, 'update', mergeupdatewrap)
+
+    try:
+        evolve = extensions.find('evolve')
+        extensions.wrapfunction(evolve, "presplitupdate", presplitupdatetopic)
+    except (KeyError, AttributeError):
+        pass
+
     cmdutil.summaryhooks.add('topic', summaryhook)
 
 
@@ -524,3 +531,18 @@
     cmdutil.extrapreimport.append('topic')
     cmdutil.extrapreimportmap['topic'] = _importtopic
     patch.patchheadermap.append(('EXP-Topic', 'topic'))
+
+## preserve topic during split
+
+def presplitupdatetopic(original, repo, ui, prev, ctx):
+    # Save topic of revision
+    topic = None
+    if util.safehasattr(ctx, 'topic'):
+        topic = ctx.topic()
+
+    # Update the working directory
+    original(repo, ui, prev, ctx)
+
+    # Restore the topic if need
+    if topic:
+        _changecurrenttopic(repo, topic)