--- a/hgext3rd/evolve/utility.py	Wed Jan 15 15:28:44 2020 +0700
+++ b/hgext3rd/evolve/utility.py	Sun Dec 08 02:17:11 2019 +0530
@@ -125,6 +125,34 @@
 
     return repo[newer[0][0]].rev()
 
+def picksplitsuccessor(ui, repo, ctx, evolvecand):
+    """choose a successor of ctx from split targets
+
+    Choose highest one if all successors are in a topological branch. And if
+    they are split over multiple topological branches, we ask user to choose
+    an evolve destination.
+
+    Return (True, succ) unless split targets are split over multiple
+    topological branches and user didn't choose any evolve destination,
+    in which case return (False, '.')
+    """
+    targets = obsutil.successorssets(repo, ctx.node())[0]
+    assert targets
+    targetrevs = [repo[r].rev() for r in targets]
+    roots = repo.revs(b'roots(%ld)', targetrevs)
+    heads = repo.revs(b'heads(%ld)', targetrevs)
+    if len(roots) > 1 or len(heads) > 1:
+        cheader = (_(b"ancestor '%s' split over multiple topological"
+                     b" branches.\nchoose an evolve destination:") %
+                   evolvecand)
+        selectedrev = revselectionprompt(ui, repo, list(heads), cheader)
+        if selectedrev is None:
+            return (False, '.')
+        succ = repo[selectedrev]
+    else:
+        succ = repo[heads.first()]
+    return (True, repo[succ].rev())
+
 def _successorrevs(repo, ctx):
     try:
         return {_singlesuccessor(repo, ctx)}