--- a/hgext3rd/evolve/__init__.py	Sat Jul 22 23:40:28 2017 +0200
+++ b/hgext3rd/evolve/__init__.py	Sun Jul 23 04:46:33 2017 +0200
@@ -2325,7 +2325,7 @@
         if not precs:
             raise error.Abort('nothing to prune')
 
-        if _disallowednewunstable(repo, revs):
+        if rewriteutil.disallowednewunstable(repo, revs):
             raise error.Abort(_("cannot prune in the middle of a stack"),
                               hint=_("new unstable changesets are not allowed"))
 
@@ -2850,7 +2850,7 @@
             if repo.revs("%ld and public()", revs):
                 raise error.Abort(_('cannot edit commit information for public '
                                     'revisions'))
-            newunstable = _disallowednewunstable(repo, revs)
+            newunstable = rewriteutil.disallowednewunstable(repo, revs)
             if newunstable:
                 msg = _('cannot edit commit information in the middle'
                         ' of a stack')
@@ -2919,18 +2919,12 @@
         raise error.Abort(_("cannot fold non-linear revisions "
                             "(multiple heads given)"))
     head = repo[heads.first()]
-    if _disallowednewunstable(repo, revs):
+    if rewriteutil.disallowednewunstable(repo, revs):
         msg = _("cannot fold chain not ending with a head or with branching")
         hint = _("new unstable changesets are not allowed")
         raise error.Abort(msg, hint=hint)
     return root, head
 
-def _disallowednewunstable(repo, revs):
-    allowunstable = obsolete.isenabled(repo, obsolete.allowunstableopt)
-    if allowunstable:
-        return revset.baseset()
-    return repo.revs("(%ld::) - %ld", revs, revs)
-
 @eh.wrapcommand('graft')
 def graftwrapper(orig, ui, repo, *revs, **kwargs):
     kwargs = dict(kwargs)

--- a/hgext3rd/evolve/rewriteutil.py	Sat Jul 22 23:40:28 2017 +0200
+++ b/hgext3rd/evolve/rewriteutil.py	Sun Jul 23 04:46:33 2017 +0200
@@ -11,6 +11,11 @@
 #   happy one piece of it (and hopefully, able to reuse it in other core
 #   commands).
 
+from mercurial import (
+    obsolete,
+    revset,
+)
+
 from . import (
     compat,
 )
@@ -25,3 +30,13 @@
         if bmchanges:
             compat.bookmarkapplychanges(repo, tr, bmchanges)
     return updatebookmarks
+
+def disallowednewunstable(repo, revs):
+    """Check that editing <revs> will not create disallowed unstable
+
+    (unstable creation is controled by some special config).
+    """
+    allowunstable = obsolete.isenabled(repo, obsolete.allowunstableopt)
+    if allowunstable:
+        return revset.baseset()
+    return repo.revs("(%ld::) - %ld", revs, revs)