--- a/hgext3rd/evolve/__init__.py	Sun Jul 23 04:46:33 2017 +0200
+++ b/hgext3rd/evolve/__init__.py	Sun Jul 23 04:54:42 2017 +0200
@@ -2751,7 +2751,7 @@
         wlock = repo.wlock()
         lock = repo.lock()
 
-        root, head = _foldcheck(repo, revs)
+        root, head = rewriteutil.foldcheck(repo, revs)
 
         tr = repo.transaction('fold')
         try:
@@ -2845,7 +2845,7 @@
                                 'not currently supported'))
 
         if opts['fold']:
-            root, head = _foldcheck(repo, revs)
+            root, head = rewriteutil.foldcheck(repo, revs)
         else:
             if repo.revs("%ld and public()", revs):
                 raise error.Abort(_('cannot edit commit information for public '
@@ -2906,25 +2906,6 @@
     finally:
         lockmod.release(lock, wlock)
 
-def _foldcheck(repo, revs):
-    roots = repo.revs('roots(%ld)', revs)
-    if len(roots) > 1:
-        raise error.Abort(_("cannot fold non-linear revisions "
-                            "(multiple roots given)"))
-    root = repo[roots.first()]
-    if root.phase() <= phases.public:
-        raise error.Abort(_("cannot fold public revisions"))
-    heads = repo.revs('heads(%ld)', revs)
-    if len(heads) > 1:
-        raise error.Abort(_("cannot fold non-linear revisions "
-                            "(multiple heads given)"))
-    head = repo[heads.first()]
-    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
-
 @eh.wrapcommand('graft')
 def graftwrapper(orig, ui, repo, *revs, **kwargs):
     kwargs = dict(kwargs)

--- a/hgext3rd/evolve/rewriteutil.py	Sun Jul 23 04:46:33 2017 +0200
+++ b/hgext3rd/evolve/rewriteutil.py	Sun Jul 23 04:54:42 2017 +0200
@@ -12,10 +12,14 @@
 #   commands).
 
 from mercurial import (
+    error,
     obsolete,
+    phases,
     revset,
 )
 
+from mercurial.i18n import _
+
 from . import (
     compat,
 )
@@ -40,3 +44,23 @@
     if allowunstable:
         return revset.baseset()
     return repo.revs("(%ld::) - %ld", revs, revs)
+
+def foldcheck(repo, revs):
+    """check that <revs> can be folded"""
+    roots = repo.revs('roots(%ld)', revs)
+    if len(roots) > 1:
+        raise error.Abort(_("cannot fold non-linear revisions "
+                            "(multiple roots given)"))
+    root = repo[roots.first()]
+    if root.phase() <= phases.public:
+        raise error.Abort(_("cannot fold public revisions"))
+    heads = repo.revs('heads(%ld)', revs)
+    if len(heads) > 1:
+        raise error.Abort(_("cannot fold non-linear revisions "
+                            "(multiple heads given)"))
+    head = repo[heads.first()]
+    if 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