mercurial/rewriteutil.py

--- a/mercurial/rewriteutil.py	Tue Apr 27 14:59:45 2021 -0700
+++ b/mercurial/rewriteutil.py	Thu Feb 11 15:11:10 2021 -0800
@@ -54,7 +54,10 @@
 
     newunstable = disallowednewunstable(repo, revs)
     if newunstable:
-        raise error.InputError(_(b"cannot %s changeset with children") % action)
+        hint = _(b"see 'hg help evolution.instability'")
+        raise error.InputError(
+            _(b"cannot %s changeset with children") % action, hint=hint
+        )
 
 
 def disallowednewunstable(repo, revs):