histedit: clean abort when there is nothing to edit

hgext/histedit.py

@@ -455,6 +455,9 b' def histedit(ui, repo, *parent, **opts):'
 
         keep = opts.get('keep', False)
         revs = between(repo, parent, topmost, keep)
+        if not revs:
+            ui.warn(_('nothing to edit\n'))
+            return 1
 
         ctxs = [repo[r] for r in revs]
         rules = opts.get('commands', '')
@@ -588,7 +591,7 b' def between(repo, old, new, keep):'
 
     When keep is false, the specified set can't have children."""
     ctxs = list(repo.set('%n::%n', old, new))
-    if not keep:
+    if ctxs and not keep:
         if repo.revs('(%ld::) - (%ld + hidden())', ctxs, ctxs):
             raise util.Abort(_('cannot edit history that would orphan nodes'))
         root = min(ctxs)

tests/test-histedit-revspec.t

@@ -60,3 +60,10 b' Run a dummy edit to make sure we get tip'
   #
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
+Run on a revision not ancestors of the current working directory.
+
+  $ hg up 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg histedit -r 4
+  nothing to edit
+  [1]