# HG changeset patch
# User Giorgos Keramidas <keramida@ceid.upatras.gr>
# Date 1154241428 -10800
# Node ID a5c43944e1eef3362d58767d0cf76bae5d26e100
# Parent  eb1bde9560bc1b031eccc4640b46cf902795c290
avoid calling (cd ...) with `nil' as a directory name

When (hg-root) cannot determine the current Mercurial root, print an
error message instead of trying to evaluate (cd nil).

diff --git a/contrib/mercurial.el b/contrib/mercurial.el
--- a/contrib/mercurial.el
+++ b/contrib/mercurial.el
@@ -718,7 +718,11 @@ code by typing `M-x find-library mercuri
       (goto-char pos)
       (end-of-line 1)
       (delete-region pos (point)))
-    (cd (hg-root))))
+    (let ((hg-root-dir (hg-root)))
+      (if (not hg-root-dir)
+	  (error "error: %s: directory is not part of a Mercurial repository."
+		 default-directory)
+	(cd (hg-root))))))
 
 (defun hg-add (path)
   "Add PATH to the Mercurial repository on the next commit.