Fix to help-buffer to ensure it returns a valid buffer (Bug#8147).

* lisp/help-mode.el (help-buffer): If we are to return the current
buffer, signal an error if it's not in Help mode.

2 files changed, 14 insertions, 6 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 707464670e9..55935189af6 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2011-03-05  Chong Yidong  <cyd@stupidchicken.com>
+
+        * help-mode.el (help-buffer): If we are to return the current
+        buffer, signal an error if it's not in Help mode (Bug#8147).
+
 2011-03-05  Reuben Thomas  <rrt@sc3d.org>
 
         * files.el (file-name-version-regexp): Handle backup files of the
diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index 724b0186679..51d18235e1b 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -409,13 +409,16 @@ restore it properly when going back."
 (defun help-buffer ()
   "Return the name of a buffer for inserting help.
 If `help-xref-following' is non-nil, this is the name of the
-current buffer.
-Otherwise, it is *Help*; if no buffer with that name currently
-exists, it is created."
+current buffer.  Signal an error if this buffer is not derived
+from `help-mode'.
+Otherwise, return \"*Help*\", creating a buffer with that name if
+it does not already exist."
   (buffer-name                          ;for with-output-to-temp-buffer
-   (if help-xref-following
-       (current-buffer)
-     (get-buffer-create "*Help*"))))
+   (if (not help-xref-following)
+       (get-buffer-create "*Help*")
+     (unless (derived-mode-p 'help-mode)
+       (error "Current buffer is not in Help mode"))
+     (current-buffer))))
 
 (defvar help-xref-override-view-map
   (let ((map (make-sparse-keymap)))