From 9f1a5113e103c789e173171ee0cda8d29de2f3d7 Mon Sep 17 00:00:00 2001
From: Stefan Monnier <monnier@iro.umontreal.ca>
Date: Mon, 23 Nov 2015 11:26:16 -0500
Subject: [PATCH] * lisp/emacs-lisp/smie.el (smie-backward-sexp): Handle BOB
 better.

---
 lisp/emacs-lisp/smie.el | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/smie.el b/lisp/emacs-lisp/smie.el
index 738bdddcddf..197861fbae2 100644
--- a/lisp/emacs-lisp/smie.el
+++ b/lisp/emacs-lisp/smie.el
@@ -809,7 +809,12 @@ Possible return values:
   nil: we skipped over an identifier, matched parentheses, ..."
   (smie-next-sexp
    (indirect-function smie-backward-token-function)
-   (indirect-function #'backward-sexp)
+   (lambda (n)
+     (if (bobp)
+         ;; Arguably backward-sexp hould signal this error for us.
+         (signal 'scan-error
+                 (list "Beginning of buffer" (point) (point)))
+       (backward-sexp n)))
    (indirect-function #'smie-op-left)
    (indirect-function #'smie-op-right)
    halfsexp))
-- 
2.39.2