* lisp/emacs-lisp/backquote.el: Fix bug with unoptimized exp.

Fixes: debbugs:19734

* lisp/emacs-lisp/backquote.el (backquote-delay-process): Don't reuse `s'
since it may be "equivalent" in some sense, yet different.
* test/automated/core-elisp-tests.el (core-elisp-tests-3-backquote): New test.

2 files changed, 6 insertions, 3 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index eac2e44ee5a..3724388dfda 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2015-01-30  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * emacs-lisp/backquote.el (backquote-delay-process): Don't reuse `s'
+        since it may be "equivalent" in some sense, yet different (bug#19734).
+
 2015-01-30  Oleh Krehel  <ohwoeowho@gmail.com>
 
         * outline.el (outline-font-lock-face): Add docstring.
diff --git a/lisp/emacs-lisp/backquote.el b/lisp/emacs-lisp/backquote.el
index 082955e0823..d5cdca2b1b5 100644
--- a/lisp/emacs-lisp/backquote.el
+++ b/lisp/emacs-lisp/backquote.el
@@ -120,9 +120,7 @@ Vectors work just like lists.  Nested backquotes are permitted."
 This simply recurses through the body."
   (let ((exp (backquote-listify (list (cons 0 (list 'quote (car s))))
                                 (backquote-process (cdr s) level))))
-    (if (eq (car-safe exp) 'quote)
-        (cons 0 (list 'quote s))
-      (cons 1 exp))))
+    (cons (if (eq (car-safe exp) 'quote) 0 1) exp)))
 
 (defun backquote-process (s &optional level)
   "Process the body of a backquote.