* lisp/emacs-lisp/backquote.el (backquote-process): Catch uses of , and ,@

with more than one argument.

Fixes: debbugs:15538

2 files changed, 12 insertions, 2 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index db02ef7a67f..fd132cad1a2 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,8 @@
 2013-10-08  Stefan Monnier  <monnier@iro.umontreal.ca>
 
+        * emacs-lisp/backquote.el (backquote-process): Catch uses of , and ,@
+        with more than one argument (bug#15538).
+
         * mpc.el (mpc-songs-jump-to): Adjust to different playlist format.
 
         * vc/pcvs.el: Use lexical-binding.
diff --git a/lisp/emacs-lisp/backquote.el b/lisp/emacs-lisp/backquote.el
index 2dc84e9ddfb..81d11ff4f77 100644
--- a/lisp/emacs-lisp/backquote.el
+++ b/lisp/emacs-lisp/backquote.el
@@ -153,11 +153,18 @@ LEVEL is only used internally and indicates the nesting level:
               (list 'quote s))))
    ((eq (car s) backquote-unquote-symbol)
     (if (<= level 0)
-        (cons 1 (nth 1 s))
+        (if (> (length s) 2)
+            ;; We could support it with: (cons 2 `(list . ,(cdr s)))
+            ;; But let's not encourage such uses.
+            (error "Multiple args to , are not supported: %S" s)
+          (cons 1 (nth 1 s)))
       (backquote-delay-process s (1- level))))
    ((eq (car s) backquote-splice-symbol)
     (if (<= level 0)
-        (cons 2 (nth 1 s))
+        (if (> (length s) 2)
+            ;; (cons 2 `(append . ,(cdr s)))
+            (error "Multiple args to ,@ are not supported: %S" s)
+          (cons 2 (nth 1 s)))
       (backquote-delay-process s (1- level))))
    ((eq (car s) backquote-backquote-symbol)
       (backquote-delay-process s (1+ level)))