Fix seq-subseq and cl-subseq for bad bounding indices

Fixes: debbugs:19434 debbugs:19519

* lisp/emacs-lisp/cl-extra.el (cl-subseq): Use seq-subseq and fix
multiple evaluation.

* lisp/emacs-lisp/seq.el (seq-subseq): Throw bad bounding indices
error.

* test/automated/seq-tests.el (test-seq-subseq): Add more tests.

1 files changed, 7 insertions, 3 deletions

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index f6740c7d7f5..b28153b7f81 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -197,14 +197,18 @@ If END is omitted, it defaults to the length of the sequence.
 If START or END is negative, it counts from the end."
   (cond ((or (stringp seq) (vectorp seq)) (substring seq start end))
         ((listp seq)
-         (let (len)
+         (let (len (errtext (format "Bad bounding indices: %s, %s" start end)))
            (and end (< end 0) (setq end (+ end (setq len (seq-length seq)))))
            (if (< start 0) (setq start (+ start (or len (setq len (seq-length seq))))))
-           (if (> start 0) (setq seq (nthcdr start seq)))
+           (when (> start 0)
+             (setq seq (nthcdr (1- start) seq))
+             (or seq (error "%s" errtext))
+             (setq seq (cdr seq)))
            (if end
                (let ((res nil))
-                 (while (>= (setq end (1- end)) start)
+                 (while (and (>= (setq end (1- end)) start) seq)
                    (push (pop seq) res))
+                 (or (= (1+ end) start) (error "%s" errtext))
                  (nreverse res))
              (seq-copy seq))))
         (t (error "Unsupported sequence: %s" seq))))