Do not allow out-of-range character position in Fcompare_strings.

* src/fns.c (validate_subarray): Add prototype.
(Fcompare_substring): Use validate_subarray to check ranges.
Adjust comment to mention that the semantics was changed.  Also see
http://lists.gnu.org/archive/html/emacs-devel/2014-06/msg00447.html.
* lisp/files.el (dir-locals-find-file, file-relative-name):
* lisp/info.el (Info-complete-menu-item):
* lisp/minibuffer.el (completion-table-subvert): Prefer string-prefix-p
to compare-strings to avoid out-of-range errors.
* lisp/subr.el (string-prefix-p): Adjust to match strict range
checking in compare-strings.
* test/automated/fns-tests.el (fns-tests-compare-string): New test.

1 files changed, 1 insertions, 3 deletions

diff --git a/lisp/info.el b/lisp/info.el
index 89ca8bdbe33..405d6a22449 100644
--- a/lisp/info.el
+++ b/lisp/info.el
@@ -2691,9 +2691,7 @@ Because of ambiguities, this should be concatenated with something like
                      (equal (nth 1 Info-complete-cache) Info-current-node)
                      (equal (nth 2 Info-complete-cache) Info-complete-next-re)
                      (equal (nth 5 Info-complete-cache) Info-complete-nodes)
-                     (let ((prev (nth 3 Info-complete-cache)))
-                       (eq t (compare-strings string 0 (length prev)
-                                              prev 0 nil t))))
+                     (string-prefix-p (nth 3 Info-complete-cache) string) t)
                 ;; We can reuse the previous list.
                 (setq completions (nth 4 Info-complete-cache))
               ;; The cache can't be used.