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.

9 files changed, 90 insertions, 64 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 80cdb66425c..c3951a08c0a 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,12 @@
+2014-06-25  Dmitry Antipov  <dmantipov@yandex.ru>
+
+        * files.el (dir-locals-find-file, file-relative-name):
+        * info.el (Info-complete-menu-item):
+        * minibuffer.el (completion-table-subvert): Prefer string-prefix-p
+        to compare-strings to avoid out-of-range errors.
+        * subr.el (string-prefix-p): Adjust to match strict range
+        checking in compare-strings.
+
 2014-06-24  Leonard Randall  <leonard.a.randall@gmail.com>  (tiny change)
 
         * textmodes/reftex-parse.el (reftex-using-biblatex-p): Make search
diff --git a/lisp/files.el b/lisp/files.el
index 9017cc96703..65f2009c7ce 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3659,10 +3659,9 @@ of no valid cache entry."
 ;;;      (setq locals-file nil))
     ;; Find the best cached value in `dir-locals-directory-cache'.
     (dolist (elt dir-locals-directory-cache)
-      (when (and (eq t (compare-strings file nil (length (car elt))
-                                        (car elt) nil nil
-                                        (memq system-type
-                                              '(windows-nt cygwin ms-dos))))
+      (when (and (string-prefix-p (car elt) file
+                                  (memq system-type
+                                        '(windows-nt cygwin ms-dos)))
                  (> (length (car elt)) (length (car dir-elt))))
         (setq dir-elt elt)))
     (if (and dir-elt
@@ -4507,18 +4506,14 @@ on a DOS/Windows machine, it returns FILENAME in expanded form."
         (let ((ancestor ".")
               (filename-dir (file-name-as-directory filename)))
           (while (not
-                  (or
-                   (eq t (compare-strings filename-dir nil (length directory)
-                                          directory nil nil fold-case))
-                   (eq t (compare-strings filename nil (length directory)
-                                          directory nil nil fold-case))))
+                  (or (string-prefix-p directory filename-dir fold-case)
+                      (string-prefix-p directory filename fold-case)))
             (setq directory (file-name-directory (substring directory 0 -1))
                   ancestor (if (equal ancestor ".")
                                ".."
                              (concat "../" ancestor))))
           ;; Now ancestor is empty, or .., or ../.., etc.
-          (if (eq t (compare-strings filename nil (length directory)
-                                     directory nil nil fold-case))
+          (if (string-prefix-p directory filename fold-case)
               ;; We matched within FILENAME's directory part.
               ;; Add the rest of FILENAME onto ANCESTOR.
               (let ((rest (substring filename (length directory))))
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.
diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 7b252b4d46d..e7e08342b47 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -244,8 +244,7 @@ The result is a completion table which completes strings of the
 form (concat S1 S) in the same way as TABLE completes strings of
 the form (concat S2 S)."
   (lambda (string pred action)
-    (let* ((str (if (eq t (compare-strings string 0 (length s1) s1 nil nil
-                                           completion-ignore-case))
+    (let* ((str (if (string-prefix-p s1 string completion-ignore-case)
                     (concat s2 (substring string (length s1)))))
            (res (if str (complete-with-action action table str pred))))
       (when res
@@ -257,8 +256,7 @@ the form (concat S2 S)."
                     (+ beg (- (length s1) (length s2))))
               . ,(and (eq (car-safe res) 'boundaries) (cddr res)))))
          ((stringp res)
-          (if (eq t (compare-strings res 0 (length s2) s2 nil nil
-                                     completion-ignore-case))
+          (if (string-prefix-p s2 string completion-ignore-case)
               (concat s1 (substring res (length s2)))))
          ((eq action t)
           (let ((bounds (completion-boundaries str table pred "")))
diff --git a/lisp/subr.el b/lisp/subr.el
index 524b7954b7e..09a085288a5 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -3677,12 +3677,14 @@ and replace a sub-expression, e.g.
       (setq matches (cons (substring string start l) matches)) ; leftover
       (apply #'concat (nreverse matches)))))
 
-(defun string-prefix-p (str1 str2 &optional ignore-case)
-  "Return non-nil if STR1 is a prefix of STR2.
+(defun string-prefix-p (prefix string &optional ignore-case)
+  "Return non-nil if PREFIX is a prefix of STRING.
 If IGNORE-CASE is non-nil, the comparison is done without paying attention
 to case differences."
-  (eq t (compare-strings str1 nil nil
-                         str2 0 (length str1) ignore-case)))
+  (let ((prefix-length (length prefix)))
+    (if (> prefix-length (length string)) nil
+      (eq t (compare-strings prefix 0 prefix-length string
+                             0 prefix-length ignore-case)))))
 
 (defun string-suffix-p (suffix string  &optional ignore-case)
   "Return non-nil if SUFFIX is a suffix of STRING.
diff --git a/src/ChangeLog b/src/ChangeLog
index 9f676a6518d..fc47fbc8978 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2014-06-25  Dmitry Antipov  <dmantipov@yandex.ru>
+
+        Do not allow out-of-range character position in Fcompare_strings.
+        * 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.
+
 2014-06-24  Paul Eggert  <eggert@cs.ucla.edu>
 
         Be more consistent about the 'Qfoo' naming convention.
diff --git a/src/fns.c b/src/fns.c
index 5074ae3b41b..85e9f482fc1 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -50,7 +50,9 @@ static Lisp_Object Qcodeset, Qdays, Qmonths, Qpaper;
 static Lisp_Object Qmd5, Qsha1, Qsha224, Qsha256, Qsha384, Qsha512;
 
 static bool internal_equal (Lisp_Object, Lisp_Object, int, bool, Lisp_Object);
-
+static void validate_subarray (Lisp_Object, Lisp_Object, Lisp_Object,
+                               ptrdiff_t, EMACS_INT *, EMACS_INT *);
+
 DEFUN ("identity", Fidentity, Sidentity, 1, 1, 0,
        doc: /* Return the argument unchanged.  */)
   (Lisp_Object arg)
@@ -232,6 +234,7 @@ string STR1, compare the part between START1 (inclusive) and END1
 \(exclusive).  If START1 is nil, it defaults to 0, the beginning of
 the string; if END1 is nil, it defaults to the length of the string.
 Likewise, in string STR2, compare the part between START2 and END2.
+Like in `substring', negative values are counted from the end.
 
 The strings are compared by the numeric values of their characters.
 For instance, STR1 is "less than" STR2 if its first differing
@@ -244,43 +247,25 @@ If string STR1 is less, the value is a negative number N;
   - 1 - N is the number of characters that match at the beginning.
 If string STR1 is greater, the value is a positive number N;
   N - 1 is the number of characters that match at the beginning.  */)
-  (Lisp_Object str1, Lisp_Object start1, Lisp_Object end1, Lisp_Object str2, Lisp_Object start2, Lisp_Object end2, Lisp_Object ignore_case)
+  (Lisp_Object str1, Lisp_Object start1, Lisp_Object end1, Lisp_Object str2,
+   Lisp_Object start2, Lisp_Object end2, Lisp_Object ignore_case)
 {
-  register ptrdiff_t end1_char, end2_char;
-  register ptrdiff_t i1, i1_byte, i2, i2_byte;
+  EMACS_INT from1, to1, from2, to2;
+  ptrdiff_t i1, i1_byte, i2, i2_byte;
 
   CHECK_STRING (str1);
   CHECK_STRING (str2);
-  if (NILP (start1))
-    start1 = make_number (0);
-  if (NILP (start2))
-    start2 = make_number (0);
-  CHECK_NATNUM (start1);
-  CHECK_NATNUM (start2);
-  if (! NILP (end1))
-    CHECK_NATNUM (end1);
-  if (! NILP (end2))
-    CHECK_NATNUM (end2);
-
-  end1_char = SCHARS (str1);
-  if (! NILP (end1) && end1_char > XINT (end1))
-    end1_char = XINT (end1);
-  if (end1_char < XINT (start1))
-    args_out_of_range (str1, start1);
-
-  end2_char = SCHARS (str2);
-  if (! NILP (end2) && end2_char > XINT (end2))
-    end2_char = XINT (end2);
-  if (end2_char < XINT (start2))
-    args_out_of_range (str2, start2);
-
-  i1 = XINT (start1);
-  i2 = XINT (start2);
+
+  validate_subarray (str1, start1, end1, SCHARS (str1), &from1, &to1);
+  validate_subarray (str2, start2, end2, SCHARS (str2), &from2, &to2);
+
+  i1 = from1;
+  i2 = from2;
 
   i1_byte = string_char_to_byte (str1, i1);
   i2_byte = string_char_to_byte (str2, i2);
 
-  while (i1 < end1_char && i2 < end2_char)
+  while (i1 < to1 && i2 < to2)
     {
       /* When we find a mismatch, we must compare the
          characters, not just the bytes.  */
@@ -307,12 +292,8 @@ If string STR1 is greater, the value is a positive number N;
 
       if (! NILP (ignore_case))
         {
-          Lisp_Object tem;
-
-          tem = Fupcase (make_number (c1));
-          c1 = XINT (tem);
-          tem = Fupcase (make_number (c2));
-          c2 = XINT (tem);
+          c1 = XINT (Fupcase (make_number (c1)));
+          c2 = XINT (Fupcase (make_number (c2)));
         }
 
       if (c1 == c2)
@@ -322,15 +303,15 @@ If string STR1 is greater, the value is a positive number N;
          past the character that we are comparing;
          hence we don't add or subtract 1 here.  */
       if (c1 < c2)
-        return make_number (- i1 + XINT (start1));
+        return make_number (- i1 + from1);
       else
-        return make_number (i1 - XINT (start1));
+        return make_number (i1 - from1);
     }
 
-  if (i1 < end1_char)
-    return make_number (i1 - XINT (start1) + 1);
-  if (i2 < end2_char)
-    return make_number (- i1 + XINT (start1) - 1);
+  if (i1 < to1)
+    return make_number (i1 - from1 + 1);
+  if (i2 < to2)
+    return make_number (- i1 + from1 - 1);
 
   return Qt;
 }
diff --git a/test/ChangeLog b/test/ChangeLog
index 08492dd4c8f..3cb03b9f2f4 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,3 +1,7 @@
+2014-06-25  Dmitry Antipov  <dmantipov@yandex.ru>
+
+        * automated/fns-tests.el (fns-tests-compare-string): New test.
+
 2014-06-24  Michael Albinus  <michael.albinus@gmx.de>
 
         * automated/tramp-tests.el (tramp-test26-process-file): Extend test
diff --git a/test/automated/fns-tests.el b/test/automated/fns-tests.el
index 21a9e4536af..461995b602e 100644
--- a/test/automated/fns-tests.el
+++ b/test/automated/fns-tests.el
@@ -69,3 +69,34 @@
     (nreverse A)
     (should (equal [nil nil nil nil nil t t t t t] (vconcat A)))
     (should (equal [t t t t t nil nil nil nil nil] (vconcat (nreverse A))))))
+
+(ert-deftest fns-tests-compare-strings ()
+  (should-error (compare-strings))
+  (should-error (compare-strings "xyzzy" "xyzzy"))
+  (should-error (compare-strings "xyzzy" 0 10 "zyxxy" 0 5))
+  (should-error (compare-strings "xyzzy" 0 5 "zyxxy" -1 2))
+  (should-error (compare-strings "xyzzy" 'foo nil "zyxxy" 0 1))
+  (should-error (compare-strings "xyzzy" 0 'foo "zyxxy" 2 3))
+  (should-error (compare-strings "xyzzy" 0 2 "zyxxy" 'foo 3))
+  (should-error (compare-strings "xyzzy" nil 3 "zyxxy" 4 'foo))
+  (should (compare-strings "" nil nil "" nil nil))
+  (should (compare-strings "" 0 0 "" 0 0))
+  (should (compare-strings "test" nil nil "test" nil nil))
+  (should (compare-strings "test" nil nil "test" nil nil t))
+  (should (compare-strings "test" nil nil "test" nil nil nil))
+  (should (compare-strings "Test" nil nil "test" nil nil t))
+  (should (= (compare-strings "Test" nil nil "test" nil nil) -1))
+  (should (= (compare-strings "Test" nil nil "test" nil nil) -1))
+  (should (= (compare-strings "test" nil nil "Test" nil nil) 1))
+  (should (= (compare-strings "foobaz" nil nil "barbaz" nil nil) 1))
+  (should (= (compare-strings "barbaz" nil nil "foobar" nil nil) -1))
+  (should (= (compare-strings "foobaz" nil nil "farbaz" nil nil) 2))
+  (should (= (compare-strings "farbaz" nil nil "foobar" nil nil) -2))
+  (should (compare-strings "abcxyz" 0 2 "abcprq" 0 2))
+  (should (compare-strings "abcxyz" 0 -3 "abcprq" 0 -3))
+  (should (= (compare-strings "abcxyz" 0 6 "abcprq" 0 6) 4))
+  (should (= (compare-strings "abcprq" 0 6 "abcxyz" 0 6) -4))
+  (should (compare-strings "xyzzy" -3 4 "azza" -3 3))
+  (should (compare-strings "こんにちはｺﾝﾆﾁﾊ" nil nil "こんにちはｺﾝﾆﾁﾊ" nil nil))
+  (should (= (compare-strings "んにちはｺﾝﾆﾁﾊこ" nil nil "こんにちはｺﾝﾆﾁﾊ" nil nil) 1))
+  (should (= (compare-strings "こんにちはｺﾝﾆﾁﾊ" nil nil "んにちはｺﾝﾆﾁﾊこ" nil nil) -1)))