bug#9185: 24.0.50; "C-s M-p" does not bring the tip of the search ring

[Juri Linkov]

> A patch that makes it work like you describe (i.e. C-s M-p gets first,
> and C-s C-s M-p gets the second) sounds OK, assuming the patch
> is not too ugly.

There are two places in isearch.el that reuse the last element of the
ring when the search string is empty.  One is `isearch-repeat' (used by
`C-s C-s') and another is `isearch-edit-string'.  The latter is questionable.
An old comment used to say:

    ;; This used to set the last search string,
    ;; but I think it is not right to do that here.
    ;; Only the string actually used should be saved.

It doesn't correspond to the actual code, so I deleted it.
I have no opinion how useless is to reuse the last element of the
ring after exiting from `isearch-edit-string' with empty input.
But with the existing functionality this place needs to adjust the ring.

So three diff hunks below fix the following cases:

1. in isearch-edit-string: C-s M-e RET M-p
2. in isearch-repeat: C-s C-s M-p
3. in isearch-ring-adjust1: C-s M-p

=== modified file 'lisp/isearch.el'
--- lisp/isearch.el     2011-07-15 13:33:07 +0000
+++ lisp/isearch.el     2011-08-23 09:51:16 +0000
@@ -1191,19 +1200,17 @@ (defun isearch-edit-string ()
                  isearch-word isearch-new-word))
 
          ;; Empty isearch-string means use default.
-         (if (= 0 (length isearch-string))
-             (setq isearch-string (or (car (if isearch-regexp
-                                               regexp-search-ring
-                                             search-ring))
-                                      "")
-
-                   isearch-message
-                   (mapconcat 'isearch-text-char-description
-                              isearch-string ""))
-           ;; This used to set the last search string,
-           ;; but I think it is not right to do that here.
-           ;; Only the string actually used should be saved.
-           ))
+         (when (= 0 (length isearch-string))
+           (setq isearch-string (or (car (if isearch-regexp
+                                             regexp-search-ring
+                                           search-ring))
+                                    "")
+
+                 isearch-message
+                 (mapconcat 'isearch-text-char-description
+                            isearch-string ""))
+           ;; After taking the last element, adjust ring to previous one.
+           (isearch-ring-adjust1 nil)))
 
        ;; This used to push the state as of before this C-s, but it adds
        ;; an inconsistent state where part of variables are from the
@@ -1290,7 +1297,9 @@ (defun isearch-repeat (direction)
                  isearch-message
                  (mapconcat 'isearch-text-char-description
                             isearch-string "")
-                 isearch-case-fold-search isearch-last-case-fold-search))
+                 isearch-case-fold-search isearch-last-case-fold-search)
+           ;; After taking the last element, adjust ring to previous one.
+           (isearch-ring-adjust1 nil))
        ;; If already have what to search for, repeat it.
        (or isearch-success
            (progn
@@ -2071,7 +2080,7 @@ (defun isearch-ring-adjust1 (advance)
        ()
       (set yank-pointer-name
           (setq yank-pointer
-                (mod (+ (or yank-pointer 0)
+                (mod (+ (or yank-pointer (if advance 0 -1))
                         (if advance -1 1))
                      length)))
       (setq isearch-string (nth yank-pointer ring)