isearch.el patch for `M-e' to put point at mismatch position

["Drew Adams" <drew.adams@oracle.com>]

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The attached patch makes `M-e' (`isearch-edit-string') put point at the first
mismatch position (or the search-string end if no mismatch).

When you hit `M-e' you are ready to edit at the mismatch position.  This makes
it easy to change or insert a char or two to make the string match.  (`C-g', on
the other hand just removes all of the mismatch.)

(This feature complements the use of highlighting to show users where the
mismatch starts.)

[-- Attachment #2: isearch-2011-05-16.patch --]
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diff -cw isearch.el isearch-patched-2011-05-16.el
*** isearch.el	Mon May 16 11:38:22 2011
--- isearch-patched-2011-05-16.el	Mon May 16 14:21:04 2011
***************
*** 1060,1065 ****
--- 1060,1080 ----
  
  (defvar minibuffer-history-symbol) ;; from external package gmhist.el
  
+ (defun isearch-fail-pos ()
+   "Position of first mismatch in search string, or its length if none."
+   (let ((cmds  isearch-cmds)
+         succ-msg)
+     (if (and isearch-success (not isearch-error))
+         (length isearch-message)
+       (while (or (not (isearch-success-state (car cmds)))
+                  (isearch-error-state (car cmds)))
+         (pop cmds))
+       (setq succ-msg  (and cmds (isearch-message-state (car cmds))))
+       (if (and (stringp succ-msg)  (< (length succ-msg) (length isearch-message))
+                (equal succ-msg (substring isearch-message 0 (length succ-msg))))
+           (length succ-msg)
+         0))))
+ 
  (defun isearch-edit-string ()
    "Edit the search string in the minibuffer.
  The following additional command keys are active while editing.
***************
*** 1139,1145 ****
  		(setq isearch-new-string
                        (read-from-minibuffer
                         (isearch-message-prefix nil nil isearch-nonincremental)
!                        isearch-string
                         minibuffer-local-isearch-map nil
                         (if isearch-regexp
  			   (cons 'regexp-search-ring
--- 1154,1160 ----
                   (setq isearch-new-string
                         (read-from-minibuffer
                          (isearch-message-prefix nil nil isearch-nonincremental)
!                         (cons isearch-string (1+ (isearch-fail-pos)))
                          minibuffer-local-isearch-map nil
                          (if isearch-regexp
                              (cons 'regexp-search-ring

Diff finished.  Mon May 16 14:23:06 2011