* lisp/isearch.el (isearch-mode-map): Bind M-s _' to isearch-toggle-symbol'.

Bind `M-s c' to `isearch-toggle-case-fold'.
(search-map): Bind `M-s _' to `isearch-forward-symbol'.
(isearch-forward): Add `M-s _' to the docstring.
(isearch-forward-symbol, isearch-toggle-case-fold)
(isearch-symbol-regexp): New functions.

Fixes: debbugs:11381

etc/NEWS

@@ -81,6 +81,12 @@ Use "coding: raw-text" instead.
 
 * Editing Changes in Emacs 24.2
 
+** Search changes
+
+*** Global `M-s _' starts a symbol (identifier) incremental search,
+and `M-s _' in Isearch toggles symbol search mode.
+`M-s c' in Isearch toggles search case-sensitivity.
+
 ** M-x move-to-column, if called interactively with no prefix arg, now
 prompts for a column number.
 

lisp/ChangeLog

@@ -1,3 +1,13 @@
+2012-05-29  Juri Linkov  <juri@jurta.org>
+
+	* isearch.el (isearch-mode-map): Bind `M-s _' to
+	`isearch-toggle-symbol'.  Bind `M-s c' to
+	`isearch-toggle-case-fold'.
+	(search-map): Bind `M-s _' to `isearch-forward-symbol'.
+	(isearch-forward): Add `M-s _' to the docstring.
+	(isearch-forward-symbol, isearch-toggle-case-fold)
+	(isearch-symbol-regexp): New functions.  (Bug#11381)
+
 2012-05-29  Juri Linkov  <juri@jurta.org>
 
 	* isearch.el (isearch-word): Add docstring.  (Bug#11381)

lisp/isearch.el

@@ -501,8 +501,10 @@ This is like `describe-bindings', but displays only Isearch keys."
     (define-key map "\M-r" 'isearch-toggle-regexp)
     (define-key map "\M-e" 'isearch-edit-string)
 
+    (define-key map "\M-sc" 'isearch-toggle-case-fold)
     (define-key map "\M-sr" 'isearch-toggle-regexp)
     (define-key map "\M-sw" 'isearch-toggle-word)
+    (define-key map "\M-s_" 'isearch-toggle-symbol)
 
     (define-key map [?\M-%] 'isearch-query-replace)
     (define-key map [?\C-\M-%] 'isearch-query-replace-regexp)
@@ -531,11 +533,11 @@ This is like `describe-bindings', but displays only Isearch keys."
 (defvar isearch-forward nil)	; Searching in the forward direction.
 (defvar isearch-regexp nil)	; Searching for a regexp.
 (defvar isearch-word nil
-  "Regexp-based search mode for words.
+  "Regexp-based search mode for words/symbols.
 If t, do incremental search for a sequence of words, ignoring punctuation.
-If the value is a function, it is called to convert the search string
-to a regexp used by regexp search functions.  The property
-`isearch-message-prefix' put on this function specifies the
+If the value is a function (e.g. `isearch-symbol-regexp'), it is called to
+convert the search string to a regexp used by regexp search functions.
+The property `isearch-message-prefix' put on this function specifies the
 prefix string displyed in the search message.")
 
 (defvar isearch-cmds nil
@@ -622,6 +624,7 @@ Each set is a vector of the form:
 (define-key global-map "\C-r" 'isearch-backward)
 (define-key esc-map "\C-r" 'isearch-backward-regexp)
 (define-key search-map "w" 'isearch-forward-word)
+(define-key search-map "_" 'isearch-forward-symbol)
 
 ;; Entry points to isearch-mode.
 
@@ -661,6 +664,7 @@ If you try to exit with the search string still empty, it invokes
 Type \\[isearch-toggle-case-fold] to toggle search case-sensitivity.
 Type \\[isearch-toggle-regexp] to toggle regular-expression mode.
 Type \\[isearch-toggle-word] to toggle word mode.
+Type \\[isearch-toggle-symbol] to toggle symbol mode.
 Type \\[isearch-edit-string] to edit the search string in the minibuffer.
 
 Also supported is a search ring of the previous 16 search strings.
@@ -728,6 +732,16 @@ See the command `isearch-forward' for more information."
   (interactive "P\np")
   (isearch-mode t nil nil (not no-recursive-edit) (null not-word)))
 
+(defun isearch-forward-symbol (&optional not-symbol no-recursive-edit)
+  "\
+Do incremental search forward for a symbol.
+The prefix argument is currently unused.
+Like ordinary incremental search except that your input is treated
+as a symbol surrounded by symbol boundary constructs \\_< and \\_>.
+See the command `isearch-forward' for more information."
+  (interactive "P\np")
+  (isearch-mode t nil nil (not no-recursive-edit) 'isearch-symbol-regexp))
+
 (defun isearch-backward (&optional regexp-p no-recursive-edit)
   "\
 Do incremental search backward.
@@ -1375,6 +1389,14 @@ Use `isearch-exit' to quit without signaling."
   (setq isearch-success t isearch-adjusted t)
   (isearch-update))
 
+(defun isearch-toggle-symbol ()
+  "Toggle symbol searching on or off."
+  (interactive)
+  (setq isearch-word (unless (eq isearch-word 'isearch-symbol-regexp)
+		       'isearch-symbol-regexp))
+  (setq isearch-success t isearch-adjusted t)
+  (isearch-update))
+
 (defun isearch-toggle-case-fold ()
   "Toggle case folding in searching on or off."
   (interactive)
@@ -1476,6 +1498,16 @@ to punctuation."
   (interactive "sWord search: ")
   (re-search-forward (word-search-regexp string t) bound noerror count))
 
+;; Symbol search
+
+(defun isearch-symbol-regexp (string &optional lax)
+  "Return a regexp which matches STRING as a symbol.
+Creates a regexp where STRING is surrounded by symbol delimiters \\_< and \\_>.
+If LAX is non-nil, the end of the string need not match a symbol boundary."
+  (concat "\\_<" (regexp-quote string) (unless lax "\\_>")))
+
+(put 'isearch-symbol-regexp 'isearch-message-prefix "symbol ")
+
 
 (defun isearch-query-replace (&optional delimited regexp-flag)
   "Start `query-replace' with string to replace from last search string.