Use defcustom.

[bpt/emacs.git] / lisp / imenu.el

;;; imenu.el --- Framework for mode-specific buffer indexes.

;; Copyright (C) 1994, 1995, 1996, 1997 Free Software Foundation, Inc.

;; Author: Ake Stenhoff <etxaksf@aom.ericsson.se>
;;         Lars Lindberg <lli@sypro.cap.se>
;; Created: 8 Feb 1994
;; Keywords: tools

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Purpose of this package:
;;   To present a framework for mode-specific buffer indexes.
;;   A buffer index is an alist of names and buffer positions.
;;   For instance all functions in a C-file and their positions.
;;
;; How it works:

;;   A mode-specific function is called to generate the index.  It is
;;   then presented to the user, who can choose from this index.
;;
;;   The package comes with a set of example functions for how to
;;   utilize this package.

;;   There are *examples* for index gathering functions/regular
;;   expressions for C/C++ and Lisp/Emacs Lisp but it is easy to
;;   customize for other modes.  A function for jumping to the chosen
;;   index position is also supplied.

;;; Thanks goes to
;;  [simon] - Simon Leinen simon@lia.di.epfl.ch
;;  [dean] - Dean Andrews ada@unison.com
;;  [alon] - Alon Albert al@mercury.co.il 
;;  [greg] - Greg Thompson gregt@porsche.visix.COM
;;  [wolfgang] - Wolfgang Bangerth zcg51122@rpool1.rus.uni-stuttgart.de
;;  [kai] - Kai Grossjohann grossjoh@linus.informatik.uni-dortmund.de
;;  [david] - David M. Smith dsmith@stats.adelaide.edu.au
;;  [christian] - Christian Egli Christian.Egli@hcsd.hac.com
;;  [karl] - Karl Fogel kfogel@floss.life.uiuc.edu

;;; Code

(eval-when-compile (require 'cl))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Customizable variables
;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defvar imenu-use-markers t
  "*Non-nil means use markers instead of integers for Imenu buffer positions.
Setting this to nil makes Imenu work faster.

This might not yet be honored by all index-building functions.")

(defvar imenu-max-item-length 60
  "*If a number, truncate Imenu entries to that length.")

(defvar imenu-auto-rescan nil
  "*Non-nil means Imenu should always rescan the buffers.")

(defvar imenu-auto-rescan-maxout 60000 
  "*Imenu auto-rescan is disabled in buffers larger than this size.
This variable is buffer-local.")

(defvar imenu-always-use-completion-buffer-p nil
  "*Set this to non-nil for displaying the index in a completion buffer.

`never' means never automatically display a listing of any kind.
A value of nil (the default) means display the index as a mouse menu
if the mouse was used to invoke `imenu'.
Another non-nil value means always display the index in a completion buffer.")

(defvar imenu-sort-function nil
  "*The function to use for sorting the index mouse-menu.

Affects only the mouse index menu.

Set this to nil if you don't want any sorting (faster).
The items in the menu are then presented in the order they were found
in the buffer.

Set it to `imenu--sort-by-name' if you want alphabetic sorting.

The function should take two arguments and return T if the first
element should come before the second.  The arguments are cons cells;
\(NAME . POSITION).  Look at `imenu--sort-by-name' for an example.")

(defvar imenu-max-items 25
  "*Maximum number of elements in a mouse menu for Imenu.")

(defvar imenu-scanning-message "Scanning buffer for index (%3d%%)"
  "*Progress message during the index scanning of the buffer.
If non-nil, user gets a message during the scanning of the buffer.

Relevant only if the mode-specific function that creates the buffer
index use `imenu-progress-message'.")

(defvar imenu-space-replacement "^"
  "*The replacement string for spaces in index names.
Used when presenting the index in a completion-buffer to make the
names work as tokens.")

(defvar imenu-level-separator ":"
  "*The separator between index names of different levels.
Used for making mouse-menu titles and for flattening nested indexes
with name concatenation.")

;;;###autoload
(defvar imenu-generic-expression nil
  "The regex pattern to use for creating a buffer index.

If non-nil this pattern is passed to `imenu--generic-function'
to create a buffer index.

The value should be an alist with elements that look like this:
 (MENU-TITLE REGEXP INDEX)
or like this:
 (MENU-TITLE REGEXP INDEX FUNCTION ARGUMENTS...)
with zero or more ARGUMENTS.  The former format creates a simple element in
the index alist when it matches; the latter creates a special element
of the form  (NAME FUNCTION NAME POSITION-MARKER ARGUMENTS...)
with FUNCTION and ARGUMENTS beiong copied from `imenu-generic-expression'.

MENU-TITLE is a string used as the title for the submenu or nil if the
entries are not nested.

REGEXP is a regexp that should match a construct in the buffer that is
to be displayed in the menu; i.e., function or variable definitions,
etc.  It contains a substring which is the name to appear in the
menu.  See the info section on Regexps for more information.

INDEX points to the substring in REGEXP that contains the name (of the
function, variable or type) that is to appear in the menu.

For emacs-lisp-mode for example PATTERN would look like:

'((nil \"^\\\\s-*(def\\\\(un\\\\|subst\\\\|macro\\\\|advice\\\\)\\\\s-+\\\\([-A-Za-z0-9+]+\\\\)\" 2)
  (\"*Vars*\" \"^\\\\s-*(def\\\\(var\\\\|const\\\\)\\\\s-+\\\\([-A-Za-z0-9+]+\\\\)\" 2)
  (\"*Types*\" \"^\\\\s-*(def\\\\(type\\\\|struct\\\\|class\\\\|ine-condition\\\\)\\\\s-+\\\\([-A-Za-z0-9+]+\\\\)\" 2))

The variable is buffer-local.")

;;;###autoload
(make-variable-buffer-local 'imenu-generic-expression)

;;;; Hooks

(defvar imenu-create-index-function 'imenu-default-create-index-function
  "The function to use for creating a buffer index.

It should be a function that takes no arguments and returns an index
of the current buffer as an alist.

Simple elements in the alist look like (INDEX-NAME . INDEX-POSITION).
Special elements look like (INDEX-NAME FUNCTION ARGUMENTS...).
A nested sub-alist element looks like (INDEX-NAME SUB-ALIST).
The function `imenu--subalist-p' tests an element and returns t
 if it is a sub-alist.

This function is called within a `save-excursion'.

The variable is buffer-local.")
(make-variable-buffer-local 'imenu-create-index-function)

(defvar imenu-prev-index-position-function 'beginning-of-defun
  "Function for finding the next index position.

If `imenu-create-index-function' is set to
`imenu-default-create-index-function', then you must set this variable
to a function that will find the next index, looking backwards in the
file.

The function should leave point at the place to be connected to the
index and it should return nil when it doesn't find another index.")
(make-variable-buffer-local 'imenu-prev-index-position-function)

(defvar imenu-extract-index-name-function nil
  "Function for extracting the index name.

This function is called after the function pointed out by
`imenu-prev-index-position-function'.")
(make-variable-buffer-local 'imenu-extract-index-name-function)

(defvar imenu-default-goto-function 'imenu-default-goto-function
  "The default function called when selecting an Imenu item.
The function in this variable is called when selecting a normal index-item.")
(make-variable-buffer-local 'imenu-default-goto-function)


(defun imenu--subalist-p (item)
  (and (consp (cdr item)) (listp (cadr item))
       (not (eq (caadr item) 'lambda))))

;;;
;;; Macro to display a progress message.
;;; RELPOS is the relative position to display.
;;; If RELPOS is nil, then the relative position in the buffer
;;; is calculated.
;;; PREVPOS is the variable in which we store the last position displayed.
(defmacro imenu-progress-message (prevpos &optional relpos reverse)
  (` (and
      imenu-scanning-message
      (let ((pos (, (if relpos
			relpos
		      (` (imenu--relative-position (, reverse)))))))
	(if (, (if relpos t
		 (` (> pos (+ 5 (, prevpos))))))
	    (progn
	      (message imenu-scanning-message pos)
	      (setq (, prevpos) pos)))))))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;
;;;; Some examples of functions utilizing the framework of this
;;;; package.
;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; Return the current/previous sexp and the location of the sexp (its
;; beginning) without moving the point.
(defun imenu-example--name-and-position ()
  (save-excursion
    (forward-sexp -1)
    ;; [ydi] modified for imenu-use-markers
    (let ((beg (if imenu-use-markers (point-marker) (point)))
	  (end (progn (forward-sexp) (point))))
      (cons (buffer-substring beg end)
	    beg))))

;;;
;;; Lisp
;;; 

(defun imenu-example--lisp-extract-index-name ()
  ;; Example of a candidate for `imenu-extract-index-name-function'.
  ;; This will generate a flat index of definitions in a lisp file.
  (save-match-data
    (and (looking-at "(def")
	 (condition-case nil
	     (progn
	       (down-list 1)
	       (forward-sexp 2)
	       (let ((beg (point))
		     (end (progn (forward-sexp -1) (point))))
		 (buffer-substring beg end)))
	   (error nil)))))

(defun imenu-example--create-lisp-index ()
  ;; Example of a candidate for `imenu-create-index-function'.
  ;; It will generate a nested index of definitions.
  (let ((index-alist '())
	(index-var-alist '())
	(index-type-alist '())
	(index-unknown-alist '())
	prev-pos)
    (goto-char (point-max))
    (imenu-progress-message prev-pos 0)
    ;; Search for the function
    (while (beginning-of-defun)
      (imenu-progress-message prev-pos nil t)
      (save-match-data
	(and (looking-at "(def")
	     (save-excursion
	       (down-list 1)
	       (cond
		((looking-at "def\\(var\\|const\\)")
		 (forward-sexp 2)
		 (push (imenu-example--name-and-position)
		       index-var-alist))
		((looking-at "def\\(un\\|subst\\|macro\\|advice\\)")
		 (forward-sexp 2)
		 (push (imenu-example--name-and-position)
		       index-alist))
		((looking-at "def\\(type\\|struct\\|class\\|ine-condition\\)")
 		 (forward-sexp 2)
 		 (if (= (char-after (1- (point))) ?\))
 		     (progn
 		       (forward-sexp -1)
 		       (down-list 1)
 		       (forward-sexp 1)))
 		 (push (imenu-example--name-and-position)
 		       index-type-alist))
		(t
		 (forward-sexp 2)
		 (push (imenu-example--name-and-position)
		       index-unknown-alist)))))))
    (imenu-progress-message prev-pos 100)
    (and index-var-alist
	 (push (cons "Variables" index-var-alist)
	       index-alist))
    (and index-type-alist
 	 (push (cons "Types" index-type-alist)
  	       index-alist))
    (and index-unknown-alist
	 (push (cons "Syntax-unknown" index-unknown-alist)
	       index-alist))
    index-alist))

;; Regular expression to find C functions
(defvar imenu-example--function-name-regexp-c
  (concat 
   "^[a-zA-Z0-9]+[ \t]?"		; type specs; there can be no
   "\\([a-zA-Z0-9_*]+[ \t]+\\)?"	; more than 3 tokens, right?
   "\\([a-zA-Z0-9_*]+[ \t]+\\)?"
   "\\([*&]+[ \t]*\\)?"			; pointer
   "\\([a-zA-Z0-9_*]+\\)[ \t]*("	; name
   ))

(defun imenu-example--create-c-index (&optional regexp)
  (let ((index-alist '())
	prev-pos char)
    (goto-char (point-min))
    (imenu-progress-message prev-pos 0)
    ;; Search for the function
    (save-match-data
      (while (re-search-forward
	      (or regexp imenu-example--function-name-regexp-c)
	      nil t)
	(imenu-progress-message prev-pos)
	(backward-up-list 1)
	(save-excursion
	  (goto-char (scan-sexps (point) 1))
	  (setq char (following-char)))
	;; Skip this function name if it is a prototype declaration.
	(if (not (eq char ?\;))
	    (push (imenu-example--name-and-position) index-alist))))
    (imenu-progress-message prev-pos 100)
    (nreverse index-alist)))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Internal variables
;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; The item to use in the index for rescanning the buffer.
(defconst imenu--rescan-item '("*Rescan*" . -99))

;; The latest buffer index.
;; Buffer local.
(defvar imenu--index-alist nil)
(make-variable-buffer-local 'imenu--index-alist)

;; The latest buffer index used to update the menu bar menu.
(defvar imenu--last-menubar-index-alist nil)
(make-variable-buffer-local 'imenu--last-menubar-index-alist)

;; History list for 'jump-to-function-in-buffer'.
;; Making this buffer local caused it not to work!
(defvar imenu--history-list nil)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Internal support functions
;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;
;;; Sort function
;;; Sorts the items depending on their index name.
;;; An item look like (NAME . POSITION).
;;;
(defun imenu--sort-by-name (item1 item2)
  (string-lessp (car item1) (car item2)))

(defun imenu--relative-position (&optional reverse)
  ;; Support function to calculate relative position in buffer
  ;; Beginning of buffer is 0 and end of buffer is 100
  ;; If REVERSE is non-nil then the beginning is 100 and the end is 0.
  (let ((pos (point))
	(total (buffer-size)))
    (and reverse (setq pos (- total pos)))
    (if (> total 50000)
	;; Avoid overflow from multiplying by 100!
	(/ (1- pos) (max (/ total 100) 1))
      (/ (* 100 (1- pos)) (max total 1)))))

;; Split LIST into sublists of max length N.
;; Example (imenu--split '(1 2 3 4 5 6 7 8) 3)-> '((1 2 3) (4 5 6) (7 8))
(defun imenu--split (list n)
  (let ((remain list)
	(result '())
	(sublist '())
	(i 0))
    (while remain
      (push (pop remain) sublist)
      (incf i)
      (and (= i n)
	   ;; We have finished a sublist
	   (progn (push (nreverse sublist) result)
		  (setq i 0)
		  (setq sublist '()))))
    ;; There might be a sublist (if the length of LIST mod n is != 0)
    ;; that has to be added to the result list.
    (and sublist
	 (push (nreverse sublist) result))
    (nreverse result)))

;;; Split the alist MENULIST into a nested alist, if it is long enough.
;;; In any case, add TITLE to the front of the alist.
(defun imenu--split-menu (menulist title)
  (let (keep-at-top tail)
    (if (memq imenu--rescan-item menulist)
	(setq keep-at-top (cons imenu--rescan-item nil)
	      menulist (delq imenu--rescan-item menulist)))
    (setq tail menulist)
    (while tail
      (if (imenu--subalist-p (car tail))
	  (setq keep-at-top (cons (car tail) keep-at-top)
		menulist (delq (car tail) menulist)))
      (setq tail (cdr tail)))
    (if imenu-sort-function
	(setq menulist
	      (sort
	       (let ((res nil)
		     (oldlist menulist))
		 ;; Copy list method from the cl package `copy-list'
		 (while (consp oldlist) (push (pop oldlist) res))
		 (prog1 (nreverse res) (setcdr res oldlist)))
	       imenu-sort-function)))
    (if (> (length menulist) imenu-max-items)
	(let ((count 0))
	  (setq menulist
		(mapcar
		 (function
		  (lambda (menu)
		    (cons (format "From: %s" (caar menu)) menu)))
		 (imenu--split menulist imenu-max-items)))))
    (cons title
	  (nconc (nreverse keep-at-top) menulist))))

;;; Split up each long alist that are nested within ALIST
;;; into nested alists.
(defun imenu--split-submenus (alist)
  (mapcar (function (lambda (elt)
		      (if (and (consp elt)
			       (stringp (car elt))
			       (listp (cdr elt)))
			  (imenu--split-menu (cdr elt) (car elt))
			elt)))
	  alist))

;;; Truncate all strings in MENULIST to imenu-max-item-length
(defun imenu--truncate-items (menulist)
  (mapcar (function
	   (lambda (item)
	     (cond
	      ((consp (cdr item))
	       (imenu--truncate-items (cdr item)))
	      (t
	       ;; truncate if necessary
	       (if (and (numberp imenu-max-item-length)
			(> (length (car item)) imenu-max-item-length))
		   (setcar item (substring (car item) 0 imenu-max-item-length)))))))
	  menulist))


(defun imenu--make-index-alist (&optional noerror)
  "Create an index-alist for the definitions in the current buffer.

Simple elements in the alist look like (INDEX-NAME . INDEX-POSITION).
Special elements look like (INDEX-NAME FUNCTION ARGUMENTS...).
A nested sub-alist element looks like (INDEX-NAME SUB-ALIST).
The function `imenu--subalist-p' tests an element and returns t
 if it is a sub-alist.

There is one simple element with negative POSITION; that's intended
as a way for the user to ask to recalculate the buffer's index alist."
  (or (and imenu--index-alist
	   (or (not imenu-auto-rescan)
	       (and imenu-auto-rescan
		    (> (buffer-size)  imenu-auto-rescan-maxout))))
      ;; Get the index; truncate if necessary
      (progn
	(setq imenu--index-alist
	      (save-excursion
		(save-restriction
		  (widen)
		  (funcall imenu-create-index-function))))
	(imenu--truncate-items imenu--index-alist)))
  (or imenu--index-alist noerror
      (error "No items suitable for an index found in this buffer"))
  (or imenu--index-alist
      (setq imenu--index-alist (list nil)))
  ;; Add a rescan option to the index.
  (cons imenu--rescan-item imenu--index-alist))

;;; Find all markers in alist and makes
;;; them point nowhere.
;;; The top-level call uses nil as the argument;
;;; non-nil arguments are in recursivecalls.
(defvar imenu--cleanup-seen)

(defun imenu--cleanup (&optional alist)
  ;; If alist is provided use that list. 
  ;; If not, empty the table of lists already seen
  ;; and use imenu--index-alist.
  (if alist
      (setq imenu--cleanup-seen (cons alist imenu--cleanup-seen))
    (setq alist imenu--index-alist imenu--cleanup-seen (list alist)))

  (and alist
       (mapcar
	(function
	 (lambda (item)
	   (cond
	    ((markerp (cdr item))
	     (set-marker (cdr item) nil))
	    ;; Don't process one alist twice.
	    ((memq (cdr item) imenu--cleanup-seen))
	    ((imenu--subalist-p item)
	     (imenu--cleanup (cdr item))))))
	alist)
       t))

(defun imenu--create-keymap-2 (alist counter &optional commands)
  (let ((map nil))
    (mapcar
     (function
      (lambda (item)
	(cond
	 ((imenu--subalist-p item)
	  (append (list (setq counter (1+ counter))
			(car item) 'keymap (car item))
		  (imenu--create-keymap-2 (cdr item) (+ counter 10) commands)))
	 (t
	  (let ((end (if commands `(lambda () (interactive)
				     (imenu--menubar-select ',item))
		       (cons '(nil) item))))
	    (cons (car item)
		  (cons (car item) end))))
	 )))
     alist)))

;; If COMMANDS is non-nil, make a real keymap
;; with a real command used as the definition.
;; If it is nil, make something suitable for x-popup-menu.
(defun imenu--create-keymap-1 (title alist &optional commands)
  (append (list 'keymap title) (imenu--create-keymap-2 alist 0 commands)))


(defun imenu--in-alist (str alist)
  "Check whether the string STR is contained in multi-level ALIST."
  (let (elt head tail res)
    (setq res nil)
    (while alist
      (setq elt (car alist) 
	    tail (cdr elt)
	    alist (cdr alist) 
	    head (car elt)) 
      ;; A nested ALIST element looks like
      ;;   (INDEX-NAME (INDEX-NAME . INDEX-POSITION) ...)
      ;; while a bottom-level element looks like
      ;;   (INDEX-NAME . INDEX-POSITION)
      ;; We are only interested in the bottom-level elements, so we need to
      ;; recurse if TAIL is a list.
      (cond ((listp tail)
	     (if (setq res (imenu--in-alist str tail))
		 (setq alist nil)))
	    ((string= str head)
	     (setq alist nil res elt))))
    res))

(defun imenu-default-create-index-function ()
  "*Wrapper for index searching functions.

Moves point to end of buffer and then repeatedly calls
`imenu-prev-index-position-function' and `imenu-extract-index-name-function'.
Their results are gathered into an index alist."
  ;; These should really be done by setting imenu-create-index-function
  ;; in these major modes.  But save that change for later.
  (cond ((and (fboundp imenu-prev-index-position-function)
	      (fboundp imenu-extract-index-name-function))
	 (let ((index-alist '())
	       prev-pos name)
	   (goto-char (point-max))
	   (imenu-progress-message prev-pos 0 t)
	   ;; Search for the function
	   (while (funcall imenu-prev-index-position-function) 
	     (imenu-progress-message prev-pos nil t)
	     (save-excursion
	       (setq name (funcall imenu-extract-index-name-function)))
	     (and (stringp name)
 		  ;; [ydi] updated for imenu-use-markers
		  (push (cons name (if imenu-use-markers (point-marker) (point)))
			index-alist)))
	   (imenu-progress-message prev-pos 100 t)
	   index-alist))
	;; Use generic expression if possible.
	((and imenu-generic-expression)
	 (imenu--generic-function imenu-generic-expression)) 
	(t
	 (error "This buffer cannot use `imenu-default-create-index-function'"))))

(defun imenu--replace-spaces (name replacement)
  ;; Replace all spaces in NAME with REPLACEMENT.
  ;; That second argument should be a string.
  (mapconcat
   (function
    (lambda (ch)
      (if (char-equal ch ?\ )
	  replacement
	(char-to-string ch))))
   name
   ""))

(defun imenu--flatten-index-alist (index-alist &optional concat-names prefix)
  ;; Takes a nested INDEX-ALIST and returns a flat index alist.
  ;; If optional CONCAT-NAMES is non-nil, then a nested index has its
  ;; name and a space concatenated to the names of the children.
  ;; Third argument PREFIX is for internal use only.
  (mapcan
   (function
    (lambda (item)
      (let* ((name (car item))
	     (pos (cdr item))
	     (new-prefix (and concat-names
			      (if prefix
				  (concat prefix imenu-level-separator name)
				name))))
	(cond
	 ((or (markerp pos) (numberp pos))
	  (list (cons new-prefix pos)))
	 (t
	  (imenu--flatten-index-alist pos new-prefix))))))
   index-alist))

;;;
;;; Generic index gathering function.
;;;

(defun imenu--generic-function (patterns)
;; Built on some ideas that Erik Naggum <erik@naggum.no> once posted
;; to comp.emacs
  "Return an index of the current buffer as an alist.

PATTERN is an alist with elements that look like this: (MENU-TITLE
REGEXP INDEX).

MENU-TITLE is a string used as the title for the submenu or nil if the
entries are not nested.

REGEXP is a regexp that should match a construct in the buffer that is
to be displayed in the menu; i.e., function or variable definitions,
etc.  It contains a substring which is the name to appear in the
menu.  See the info section on Regexps for more information.

INDEX points to the substring in REGEXP that contains the name (of the
function, variable or type) that is to appear in the menu.

For emacs-lisp-mode for example PATTERN would look like:

'((nil \"^\\\\s-*(def\\\\(un\\\\|subst\\\\|macro\\\\|advice\\\\)\\\\s-+\\\\([-A-Za-z0-9]+\\\\)\" 2)
  (\"*Vars*\" \"^\\\\s-*(def\\\\(var\\\\|const\\\\)\\\\s-+\\\\([-A-Za-z0-9]+\\\\)\" 2)
  (\"*Types*\" \"^\\\\s-*(def\\\\(type\\\\|struct\\\\|class\\\\|ine-condition\\\\)\\\\s-+\\\\([-A-Za-z0-9]+\\\\)\" 2))'

Returns an index of the current buffer as an alist.  The elements in
the alist look like: (INDEX-NAME . INDEX-POSITION).  They may also be
nested index lists like (INDEX-NAME . INDEX-ALIST) depending on
pattern.

\(imenu--generic-function PATTERN\)."

  (let ((index-alist (list 'dummy))
        (found nil)
	(global-regexp 
	 (concat "\\(" 
		 (mapconcat
		  (function (lambda (pattern) (identity (cadr pattern)))) 
		  patterns "\\)\\|\\(") 
		 "\\)"))
	prev-pos)

    (goto-char (point-max))
    (imenu-progress-message prev-pos 0 t)
    (save-match-data
      (while (re-search-backward global-regexp nil t)
	(imenu-progress-message prev-pos nil t)
        (setq found nil)
	(save-excursion
	  (goto-char (match-beginning 0))
	  (mapcar 
	   (function 
	    (lambda (pat) 
	      (let ((menu-title (car pat))
		    (regexp (cadr pat))
		    (index (caddr pat))
		    (function (cadddr pat))
		    (rest (cddddr pat)))
		(if (and (not found) ; Only allow one entry;
			 (looking-at regexp))
		    (let ((beg (match-beginning index))
			  (end (match-end index)))
		      (setq found t)
		      (push 
		       (let ((name
			      (buffer-substring-no-properties beg end)))
			 ;; [ydi] updated for imenu-use-markers
			 (if imenu-use-markers
			     (setq beg (set-marker (make-marker) beg)))
			 (if function
			     (nconc (list name beg function)
				    rest)
			   (cons name beg)))
		       (cdr 
			(or (assoc menu-title index-alist)
			    (car (push 
				  (cons menu-title '()) 
				  index-alist))))))))))
	   patterns))))
    (imenu-progress-message prev-pos 100 t)
    (let ((main-element (assq nil index-alist)))
      (nconc (delq main-element (delq 'dummy index-alist))
	     (cdr main-element)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; The main functions for this package!
;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun imenu--completion-buffer (index-alist &optional prompt)
  "Let the user select from INDEX-ALIST in a completion buffer with PROMPT.

Returns t for rescan and otherwise a position number."
  ;; Create a list for this buffer only when needed.
  (let (name choice
	     (prepared-index-alist
	      (mapcar
	       (function
		(lambda (item)
		  (cons (imenu--replace-spaces (car item) imenu-space-replacement)
			(cdr item))))
	       index-alist)))
    (if (eq imenu-always-use-completion-buffer-p 'never)
  	(setq name (completing-read (or prompt "Index item: ")
  				    prepared-index-alist
 				    nil t nil 'imenu--history-list))
      (save-window-excursion
	;; Display the completion buffer
	(with-output-to-temp-buffer "*Completions*"
	  (display-completion-list
	   (all-completions "" prepared-index-alist )))
	(let ((minibuffer-setup-hook
	       (function (lambda ()
			   (let ((buffer (current-buffer)))
			     (save-excursion
			       (set-buffer "*Completions*")
			       (setq completion-reference-buffer buffer)))))))
	  ;; Make a completion question
	  (setq name (completing-read (or prompt "Index item: ")
				      prepared-index-alist
				      nil t nil 'imenu--history-list)))))
    (cond ((not (stringp name))
	   nil)
	  ((string= name (car imenu--rescan-item))
	   t)
	  (t
	   (setq choice (assoc name prepared-index-alist))
	   (if (imenu--subalist-p choice)
	       (imenu--completion-buffer (cdr choice) prompt)
	     choice)))))

(defun imenu--mouse-menu (index-alist event &optional title)
  "Let the user select from a buffer index from a mouse menu.

INDEX-ALIST is the buffer index and EVENT is a mouse event.

Returns t for rescan and otherwise an element or subelement of INDEX-ALIST."
  (setq index-alist (imenu--split-submenus index-alist))
  (let* ((menu 	(imenu--split-menu index-alist
		 (or title (buffer-name))))
	 position)
    (setq menu (imenu--create-keymap-1 (car menu) 
				       (if (< 1 (length (cdr menu)))
					   (cdr menu)
					 (cdr (car (cdr menu))))))
    (setq position (x-popup-menu event menu))
    (cond ((eq position nil)
	   position)
	  ;; If one call to x-popup-menu handled the nested menus,
	  ;; find the result by looking down the menus here.
	  ((and (listp position)
		(numberp (car position))
		(stringp (nth (1- (length position)) position)))
	   (let ((final menu))
	     (while position
	       (setq final (assoc (car position) final))
	       (setq position (cdr position)))
             (or (string= (car final) (car imenu--rescan-item))
                 (cdr (cdr (cdr final))))))
	  ;; If x-popup-menu went just one level and found a leaf item,
	  ;; return the INDEX-ALIST element for that.
	  ((and (consp position)
		(stringp (car position))
		(null (cdr position)))
	   (or (string= (car position) (car imenu--rescan-item))
	       (assq (car position) index-alist)))
	  ;; If x-popup-menu went just one level
	  ;; and found a non-leaf item (a submenu),
	  ;; recurse to handle the rest.
	  ((listp position)
	   (imenu--mouse-menu position event
			      (if title
				  (concat title imenu-level-separator
					  (car (rassq position index-alist)))
				(car (rassq position index-alist))))))))

(defun imenu-choose-buffer-index (&optional prompt alist)
  "Let the user select from a buffer index and return the chosen index.

If the user originally activated this function with the mouse, a mouse
menu is used.  Otherwise a completion buffer is used and the user is
prompted with PROMPT.

If you call this function with index alist ALIST, then it lets the user
select from ALIST.

With no index alist ALIST, it calls `imenu--make-index-alist' to
create the index alist.

If `imenu-always-use-completion-buffer-p' is non-nil, then the
completion buffer is always used, no matter if the mouse was used or
not.

The returned value is of the form (INDEX-NAME . INDEX-POSITION)."
  (let (index-alist
	(mouse-triggered (listp last-nonmenu-event))
	(result t) )
    ;; If selected by mouse, see to that the window where the mouse is
    ;; really is selected.
    (and mouse-triggered
	 (not (equal last-nonmenu-event '(menu-bar)))
	 (let ((window (posn-window (event-start last-nonmenu-event))))
	   (or (framep window) (null window) (select-window window))))
    ;; Create a list for this buffer only when needed.
    (while (eq result t)
      (setq index-alist (if alist alist (imenu--make-index-alist)))
      (setq result
	    (if (and mouse-triggered
		     (not imenu-always-use-completion-buffer-p))
		(imenu--mouse-menu index-alist last-nonmenu-event)
	      (imenu--completion-buffer index-alist prompt)))
      (and (eq result t)
	   (imenu--cleanup)
	   (setq imenu--index-alist nil)))
    result))

;;;###autoload
(defun imenu-add-to-menubar (name)
  "Adds an `imenu' entry to the menu bar for the current buffer.
NAME is a string used to name the menu bar item.
See the command `imenu' for more information."
  (interactive "sImenu menu item name: ")
  (if (or (and (fboundp imenu-prev-index-position-function)
		   (fboundp imenu-extract-index-name-function))
	      (and imenu-generic-expression))
	 (let ((newmap (make-sparse-keymap))
	       (menu-bar (lookup-key (current-local-map) [menu-bar])))
	   (define-key newmap [menu-bar]
	     (append (make-sparse-keymap) menu-bar))
	   (define-key newmap [menu-bar index]
	     (cons name (nconc (make-sparse-keymap "Imenu")
			       (make-sparse-keymap))))
	   (use-local-map (append newmap (current-local-map)))
	   (add-hook 'menu-bar-update-hook 'imenu-update-menubar))
    (error "The mode `%s' does not support Imenu" mode-name)))

(defvar imenu-buffer-menubar nil)

(defun imenu-update-menubar ()
  (and (current-local-map)
       (keymapp (lookup-key (current-local-map) [menu-bar index]))
       (let ((index-alist (imenu--make-index-alist t)))
	 ;; Don't bother updating if the index-alist has not changed
	 ;; since the last time we did it.
	 (or (equal index-alist imenu--last-menubar-index-alist)
	     (let (menu menu1 old)
	       (setq imenu--last-menubar-index-alist index-alist)
	       (setq index-alist (imenu--split-submenus index-alist))
	       (setq menu (imenu--split-menu index-alist
			   (buffer-name)))
	       (setq menu1 (imenu--create-keymap-1 (car menu) 
						   (if (< 1 (length (cdr menu)))
						       (cdr menu)
						     (cdr (car (cdr menu))))
						   t))
	       (setq old (lookup-key (current-local-map) [menu-bar index]))
	       (setcdr old (cdr menu1)))))))

(defun imenu--menubar-select (item)
  "Use Imenu to select the function or variable named in this menu item."
  (if (equal item imenu--rescan-item)
      (progn
	(imenu--cleanup)
	(setq imenu--index-alist nil)
	(imenu-update-menubar))
    (imenu item)))

(defun imenu-default-goto-function (name position &optional rest)
  "This function is used for moving the point to POSITION. 
The NAME and REST parameters are not used, they are here just to make
this function have the same interface as a function placed in a special 
index-item."
  (if (or (< position (point-min))
	  (> position (point-max)))
      ;; widen if outside narrowing
      (widen))
  (goto-char position))

;;;###autoload
(defun imenu (index-item)
  "Jump to a place in the buffer chosen using a buffer menu or mouse menu.
See `imenu-choose-buffer-index' for more information."
  (interactive (list (imenu-choose-buffer-index)))
  ;; Convert a string to an alist element.
  (if (stringp index-item)
      (setq index-item (assoc index-item (imenu--make-index-alist))))
  (and index-item
       (progn
	 (push-mark)
	 (let* ((is-special-item (listp (cdr index-item)))
		(function 
		 (if is-special-item
		     (caddr index-item) imenu-default-goto-function))
	       (position (if is-special-item
			     (cadr index-item) (cdr index-item)))
	       (rest (if is-special-item (cddr index-item))))
	   (apply function (car index-item) position rest)))))

(provide 'imenu)

;;; imenu.el ends here