wid-edit.el

;;; wid-edit.el --- Functions for creating and using widgets -*-byte-compile-dynamic: t;-*-
;;
;; Copyright (C) 1996, 1997, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
;;
;; Author: Per Abrahamsen <abraham@dina.kvl.dk>
;; Maintainer: FSF
;; Keywords: extensions

;; 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.

;;; Wishlist items (from widget.texi):

;; * The `menu-choice' tag should be prettier, something like the
;;   abbreviated menus in Open Look.

;; * Finish `:tab-order'.

;; * Make indentation work with glyphs and proportional fonts.

;; * Add commands to show overview of object and class hierarchies to
;;   the browser.

;; * Find a way to disable mouse highlight for inactive widgets.

;; * Find a way to make glyphs look inactive.

;; * Add `key-binding' widget.

;; * Add `widget' widget for editing widget specifications.

;; * Find clean way to implement variable length list.  See
;;   `TeX-printer-list' for an explanation.

;; * `C-h' in `widget-prompt-value' should give type specific help.

;; * A mailto widget. [This should work OK as a url-link if with
;;   browse-url-browser-function' set up appropriately.]

;;; Commentary:
;;
;; See `widget.el'.

;;; Code:

;;; Compatibility.

(defun widget-event-point (event)
  "Character position of the end of event if that exists, or nil."
  (posn-point (event-end event)))

(autoload 'pp-to-string "pp")
(autoload 'Info-goto-node "info")

(defun widget-button-release-event-p (event)
  "Non-nil if EVENT is a mouse-button-release event object."
  (and (eventp event)
       (memq (event-basic-type event) '(mouse-1 mouse-2 mouse-3))
       (or (memq 'click (event-modifiers event))
	   (memq  'drag (event-modifiers event)))))

;;; Customization.

(defgroup widgets nil
  "Customization support for the Widget Library."
  :link '(custom-manual "(widget)Top")
  :link '(emacs-library-link :tag "Lisp File" "widget.el")
  :prefix "widget-"
  :group 'extensions
  :group 'hypermedia)

(defgroup widget-documentation nil
  "Options controling the display of documentation strings."
  :group 'widgets)

(defgroup widget-faces nil
  "Faces used by the widget library."
  :group 'widgets
  :group 'faces)

(defvar widget-documentation-face 'widget-documentation-face
  "Face used for documentation strings in widgets.
This exists as a variable so it can be set locally in certain buffers.")

(defface widget-documentation-face '((((class color)
				       (background dark))
				      (:foreground "lime green"))
				     (((class color)
				       (background light))
				      (:foreground "dark green"))
				     (t nil))
  "Face used for documentation text."
  :group 'widget-documentation
  :group 'widget-faces)

(defvar widget-button-face 'widget-button-face
  "Face used for buttons in widgets.
This exists as a variable so it can be set locally in certain buffers.")

(defface widget-button-face '((t (:weight bold)))
  "Face used for widget buttons."
  :group 'widget-faces)

(defcustom widget-mouse-face 'highlight
  "Face used for widget buttons when the mouse is above them."
  :type 'face
  :group 'widget-faces)

;; TTY gets special definitions here and in the next defface, because
;; the gray colors defined for other displays cause black text on a black
;; background, at least on light-background TTYs.
(defface widget-field-face '((((type tty))
			      :background "yellow3"
			      :foreground "black")
			     (((class grayscale color)
			       (background light))
			      :background "gray85")
			     (((class grayscale color)
			       (background dark))
			      :background "dim gray")
			     (t
			      :slant italic))
  "Face used for editable fields."
  :group 'widget-faces)

(defface widget-single-line-field-face '((((type tty))
					  :background "green3"
					  :foreground "black")
					 (((class grayscale color)
					   (background light))
					  :background "gray85")
					 (((class grayscale color)
					   (background dark))
					  :background "dim gray")
					 (t
					  :slant italic))
  "Face used for editable fields spanning only a single line."
  :group 'widget-faces)

;;; This causes display-table to be loaded, and not usefully.
;;;(defvar widget-single-line-display-table
;;;  (let ((table (make-display-table)))
;;;    (aset table 9  "^I")
;;;    (aset table 10 "^J")
;;;    table)
;;;  "Display table used for single-line editable fields.")

;;;(when (fboundp 'set-face-display-table)
;;;  (set-face-display-table 'widget-single-line-field-face
;;;			  widget-single-line-display-table))

;;; Utility functions.
;;
;; These are not really widget specific.

(defun widget-princ-to-string (object)
  "Return string representation of OBJECT, any Lisp object.
No quoting characters are used; no delimiters are printed around
the contents of strings."
  (with-output-to-string
      (princ object)))

(defun widget-clear-undo ()
  "Clear all undo information."
  (buffer-disable-undo (current-buffer))
  (buffer-enable-undo))

(defcustom widget-menu-max-size 40
  "Largest number of items allowed in a popup-menu.
Larger menus are read through the minibuffer."
  :group 'widgets
  :type 'integer)

(defcustom widget-menu-max-shortcuts 40
  "Largest number of items for which it works to choose one with a character.
For a larger number of items, the minibuffer is used."
  :group 'widgets
  :type 'integer)

(defcustom widget-menu-minibuffer-flag nil
  "*Control how to ask for a choice from the keyboard.
Non-nil means use the minibuffer;
nil means read a single character."
  :group 'widgets
  :type 'boolean)

(defun widget-choose (title items &optional event)
  "Choose an item from a list.

First argument TITLE is the name of the list.
Second argument ITEMS is an list whose members are either
 (NAME . VALUE), to indicate selectable items, or just strings to
 indicate unselectable items.
Optional third argument EVENT is an input event.

The user is asked to choose between each NAME from the items alist,
and the VALUE of the chosen element will be returned.  If EVENT is a
mouse event, and the number of elements in items is less than
`widget-menu-max-size', a popup menu will be used, otherwise the
minibuffer."
  (cond ((and (< (length items) widget-menu-max-size)
	      event (display-popup-menus-p))
	 ;; Mouse click.
	 (x-popup-menu event
		       (list title (cons "" items))))
	((or widget-menu-minibuffer-flag
	     (> (length items) widget-menu-max-shortcuts))
	 ;; Read the choice of name from the minibuffer.
	 (setq items (widget-remove-if 'stringp items))
	 (let ((val (completing-read (concat title ": ") items nil t)))
	   (if (stringp val)
	       (let ((try (try-completion val items)))
		 (when (stringp try)
		   (setq val try))
		 (cdr (assoc val items))))))
	(t
	 ;; Construct a menu of the choices
	 ;; and then use it for prompting for a single character.
	 (let* ((overriding-terminal-local-map (make-sparse-keymap))
		(next-digit ?0)
		map choice some-choice-enabled value)
	   ;; Define SPC as a prefix char to get to this menu.
	   (define-key overriding-terminal-local-map " "
	     (setq map (make-sparse-keymap title)))
	   (save-excursion
	     (set-buffer (get-buffer-create " widget-choose"))
	     (erase-buffer)
	     (insert "Available choices:\n\n")
	     (while items
	       (setq choice (car items) items (cdr items))
	       (if (consp choice)
		   (let* ((name (car choice))
			 (function (cdr choice)))
		     (insert (format "%c = %s\n" next-digit name))
		     (define-key map (vector next-digit) function)
		     (setq some-choice-enabled t)))
	       ;; Allocate digits to disabled alternatives
	       ;; so that the digit of a given alternative never varies.
	       (setq next-digit (1+ next-digit)))
	     (insert "\nC-g = Quit"))
	   (or some-choice-enabled
	       (error "None of the choices is currently meaningful"))
	   (define-key map [?\C-g] 'keyboard-quit)
	   (define-key map [t] 'keyboard-quit)
	   (define-key map [?\M-\C-v] 'scroll-other-window)
	   (define-key map [?\M--] 'negative-argument)
	   (setcdr map (nreverse (cdr map)))
	   ;; Read a char with the menu, and return the result
	   ;; that corresponds to it.
	   (save-window-excursion
	     (let ((buf (get-buffer " widget-choose")))
	       (fit-window-to-buffer (display-buffer buf))
	       (let ((cursor-in-echo-area t)
		     keys
		     (char 0)
		     (arg 1))
		 (while (not (or (and (>= char ?0) (< char next-digit))
				 (eq value 'keyboard-quit)))
		   ;; Unread a SPC to lead to our new menu.
		   (setq unread-command-events (cons ?\ unread-command-events))
		   (setq keys (read-key-sequence title))
		   (setq value
			 (lookup-key overriding-terminal-local-map keys t)
			 char (string-to-char (substring keys 1)))
		   (cond ((eq value 'scroll-other-window)
			  (let ((minibuffer-scroll-window
				 (get-buffer-window buf)))
			    (if (> 0 arg)
				(scroll-other-window-down
				 (window-height minibuffer-scroll-window))
			      (scroll-other-window))
			    (setq arg 1)))
			 ((eq value 'negative-argument)
			  (setq arg -1))
			 (t
			  (setq arg 1)))))))
	   (when (eq value 'keyboard-quit)
	     (error "Canceled"))
	   value))))

(defun widget-remove-if (predictate list)
  (let (result (tail list))
    (while tail
      (or (funcall predictate (car tail))
	  (setq result (cons (car tail) result)))
      (setq tail (cdr tail)))
    (nreverse result)))

;;; Widget text specifications.
;; 
;; These functions are for specifying text properties.

(defvar widget-field-add-space t
  "Non-nil means add extra space at the end of editable text fields.
If you don't add the space, it will become impossible to edit a zero
size field.")

(defvar widget-field-use-before-change t
  "Non-nil means use `before-change-functions' to track editable fields.
This enables the use of undo, but doesn't work on Emacs 19.34 and earlier.
Using before hooks also means that the :notify function can't know the
new value.")

(defun widget-specify-field (widget from to)
  "Specify editable button for WIDGET between FROM and TO."
  ;; Terminating space is not part of the field, but necessary in
  ;; order for local-map to work.  Remove next sexp if local-map works
  ;; at the end of the overlay.
  (save-excursion
    (goto-char to)
    (cond ((null (widget-get widget :size))
	   (forward-char 1))
	  (widget-field-add-space
	   (insert-and-inherit " ")))
    (setq to (point)))
  (let ((keymap (widget-get widget :keymap))
	(face (or (widget-get widget :value-face) 'widget-field-face))
	(help-echo (widget-get widget :help-echo))
	(rear-sticky
	 (or (not widget-field-add-space) (widget-get widget :size))))
    (if (functionp help-echo)
      (setq help-echo 'widget-mouse-help))    
    (when (= (char-before to) ?\n)
      ;; When the last character in the field is a newline, we want to
      ;; give it a `field' char-property of `boundary', which helps the
      ;; C-n/C-p act more naturally when entering/leaving the field.  We
     ;; do this by making a small secondary overlay to contain just that
      ;; one character.
      (let ((overlay (make-overlay (1- to) to nil t nil)))
	(overlay-put overlay 'field 'boundary)
	;; Use `local-map' here, not `keymap', so that normal editing
	;; works in the field when, say, Custom uses `suppress-keymap'.
	(overlay-put overlay 'local-map keymap)
	(overlay-put overlay 'face face)
	(overlay-put overlay 'help-echo help-echo))
      (setq to (1- to))
      (setq rear-sticky t))
    (let ((overlay (make-overlay from to nil nil rear-sticky)))
      (widget-put widget :field-overlay overlay)
      ;;(overlay-put overlay 'detachable nil)
      (overlay-put overlay 'field widget)
      (overlay-put overlay 'local-map keymap)
      (overlay-put overlay 'face face)
      (overlay-put overlay 'help-echo help-echo)))
  (widget-specify-secret widget))

(defun widget-specify-secret (field)
  "Replace text in FIELD with value of `:secret', if non-nil."
  (let ((secret (widget-get field :secret))
	(size (widget-get field :size)))
    (when secret
      (let ((begin (widget-field-start field))
	    (end (widget-field-end field)))
	(when size
	  (while (and (> end begin)
		      (eq (char-after (1- end)) ?\ ))
	    (setq end (1- end))))
	(while (< begin end)
	  (let ((old (char-after begin)))
	    (unless (eq old secret)
	      (subst-char-in-region begin (1+ begin) old secret)
	      (put-text-property begin (1+ begin) 'secret old))
	    (setq begin (1+ begin))))))))

(defun widget-specify-button (widget from to)
  "Specify button for WIDGET between FROM and TO."
  (let ((overlay (make-overlay from to nil t nil))
	(help-echo (widget-get widget :help-echo)))
    (widget-put widget :button-overlay overlay)
    (if (functionp help-echo)
      (setq help-echo 'widget-mouse-help))
    (overlay-put overlay 'button widget)
    (overlay-put overlay 'keymap (widget-get widget :keymap))
    ;; We want to avoid the face with image buttons.
    (unless (widget-get widget :suppress-face)
      (overlay-put overlay 'face (widget-apply widget :button-face-get))
      (overlay-put overlay 'mouse-face widget-mouse-face))
    (overlay-put overlay 'help-echo help-echo)))

(defun widget-mouse-help (window overlay point)
  "Help-echo callback for widgets whose :help-echo is a function."
  (with-current-buffer (overlay-buffer overlay)
    (let* ((widget (widget-at (overlay-start overlay)))
	   (help-echo (if widget (widget-get widget :help-echo))))
      (if (functionp help-echo)
	  (funcall help-echo widget)
	help-echo))))

(defun widget-specify-sample (widget from to)
  "Specify sample for WIDGET between FROM and TO."
  (let ((overlay (make-overlay from to nil t nil)))
    (overlay-put overlay 'face (widget-apply widget :sample-face-get))
    (widget-put widget :sample-overlay overlay)))

(defun widget-specify-doc (widget from to)
  "Specify documentation for WIDGET between FROM and TO."
  (let ((overlay (make-overlay from to nil t nil)))
    (overlay-put overlay 'widget-doc widget)
    (overlay-put overlay 'face widget-documentation-face)
    (widget-put widget :doc-overlay overlay)))

(defmacro widget-specify-insert (&rest form)
  "Execute FORM without inheriting any text properties."
  `(save-restriction
    (let ((inhibit-read-only t)
	  (inhibit-modification-hooks t)
	  result)
      (insert "<>")
      (narrow-to-region (- (point) 2) (point))
      (goto-char (1+ (point-min)))
      (setq result (progn ,@form))
      (delete-region (point-min) (1+ (point-min)))
      (delete-region (1- (point-max)) (point-max))
      (goto-char (point-max))
      result)))

(defface widget-inactive-face '((((class grayscale color)
				  (background dark))
				 (:foreground "light gray"))
				(((class grayscale color)
				  (background light))
				 (:foreground "dim gray"))
				(t
				 (:slant italic)))
  "Face used for inactive widgets."
  :group 'widget-faces)

(defun widget-specify-inactive (widget from to)
  "Make WIDGET inactive for user modifications."
  (unless (widget-get widget :inactive)
    (let ((overlay (make-overlay from to nil t nil)))
      (overlay-put overlay 'face 'widget-inactive-face)
      ;; This is disabled, as it makes the mouse cursor change shape.
      ;; (overlay-put overlay 'mouse-face 'widget-inactive-face)
      (overlay-put overlay 'evaporate t)
      (overlay-put overlay 'priority 100)
      (overlay-put overlay 'modification-hooks '(widget-overlay-inactive))
      (widget-put widget :inactive overlay))))

(defun widget-overlay-inactive (&rest junk)
  "Ignoring the arguments, signal an error."
  (unless inhibit-read-only
    (error "The widget here is not active")))


(defun widget-specify-active (widget)
  "Make WIDGET active for user modifications."
  (let ((inactive (widget-get widget :inactive)))
    (when inactive
      (delete-overlay inactive)
      (widget-put widget :inactive nil))))

;;; Widget Properties.

(defsubst widget-type (widget)
  "Return the type of WIDGET, a symbol."
  (car widget))

;;;###autoload
(defun widgetp (widget)
  "Return non-nil iff WIDGET is a widget."
  (if (symbolp widget)
      (get widget 'widget-type)
    (and (consp widget)
	 (symbolp (car widget))
	 (get (car widget) 'widget-type))))

(defun widget-get-indirect (widget property)
  "In WIDGET, get the value of PROPERTY.
If the value is a symbol, return its binding.
Otherwise, just return the value."
  (let ((value (widget-get widget property)))
    (if (symbolp value)
	(symbol-value value)
      value)))

(defun widget-member (widget property)
  "Non-nil iff there is a definition in WIDGET for PROPERTY."
  (cond ((plist-member (cdr widget) property)
	 t)
	((car widget)
	 (widget-member (get (car widget) 'widget-type) property))
	(t nil)))

(defun widget-value (widget)
  "Extract the current value of WIDGET."
  (widget-apply widget
		:value-to-external (widget-apply widget :value-get)))

(defun widget-value-set (widget value)
  "Set the current value of WIDGET to VALUE."
  (widget-apply widget
		:value-set (widget-apply widget
					 :value-to-internal value)))

(defun widget-default-get (widget)
  "Extract the default value of WIDGET."
  (or (widget-get widget :value)
      (widget-apply widget :default-get)))

(defun widget-match-inline (widget vals)
  "In WIDGET, match the start of VALS."
  (cond ((widget-get widget :inline)
	 (widget-apply widget :match-inline vals))
	((and (listp vals)
	      (widget-apply widget :match (car vals)))
	 (cons (list (car vals)) (cdr vals)))
	(t nil)))

(defun widget-apply-action (widget &optional event)
  "Apply :action in WIDGET in response to EVENT."
  (if (widget-apply widget :active)
      (widget-apply widget :action event)
    (error "Attempt to perform action on inactive widget")))

;;; Helper functions.
;;
;; These are widget specific.

;;;###autoload
(defun widget-prompt-value (widget prompt &optional value unbound)
  "Prompt for a value matching WIDGET, using PROMPT.
The current value is assumed to be VALUE, unless UNBOUND is non-nil."
  (unless (listp widget)
    (setq widget (list widget)))
  (setq prompt (format "[%s] %s" (widget-type widget) prompt))
  (setq widget (widget-convert widget))
  (let ((answer (widget-apply widget :prompt-value prompt value unbound)))
    (unless (widget-apply widget :match answer)
      (error "Value does not match %S type" (car widget)))
    answer))

(defun widget-get-sibling (widget)
  "Get the item WIDGET is assumed to toggle.
This is only meaningful for radio buttons or checkboxes in a list."
  (let* ((children (widget-get (widget-get widget :parent) :children))
	 child)
    (catch 'child
      (while children
	(setq child (car children)
	      children (cdr children))
	(when (eq (widget-get child :button) widget)
	  (throw 'child child)))
      nil)))

(defun widget-map-buttons (function &optional buffer maparg)
  "Map FUNCTION over the buttons in BUFFER.
FUNCTION is called with the arguments WIDGET and MAPARG.

If FUNCTION returns non-nil, the walk is cancelled.

The arguments MAPARG, and BUFFER default to nil and (current-buffer),
respectively."
  (let ((cur (point-min))
	(widget nil)
	(parent nil)
	(overlays (if buffer
		      (save-excursion (set-buffer buffer) (overlay-lists))
		    (overlay-lists))))
    (setq overlays (append (car overlays) (cdr overlays)))
    (while (setq cur (pop overlays))
      (setq widget (overlay-get cur 'button))
      (if (and widget (funcall function widget maparg))
	  (setq overlays nil)))))

;;; Images.

(defcustom widget-image-directory (file-name-as-directory
				   (expand-file-name "custom" data-directory))
  "Where widget button images are located.
If this variable is nil, widget will try to locate the directory
automatically."
  :group 'widgets
  :type 'directory)

(defcustom widget-image-enable t
  "If non nil, use image buttons in widgets when available."
  :version "21.1"
  :group 'widgets
  :type 'boolean)

(defcustom widget-image-conversion
  '((xpm ".xpm") (gif ".gif") (png ".png") (jpeg ".jpg" ".jpeg")
    (xbm ".xbm"))
  "Conversion alist from image formats to file name suffixes."
  :group 'widgets
  :type '(repeat (cons :format "%v"
		       (symbol :tag "Image Format" unknown)
		       (repeat :tag "Suffixes"
			       (string :format "%v")))))

(defun widget-image-find (image)
  "Create a graphical button from IMAGE.
IMAGE should either already be an image, or be a file name sans
extension (xpm, xbm, gif, jpg, or png) located in
`widget-image-directory' or otherwise where `find-image' will find it."
  (cond ((not (and image widget-image-enable (display-graphic-p)))
	 ;; We don't want or can't use images.
	 nil)
	((and (consp image)
	      (eq 'image (car image)))
	 ;; Already an image spec.  Use it.
	 image)
	((stringp image)
	 ;; A string.  Look it up in relevant directories.
	 (let* ((load-path (cons widget-image-directory load-path))
		specs)
	   (dolist (elt widget-image-conversion)
	     (dolist (ext (cdr elt))
	       (push (list :type (car elt) :file (concat image ext)) specs)))
	   (setq specs (nreverse specs))
	   (find-image specs)))
	(t
	 ;; Oh well.
	 nil)))

(defvar widget-button-pressed-face 'widget-button-pressed-face
  "Face used for pressed buttons in widgets.
This exists as a variable so it can be set locally in certain
buffers.")

(defun widget-image-insert (widget tag image &optional down inactive)
  "In WIDGET, insert the text TAG or, if supported, IMAGE.
IMAGE should either be an image or an image file name sans extension
\(xpm, xbm, gif, jpg, or png) located in `widget-image-directory'.

Optional arguments DOWN and INACTIVE are used instead of IMAGE when the
button is pressed or inactive, respectively.  These are currently ignored."
  (if (and (display-graphic-p)
	   (setq image (widget-image-find image)))
      (progn (widget-put widget :suppress-face t)
	     (insert-image image
			   (propertize
			    tag 'mouse-face widget-button-pressed-face)))
    (insert tag)))

;;; Buttons.

(defgroup widget-button nil
  "The look of various kinds of buttons."
  :group 'widgets)

(defcustom widget-button-prefix ""
  "String used as prefix for buttons."
  :type 'string
  :group 'widget-button)

(defcustom widget-button-suffix ""
  "String used as suffix for buttons."
  :type 'string
  :group 'widget-button)

;;; Creating Widgets.

;;;###autoload
(defun widget-create (type &rest args)
  "Create widget of TYPE.
The optional ARGS are additional keyword arguments."
  (let ((widget (apply 'widget-convert type args)))
    (widget-apply widget :create)
    widget))

(defun widget-create-child-and-convert (parent type &rest args)
  "As part of the widget PARENT, create a child widget TYPE.
The child is converted, using the keyword arguments ARGS."
  (let ((widget (apply 'widget-convert type args)))
    (widget-put widget :parent parent)
    (unless (widget-get widget :indent)
      (widget-put widget :indent (+ (or (widget-get parent :indent) 0)
				    (or (widget-get widget :extra-offset) 0)
				    (widget-get parent :offset))))
    (widget-apply widget :create)
    widget))

(defun widget-create-child (parent type)
  "Create widget of TYPE."
  (let ((widget (copy-sequence type)))
    (widget-put widget :parent parent)
    (unless (widget-get widget :indent)
      (widget-put widget :indent (+ (or (widget-get parent :indent) 0)
				    (or (widget-get widget :extra-offset) 0)
				    (widget-get parent :offset))))
    (widget-apply widget :create)
    widget))

(defun widget-create-child-value (parent type value)
  "Create widget of TYPE with value VALUE."
  (let ((widget (copy-sequence type)))
    (widget-put widget :value (widget-apply widget :value-to-internal value))
    (widget-put widget :parent parent)
    (unless (widget-get widget :indent)
      (widget-put widget :indent (+ (or (widget-get parent :indent) 0)
				    (or (widget-get widget :extra-offset) 0)
				    (widget-get parent :offset))))
    (widget-apply widget :create)
    widget))

;;;###autoload
(defun widget-delete (widget)
  "Delete WIDGET."
  (widget-apply widget :delete))

(defun widget-convert (type &rest args)
  "Convert TYPE to a widget without inserting it in the buffer.
The optional ARGS are additional keyword arguments."
  ;; Don't touch the type.
  (let* ((widget (if (symbolp type)
		     (list type)
		   (copy-sequence type)))
	 (current widget)
	 done
	 (keys args))
    ;; First set the :args keyword.
    (while (cdr current)		;Look in the type.
      (if (and (keywordp (cadr current))
	       ;; If the last element is a keyword,
	       ;; it is still the :args element,
	       ;; even though it is a keyword.
	       (cddr current))
	  (if (eq (cadr current) :args)
	      ;; If :args is explicitly specified, obey it.
	      (setq current nil)
	    ;; Some other irrelevant keyword.
	    (setq current (cdr (cdr current))))
	(setcdr current (list :args (cdr current)))
	(setq current nil)))
    (while (and args (not done))	;Look in ARGS.
      (cond ((eq (car args) :args)
	     ;; Handle explicit specification of :args.
	     (setq args (cadr args)
		   done t))
	    ((keywordp (car args))
	     (setq args (cddr args)))
	    (t (setq done t))))
    (when done
      (widget-put widget :args args))
    ;; Then Convert the widget.
    (setq type widget)
    (while type
      (let ((convert-widget (plist-get (cdr type) :convert-widget)))
	(if convert-widget
	    (setq widget (funcall convert-widget widget))))
      (setq type (get (car type) 'widget-type)))
    ;; Finally set the keyword args.
    (while keys
      (let ((next (nth 0 keys)))
	(if (keywordp next)
	    (progn
	      (widget-put widget next (nth 1 keys))
	      (setq keys (nthcdr 2 keys)))
	  (setq keys nil))))
    ;; Convert the :value to internal format.
    (if (widget-member widget :value)
	(widget-put widget
		    :value (widget-apply widget
					 :value-to-internal
					 (widget-get widget :value))))
    ;; Return the newly create widget.
    widget))

;;;###autoload
(defun widget-insert (&rest args)
  "Call `insert' with ARGS even if surrounding text is read only."
  (let ((inhibit-read-only t)
	(inhibit-modification-hooks t))
    (apply 'insert args)))

(defun widget-convert-text (type from to
				 &optional button-from button-to
				 &rest args)
  "Return a widget of type TYPE with endpoint FROM TO.
Optional ARGS are extra keyword arguments for TYPE.
and TO will be used as the widgets end points. If optional arguments
BUTTON-FROM and BUTTON-TO are given, these will be used as the widgets
button end points.
Optional ARGS are extra keyword arguments for TYPE."
  (let ((widget (apply 'widget-convert type :delete 'widget-leave-text args))
	(from (copy-marker from))
	(to (copy-marker to)))
    (set-marker-insertion-type from t)
    (set-marker-insertion-type to nil)
    (widget-put widget :from from)
    (widget-put widget :to to)
    (when button-from
      (widget-specify-button widget button-from button-to))
    widget))

(defun widget-convert-button (type from to &rest args)
  "Return a widget of type TYPE with endpoint FROM TO.
Optional ARGS are extra keyword arguments for TYPE.
No text will be inserted to the buffer, instead the text between FROM
and TO will be used as the widgets end points, as well as the widgets
button end points."
  (apply 'widget-convert-text type from to from to args))

(defun widget-leave-text (widget)
  "Remove markers and overlays from WIDGET and its children."
  (let ((button (widget-get widget :button-overlay))
	(sample (widget-get widget :sample-overlay))
	(doc (widget-get widget :doc-overlay))
	(field (widget-get widget :field-overlay)))
    (set-marker (widget-get widget :from) nil)
    (set-marker (widget-get widget :to) nil)
    (when button
      (delete-overlay button))
    (when sample
      (delete-overlay sample))
    (when doc
      (delete-overlay doc))
    (when field
      (delete-overlay field))
    (mapc 'widget-leave-text (widget-get widget :children))))

;;; Keymap and Commands.

;;;###autoload
(defvar widget-keymap
  (let ((map (make-sparse-keymap)))
    (define-key map "\t" 'widget-forward)
    (define-key map [(shift tab)] 'widget-backward)
    (define-key map [backtab] 'widget-backward)
    (define-key map [down-mouse-2] 'widget-button-click)
    (define-key map "\C-m" 'widget-button-press)
    map)
  "Keymap containing useful binding for buffers containing widgets.
Recommended as a parent keymap for modes using widgets.")

(defvar widget-global-map global-map
  "Keymap used for events a widget does not handle itself.")
(make-variable-buffer-local 'widget-global-map)

(defvar widget-field-keymap
  (let ((map (copy-keymap widget-keymap)))
    (define-key map "\C-k" 'widget-kill-line)
    (define-key map "\M-\t" 'widget-complete)
    (define-key map "\C-m" 'widget-field-activate)
    ;; Since the widget code uses a `field' property to identify fields,
    ;; ordinary beginning-of-line does the right thing.
    ;;  (define-key map "\C-a" 'widget-beginning-of-line)
    (define-key map "\C-e" 'widget-end-of-line)
    map)
  "Keymap used inside an editable field.")

(defvar widget-text-keymap
  (let ((map (copy-keymap widget-keymap)))
    ;; Since the widget code uses a `field' property to identify fields,
    ;; ordinary beginning-of-line does the right thing.
    ;;  (define-key map "\C-a" 'widget-beginning-of-line)
    (define-key map "\C-e" 'widget-end-of-line)
    map)
  "Keymap used inside a text field.")

(defun widget-field-activate (pos &optional event)
  "Invoke the editable field at point."
  (interactive "@d")
  (let ((field (widget-field-at pos)))
    (if field
	(widget-apply-action field event)
      (call-interactively
       (lookup-key widget-global-map (this-command-keys))))))

(defface widget-button-pressed-face
  '((((class color))
     (:foreground "red"))
    (t
     (:weight bold :underline t)))
  "Face used for pressed buttons."
  :group 'widget-faces)

(defun widget-button-click (event)
  "Invoke the button that the mouse is pointing at."
  (interactive "e")
  (if (widget-event-point event)
      (let* ((pos (widget-event-point event))
	     (start (event-start event))
	     (button (get-char-property 
		      pos 'button (and (windowp (posn-window start))
				       (window-buffer (posn-window start))))))
	(if button
	    ;; Mouse click on a widget button.  Do the following
	    ;; in a save-excursion so that the click on the button
	    ;; doesn't change point.
	    (save-selected-window
	      (select-window (posn-window (event-start event)))
	      (save-excursion
		(goto-char (posn-point (event-start event)))
		(let* ((overlay (widget-get button :button-overlay))
		       (face (overlay-get overlay 'face))
		       (mouse-face (overlay-get overlay 'mouse-face)))
		  (unwind-protect
		      ;; Read events, including mouse-movement events
		      ;; until we receive a release event.  Highlight/
		      ;; unhighlight the button the mouse was initially
		      ;; on when we move over it.
		      (let ((track-mouse t))
			(save-excursion
			  (when face	; avoid changing around image
			    (overlay-put overlay
					 'face widget-button-pressed-face)
			    (overlay-put overlay
					 'mouse-face widget-button-pressed-face))
			  (unless (widget-apply button :mouse-down-action event)
			    (while (not (widget-button-release-event-p event))
			      (setq event (read-event)
				    pos (widget-event-point event))
			      (if (and pos
				       (eq (get-char-property pos 'button)
					   button))
				  (when face
				    (overlay-put overlay
						 'face
						 widget-button-pressed-face)
				    (overlay-put overlay
						 'mouse-face
						 widget-button-pressed-face))
				(overlay-put overlay 'face face)
				(overlay-put overlay 'mouse-face mouse-face))))

			  ;; When mouse is released over the button, run
			  ;; its action function.
			  (when (and pos
				     (eq (get-char-property pos 'button) button))
			    (widget-apply-action button event))))
		    (overlay-put overlay 'face face)
		    (overlay-put overlay 'mouse-face mouse-face))))

	      (unless (pos-visible-in-window-p (widget-event-point event))
		(mouse-set-point event)
		(beginning-of-line)
		(recenter))
	      )

	    (let ((up t) command)
	      ;; Mouse click not on a widget button.  Find the global
	      ;; command to run, and check whether it is bound to an
	      ;; up event.
	      (mouse-set-point event)
	      (if (memq (event-basic-type event) '(mouse-1 down-mouse-1))
		  (cond ((setq command	;down event
			       (lookup-key widget-global-map [down-mouse-1]))
			 (setq up nil))
			((setq command	;up event
			       (lookup-key widget-global-map [mouse-1]))))
		(cond ((setq command	;down event
			     (lookup-key widget-global-map [down-mouse-2]))
		       (setq up nil))
		      ((setq command	;up event
			     (lookup-key widget-global-map [mouse-2])))))
	      (when up
		;; Don't execute up events twice.
		(while (not (widget-button-release-event-p event))
		  (setq event (read-event))))
	      (when command
		(call-interactively command)))))
    (message "You clicked somewhere weird.")))

(defun widget-button-press (pos &optional event)
  "Invoke button at POS."
  (interactive "@d")
  (let ((button (get-char-property pos 'button)))
    (if button
	(widget-apply-action button event)
      (let ((command (lookup-key widget-global-map (this-command-keys))))
	(when (commandp command)
	  (call-interactively command))))))

(defun widget-tabable-at (&optional pos)
  "Return the tabable widget at POS, or nil.
POS defaults to the value of (point)."
  (let ((widget (widget-at pos)))
    (if widget
	(let ((order (widget-get widget :tab-order)))
	  (if order
	      (if (>= order 0)
		  widget)
	    widget)))))

(defvar widget-use-overlay-change t
  "If non-nil, use overlay change functions to tab around in the buffer.
This is much faster, but doesn't work reliably on Emacs 19.34.")

(defun widget-move (arg)
  "Move point to the ARG next field or button.
ARG may be negative to move backward."
  (or (bobp) (> arg 0) (backward-char))
  (let ((pos (point))
	(number arg)
	(old (widget-tabable-at))
	new)
    ;; Forward.
    (while (> arg 0)
      (cond ((eobp)
	     (goto-char (point-min)))
	    (widget-use-overlay-change
	     (goto-char (next-overlay-change (point))))
	    (t
	     (forward-char 1)))
      (and (eq pos (point))
	   (eq arg number)
	   (error "No buttons or fields found"))
      (let ((new (widget-tabable-at)))
	(when new
	  (unless (eq new old)
	    (setq arg (1- arg))
	    (setq old new)))))
    ;; Backward.
    (while (< arg 0)
      (cond ((bobp)
	     (goto-char (point-max)))
	    (widget-use-overlay-change
	     (goto-char (previous-overlay-change (point))))
	    (t
	     (backward-char 1)))
      (and (eq pos (point))
	   (eq arg number)
	   (error "No buttons or fields found"))
      (let ((new (widget-tabable-at)))
	(when new
	  (unless (eq new old)
	    (setq arg (1+ arg))))))
    (let ((new (widget-tabable-at)))
      (while (eq (widget-tabable-at) new)
	(backward-char)))
    (forward-char))
  (widget-echo-help (point))
  (run-hooks 'widget-move-hook))

(defun widget-forward (arg)
  "Move point to the next field or button.
With optional ARG, move across that many fields."
  (interactive "p")
  (run-hooks 'widget-forward-hook)
  (widget-move arg))

(defun widget-backward (arg)
  "Move point to the previous field or button.
With optional ARG, move across that many fields."
  (interactive "p")
  (run-hooks 'widget-backward-hook)
  (widget-move (- arg)))

;; Since the widget code uses a `field' property to identify fields,
;; ordinary beginning-of-line does the right thing.
(defalias 'widget-beginning-of-line 'beginning-of-line)

(defun widget-end-of-line ()
  "Go to end of field or end of line, whichever is first.
Trailing spaces at the end of padded fields are not considered part of
the field."
  (interactive)
  ;; Ordinary end-of-line does the right thing, because we're inside
  ;; text with a `field' property.
  (end-of-line)
  (unless (eolp)
    ;; ... except that we want to ignore trailing spaces in fields that
    ;; aren't terminated by a newline, because they are used as padding,
    ;; and ignored when extracting the entered value of the field.
    (skip-chars-backward " " (field-beginning (1- (point))))))

(defun widget-kill-line ()
  "Kill to end of field or end of line, whichever is first."
  (interactive)
  (let* ((field (widget-field-find (point)))
	 (end (and field (widget-field-end field))))
    (if (and field (> (line-beginning-position 2) end))
	(kill-region (point) end)
      (call-interactively 'kill-line))))

(defcustom widget-complete-field (lookup-key global-map "\M-\t")
  "Default function to call for completion inside fields."
  :options '(ispell-complete-word complete-tag lisp-complete-symbol)
  :type 'function
  :group 'widgets)

(defun widget-complete ()
  "Complete content of editable field from point.
When not inside a field, move to the previous button or field."
  (interactive)
  (let ((field (widget-field-find (point))))
    (if field
	(widget-apply field :complete)
      (error "Not in an editable field"))))

;;; Setting up the buffer.

(defvar widget-field-new nil)
;; List of all newly created editable fields in the buffer.
(make-variable-buffer-local 'widget-field-new)

(defvar widget-field-list nil)
;; List of all editable fields in the buffer.
(make-variable-buffer-local 'widget-field-list)

(defun widget-at (&optional pos)
  "The button or field at POS (default, point)."
  (or (get-char-property (or pos (point)) 'button)
      (widget-field-at pos)))

;;;###autoload
(defun widget-setup ()
  "Setup current buffer so editing string widgets works."
  (let ((inhibit-read-only t)
	(inhibit-modification-hooks t)
	field)
    (while widget-field-new
      (setq field (car widget-field-new)
	    widget-field-new (cdr widget-field-new)
	    widget-field-list (cons field widget-field-list))
      (let ((from (car (widget-get field :field-overlay)))
	    (to (cdr (widget-get field :field-overlay))))
	(widget-specify-field field
			      (marker-position from) (marker-position to))
	(set-marker from nil)
	(set-marker to nil))))
  (widget-clear-undo)
  (widget-add-change))

(defvar widget-field-last nil)
;; Last field containing point.
(make-variable-buffer-local 'widget-field-last)

(defvar widget-field-was nil)
;; The widget data before the change.
(make-variable-buffer-local 'widget-field-was)

(defun widget-field-at (pos)
  "Return the widget field at POS, or nil if none."
  (let ((field (get-char-property (or pos (point)) 'field)))
    (if (eq field 'boundary)
	nil
      field)))

(defun widget-field-buffer (widget)
  "Return the start of WIDGET's editing field."
  (let ((overlay (widget-get widget :field-overlay)))
    (cond ((overlayp overlay)
	   (overlay-buffer overlay))
	  ((consp overlay)
	   (marker-buffer (car overlay))))))

(defun widget-field-start (widget)
  "Return the start of WIDGET's editing field."
  (let ((overlay (widget-get widget :field-overlay)))
    (if (overlayp overlay)
	(overlay-start overlay)
      (car overlay))))