lisp/button.el

   1 ;;; button.el --- clickable buttons
   2 ;;
   3 ;; Copyright (C) 2001-2017 Free Software Foundation, Inc.
   4 ;;
   5 ;; Author: Miles Bader <miles@gnu.org>
   6 ;; Keywords: extensions
   7 ;; Package: emacs
   8 ;;
   9 ;; This file is part of GNU Emacs.
  10 ;;
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25 ;;
  26 ;; This package defines functions for inserting and manipulating
  27 ;; clickable buttons in Emacs buffers, such as might be used for help
  28 ;; hyperlinks, etc.
  29 ;;
  30 ;; In some ways it duplicates functionality also offered by the
  31 ;; `widget' package, but the button package has the advantage that it
  32 ;; is (1) much faster, (2) much smaller, and (3) much, much, simpler
  33 ;; (the code, that is, not the interface).
  34 ;;
  35 ;; Buttons can either use overlays, in which case the button is
  36 ;; represented by the overlay itself, or text-properties, in which case
  37 ;; the button is represented by a marker or buffer-position pointing
  38 ;; somewhere in the button.  In the latter case, no markers into the
  39 ;; buffer are retained, which is important for speed if there are are
  40 ;; extremely large numbers of buttons.  Note however that if there is
  41 ;; an existing face text-property at the site of the button, the
  42 ;; button face may not be visible.  Using overlays avoids this.
  43 ;;
  44 ;; Using `define-button-type' to define default properties for buttons
  45 ;; is not necessary, but it is encouraged, since doing so makes the
  46 ;; resulting code clearer and more efficient.
  47 ;;
  48
  49 ;;; Code:
  50
  51 \f
  52 ;; Globals
  53
  54 ;; Use color for the MS-DOS port because it doesn't support underline.
  55 ;; FIXME if MS-DOS correctly answers the (supports) question, it need
  56 ;; no longer be a special case.
  57 (defface button '((t :inherit link))
  58   "Default face used for buttons."
  59   :group 'basic-faces)
  60
  61 (defvar button-map
  62   (let ((map (make-sparse-keymap)))
  63     ;; The following definition needs to avoid using escape sequences that
  64     ;; might get converted to ^M when building loaddefs.el
  65     (define-key map [(control ?m)] 'push-button)
  66     (define-key map [mouse-2] 'push-button)
  67     ;; FIXME: You'd think that for keymaps coming from text-properties on the
  68     ;; mode-line or header-line, the `mode-line' or `header-line' prefix
  69     ;; shouldn't be necessary!
  70     (define-key map [mode-line mouse-2] 'push-button)
  71     (define-key map [header-line mouse-2] 'push-button)
  72     map)
  73   "Keymap used by buttons.")
  74
  75 (defvar button-buffer-map
  76   (let ((map (make-sparse-keymap)))
  77     (define-key map [?\t] 'forward-button)
  78     (define-key map "\e\t" 'backward-button)
  79     (define-key map [backtab] 'backward-button)
  80     map)
  81   "Keymap useful for buffers containing buttons.
  82 Mode-specific keymaps may want to use this as their parent keymap.")
  83
  84 ;; Default properties for buttons
  85 (put 'default-button 'face 'button)
  86 (put 'default-button 'mouse-face 'highlight)
  87 (put 'default-button 'keymap button-map)
  88 (put 'default-button 'type 'button)
  89 ;; action may be either a function to call, or a marker to go to
  90 (put 'default-button 'action 'ignore)
  91 (put 'default-button 'help-echo (purecopy "mouse-2, RET: Push this button"))
  92 ;; Make overlay buttons go away if their underlying text is deleted.
  93 (put 'default-button 'evaporate t)
  94 ;; Prevent insertions adjacent to the text-property buttons from
  95 ;; inheriting its properties.
  96 (put 'default-button 'rear-nonsticky t)
  97
  98 ;; A `category-symbol' property for the default button type
  99 (put 'button 'button-category-symbol 'default-button)
 100
 101 \f
 102 ;; Button types (which can be used to hold default properties for buttons)
 103
 104 ;; Because button-type properties are inherited by buttons using the
 105 ;; special `category' property (implemented by both overlays and
 106 ;; text-properties), we need to store them on a symbol to which the
 107 ;; `category' properties can point.  Instead of using the symbol that's
 108 ;; the name of each button-type, however, we use a separate symbol (with
 109 ;; `-button' appended, and uninterned) to store the properties.  This is
 110 ;; to avoid name clashes.
 111
 112 ;; [this is an internal function]
 113 (defsubst button-category-symbol (type)
 114   "Return the symbol used by button-type TYPE to store properties.
 115 Buttons inherit them by setting their `category' property to that symbol."
 116   (or (get type 'button-category-symbol)
 117       (error "Unknown button type `%s'" type)))
 118
 119 (defun define-button-type (name &rest properties)
 120   "Define a `button type' called NAME (a symbol).
 121 The remaining arguments form a sequence of PROPERTY VALUE pairs,
 122 specifying properties to use as defaults for buttons with this type
 123 \(a button's type may be set by giving it a `type' property when
 124 creating the button, using the :type keyword argument).
 125
 126 In addition, the keyword argument :supertype may be used to specify a
 127 button-type from which NAME inherits its default property values
 128 \(however, the inheritance happens only when NAME is defined; subsequent
 129 changes to a supertype are not reflected in its subtypes)."
 130   (let ((catsym (make-symbol (concat (symbol-name name) "-button")))
 131         (super-catsym
 132          (button-category-symbol
 133           (or (plist-get properties 'supertype)
 134               (plist-get properties :supertype)
 135               'button))))
 136     ;; Provide a link so that it's easy to find the real symbol.
 137     (put name 'button-category-symbol catsym)
 138     ;; Initialize NAME's properties using the global defaults.
 139     (let ((default-props (symbol-plist super-catsym)))
 140       (while default-props
 141         (put catsym (pop default-props) (pop default-props))))
 142     ;; Add NAME as the `type' property, which will then be returned as
 143     ;; the type property of individual buttons.
 144     (put catsym 'type name)
 145     ;; Add the properties in PROPERTIES to the real symbol.
 146     (while properties
 147       (let ((prop (pop properties)))
 148         (when (eq prop :supertype)
 149           (setq prop 'supertype))
 150         (put catsym prop (pop properties))))
 151     ;; Make sure there's a `supertype' property
 152     (unless (get catsym 'supertype)
 153       (put catsym 'supertype 'button))
 154     name))
 155
 156 (defun button-type-put (type prop val)
 157   "Set the button-type TYPE's PROP property to VAL."
 158   (put (button-category-symbol type) prop val))
 159
 160 (defun button-type-get (type prop)
 161   "Get the property of button-type TYPE named PROP."
 162   (get (button-category-symbol type) prop))
 163
 164 (defun button-type-subtype-p (type supertype)
 165   "Return t if button-type TYPE is a subtype of SUPERTYPE."
 166   (or (eq type supertype)
 167       (and type
 168            (button-type-subtype-p (button-type-get type 'supertype)
 169                                   supertype))))
 170
 171 \f
 172 ;; Button properties and other attributes
 173
 174 (defun button-start (button)
 175   "Return the position at which BUTTON starts."
 176   (if (overlayp button)
 177       (overlay-start button)
 178     ;; Must be a text-property button.
 179     (or (previous-single-property-change (1+ button) 'button)
 180         (point-min))))
 181
 182 (defun button-end (button)
 183   "Return the position at which BUTTON ends."
 184   (if (overlayp button)
 185       (overlay-end button)
 186     ;; Must be a text-property button.
 187     (or (next-single-property-change button 'button)
 188         (point-max))))
 189
 190 (defun button-get (button prop)
 191   "Get the property of button BUTTON named PROP."
 192   (cond ((overlayp button)
 193          (overlay-get button prop))
 194         ((button--area-button-p button)
 195          (get-text-property (cdr button)
 196                             prop (button--area-button-string button)))
 197         (t ; Must be a text-property button.
 198          (get-text-property button prop))))
 199
 200 (defun button-put (button prop val)
 201   "Set BUTTON's PROP property to VAL."
 202   ;; Treat some properties specially.
 203   (cond ((memq prop '(type :type))
 204          ;; We translate a `type' property a `category' property, since
 205          ;; that's what's actually used by overlays/text-properties for
 206          ;; inheriting properties.
 207          (setq prop 'category)
 208          (setq val (button-category-symbol val)))
 209         ((eq prop 'category)
 210          ;; Disallow updating the `category' property directly.
 211          (error "Button `category' property may not be set directly")))
 212   ;; Add the property.
 213   (cond ((overlayp button)
 214          (overlay-put button prop val))
 215         ((button--area-button-p button)
 216          (setq button (button--area-button-string button))
 217          (put-text-property 0 (length button) prop val button))
 218         (t ; Must be a text-property button.
 219          (put-text-property
 220           (or (previous-single-property-change (1+ button) 'button)
 221               (point-min))
 222           (or (next-single-property-change button 'button)
 223               (point-max))
 224           prop val))))
 225
 226 (defun button-activate (button &optional use-mouse-action)
 227   "Call BUTTON's `action' property.
 228 If USE-MOUSE-ACTION is non-nil, invoke the button's `mouse-action'
 229 property instead of `action'; if the button has no `mouse-action',
 230 the value of `action' is used instead.
 231
 232 The action can either be a marker or a function.  If it's a
 233 marker then goto it.  Otherwise it it is a function then it is
 234 called with BUTTON as only argument.  BUTTON is either an
 235 overlay, a buffer position, or (for buttons in the mode-line or
 236 header-line) a string."
 237   (let ((action (or (and use-mouse-action (button-get button 'mouse-action))
 238                     (button-get button 'action))))
 239     (if (markerp action)
 240         (save-selected-window
 241           (select-window (display-buffer (marker-buffer action)))
 242           (goto-char action)
 243           (recenter 0))
 244       (funcall action button))))
 245
 246 (defun button-label (button)
 247   "Return BUTTON's text label."
 248   (if (button--area-button-p button)
 249       (substring-no-properties (button--area-button-string button))
 250     (buffer-substring-no-properties (button-start button)
 251                                     (button-end button))))
 252
 253 (defsubst button-type (button)
 254   "Return BUTTON's button-type."
 255   (button-get button 'type))
 256
 257 (defun button-has-type-p (button type)
 258   "Return t if BUTTON has button-type TYPE, or one of TYPE's subtypes."
 259   (button-type-subtype-p (button-get button 'type) type))
 260
 261 (defun button--area-button-p (b)
 262   "Return non-nil if BUTTON is an area button.
 263 Such area buttons are used for buttons in the mode-line and header-line."
 264   (stringp (car-safe b)))
 265
 266 (defalias 'button--area-button-string #'car
 267   "Return area button BUTTON's button-string.")
 268 \f
 269 ;; Creating overlay buttons
 270
 271 (defun make-button (beg end &rest properties)
 272   "Make a button from BEG to END in the current buffer.
 273 The remaining arguments form a sequence of PROPERTY VALUE pairs,
 274 specifying properties to add to the button.
 275 In addition, the keyword argument :type may be used to specify a
 276 button-type from which to inherit other properties; see
 277 `define-button-type'.
 278
 279 Also see `make-text-button', `insert-button'."
 280   (let ((overlay (make-overlay beg end nil t nil)))
 281     (while properties
 282       (button-put overlay (pop properties) (pop properties)))
 283     ;; Put a pointer to the button in the overlay, so it's easy to get
 284     ;; when we don't actually have a reference to the overlay.
 285     (overlay-put overlay 'button overlay)
 286     ;; If the user didn't specify a type, use the default.
 287     (unless (overlay-get overlay 'category)
 288       (overlay-put overlay 'category 'default-button))
 289     ;; OVERLAY is the button, so return it
 290     overlay))
 291
 292 (defun insert-button (label &rest properties)
 293   "Insert a button with the label LABEL.
 294 The remaining arguments form a sequence of PROPERTY VALUE pairs,
 295 specifying properties to add to the button.
 296 In addition, the keyword argument :type may be used to specify a
 297 button-type from which to inherit other properties; see
 298 `define-button-type'.
 299
 300 Also see `insert-text-button', `make-button'."
 301   (apply #'make-button
 302          (prog1 (point) (insert label))
 303          (point)
 304          properties))
 305
 306 \f
 307 ;; Creating text-property buttons
 308
 309 (defun make-text-button (beg end &rest properties)
 310   "Make a button from BEG to END in the current buffer.
 311 The remaining arguments form a sequence of PROPERTY VALUE pairs,
 312 specifying properties to add to the button.
 313 In addition, the keyword argument :type may be used to specify a
 314 button-type from which to inherit other properties; see
 315 `define-button-type'.
 316
 317 This function is like `make-button', except that the button is actually
 318 part of the text instead of being a property of the buffer.  That is,
 319 this function uses text properties, the other uses overlays.
 320 Creating large numbers of buttons can also be somewhat faster
 321 using `make-text-button'.  Note, however, that if there is an existing
 322 face property at the site of the button, the button face may not be visible.
 323 You may want to use `make-button' in that case.
 324
 325 BEG can also be a string, in which case it is made into a button.
 326
 327 Also see `insert-text-button'."
 328   (let ((object nil)
 329         (type-entry
 330          (or (plist-member properties 'type)
 331              (plist-member properties :type))))
 332     (when (stringp beg)
 333       (setq object beg beg 0 end (length object)))
 334     ;; Disallow setting the `category' property directly.
 335     (when (plist-get properties 'category)
 336       (error "Button `category' property may not be set directly"))
 337     (if (null type-entry)
 338         ;; The user didn't specify a `type' property, use the default.
 339         (setq properties (cons 'category (cons 'default-button properties)))
 340       ;; The user did specify a `type' property.  Translate it into a
 341       ;; `category' property, which is what's actually used by
 342       ;; text-properties for inheritance.
 343       (setcar type-entry 'category)
 344       (setcar (cdr type-entry)
 345               (button-category-symbol (car (cdr type-entry)))))
 346     ;; Now add all the text properties at once
 347     (add-text-properties beg end
 348                          ;; Each button should have a non-eq `button'
 349                          ;; property so that next-single-property-change can
 350                          ;; detect boundaries reliably.
 351                          (cons 'button (cons (list t) properties))
 352                          object)
 353     ;; Return something that can be used to get at the button.
 354     (or object beg)))
 355
 356 (defun insert-text-button (label &rest properties)
 357   "Insert a button with the label LABEL.
 358 The remaining arguments form a sequence of PROPERTY VALUE pairs,
 359 specifying properties to add to the button.
 360 In addition, the keyword argument :type may be used to specify a
 361 button-type from which to inherit other properties; see
 362 `define-button-type'.
 363
 364 This function is like `insert-button', except that the button is
 365 actually part of the text instead of being a property of the buffer.
 366 Creating large numbers of buttons can also be somewhat faster using
 367 `insert-text-button'.
 368
 369 Also see `make-text-button'."
 370   (apply #'make-text-button
 371          (prog1 (point) (insert label))
 372          (point)
 373          properties))
 374
 375 \f
 376 ;; Finding buttons in a buffer
 377
 378 (defun button-at (pos)
 379   "Return the button at position POS in the current buffer, or nil.
 380 If the button at POS is a text property button, the return value
 381 is a marker pointing to POS."
 382   (let ((button (get-char-property pos 'button)))
 383     (if (or (overlayp button) (null button))
 384         button
 385       ;; Must be a text-property button; return a marker pointing to it.
 386       (copy-marker pos t))))
 387
 388 (defun next-button (pos &optional count-current)
 389   "Return the next button after position POS in the current buffer.
 390 If COUNT-CURRENT is non-nil, count any button at POS in the search,
 391 instead of starting at the next button."
 392     (unless count-current
 393       ;; Search for the next button boundary.
 394       (setq pos (next-single-char-property-change pos 'button)))
 395     (and (< pos (point-max))
 396          (or (button-at pos)
 397              ;; We must have originally been on a button, and are now in
 398              ;; the inter-button space.  Recurse to find a button.
 399              (next-button pos))))
 400
 401 (defun previous-button (pos &optional count-current)
 402   "Return the previous button before position POS in the current buffer.
 403 If COUNT-CURRENT is non-nil, count any button at POS in the search,
 404 instead of starting at the next button."
 405   (let ((button (button-at pos)))
 406     (if button
 407         (if count-current
 408             button
 409           ;; We started out on a button, so move to its start and look
 410           ;; for the previous button boundary.
 411           (setq pos (previous-single-char-property-change
 412                      (button-start button) 'button))
 413           (let ((new-button (button-at pos)))
 414             (if new-button
 415                 ;; We are in a button again; this can happen if there
 416                 ;; are adjacent buttons (or at bob).
 417                 (unless (= pos (button-start button)) new-button)
 418               ;; We are now in the space between buttons.
 419               (previous-button pos))))
 420       ;; We started out in the space between buttons.
 421       (setq pos (previous-single-char-property-change pos 'button))
 422       (or (button-at pos)
 423           (and (> pos (point-min))
 424                (button-at (1- pos)))))))
 425
 426 \f
 427 ;; User commands
 428
 429 (defun push-button (&optional pos use-mouse-action)
 430   "Perform the action specified by a button at location POS.
 431 POS may be either a buffer position or a mouse-event.  If
 432 USE-MOUSE-ACTION is non-nil, invoke the button's `mouse-action'
 433 property instead of its `action' property; if the button has no
 434 `mouse-action', the value of `action' is used instead.
 435
 436 The action in both cases may be either a function to call or a
 437 marker to display and is invoked using `button-activate' (which
 438 see).
 439
 440 POS defaults to point, except when `push-button' is invoked
 441 interactively as the result of a mouse-event, in which case, the
 442 mouse event is used.
 443 If there's no button at POS, do nothing and return nil, otherwise
 444 return t."
 445   (interactive
 446    (list (if (integerp last-command-event) (point) last-command-event)))
 447   (if (and (not (integerp pos)) (eventp pos))
 448       ;; POS is a mouse event; switch to the proper window/buffer
 449       (let ((posn (event-start pos)))
 450         (with-current-buffer (window-buffer (posn-window posn))
 451           (if (posn-string posn)
 452               ;; mode-line, header-line, or display string event.
 453               (button-activate (posn-string posn) t)
 454             (push-button (posn-point posn) t))))
 455     ;; POS is just normal position
 456     (let ((button (button-at (or pos (point)))))
 457       (when button
 458         (button-activate button use-mouse-action)
 459         t))))
 460
 461 (defun forward-button (n &optional wrap display-message)
 462   "Move to the Nth next button, or Nth previous button if N is negative.
 463 If N is 0, move to the start of any button at point.
 464 If WRAP is non-nil, moving past either end of the buffer continues from the
 465 other end.
 466 If DISPLAY-MESSAGE is non-nil, the button's help-echo string is displayed.
 467 Any button with a non-nil `skip' property is skipped over.
 468 Returns the button found."
 469   (interactive "p\nd\nd")
 470   (let (button)
 471     (if (zerop n)
 472         ;; Move to start of current button
 473         (if (setq button (button-at (point)))
 474             (goto-char (button-start button)))
 475       ;; Move to Nth next button
 476       (let ((iterator (if (> n 0) #'next-button #'previous-button))
 477             (wrap-start (if (> n 0) (point-min) (point-max)))
 478             opoint fail)
 479         (setq n (abs n))
 480         (setq button t)                 ; just to start the loop
 481         (while (and (null fail) (> n 0) button)
 482           (setq button (funcall iterator (point)))
 483           (when (and (not button) wrap)
 484             (setq button (funcall iterator wrap-start t)))
 485           (when button
 486             (goto-char (button-start button))
 487             ;; Avoid looping forever (e.g., if all the buttons have
 488             ;; the `skip' property).
 489             (cond ((null opoint)
 490                    (setq opoint (point)))
 491                   ((= opoint (point))
 492                    (setq fail t)))
 493             (unless (button-get button 'skip)
 494               (setq n (1- n)))))))
 495     (if (null button)
 496         (error (if wrap "No buttons!" "No more buttons"))
 497       (let ((msg (and display-message (button-get button 'help-echo))))
 498         (when msg
 499           (message "%s" msg)))
 500       button)))
 501
 502 (defun backward-button (n &optional wrap display-message)
 503   "Move to the Nth previous button, or Nth next button if N is negative.
 504 If N is 0, move to the start of any button at point.
 505 If WRAP is non-nil, moving past either end of the buffer continues from the
 506 other end.
 507 If DISPLAY-MESSAGE is non-nil, the button's help-echo string is displayed.
 508 Any button with a non-nil `skip' property is skipped over.
 509 Returns the button found."
 510   (interactive "p\nd\nd")
 511   (forward-button (- n) wrap display-message))
 512
 513
 514 (provide 'button)
 515
 516 ;;; button.el ends here