lisp/help-at-pt.el

   1 ;;; help-at-pt.el --- local help through the keyboard
   2
   3 ;; Copyright (C) 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   4
   5 ;; Author: Luc Teirlinck <teirllm@auburn.edu>
   6 ;; Keywords: help
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software; you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation; either version 3, or (at your option)
  13 ;; any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  22 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  23 ;; Boston, MA 02110-1301, USA.
  24
  25 ;;; Commentary:
  26
  27 ;; This file contains functionality to make the help provided by the
  28 ;; help-echo text or overlay property available to the keyboard user.
  29 ;; It also supports a more keyboard oriented alternative to
  30 ;; `help-echo', namely a new text or overlay property `kbd-help'.
  31 ;;
  32 ;; It provides facilities to access the local help available at point
  33 ;; either on demand, using the command `display-local-help', or
  34 ;; automatically after a suitable idle time, through the customizable
  35 ;; variable `help-at-pt-display-when-idle'.
  36 ;;
  37 ;; You can get a more global overview of the local help available in
  38 ;; the buffer, using the commands `scan-buf-next-region' and
  39 ;; `scan-buf-previous-region', which move to the start of the next or
  40 ;; previous region with available local help and print the help found
  41 ;; there.
  42 ;;
  43 ;; Suggested key bindings:
  44 ;;
  45 ;; (global-set-key [C-tab] 'scan-buf-next-region)
  46 ;; (global-set-key [C-M-tab] 'scan-buf-previous-region)
  47 ;;
  48 ;; You do not have to do anything special to use the functionality
  49 ;; provided by this file, because all important functions autoload.
  50
  51 ;;; Code:
  52
  53 (defgroup help-at-pt nil
  54   "Features for displaying local help."
  55   :group 'help
  56   :version "22.1")
  57
  58 ;;;###autoload
  59 (defun help-at-pt-string (&optional kbd)
  60   "Return the help-echo string at point.
  61 Normally, the string produced by the `help-echo' text or overlay
  62 property, or nil, is returned.
  63 If KBD is non-nil, `kbd-help' is used instead, and any
  64 `help-echo' property is ignored.  In this case, the return value
  65 can also be t, if that is the value of the `kbd-help' property."
  66   (let* ((prop (if kbd 'kbd-help 'help-echo))
  67          (pair (get-char-property-and-overlay (point) prop))
  68          (val (car pair))
  69          (ov (cdr pair)))
  70     (if (functionp val)
  71         (funcall val (selected-window) (if ov ov (current-buffer)) (point))
  72       (eval val))))
  73
  74 ;;;###autoload
  75 (defun help-at-pt-kbd-string ()
  76   "Return the keyboard help string at point.
  77 If the `kbd-help' text or overlay property at point produces a
  78 string, return it.  Otherwise, use the `help-echo' property.  If
  79 this produces no string either, return nil."
  80   (let ((kbd (help-at-pt-string t))
  81         (echo (help-at-pt-string)))
  82     (if (and kbd (not (eq kbd t))) kbd echo)))
  83
  84 ;;;###autoload
  85 (defun display-local-help (&optional arg)
  86   "Display local help in the echo area.
  87 This displays a short help message, namely the string produced by
  88 the `kbd-help' property at point.  If `kbd-help' does not produce
  89 a string, but the `help-echo' property does, then that string is
  90 printed instead.
  91
  92 A numeric argument ARG prevents display of a message in case
  93 there is no help.  While ARG can be used interactively, it is
  94 mainly meant for use from Lisp."
  95   (interactive "P")
  96   (let ((help (help-at-pt-kbd-string)))
  97     (if help
  98         (message "%s" help)
  99       (if (not arg) (message "No local help at point")))))
 100
 101 (defvar help-at-pt-timer nil
 102   "Non-nil means that a timer is set that checks for local help.
 103 If non-nil, this is the value returned by the call of
 104 `run-with-idle-timer' that set that timer.  This variable is used
 105 internally to enable `help-at-pt-display-when-idle'.  Do not set it
 106 yourself.")
 107
 108 (defcustom help-at-pt-timer-delay 1
 109   "*Delay before displaying local help.
 110 This is used if `help-at-pt-display-when-idle' is enabled.
 111 The value may be an integer or floating point number.
 112
 113 If a timer is already active, there are two ways to make the new
 114 value take effect immediately.  After setting the value, you can
 115 first call `help-at-pt-cancel-timer' and then set a new timer
 116 with `help-at-pt-set-timer'.  Alternatively, you can set this
 117 variable through Custom.  This will not set a timer if none is
 118 active, but if one is already active, Custom will make it use the
 119 new value."
 120   :group 'help-at-pt
 121   :type 'number
 122   :initialize 'custom-initialize-default
 123   :set (lambda (variable value)
 124          (set-default variable value)
 125          (and (boundp 'help-at-pt-timer)
 126               help-at-pt-timer
 127               (timer-set-idle-time help-at-pt-timer value t))))
 128
 129 ;;;###autoload
 130 (defun help-at-pt-cancel-timer ()
 131   "Cancel any timer set by `help-at-pt-set-timer'.
 132 This disables `help-at-pt-display-when-idle'."
 133   (interactive)
 134   (let ((inhibit-quit t))
 135     (when help-at-pt-timer
 136       (cancel-timer help-at-pt-timer)
 137       (setq help-at-pt-timer nil))))
 138
 139 ;;;###autoload
 140 (defun help-at-pt-set-timer ()
 141   "Enable `help-at-pt-display-when-idle'.
 142 This is done by setting a timer, if none is currently active."
 143   (interactive)
 144   (unless help-at-pt-timer
 145     (setq help-at-pt-timer
 146           (run-with-idle-timer
 147            help-at-pt-timer-delay t #'help-at-pt-maybe-display))))
 148
 149 ;;;###autoload
 150 (defcustom help-at-pt-display-when-idle 'never
 151   "*Automatically show local help on point-over.
 152 If the value is t, the string obtained from any `kbd-help' or
 153 `help-echo' property at point is automatically printed in the
 154 echo area, if nothing else is already displayed there, or after a
 155 quit.  If both `kbd-help' and `help-echo' produce help strings,
 156 `kbd-help' is used.  If the value is a list, the help only gets
 157 printed if there is a text or overlay property at point that is
 158 included in this list.  Suggested properties are `keymap',
 159 `local-map', `button' and `kbd-help'.  Any value other than t or
 160 a non-empty list disables the feature.
 161
 162 This variable only takes effect after a call to
 163 `help-at-pt-set-timer'.  The help gets printed after Emacs has
 164 been idle for `help-at-pt-timer-delay' seconds.  You can call
 165 `help-at-pt-cancel-timer' to cancel the timer set by, and the
 166 effect of, `help-at-pt-set-timer'.
 167
 168 When this variable is set through Custom, `help-at-pt-set-timer'
 169 is called automatically, unless the value is `never', in which
 170 case `help-at-pt-cancel-timer' is called.  Specifying an empty
 171 list of properties through Custom will set the timer, thus
 172 enabling buffer local values.  It sets the actual value to nil.
 173 Thus, Custom distinguishes between a nil value and other values
 174 that disable the feature, which Custom identifies with `never'.
 175 The default is `never'."
 176   :group 'help-at-pt
 177   :type '(choice  (const :tag "Always"
 178                          :format "%t\n%h"
 179                          :doc
 180                          "This choice can get noisy.
 181 The text printed from the `help-echo' property is often only
 182 relevant when using the mouse.  If you mind about too many
 183 messages getting printed in the echo area, use \"In certain
 184 situations\".  See the documentation there for more information."
 185                          t)
 186                   (repeat :tag "In certain situations"
 187                           ;; unless we specify 0 offset the doc string
 188                           ;; for this choice gets indented very
 189                           ;; differently than for the other two
 190                           ;; choices, when "More" is selected.
 191                           :offset 0
 192                           :format "%{%t%}:\n%v%i\n%h"
 193                           :doc
 194                           "This choice lets you specify a list of \
 195 text properties.
 196 Presence of any of these properties will trigger display of
 197 available local help on point-over.
 198 If you use this alternative through Custom without listing any
 199 properties, a timer will be set anyway.  This will enable buffer
 200 local values.  Use \"Never\" if you do not want a timer to be set.
 201
 202 Suggested properties:
 203 The `keymap' and `local-map' properties change keybindings in
 204 parts of the buffer.  Some of these keymaps are mode independent
 205 and are not mentioned in the mode documentation.  Hence, the help
 206 text is likely to be useful.
 207 Specifying `button' is relevant in Custom and similar buffers.
 208 In these buffers, most, but not all, of the text shown this way is
 209 available by default when using tab, but not on regular point-over.
 210 The presence of a `kbd-help' property guarantees that non mouse
 211 specific help is available."
 212                           :value (keymap local-map button kbd-help)
 213                           symbol)
 214                   (other :tag "Never"
 215                          :format "%t\n%h"
 216                          :doc
 217                          "This choice normally disables buffer local values.
 218 If you choose this value through Custom and a timer checking for
 219 local help is currently active, it will be canceled.  No new
 220 timer will be set.  Call `help-at-pt-set-timer' after choosing
 221 this option, or use \"In certain situations\" and specify no text
 222 properties, to enable buffer local values."
 223                          never))
 224   :initialize 'custom-initialize-default
 225   :set #'(lambda (variable value)
 226            (set-default variable value)
 227            (if (eq value 'never)
 228                (help-at-pt-cancel-timer)
 229              (help-at-pt-set-timer)))
 230   :set-after '(help-at-pt-timer-delay)
 231   :require 'help-at-pt)
 232
 233 ;; Function for use in `help-at-pt-set-timer'.
 234 (defun help-at-pt-maybe-display ()
 235   (and (or (eq help-at-pt-display-when-idle t)
 236            (and (consp help-at-pt-display-when-idle)
 237                 (catch 'found
 238                   (dolist (prop help-at-pt-display-when-idle)
 239                     (if (get-char-property (point) prop)
 240                         (throw 'found t))))))
 241        (or (not (current-message))
 242            (string= (current-message) "Quit"))
 243        (display-local-help t)))
 244
 245 ;;;###autoload
 246 (defun scan-buf-move-to-region (prop &optional arg hook)
 247   "Go to the start of the next region with non-nil PROP property.
 248 Then run HOOK, which should be a quoted symbol that is a normal
 249 hook variable, or an expression evaluating to such a symbol.
 250 Adjacent areas with different non-nil PROP properties are
 251 considered different regions.
 252
 253 With numeric argument ARG, move to the start of the ARGth next
 254 such region, then run HOOK.  If ARG is negative, move backward.
 255 If point is already in a region, then that region does not count
 256 toward ARG.  If ARG is 0 and point is inside a region, move to
 257 the start of that region.  If ARG is 0 and point is not in a
 258 region, print a message to that effect, but do not move point and
 259 do not run HOOK.  If there are not enough regions to move over,
 260 an error results and the number of available regions is mentioned
 261 in the error message.  Point is not moved and HOOK is not run."
 262   (cond ((> arg 0)
 263          (if (= (point) (point-max))
 264              (error "No further `%s' regions" prop))
 265          (let ((pos (point)))
 266            (dotimes (x arg)
 267              (setq pos (next-single-char-property-change pos prop))
 268              (unless (get-char-property pos prop)
 269                (setq pos (next-single-char-property-change pos prop))
 270                (unless (get-char-property pos prop)
 271                  (cond ((= x 0)
 272                         (error "No further `%s' regions" prop))
 273                        ((= x 1)
 274                         (error "There is only one further `%s' region" prop))
 275                        (t
 276                         (error
 277                          "There are only %d further `%s' regions"
 278                          x prop))))))
 279            (goto-char pos)
 280            (run-hooks hook)))
 281         ((= arg 0)
 282          (let ((val (get-char-property (point) prop)))
 283            (cond ((not val)
 284                   (message "Point is not in a `%s' region" prop))
 285                  ((eq val (get-char-property (1- (point)) prop))
 286                   (goto-char
 287                    (previous-single-char-property-change (point) prop))
 288                   (run-hooks hook))
 289                  (t (run-hooks hook)))))
 290         ((< arg 0)
 291          (let ((pos (point)) (val (get-char-property (point) prop)))
 292            (and val
 293                 (eq val (get-char-property (1- pos) prop))
 294                 (setq pos
 295                       (previous-single-char-property-change pos prop)))
 296            (if (= pos (point-min))
 297                (error "No prior `%s' regions" prop))
 298            (dotimes (x (- arg))
 299              (setq pos (previous-single-char-property-change pos prop))
 300              (unless (get-char-property pos prop)
 301                (setq pos (previous-single-char-property-change pos prop))
 302                (unless (get-char-property pos prop)
 303                  (cond ((= x 0)
 304                         (error "No prior `%s' regions" prop))
 305                        ((= x 1)
 306                         (error "There is only one prior `%s' region" prop))
 307                        (t
 308                         (error "There are only %d prior `%s' regions"
 309                                x prop))))))
 310            (goto-char pos)
 311            (run-hooks hook)))))
 312
 313 ;; To be moved to a different file and replaced by a defcustom in a
 314 ;; future version.
 315 (defvar scan-buf-move-hook '(display-local-help)
 316   "Normal hook run by `scan-buf-next-region'.
 317 Also used by `scan-buf-previous-region'.  The hook is run after
 318 positioning point.")
 319
 320 ;;;###autoload
 321 (defun scan-buf-next-region (&optional arg)
 322   "Go to the start of the next region with non-nil help-echo.
 323 Print the help found there using `display-local-help'.  Adjacent
 324 areas with different non-nil help-echo properties are considered
 325 different regions.
 326
 327 With numeric argument ARG, move to the start of the ARGth next
 328 help-echo region.  If ARG is negative, move backward.  If point
 329 is already in a help-echo region, then that region does not count
 330 toward ARG.  If ARG is 0 and point is inside a help-echo region,
 331 move to the start of that region.  If ARG is 0 and point is not
 332 in such a region, just print a message to that effect.  If there
 333 are not enough regions to move over, an error results and the
 334 number of available regions is mentioned in the error message.
 335
 336 A potentially confusing subtlety is that point can be in a
 337 help-echo region without any local help being available.  This is
 338 because `help-echo' can be a function evaluating to nil.  This
 339 rarely happens in practice."
 340   (interactive "p")
 341   (scan-buf-move-to-region 'help-echo arg 'scan-buf-move-hook))
 342
 343 ;;;###autoload
 344 (defun scan-buf-previous-region (&optional arg)
 345   "Go to the start of the previous region with non-nil help-echo.
 346 Print the help found there using `display-local-help'.  Adjacent
 347 areas with different non-nil help-echo properties are considered
 348 different regions.  With numeric argument ARG, behaves like
 349 `scan-buf-next-region' with argument -ARG.."
 350   (interactive "p")
 351   (scan-buf-move-to-region 'help-echo (- arg) 'scan-buf-move-hook))
 352
 353 (add-hook 'help-at-pt-unload-hook 'help-at-pt-cancel-timer)
 354
 355 (provide 'help-at-pt)
 356
 357 ;;; arch-tag: d0b8b86d-d23f-45d0-a82d-208d6205a583
 358 ;;; help-at-pt.el ends here