* decompress.c (Fzlib_decompress_region): Try to clarify 'avail_out'.
[emacs.git] / lisp / help-at-pt.el
blobf3bcabf0a185106291687ed0075d10e198879125
1 ;;; help-at-pt.el --- local help through the keyboard
3 ;; Copyright (C) 2003-2013 Free Software Foundation, Inc.
5 ;; Author: Luc Teirlinck <teirllm@auburn.edu>
6 ;; Keywords: help
8 ;; This file is part of GNU Emacs.
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 of the License, or
13 ;; (at your option) any later version.
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.
20 ;; You should have received a copy of the GNU General Public License
21 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
23 ;;; Commentary:
25 ;; This file contains functionality to make the help provided by the
26 ;; help-echo text or overlay property available to the keyboard user.
27 ;; It also supports a more keyboard oriented alternative to
28 ;; `help-echo', namely a new text or overlay property `kbd-help'.
30 ;; It provides facilities to access the local help available at point
31 ;; either on demand, using the command `display-local-help', or
32 ;; automatically after a suitable idle time, through the customizable
33 ;; variable `help-at-pt-display-when-idle'.
35 ;; You can get a more global overview of the local help available in
36 ;; the buffer, using the commands `scan-buf-next-region' and
37 ;; `scan-buf-previous-region', which move to the start of the next or
38 ;; previous region with available local help and print the help found
39 ;; there.
41 ;; Suggested key bindings:
43 ;; (global-set-key [C-tab] 'scan-buf-next-region)
44 ;; (global-set-key [C-M-tab] 'scan-buf-previous-region)
46 ;; You do not have to do anything special to use the functionality
47 ;; provided by this file, because all important functions autoload.
49 ;;; Code:
51 (defgroup help-at-pt nil
52 "Features for displaying local help."
53 :group 'help
54 :version "22.1")
56 ;;;###autoload
57 (defun help-at-pt-string (&optional kbd)
58 "Return the help-echo string at point.
59 Normally, the string produced by the `help-echo' text or overlay
60 property, or nil, is returned.
61 If KBD is non-nil, `kbd-help' is used instead, and any
62 `help-echo' property is ignored. In this case, the return value
63 can also be t, if that is the value of the `kbd-help' property."
64 (let* ((prop (if kbd 'kbd-help 'help-echo))
65 (pair (get-char-property-and-overlay (point) prop))
66 (val (car pair))
67 (ov (cdr pair)))
68 (if (functionp val)
69 (funcall val (selected-window) (if ov ov (current-buffer)) (point))
70 (eval val))))
72 ;;;###autoload
73 (defun help-at-pt-kbd-string ()
74 "Return the keyboard help string at point.
75 If the `kbd-help' text or overlay property at point produces a
76 string, return it. Otherwise, use the `help-echo' property.
77 If this produces no string either, return nil."
78 (let ((kbd (help-at-pt-string t))
79 (echo (help-at-pt-string)))
80 (if (and kbd (not (eq kbd t))) kbd echo)))
82 ;;;###autoload
83 (defun display-local-help (&optional arg)
84 "Display local help in the echo area.
85 This displays a short help message, namely the string produced by
86 the `kbd-help' property at point. If `kbd-help' does not produce
87 a string, but the `help-echo' property does, then that string is
88 printed instead.
90 A numeric argument ARG prevents display of a message in case
91 there is no help. While ARG can be used interactively, it is
92 mainly meant for use from Lisp."
93 (interactive "P")
94 (let ((help (help-at-pt-kbd-string)))
95 (if help
96 (message "%s" help)
97 (if (not arg) (message "No local help at point")))))
99 (defvar help-at-pt-timer nil
100 "Non-nil means that a timer is set that checks for local help.
101 If non-nil, this is the value returned by the call of
102 `run-with-idle-timer' that set that timer. This variable is used
103 internally to enable `help-at-pt-display-when-idle'. Do not set it
104 yourself.")
106 (defcustom help-at-pt-timer-delay 1
107 "Delay before displaying local help.
108 This is used if `help-at-pt-display-when-idle' is enabled.
109 The value may be an integer or floating point number.
111 If a timer is already active, there are two ways to make the new
112 value take effect immediately. After setting the value, you can
113 first call `help-at-pt-cancel-timer' and then set a new timer
114 with `help-at-pt-set-timer'. Alternatively, you can set this
115 variable through Custom. This will not set a timer if none is
116 active, but if one is already active, Custom will make it use the
117 new value."
118 :group 'help-at-pt
119 :type 'number
120 :initialize 'custom-initialize-default
121 :set (lambda (variable value)
122 (set-default variable value)
123 (and (boundp 'help-at-pt-timer)
124 help-at-pt-timer
125 (timer-set-idle-time help-at-pt-timer value t))))
127 ;;;###autoload
128 (defun help-at-pt-cancel-timer ()
129 "Cancel any timer set by `help-at-pt-set-timer'.
130 This disables `help-at-pt-display-when-idle'."
131 (interactive)
132 (let ((inhibit-quit t))
133 (when help-at-pt-timer
134 (cancel-timer help-at-pt-timer)
135 (setq help-at-pt-timer nil))))
137 ;;;###autoload
138 (defun help-at-pt-set-timer ()
139 "Enable `help-at-pt-display-when-idle'.
140 This is done by setting a timer, if none is currently active."
141 (interactive)
142 (unless help-at-pt-timer
143 (setq help-at-pt-timer
144 (run-with-idle-timer
145 help-at-pt-timer-delay t #'help-at-pt-maybe-display))))
147 ;;;###autoload
148 (defcustom help-at-pt-display-when-idle 'never
149 "Automatically show local help on point-over.
150 If the value is t, the string obtained from any `kbd-help' or
151 `help-echo' property at point is automatically printed in the
152 echo area, if nothing else is already displayed there, or after a
153 quit. If both `kbd-help' and `help-echo' produce help strings,
154 `kbd-help' is used. If the value is a list, the help only gets
155 printed if there is a text or overlay property at point that is
156 included in this list. Suggested properties are `keymap',
157 `local-map', `button' and `kbd-help'. Any value other than t or
158 a non-empty list disables the feature.
160 This variable only takes effect after a call to
161 `help-at-pt-set-timer'. The help gets printed after Emacs has
162 been idle for `help-at-pt-timer-delay' seconds. You can call
163 `help-at-pt-cancel-timer' to cancel the timer set by, and the
164 effect of, `help-at-pt-set-timer'.
166 When this variable is set through Custom, `help-at-pt-set-timer'
167 is called automatically, unless the value is `never', in which
168 case `help-at-pt-cancel-timer' is called. Specifying an empty
169 list of properties through Custom will set the timer, thus
170 enabling buffer local values. It sets the actual value to nil.
171 Thus, Custom distinguishes between a nil value and other values
172 that disable the feature, which Custom identifies with `never'.
173 The default is `never'."
174 :group 'help-at-pt
175 :type '(choice (const :tag "Always"
176 :format "%t\n%h"
177 :doc
178 "This choice can get noisy.
179 The text printed from the `help-echo' property is often only
180 relevant when using the mouse. If you mind about too many
181 messages getting printed in the echo area, use \"In certain
182 situations\". See the documentation there for more information."
184 (repeat :tag "In certain situations"
185 ;; unless we specify 0 offset the doc string
186 ;; for this choice gets indented very
187 ;; differently than for the other two
188 ;; choices, when "More" is selected.
189 :offset 0
190 :format "%{%t%}:\n%v%i\n%h"
191 :doc
192 "This choice lets you specify a list of \
193 text properties.
194 Presence of any of these properties will trigger display of
195 available local help on point-over.
196 If you use this alternative through Custom without listing any
197 properties, a timer will be set anyway. This will enable buffer
198 local values. Use \"Never\" if you do not want a timer to be set.
200 Suggested properties:
201 The `keymap' and `local-map' properties change keybindings in
202 parts of the buffer. Some of these keymaps are mode independent
203 and are not mentioned in the mode documentation. Hence, the help
204 text is likely to be useful.
205 Specifying `button' is relevant in Custom and similar buffers.
206 In these buffers, most, but not all, of the text shown this way is
207 available by default when using tab, but not on regular point-over.
208 The presence of a `kbd-help' property guarantees that non mouse
209 specific help is available."
210 :value (keymap local-map button kbd-help)
211 symbol)
212 (other :tag "Never"
213 :format "%t\n%h"
214 :doc
215 "This choice normally disables buffer local values.
216 If you choose this value through Custom and a timer checking for
217 local help is currently active, it will be canceled. No new
218 timer will be set. Call `help-at-pt-set-timer' after choosing
219 this option, or use \"In certain situations\" and specify no text
220 properties, to enable buffer local values."
221 never))
222 :initialize 'custom-initialize-default
223 :set #'(lambda (variable value)
224 (set-default variable value)
225 (if (eq value 'never)
226 (help-at-pt-cancel-timer)
227 (help-at-pt-set-timer)))
228 :set-after '(help-at-pt-timer-delay)
229 :require 'help-at-pt)
231 ;; Function for use in `help-at-pt-set-timer'.
232 (defun help-at-pt-maybe-display ()
233 (and (or (eq help-at-pt-display-when-idle t)
234 (and (consp help-at-pt-display-when-idle)
235 (catch 'found
236 (dolist (prop help-at-pt-display-when-idle)
237 (if (get-char-property (point) prop)
238 (throw 'found t))))))
239 (or (not (current-message))
240 (string= (current-message) "Quit"))
241 (display-local-help t)))
243 ;;;###autoload
244 (defun scan-buf-move-to-region (prop &optional arg hook)
245 "Go to the start of the next region with non-nil PROP property.
246 Then run HOOK, which should be a quoted symbol that is a normal
247 hook variable, or an expression evaluating to such a symbol.
248 Adjacent areas with different non-nil PROP properties are
249 considered different regions.
251 With numeric argument ARG, move to the start of the ARGth next
252 such region, then run HOOK. If ARG is negative, move backward.
253 If point is already in a region, then that region does not count
254 toward ARG. If ARG is 0 and point is inside a region, move to
255 the start of that region. If ARG is 0 and point is not in a
256 region, print a message to that effect, but do not move point and
257 do not run HOOK. If there are not enough regions to move over,
258 an error results and the number of available regions is mentioned
259 in the error message. Point is not moved and HOOK is not run."
260 (cond ((> arg 0)
261 (if (= (point) (point-max))
262 (error "No further `%s' regions" prop))
263 (let ((pos (point)))
264 (dotimes (x arg)
265 (setq pos (next-single-char-property-change pos prop))
266 (unless (get-char-property pos prop)
267 (setq pos (next-single-char-property-change pos prop))
268 (unless (get-char-property pos prop)
269 (cond ((= x 0)
270 (error "No further `%s' regions" prop))
271 ((= x 1)
272 (error "There is only one further `%s' region" prop))
274 (error
275 "There are only %d further `%s' regions"
276 x prop))))))
277 (goto-char pos)
278 (run-hooks hook)))
279 ((= arg 0)
280 (let ((val (get-char-property (point) prop)))
281 (cond ((not val)
282 (message "Point is not in a `%s' region" prop))
283 ((eq val (get-char-property (1- (point)) prop))
284 (goto-char
285 (previous-single-char-property-change (point) prop))
286 (run-hooks hook))
287 (t (run-hooks hook)))))
288 ((< arg 0)
289 (let ((pos (point)) (val (get-char-property (point) prop)))
290 (and val
291 (eq val (get-char-property (1- pos) prop))
292 (setq pos
293 (previous-single-char-property-change pos prop)))
294 (if (= pos (point-min))
295 (error "No prior `%s' regions" prop))
296 (dotimes (x (- arg))
297 (setq pos (previous-single-char-property-change pos prop))
298 (unless (get-char-property pos prop)
299 (setq pos (previous-single-char-property-change pos prop))
300 (unless (get-char-property pos prop)
301 (cond ((= x 0)
302 (error "No prior `%s' regions" prop))
303 ((= x 1)
304 (error "There is only one prior `%s' region" prop))
306 (error "There are only %d prior `%s' regions"
307 x prop))))))
308 (goto-char pos)
309 (run-hooks hook)))))
311 ;; To be moved to a different file and replaced by a defcustom in a
312 ;; future version.
313 (defvar scan-buf-move-hook '(display-local-help)
314 "Normal hook run by `scan-buf-next-region'.
315 Also used by `scan-buf-previous-region'. The hook is run after
316 positioning point.")
318 ;;;###autoload
319 (defun scan-buf-next-region (&optional arg)
320 "Go to the start of the next region with non-nil help-echo.
321 Print the help found there using `display-local-help'. Adjacent
322 areas with different non-nil help-echo properties are considered
323 different regions.
325 With numeric argument ARG, move to the start of the ARGth next
326 help-echo region. If ARG is negative, move backward. If point
327 is already in a help-echo region, then that region does not count
328 toward ARG. If ARG is 0 and point is inside a help-echo region,
329 move to the start of that region. If ARG is 0 and point is not
330 in such a region, just print a message to that effect. If there
331 are not enough regions to move over, an error results and the
332 number of available regions is mentioned in the error message.
334 A potentially confusing subtlety is that point can be in a
335 help-echo region without any local help being available. This is
336 because `help-echo' can be a function evaluating to nil. This
337 rarely happens in practice."
338 (interactive "p")
339 (scan-buf-move-to-region 'help-echo arg 'scan-buf-move-hook))
341 ;;;###autoload
342 (defun scan-buf-previous-region (&optional arg)
343 "Go to the start of the previous region with non-nil help-echo.
344 Print the help found there using `display-local-help'. Adjacent
345 areas with different non-nil help-echo properties are considered
346 different regions. With numeric argument ARG, behaves like
347 `scan-buf-next-region' with argument -ARG."
348 (interactive "p")
349 (scan-buf-move-to-region 'help-echo (- arg) 'scan-buf-move-hook))
351 (provide 'help-at-pt)
353 ;;; help-at-pt.el ends here