summaryrefslogtreecommitdiff
path: root/lisp/help-fns.el
blob: a94c0ed9dea459956ad895c619416a6814d7cd13 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
;;; help-fns.el --- Complex help functions

;; Copyright (C) 1985, 86, 93, 94, 98, 1999, 2000, 01, 02, 03, 2004
;;   Free Software Foundation, Inc.

;; Maintainer: FSF
;; Keywords: help, internal

;; This file is part of GNU Emacs.

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

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

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

;;; Commentary:

;; This file contains those help commands which are complicated, and
;; which may not be used in every session.  For example
;; `describe-function' will probably be heavily used when doing elisp
;; programming, but not if just editing C files.  Simpler help commands
;; are in help.el

;;; Code:

(require 'help-mode)


;;;###autoload
(defun help-with-tutorial (&optional arg)
  "Select the Emacs learn-by-doing tutorial.
If there is a tutorial version written in the language
of the selected language environment, that version is used.
If there's no tutorial in that language, `TUTORIAL' is selected.
With ARG, you are asked to choose which language."
  (interactive "P")
  (let ((lang (if arg
		    (let ((minibuffer-setup-hook minibuffer-setup-hook))
		      (add-hook 'minibuffer-setup-hook
				'minibuffer-completion-help)
		      (read-language-name 'tutorial "Language: " "English"))
		(if (get-language-info current-language-environment 'tutorial)
		    current-language-environment
		  "English")))
	file filename)
    (setq filename (get-language-info lang 'tutorial))
    (setq file (expand-file-name (concat "~/" filename)))
    (delete-other-windows)
    (if (get-file-buffer file)
	(switch-to-buffer (get-file-buffer file))
      (switch-to-buffer (create-file-buffer file))
      (setq buffer-file-name file)
      (setq default-directory (expand-file-name "~/"))
      (setq buffer-auto-save-file-name nil)
      (insert-file-contents (expand-file-name filename data-directory))
      (hack-local-variables)
      (goto-char (point-min))
      (search-forward "\n<<")
      (beginning-of-line)
      ;; Convert the <<...>> line to the proper [...] line,
      ;; or just delete the <<...>> line if a [...] line follows.
      (cond ((save-excursion
	       (forward-line 1)
	       (looking-at "\\["))
	     (delete-region (point) (progn (forward-line 1) (point))))
	    ((looking-at "<<Blank lines inserted.*>>")
	     (replace-match "[Middle of page left blank for didactic purposes.   Text continues below]"))
	    (t
	     (looking-at "<<")
	     (replace-match "[")
	     (search-forward ">>")
	     (replace-match "]")))
      (beginning-of-line)
      (let ((n (- (window-height (selected-window))
		  (count-lines (point-min) (point))
		  6)))
	(if (< n 8)
	    (progn
	      ;; For a short gap, we don't need the [...] line,
	      ;; so delete it.
	      (delete-region (point) (progn (end-of-line) (point)))
	      (newline n))
	  ;; Some people get confused by the large gap.
	  (newline (/ n 2))

	  ;; Skip the [...] line (don't delete it).
	  (forward-line 1)
	  (newline (- n (/ n 2)))))
      (goto-char (point-min))
      (set-buffer-modified-p nil))))

;;;###autoload
(defun locate-library (library &optional nosuffix path interactive-call)
  "Show the precise file name of Emacs library LIBRARY.
This command searches the directories in `load-path' like `\\[load-library]'
to find the file that `\\[load-library] RET LIBRARY RET' would load.
Optional second arg NOSUFFIX non-nil means don't add suffixes `load-suffixes'
to the specified name LIBRARY.

If the optional third arg PATH is specified, that list of directories
is used instead of `load-path'.

When called from a program, the file name is normaly returned as a
string.  When run interactively, the argument INTERACTIVE-CALL is t,
and the file name is displayed in the echo area."
  (interactive (list (completing-read "Locate library: "
				      'locate-file-completion
				      (cons load-path load-suffixes))
		     nil nil
		     t))
  (let ((file (locate-file library
			   (or path load-path)
			   (append (unless nosuffix load-suffixes) '("")))))
    (if interactive-call
	(if file
	    (message "Library is file %s" (abbreviate-file-name file))
	  (message "No library %s in search path" library)))
    file))


;; Functions

;;;###autoload
(defun describe-function (function)
  "Display the full documentation of FUNCTION (a symbol)."
  (interactive
   (let ((fn (function-called-at-point))
	 (enable-recursive-minibuffers t)
	 val)
     (setq val (completing-read (if fn
				    (format "Describe function (default %s): " fn)
				  "Describe function: ")
				obarray 'fboundp t nil nil (symbol-name fn)))
     (list (if (equal val "")
	       fn (intern val)))))
  (if (null function)
      (message "You didn't specify a function")
    (help-setup-xref (list #'describe-function function) (interactive-p))
    (save-excursion
      (with-output-to-temp-buffer (help-buffer)
	(prin1 function)
	;; Use " is " instead of a colon so that
	;; it is easier to get out the function name using forward-sexp.
	(princ " is ")
	(describe-function-1 function)
	(print-help-return-message)
	(with-current-buffer standard-output
	  ;; Return the text we displayed.
	  (buffer-string))))))

(defun help-split-fundoc (doc def)
  "Split a function docstring DOC into the actual doc and the usage info.
Return (USAGE . DOC) or nil if there's no usage info.
DEF is the function whose usage we're looking for in DOC."
  ;; Functions can get the calling sequence at the end of the doc string.
  ;; In cases where `function' has been fset to a subr we can't search for
  ;; function's name in the doc string so we use `fn' as the anonymous
  ;; function name instead.
  (when (and doc (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" doc))
    (cons (format "(%s%s"
		  ;; Replace `fn' with the actual function name.
		  (if (consp def) "anonymous" def)
		  (match-string 1 doc))
	  (substring doc 0 (match-beginning 0)))))

(defun help-add-fundoc-usage (doc arglist)
  "Add the usage info to the docstring DOC.
If DOC already has a usage info, then just return DOC unchanged.
The usage info is built from ARGLIST.  DOC can be nil.
ARGLIST can also be t or a string of the form \"(fun ARG1 ARG2 ...)\"."
  (unless (stringp doc) (setq doc "Not documented"))
  (if (or (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" doc) (eq arglist t))
      doc
    (format "%s%s%S" doc
	    (if (string-match "\n?\n\\'" doc)
		(if (< (- (match-end 0) (match-beginning 0)) 2) "\n" "")
	      "\n\n")
	    (if (and (stringp arglist)
		     (string-match "\\`([^ ]+\\(.*\\))\\'" arglist))
		(concat "(fn" (match-string 1 arglist) ")")
	      (help-make-usage 'fn arglist)))))

(defun help-function-arglist (def)
  ;; Handle symbols aliased to other symbols.
  (if (and (symbolp def) (fboundp def)) (setq def (indirect-function def)))
  ;; If definition is a macro, find the function inside it.
  (if (eq (car-safe def) 'macro) (setq def (cdr def)))
  (cond
   ((byte-code-function-p def) (aref def 0))
   ((eq (car-safe def) 'lambda) (nth 1 def))
   ((and (eq (car-safe def) 'autoload) (not (eq (nth 4 def) 'keymap)))
    "[Arg list not available until function definition is loaded.]")
   (t t)))

(defun help-make-usage (function arglist)
  (cons (if (symbolp function) function 'anonymous)
	(mapcar (lambda (arg)
		  (if (not (symbolp arg))
		      (if (and (consp arg) (symbolp (car arg)))
			  ;; CL style default values for optional args.
			  (cons (intern (upcase (symbol-name (car arg))))
				(cdr arg))
			arg)
		    (let ((name (symbol-name arg)))
		      (if (string-match "\\`&" name) arg
			(intern (upcase name))))))
		arglist)))

(defun help-C-file-name (subr-or-var kind)
  "Return the name of the C file where SUBR-OR-VAR is defined.
KIND should be `var' for a variable or `subr' for a subroutine."
  (let ((docbuf (get-buffer-create " *DOC*"))
	(name (if (eq 'var kind)
		  (concat "V" (symbol-name subr-or-var))
		(concat "F" (subr-name subr-or-var)))))
    (with-current-buffer docbuf
      (goto-char (point-min))
      (if (eobp)
	  (insert-file-contents-literally
	   (expand-file-name internal-doc-file-name doc-directory)))
      (search-forward (concat "" name "\n"))
      (re-search-backward "S\\(.*\\)")
      (let ((file (match-string 1)))
	(if (string-match "\\.\\(o\\|obj\\)\\'" file)
	    (setq file (replace-match ".c" t t file)))
	(if (string-match "\\.c\\'" file)
	    (concat "src/" file)
	  file)))))

(defface help-argument-name '((t (:weight bold)))
  "Face to highlight function arguments in docstrings.")

(defun help-do-arg-highlight (doc args)
  (while args
    (let ((arg (prog1 (car args) (setq args (cdr args)))))
      (setq doc (replace-regexp-in-string
                 (concat "\\<\\(" arg "\\)\\(?:es\\|s\\|th\\)?\\>")
                 (propertize arg 'face 'help-argument-name)
                 doc t t 1))))
  doc)

(defun help-highlight-arguments (usage doc &rest args)
  (when usage
    (let ((case-fold-search nil)
          (next (not args)))
      ;; Make a list of all arguments
      (with-temp-buffer
        (insert usage)
        (goto-char (point-min))
        ;; Make a list of all arguments
        (while next
          (if (not (re-search-forward " \\([\\[(]?\\)\\([^] &)\.]+\\)" nil t))
              (setq next nil)
            (setq args (cons (match-string 2) args))
            (when (string= (match-string 1) "(")
              ;; A pesky CL-style optional argument with default value,
              ;; so let's skip over it
              (search-backward "(")
              (goto-char (scan-sexps (point) 1)))))
        ;; Highlight aguments in the USAGE string
        (setq usage (help-do-arg-highlight (buffer-string) args)))
      ;; Highlight arguments in the DOC string
      (setq doc (and doc (help-do-arg-highlight doc args)))
      ;; Return value is like the one from help-split-fundoc, but highlighted
      (cons usage doc))))

;;;###autoload
(defun describe-function-1 (function)
  (let* ((def (if (symbolp function)
		  (symbol-function function)
		function))
	 file-name string
	 (beg (if (commandp def) "an interactive " "a ")))
    (setq string
	  (cond ((or (stringp def)
		     (vectorp def))
		 "a keyboard macro")
		((subrp def)
		 (if (eq 'unevalled (cdr (subr-arity def)))
		     (concat beg "special form")
		   (concat beg "built-in function")))
		((byte-code-function-p def)
		 (concat beg "compiled Lisp function"))
		((symbolp def)
		 (while (symbolp (symbol-function def))
		   (setq def (symbol-function def)))
		 (format "an alias for `%s'" def))
		((eq (car-safe def) 'lambda)
		 (concat beg "Lisp function"))
		((eq (car-safe def) 'macro)
		 "a Lisp macro")
		((eq (car-safe def) 'autoload)
		 (setq file-name (nth 1 def))
		 (format "%s autoloaded %s"
			 (if (commandp def) "an interactive" "an")
			 (if (eq (nth 4 def) 'keymap) "keymap"
			   (if (nth 4 def) "Lisp macro" "Lisp function"))
			 ))
                ((keymapp def)
                 (let ((is-full nil)
                       (elts (cdr-safe def)))
                   (while elts
                     (if (char-table-p (car-safe elts))
                         (setq is-full t
                               elts nil))
                     (setq elts (cdr-safe elts)))
                   (if is-full
                       "a full keymap"
                     "a sparse keymap")))
		(t "")))
    (princ string)
    (with-current-buffer standard-output
      (save-excursion
	(save-match-data
	  (if (re-search-backward "alias for `\\([^`']+\\)'" nil t)
	      (help-xref-button 1 'help-function def)))))
    (or file-name
	(setq file-name (symbol-file function)))
    (when (equal file-name "loaddefs.el")
      ;; Find the real def site of the preloaded function.
      ;; This is necessary only for defaliases.
      (let ((location
	     (condition-case nil
		 (find-function-search-for-symbol function nil "loaddefs.el")
	       (error nil))))
	(when location
	  (with-current-buffer (car location)
	    (goto-char (cdr location))
	    (when (re-search-backward
		   "^;;; Generated autoloads from \\(.*\\)" nil t)
	      (setq file-name (match-string 1)))))))
    (when (and (null file-name) (subrp def))
      ;; Find the C source file name.
      (setq file-name (if (get-buffer " *DOC*")
			  (help-C-file-name def 'subr)
			'C-source)))
    (when file-name
      (princ " in `")
      ;; We used to add .el to the file name,
      ;; but that's completely wrong when the user used load-file.
      (princ (if (eq file-name 'C-source) "C source code" file-name))
      (princ "'")
      ;; Make a hyperlink to the library.
      (with-current-buffer standard-output
        (save-excursion
	  (re-search-backward "`\\([^`']+\\)'" nil t)
	  (help-xref-button 1 'help-function-def function file-name))))
    (princ ".")
    (terpri)
    (when (commandp function)
      (let* ((remapped (command-remapping function))
	     (keys (where-is-internal
		    (or remapped function) overriding-local-map nil nil))
	     non-modified-keys)
	;; Which non-control non-meta keys run this command?
	(dolist (key keys)
	  (if (member (event-modifiers (aref key 0)) '(nil (shift)))
	      (push key non-modified-keys)))
	(when remapped
	  (princ "It is remapped to `")
	  (princ (symbol-name remapped))
	  (princ "'"))

	(when keys
	  (princ (if remapped " which is bound to " "It is bound to "))
	  ;; FIXME: This list can be very long (f.ex. for self-insert-command).
	  ;; If there are many, remove them from KEYS.
	  (if (< (length non-modified-keys) 10)
	      (princ (mapconcat 'key-description keys ", "))
	    (dolist (key non-modified-keys)
	      (setq keys (delq key keys)))
	    (if keys
		(progn
		  (princ (mapconcat 'key-description keys ", "))
		  (princ ", and many ordinary text characters"))
	      (princ "many ordinary text characters"))))
	(when (or remapped keys non-modified-keys)
	  (princ ".")
	  (terpri))))
    (let* ((arglist (help-function-arglist def))
	   (doc (documentation function))
	   (usage (help-split-fundoc doc function)))
      (with-current-buffer standard-output
        ;; If definition is a keymap, skip arglist note.
        (unless (keymapp def)
          (let* ((use (cond
                        (usage (setq doc (cdr usage)) (car usage))
                        ((listp arglist)
                         (format "%S" (help-make-usage function arglist)))
                        ((stringp arglist) arglist)
                        ;; Maybe the arglist is in the docstring of the alias.
                        ((let ((fun function))
                           (while (and (symbolp fun)
                                       (setq fun (symbol-function fun))
                                       (not (setq usage (help-split-fundoc
                                                         (documentation fun)
                                                         function)))))
                           usage)
                         (car usage))
                        ((or (stringp def)
                             (vectorp def))
                         (format "\nMacro: %s" (format-kbd-macro def)))
                        (t "[Missing arglist.  Please make a bug report.]")))
                 (high (help-highlight-arguments use doc)))
            (insert (car high) "\n")
            (setq doc (cdr high))))
        (let ((obsolete (and
                         ;; function might be a lambda construct.
                         (symbolp function)
                         (get function 'byte-obsolete-info))))
          (when obsolete
            (princ "\nThis function is obsolete")
            (when (nth 2 obsolete)
              (insert (format " since %s" (nth 2 obsolete))))
            (insert ";\n"
                    (if (stringp (car obsolete)) (car obsolete)
                      (format "use `%s' instead." (car obsolete)))
                    "\n"))
          (insert "\n"
                  (or doc "Not documented.")))))))


;; Variables

;;;###autoload
(defun variable-at-point ()
  "Return the bound variable symbol found around point.
Return 0 if there is no such symbol."
  (condition-case ()
      (with-syntax-table emacs-lisp-mode-syntax-table
	(save-excursion
	  (or (not (zerop (skip-syntax-backward "_w")))
	      (eq (char-syntax (following-char)) ?w)
	      (eq (char-syntax (following-char)) ?_)
	      (forward-sexp -1))
	  (skip-chars-forward "'")
	  (let ((obj (read (current-buffer))))
	    (or (and (symbolp obj) (boundp obj) obj)
		0))))
    (error 0)))

;;;###autoload
(defun describe-variable (variable &optional buffer)
  "Display the full documentation of VARIABLE (a symbol).
Returns the documentation as a string, also.
If VARIABLE has a buffer-local value in BUFFER (default to the current buffer),
it is displayed along with the global value."
  (interactive
   (let ((v (variable-at-point))
	 (enable-recursive-minibuffers t)
	 val)
     (setq val (completing-read (if (symbolp v)
				    (format
				     "Describe variable (default %s): " v)
				  "Describe variable: ")
				obarray 'boundp t nil nil
				(if (symbolp v) (symbol-name v))))
     (list (if (equal val "")
	       v (intern val)))))
  (unless (buffer-live-p buffer) (setq buffer (current-buffer)))
  (if (not (symbolp variable))
      (message "You did not specify a variable")
    (save-excursion
      (let* ((valvoid (not (with-current-buffer buffer (boundp variable))))
	     ;; Extract the value before setting up the output buffer,
	     ;; in case `buffer' *is* the output buffer.
	     (val (unless valvoid (buffer-local-value variable buffer))))
	(help-setup-xref (list #'describe-variable variable buffer)
			 (interactive-p))
	(with-output-to-temp-buffer (help-buffer)
	  (with-current-buffer buffer
	    (prin1 variable)
	    (if valvoid
		(princ " is void")
	      (with-current-buffer standard-output
		(princ "'s value is ")
		(terpri)
		(let ((from (point)))
		  (pp val)
		  (help-xref-on-pp from (point))
		  (if (< (point) (+ from 20))
		      (delete-region (1- from) from)))))
	    (terpri)
	    (when (local-variable-p variable)
	      (princ (format "%socal in buffer %s; "
			     (if (get variable 'permanent-local)
				 "Permanently l" "L")
			     (buffer-name)))
	      (if (not (default-boundp variable))
		  (princ "globally void")
		(let ((val (default-value variable)))
		  (with-current-buffer standard-output
		    (princ "global value is ")
		    (terpri)
		    ;; Fixme: pp can take an age if you happen to
		    ;; ask for a very large expression.  We should
		    ;; probably print it raw once and check it's a
		    ;; sensible size before prettyprinting.  -- fx
		    (let ((from (point)))
		      (pp val)
		      (help-xref-on-pp from (point))
		      (if (< (point) (+ from 20))
			(delete-region (1- from) from))))))
	      (terpri))
	    (terpri)
	    (with-current-buffer standard-output
	      (when (> (count-lines (point-min) (point-max)) 10)
		;; Note that setting the syntax table like below
		;; makes forward-sexp move over a `'s' at the end
		;; of a symbol.
		(set-syntax-table emacs-lisp-mode-syntax-table)
		(goto-char (point-min))
		(if valvoid
		    (forward-line 1)
		  (forward-sexp 1)
		  (delete-region (point) (progn (end-of-line) (point)))
		  (insert " value is shown below.\n\n")
		  (save-excursion
		    (insert "\n\nValue:"))))
	      ;; Add a note for variables that have been make-var-buffer-local.
	      (when (and (local-variable-if-set-p variable)
			 (or (not (local-variable-p variable))
			     (with-temp-buffer
			       (local-variable-if-set-p variable))))
		(save-excursion
		  (forward-line -1)
		  (insert "Automatically becomes buffer-local when set in any fashion.\n"))))
 	    ;; Mention if it's an alias
            (let* ((alias (condition-case nil
                             (indirect-variable variable)
                           (error variable)))
                   (obsolete (get variable 'byte-obsolete-variable))
                   (doc (or (documentation-property variable 'variable-documentation)
                            (documentation-property alias 'variable-documentation))))
              (unless (eq alias variable)
                (princ (format "This variable is an alias for `%s'." alias))
                (terpri)
                (terpri))
              (when obsolete
                (princ "This variable is obsolete")
                (if (cdr obsolete) (princ (format " since %s" (cdr obsolete))))
                (princ ";") (terpri)
                (princ (if (stringp (car obsolete)) (car obsolete)
                         (format "use `%s' instead." (car obsolete))))
                (terpri)
                (terpri))
              (princ (or doc "Not documented as a variable.")))
	    ;; Make a link to customize if this variable can be customized.
	    (if (custom-variable-p variable)
		(let ((customize-label "customize"))
		  (terpri)
		  (terpri)
		  (princ (concat "You can " customize-label " this variable."))
		  (with-current-buffer standard-output
		    (save-excursion
		      (re-search-backward
		       (concat "\\(" customize-label "\\)") nil t)
		      (help-xref-button 1 'help-customize-variable variable)))))
	    ;; Make a hyperlink to the library if appropriate.  (Don't
	    ;; change the format of the buffer's initial line in case
	    ;; anything expects the current format.)
	    (let ((file-name (symbol-file (cons 'defvar variable))))
	      (when (equal file-name "loaddefs.el")
		;; Find the real def site of the preloaded variable.
		(let ((location
		       (condition-case nil
			   (find-variable-noselect variable file-name)
			 (error nil))))
		  (when location
		    (with-current-buffer (car location)
		      (goto-char (cdr location))
		      (when (re-search-backward
			     "^;;; Generated autoloads from \\(.*\\)" nil t)
			(setq file-name (match-string 1)))))))
	      (when (and (null file-name)
			 (integerp (get variable 'variable-documentation)))
		;; It's a variable not defined in Elisp but in C.
		(setq file-name
		      (if (get-buffer " *DOC*")
			  (help-C-file-name variable 'var)
			'C-source)))
	      (when file-name
		(princ "\n\nDefined in `")
		(princ (if (eq file-name 'C-source) "C source code" file-name))
		(princ "'.")
		(with-current-buffer standard-output
		  (save-excursion
		    (re-search-backward "`\\([^`']+\\)'" nil t)
		    (help-xref-button 1 'help-variable-def
				      variable file-name)))))

	    (print-help-return-message)
	    (save-excursion
	      (set-buffer standard-output)
	      ;; Return the text we displayed.
	      (buffer-string))))))))


;;;###autoload
(defun describe-syntax (&optional buffer)
  "Describe the syntax specifications in the syntax table of BUFFER.
The descriptions are inserted in a help buffer, which is then displayed.
BUFFER defaults to the current buffer."
  (interactive)
  (setq buffer (or buffer (current-buffer)))
  (help-setup-xref (list #'describe-syntax buffer) (interactive-p))
  (with-output-to-temp-buffer (help-buffer)
    (let ((table (with-current-buffer buffer (syntax-table))))
      (with-current-buffer standard-output
	(describe-vector table 'internal-describe-syntax-value)
	(while (setq table (char-table-parent table))
	  (insert "\nThe parent syntax table is:")
	  (describe-vector table 'internal-describe-syntax-value))))))

(defun help-describe-category-set (value)
  (insert (cond
	   ((null value) "default")
	   ((char-table-p value) "deeper char-table ...")
	   (t (condition-case err
		  (category-set-mnemonics value)
		(error "invalid"))))))

;;;###autoload
(defun describe-categories (&optional buffer)
  "Describe the category specifications in the current category table.
The descriptions are inserted in a buffer, which is then displayed.
If BUFFER is non-nil, then describe BUFFER's category table instead.
BUFFER should be a buffer or a buffer name."
  (interactive)
  (setq buffer (or buffer (current-buffer)))
  (help-setup-xref (list #'describe-categories buffer) (interactive-p))
  (with-output-to-temp-buffer (help-buffer)
    (let ((table (with-current-buffer buffer (category-table))))
      (with-current-buffer standard-output
	(describe-vector table 'help-describe-category-set)
	(let ((docs (char-table-extra-slot table 0)))
	  (if (or (not (vectorp docs)) (/= (length docs) 95))
	      (insert "Invalid first extra slot in this char table\n")
	    (insert "Meanings of mnemonic characters are:\n")
	    (dotimes (i 95)
	      (let ((elt (aref docs i)))
		(when elt
		  (insert (+ i ?\ ) ": " elt "\n"))))
	    (while (setq table (char-table-parent table))
	      (insert "\nThe parent category table is:")
	      (describe-vector table 'help-describe-category-set))))))))

(provide 'help-fns)

;;; arch-tag: 9e10331c-ae81-4d13-965d-c4819aaab0b3
;;; help-fns.el ends here