lisp/help-mode.el

   1 ;;; help-mode.el --- `help-mode' used by *Help* buffers
   2
   3 ;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999, 2000, 2001, 2002,
   4 ;;   2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   5
   6 ;; Maintainer: FSF
   7 ;; Keywords: help, internal
   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, or (at your option)
  14 ;; 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; see the file COPYING.  If not, write to the
  23 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  24 ;; Boston, MA 02110-1301, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; Defines `help-mode', which is the mode used by *Help* buffers, and
  29 ;; associated support machinery, such as adding hyperlinks, etc.,
  30
  31 ;;; Code:
  32
  33 (require 'button)
  34 (require 'view)
  35
  36 (defvar help-mode-map (make-sparse-keymap)
  37   "Keymap for help mode.")
  38
  39 (set-keymap-parent help-mode-map button-buffer-map)
  40
  41 (define-key help-mode-map [mouse-2] 'help-follow-mouse)
  42 (define-key help-mode-map "\C-c\C-b" 'help-go-back)
  43 (define-key help-mode-map "\C-c\C-f" 'help-go-forward)
  44 (define-key help-mode-map "\C-c\C-c" 'help-follow-symbol)
  45 ;; Documentation only, since we use minor-mode-overriding-map-alist.
  46 (define-key help-mode-map "\r" 'help-follow)
  47
  48 (defvar help-xref-stack nil
  49   "A stack of ways by which to return to help buffers after following xrefs.
  50 Used by `help-follow' and `help-xref-go-back'.
  51 An element looks like (POSITION FUNCTION ARGS...).
  52 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  53 (put 'help-xref-stack 'permanent-local t)
  54 (make-variable-buffer-local 'help-xref-stack)
  55
  56 (defvar help-xref-forward-stack nil
  57   "The stack of used to navigate help forwards  after using the back button.
  58 Used by `help-follow' and `help-xref-go-forward'.
  59 An element looks like (POSITION FUNCTION ARGS...).
  60 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  61 (put 'help-xref-forward-stack 'permanent-local t)
  62 (make-variable-buffer-local 'help-xref-forward-stack)
  63
  64 (defvar help-xref-stack-item nil
  65   "An item for `help-follow' in this buffer to push onto `help-xref-stack'.
  66 The format is (FUNCTION ARGS...).")
  67 (put 'help-xref-stack-item 'permanent-local t)
  68 (make-variable-buffer-local 'help-xref-stack-item)
  69
  70 (defvar help-xref-stack-forward-item nil
  71   "An item for `help-go-back' to push onto `help-xref-forward-stack'.
  72 The format is (FUNCTION ARGS...).")
  73 (put 'help-xref-stack-forward-item 'permanent-local t)
  74 (make-variable-buffer-local 'help-xref-stack-forward-item)
  75
  76 (setq-default help-xref-stack nil help-xref-stack-item nil)
  77 (setq-default help-xref-forward-stack nil help-xref-forward-stack-item nil)
  78
  79 (defcustom help-mode-hook nil
  80   "Hook run by `help-mode'."
  81   :type 'hook
  82   :group 'help)
  83 \f
  84 ;; Button types used by help
  85
  86 (define-button-type 'help-xref
  87   'follow-link t
  88   'action #'help-button-action)
  89
  90 (defun help-button-action (button)
  91   "Call BUTTON's help function."
  92   (help-do-xref (button-start button)
  93                 (button-get button 'help-function)
  94                 (button-get button 'help-args)))
  95
  96 ;; These 6 calls to define-button-type were generated in a dolist
  97 ;; loop, but that is bad because it means these button types don't
  98 ;; have an easily found definition.
  99
 100 (define-button-type 'help-function
 101   :supertype 'help-xref
 102   'help-function 'describe-function
 103   'help-echo (purecopy "mouse-2, RET: describe this function"))
 104
 105 (define-button-type 'help-variable
 106   :supertype 'help-xref
 107   'help-function 'describe-variable
 108   'help-echo (purecopy "mouse-2, RET: describe this variable"))
 109
 110 (define-button-type 'help-face
 111   :supertype 'help-xref
 112   'help-function 'describe-face
 113   'help-echo (purecopy "mouse-2, RET: describe this face"))
 114
 115 (define-button-type 'help-coding-system
 116   :supertype 'help-xref
 117   'help-function 'describe-coding-system
 118   'help-echo (purecopy "mouse-2, RET: describe this coding system"))
 119
 120 (define-button-type 'help-input-method
 121   :supertype 'help-xref
 122   'help-function 'describe-input-method
 123   'help-echo (purecopy "mouse-2, RET: describe this input method"))
 124
 125 (define-button-type 'help-character-set
 126   :supertype 'help-xref
 127   'help-function 'describe-character-set
 128   'help-echo (purecopy "mouse-2, RET: describe this character set"))
 129
 130 ;; make some more ideosyncratic button types
 131
 132 (define-button-type 'help-symbol
 133   :supertype 'help-xref
 134   'help-function #'help-xref-interned
 135   'help-echo (purecopy "mouse-2, RET: describe this symbol"))
 136
 137 (define-button-type 'help-back
 138   :supertype 'help-xref
 139   'help-function #'help-xref-go-back
 140   'help-echo (purecopy "mouse-2, RET: go back to previous help buffer"))
 141
 142 (define-button-type 'help-forward
 143   :supertype 'help-xref
 144   'help-function #'help-xref-go-forward
 145   'help-echo (purecopy "mouse-2, RET: move forward to next help buffer"))
 146
 147 (define-button-type 'help-info
 148   :supertype 'help-xref
 149   'help-function #'info
 150   'help-echo (purecopy "mouse-2, RET: read this Info node"))
 151
 152 (define-button-type 'help-url
 153   :supertype 'help-xref
 154   'help-function #'browse-url
 155   'help-echo (purecopy "mouse-2, RET: view this URL in a browser"))
 156
 157 (define-button-type 'help-customize-variable
 158   :supertype 'help-xref
 159   'help-function (lambda (v)
 160                    (customize-variable v))
 161   'help-echo (purecopy "mouse-2, RET: customize variable"))
 162
 163 (define-button-type 'help-customize-face
 164   :supertype 'help-xref
 165   'help-function (lambda (v)
 166                    (customize-face v))
 167   'help-echo (purecopy "mouse-2, RET: customize face"))
 168
 169 (define-button-type 'help-function-def
 170   :supertype 'help-xref
 171   'help-function (lambda (fun file)
 172                    (require 'find-func)
 173                    (when (eq file 'C-source)
 174                      (setq file
 175                            (help-C-file-name (indirect-function fun) 'fun)))
 176                    ;; Don't use find-function-noselect because it follows
 177                    ;; aliases (which fails for built-in functions).
 178                    (let ((location
 179                           (find-function-search-for-symbol fun nil file)))
 180                      (pop-to-buffer (car location))
 181                      (if (cdr location)
 182                          (goto-char (cdr location))
 183                        (message "Unable to find location in file"))))
 184   'help-echo (purecopy "mouse-2, RET: find function's definition"))
 185
 186 (define-button-type 'help-variable-def
 187   :supertype 'help-xref
 188   'help-function (lambda (var &optional file)
 189                    (when (eq file 'C-source)
 190                      (setq file (help-C-file-name var 'var)))
 191                    (let ((location (find-variable-noselect var file)))
 192                      (pop-to-buffer (car location))
 193                      (if (cdr location)
 194                        (goto-char (cdr location))
 195                        (message "Unable to find location in file"))))
 196   'help-echo (purecopy "mouse-2, RET: find variable's definition"))
 197
 198 (define-button-type 'help-face-def
 199   :supertype 'help-xref
 200   'help-function (lambda (fun file)
 201                    (require 'find-func)
 202                    ;; Don't use find-function-noselect because it follows
 203                    ;; aliases (which fails for built-in functions).
 204                    (let ((location
 205                           (find-function-search-for-symbol fun 'defface file)))
 206                      (pop-to-buffer (car location))
 207                      (if (cdr location)
 208                          (goto-char (cdr location))
 209                        (message "Unable to find location in file"))))
 210   'help-echo (purecopy "mouse-2, RET: find face's definition"))
 211
 212 \f
 213 ;;;###autoload
 214 (defun help-mode ()
 215   "Major mode for viewing help text and navigating references in it.
 216 Entry to this mode runs the normal hook `help-mode-hook'.
 217 Commands:
 218 \\{help-mode-map}"
 219   (interactive)
 220   (kill-all-local-variables)
 221   (use-local-map help-mode-map)
 222   (setq mode-name "Help")
 223   (setq major-mode 'help-mode)
 224
 225   (view-mode)
 226   (set (make-local-variable 'view-no-disable-on-exit) t)
 227   ;; With Emacs 22 `view-exit-action' could delete the selected window
 228   ;; disregarding whether the help buffer was shown in that window at
 229   ;; all.  Since `view-exit-action' is called with the help buffer as
 230   ;; argument it seems more appropriate to have it work on the buffer
 231   ;; only and leave it to `view-mode-exit' to delete any associated
 232   ;; window(s).
 233   (setq view-exit-action
 234         (lambda (buffer)
 235           ;; Use `with-current-buffer' to make sure that `bury-buffer'
 236           ;; also removes BUFFER from the selected window.
 237           (with-current-buffer buffer
 238             (bury-buffer))))
 239
 240   (run-mode-hooks 'help-mode-hook))
 241
 242 ;;;###autoload
 243 (defun help-mode-setup ()
 244   (help-mode)
 245   (setq buffer-read-only nil))
 246
 247 ;;;###autoload
 248 (defun help-mode-finish ()
 249   (if (eq help-window t)
 250       ;; If `help-window' is t, `view-return-to-alist' is handled by
 251       ;; `with-help-window'.  In this case set `help-window' to the
 252       ;; selected window since now is the only moment where we can
 253       ;; unambiguously identify it.
 254       (setq help-window (selected-window))
 255     (let ((entry (assq (selected-window) view-return-to-alist)))
 256       (if entry
 257           ;; When entering Help mode from the Help window,
 258           ;; such as by following a link, preserve the same
 259           ;; meaning for the q command.
 260           ;; (setcdr entry (cons (selected-window) help-return-method))
 261           nil
 262         (setq view-return-to-alist
 263               (cons (cons (selected-window) help-return-method)
 264                     view-return-to-alist)))))
 265
 266   (when (eq major-mode 'help-mode)
 267     ;; View mode's read-only status of existing *Help* buffer is lost
 268     ;; by with-output-to-temp-buffer.
 269     (toggle-read-only 1)
 270     (help-make-xrefs (current-buffer))))
 271 \f
 272 ;; Grokking cross-reference information in doc strings and
 273 ;; hyperlinking it.
 274
 275 ;; This may have some scope for extension and the same or something
 276 ;; similar should be done for widget doc strings, which currently use
 277 ;; another mechanism.
 278
 279 (defvar help-back-label (purecopy "[back]")
 280   "Label to use by `help-make-xrefs' for the go-back reference.")
 281
 282 (defvar help-forward-label (purecopy "[forward]")
 283   "Label to use by `help-make-xrefs' for the go-forward reference.")
 284
 285 (defconst help-xref-symbol-regexp
 286   (purecopy (concat "\\(\\<\\(\\(variable\\|option\\)\\|"  ; Link to var
 287                     "\\(function\\|command\\)\\|"          ; Link to function
 288                     "\\(face\\)\\|"                        ; Link to face
 289                     "\\(symbol\\|program\\|property\\)\\|" ; Don't link
 290                     "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)"
 291                     "[ \t\n]+\\)?"
 292                     ;; Note starting with word-syntax character:
 293                     "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"))
 294   "Regexp matching doc string references to symbols.
 295
 296 The words preceding the quoted symbol can be used in doc strings to
 297 distinguish references to variables, functions and symbols.")
 298
 299 (defvar help-xref-mule-regexp nil
 300   "Regexp matching doc string references to MULE-related keywords.
 301
 302 It is usually nil, and is temporarily bound to an appropriate regexp
 303 when help commands related to multilingual environment (e.g.,
 304 `describe-coding-system') are invoked.")
 305
 306
 307 (defconst help-xref-info-regexp
 308   (purecopy "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+`\\([^']+\\)'")
 309   "Regexp matching doc string references to an Info node.")
 310
 311 (defconst help-xref-url-regexp
 312   (purecopy "\\<[Uu][Rr][Ll][ \t\n]+`\\([^']+\\)'")
 313   "Regexp matching doc string references to a URL.")
 314
 315 ;;;###autoload
 316 (defun help-setup-xref (item interactive-p)
 317   "Invoked from commands using the \"*Help*\" buffer to install some xref info.
 318
 319 ITEM is a (FUNCTION . ARGS) pair appropriate for recreating the help
 320 buffer after following a reference.  INTERACTIVE-P is non-nil if the
 321 calling command was invoked interactively.  In this case the stack of
 322 items for help buffer \"back\" buttons is cleared.
 323
 324 This should be called very early, before the output buffer is cleared,
 325 because we want to record the \"previous\" position of point so we can
 326 restore it properly when going back."
 327   (with-current-buffer (help-buffer)
 328     (when help-xref-stack-item
 329       (push (cons (point) help-xref-stack-item) help-xref-stack)
 330       (setq help-xref-forward-stack nil))
 331     (when interactive-p
 332       (let ((tail (nthcdr 10 help-xref-stack)))
 333         ;; Truncate the stack.
 334         (if tail (setcdr tail nil))))
 335     (setq help-xref-stack-item item)))
 336
 337 (defvar help-xref-following nil
 338   "Non-nil when following a help cross-reference.")
 339
 340 ;;;###autoload
 341 (defun help-buffer ()
 342   (buffer-name                          ;for with-output-to-temp-buffer
 343    (if help-xref-following
 344        (current-buffer)
 345      (get-buffer-create "*Help*"))))
 346
 347 (defvar help-xref-override-view-map
 348   (let ((map (make-sparse-keymap)))
 349     (set-keymap-parent map view-mode-map)
 350     (define-key map "\r" nil)
 351     map)
 352   "Replacement keymap for `view-mode' in help buffers.")
 353
 354 ;;;###autoload
 355 (defun help-make-xrefs (&optional buffer)
 356   "Parse and hyperlink documentation cross-references in the given BUFFER.
 357
 358 Find cross-reference information in a buffer and activate such cross
 359 references for selection with `help-follow'.  Cross-references have
 360 the canonical form `...'  and the type of reference may be
 361 disambiguated by the preceding word(s) used in
 362 `help-xref-symbol-regexp'.  Faces only get cross-referenced if
 363 preceded or followed by the word `face'.  Variables without
 364 variable documentation do not get cross-referenced, unless
 365 preceded by the word `variable' or `option'.
 366
 367 If the variable `help-xref-mule-regexp' is non-nil, find also
 368 cross-reference information related to multilingual environment
 369 \(e.g., coding-systems).  This variable is also used to disambiguate
 370 the type of reference as the same way as `help-xref-symbol-regexp'.
 371
 372 A special reference `back' is made to return back through a stack of
 373 help buffers.  Variable `help-back-label' specifies the text for
 374 that."
 375   (interactive "b")
 376   (save-excursion
 377     (set-buffer (or buffer (current-buffer)))
 378     (goto-char (point-min))
 379     ;; Skip the header-type info, though it might be useful to parse
 380     ;; it at some stage (e.g. "function in `library'").
 381     (forward-paragraph)
 382     (let ((old-modified (buffer-modified-p)))
 383       (let ((stab (syntax-table))
 384             (case-fold-search t)
 385             (inhibit-read-only t))
 386         (set-syntax-table emacs-lisp-mode-syntax-table)
 387         ;; The following should probably be abstracted out.
 388         (unwind-protect
 389             (progn
 390               ;; Info references
 391               (save-excursion
 392                 (while (re-search-forward help-xref-info-regexp nil t)
 393                   (let ((data (match-string 2)))
 394                     (save-match-data
 395                       (unless (string-match "^([^)]+)" data)
 396                         (setq data (concat "(emacs)" data))))
 397                     (help-xref-button 2 'help-info data))))
 398               ;; URLs
 399               (save-excursion
 400                 (while (re-search-forward help-xref-url-regexp nil t)
 401                   (let ((data (match-string 1)))
 402                     (help-xref-button 1 'help-url data))))
 403               ;; Mule related keywords.  Do this before trying
 404               ;; `help-xref-symbol-regexp' because some of Mule
 405               ;; keywords have variable or function definitions.
 406               (if help-xref-mule-regexp
 407                   (save-excursion
 408                     (while (re-search-forward help-xref-mule-regexp nil t)
 409                       (let* ((data (match-string 7))
 410                              (sym (intern-soft data)))
 411                         (cond
 412                          ((match-string 3) ; coding system
 413                           (and sym (coding-system-p sym)
 414                                (help-xref-button 6 'help-coding-system sym)))
 415                          ((match-string 4) ; input method
 416                           (and (assoc data input-method-alist)
 417                                (help-xref-button 7 'help-input-method data)))
 418                          ((or (match-string 5) (match-string 6)) ; charset
 419                           (and sym (charsetp sym)
 420                                (help-xref-button 7 'help-character-set sym)))
 421                          ((assoc data input-method-alist)
 422                           (help-xref-button 7 'help-character-set data))
 423                          ((and sym (coding-system-p sym))
 424                           (help-xref-button 7 'help-coding-system sym))
 425                          ((and sym (charsetp sym))
 426                           (help-xref-button 7 'help-character-set sym)))))))
 427               ;; Quoted symbols
 428               (save-excursion
 429                 (while (re-search-forward help-xref-symbol-regexp nil t)
 430                   (let* ((data (match-string 8))
 431                          (sym (intern-soft data)))
 432                     (if sym
 433                         (cond
 434                          ((match-string 3)  ; `variable' &c
 435                           (and (or (boundp sym) ; `variable' doesn't ensure
 436                                         ; it's actually bound
 437                                    (get sym 'variable-documentation))
 438                                (help-xref-button 8 'help-variable sym)))
 439                          ((match-string 4)   ; `function' &c
 440                           (and (fboundp sym) ; similarly
 441                                (help-xref-button 8 'help-function sym)))
 442                          ((match-string 5) ; `face'
 443                           (and (facep sym)
 444                                (help-xref-button 8 'help-face sym)))
 445                          ((match-string 6)) ; nothing for `symbol'
 446                          ((match-string 7)
 447 ;;;  this used:
 448 ;;;                       #'(lambda (arg)
 449 ;;;                           (let ((location
 450 ;;;                                  (find-function-noselect arg)))
 451 ;;;                             (pop-to-buffer (car location))
 452 ;;;                             (goto-char (cdr location))))
 453                           (help-xref-button 8 'help-function-def sym))
 454                          ((and
 455                            (facep sym)
 456                            (save-match-data (looking-at "[ \t\n]+face\\W")))
 457                           (help-xref-button 8 'help-face sym))
 458                          ((and (or (boundp sym)
 459                                    (get sym 'variable-documentation))
 460                                (fboundp sym))
 461                           ;; We can't intuit whether to use the
 462                           ;; variable or function doc -- supply both.
 463                           (help-xref-button 8 'help-symbol sym))
 464                          ((and
 465                            (or (boundp sym)
 466                                (get sym 'variable-documentation))
 467                            (or
 468                             (documentation-property
 469                              sym 'variable-documentation)
 470                             (condition-case nil
 471                                 (documentation-property
 472                                  (indirect-variable sym)
 473                                  'variable-documentation)
 474                               (cyclic-variable-indirection nil))))
 475                           (help-xref-button 8 'help-variable sym))
 476                          ((fboundp sym)
 477                           (help-xref-button 8 'help-function sym)))))))
 478               ;; An obvious case of a key substitution:
 479               (save-excursion
 480                 (while (re-search-forward
 481                         ;; Assume command name is only word and symbol
 482                         ;; characters to get things like `use M-x foo->bar'.
 483                         ;; Command required to end with word constituent
 484                         ;; to avoid `.' at end of a sentence.
 485                         "\\<M-x\\s-+\\(\\sw\\(\\sw\\|\\s_\\)*\\sw\\)" nil t)
 486                   (let ((sym (intern-soft (match-string 1))))
 487                     (if (fboundp sym)
 488                         (help-xref-button 1 'help-function sym)))))
 489               ;; Look for commands in whole keymap substitutions:
 490               (save-excursion
 491                 ;; Make sure to find the first keymap.
 492                 (goto-char (point-min))
 493                 ;; Find a header and the column at which the command
 494                 ;; name will be found.
 495
 496                 ;; If the keymap substitution isn't the last thing in
 497                 ;; the doc string, and if there is anything on the
 498                 ;; same line after it, this code won't recognize the end of it.
 499                 (while (re-search-forward "^key +binding\n\\(-+ +\\)-+\n\n"
 500                                           nil t)
 501                   (let ((col (- (match-end 1) (match-beginning 1))))
 502                     (while
 503                         (and (not (eobp))
 504                              ;; Stop at a pair of blank lines.
 505                              (not (looking-at "\n\\s-*\n")))
 506                       ;; Skip a single blank line.
 507                       (and (eolp) (forward-line))
 508                       (end-of-line)
 509                       (skip-chars-backward "^ \t\n")
 510                       (if (and (>= (current-column) col)
 511                                (looking-at "\\(\\sw\\|\\s_\\)+$"))
 512                           (let ((sym (intern-soft (match-string 0))))
 513                             (if (fboundp sym)
 514                                 (help-xref-button 0 'help-function sym))))
 515                       (forward-line))))))
 516           (set-syntax-table stab))
 517         ;; Delete extraneous newlines at the end of the docstring
 518         (goto-char (point-max))
 519         (while (and (not (bobp)) (bolp))
 520           (delete-char -1))
 521         (insert "\n")
 522         (when (or help-xref-stack help-xref-forward-stack)
 523           (insert "\n"))
 524         ;; Make a back-reference in this buffer if appropriate.
 525         (when help-xref-stack
 526           (help-insert-xref-button help-back-label 'help-back
 527                                    (current-buffer)))
 528         ;; Make a forward-reference in this buffer if appropriate.
 529         (when help-xref-forward-stack
 530           (when help-xref-stack
 531             (insert "\t"))
 532           (help-insert-xref-button help-forward-label 'help-forward
 533                                    (current-buffer)))
 534         (when (or help-xref-stack help-xref-forward-stack)
 535           (insert "\n")))
 536       ;; View mode steals RET from us.
 537       (set (make-local-variable 'minor-mode-overriding-map-alist)
 538            (list (cons 'view-mode help-xref-override-view-map)))
 539       (set-buffer-modified-p old-modified))))
 540
 541 ;;;###autoload
 542 (defun help-xref-button (match-number type &rest args)
 543   "Make a hyperlink for cross-reference text previously matched.
 544 MATCH-NUMBER is the subexpression of interest in the last matched
 545 regexp.  TYPE is the type of button to use.  Any remaining arguments are
 546 passed to the button's help-function when it is invoked.
 547 See `help-make-xrefs'."
 548   ;; Don't mung properties we've added specially in some instances.
 549   (unless (button-at (match-beginning match-number))
 550     (make-text-button (match-beginning match-number)
 551                       (match-end match-number)
 552                       'type type 'help-args args)))
 553
 554 ;;;###autoload
 555 (defun help-insert-xref-button (string type &rest args)
 556   "Insert STRING and make a hyperlink from cross-reference text on it.
 557 TYPE is the type of button to use.  Any remaining arguments are passed
 558 to the button's help-function when it is invoked.
 559 See `help-make-xrefs'."
 560   (unless (button-at (point))
 561     (insert-text-button string 'type type 'help-args args)))
 562
 563 ;;;###autoload
 564 (defun help-xref-on-pp (from to)
 565   "Add xrefs for symbols in `pp's output between FROM and TO."
 566   (if (> (- to from) 5000) nil
 567     (with-syntax-table emacs-lisp-mode-syntax-table
 568       (save-excursion
 569         (save-restriction
 570           (narrow-to-region from to)
 571           (goto-char (point-min))
 572           (condition-case nil
 573               (while (not (eobp))
 574                 (cond
 575                  ((looking-at "\"") (forward-sexp 1))
 576                  ((looking-at "#<") (search-forward ">" nil 'move))
 577                  ((looking-at "\\(\\(\\sw\\|\\s_\\)+\\)")
 578                   (let* ((sym (intern-soft (match-string 1)))
 579                          (type (cond ((fboundp sym) 'help-function)
 580                                      ((or (memq sym '(t nil))
 581                                           (keywordp sym))
 582                                       nil)
 583                                      ((and sym
 584                                            (or (boundp sym)
 585                                                (get sym
 586                                                     'variable-documentation)))
 587                                       'help-variable))))
 588                     (when type (help-xref-button 1 type sym)))
 589                   (goto-char (match-end 1)))
 590                  (t (forward-char 1))))
 591             (error nil)))))))
 592
 593 \f
 594 ;; Additional functions for (re-)creating types of help buffers.
 595 (defun help-xref-interned (symbol)
 596   "Follow a hyperlink which appeared to be an arbitrary interned SYMBOL.
 597 Both variable, function and face documentation are extracted into a single
 598 help buffer."
 599   (with-current-buffer (help-buffer)
 600     ;; Push the previous item on the stack before clobbering the output buffer.
 601     (help-setup-xref nil nil)
 602     (let ((facedoc (when (facep symbol)
 603                      ;; Don't record the current entry in the stack.
 604                      (setq help-xref-stack-item nil)
 605                      (describe-face symbol)))
 606           (fdoc (when (fboundp symbol)
 607                   ;; Don't record the current entry in the stack.
 608                   (setq help-xref-stack-item nil)
 609                   (describe-function symbol)))
 610           (sdoc (when (or (boundp symbol)
 611                           (get symbol 'variable-documentation))
 612                   ;; Don't record the current entry in the stack.
 613                   (setq help-xref-stack-item nil)
 614                   (describe-variable symbol))))
 615       (cond
 616        (sdoc
 617         ;; We now have a help buffer on the variable.
 618         ;; Insert the function and face text before it.
 619         (when (or fdoc facedoc)
 620           (goto-char (point-min))
 621           (let ((inhibit-read-only t))
 622             (when fdoc
 623               (insert fdoc "\n\n")
 624               (when facedoc
 625                 (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
 626                         " is also a " "face." "\n\n")))
 627             (when facedoc
 628               (insert facedoc "\n\n"))
 629             (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
 630                     " is also a " "variable." "\n\n"))
 631           ;; Don't record the `describe-variable' item in the stack.
 632           (setq help-xref-stack-item nil)
 633           (help-setup-xref (list #'help-xref-interned symbol) nil)))
 634        (fdoc
 635         ;; We now have a help buffer on the function.
 636         ;; Insert face text before it.
 637         (when facedoc
 638           (goto-char (point-max))
 639           (let ((inhibit-read-only t))
 640             (insert "\n\n" (make-string 30 ?-) "\n\n" (symbol-name symbol)
 641                     " is also a " "face." "\n\n" facedoc))
 642           ;; Don't record the `describe-function' item in the stack.
 643           (setq help-xref-stack-item nil)
 644           (help-setup-xref (list #'help-xref-interned symbol) nil)))))))
 645
 646 \f
 647 ;; Navigation/hyperlinking with xrefs
 648
 649 (defun help-xref-go-back (buffer)
 650   "From BUFFER, go back to previous help buffer text using `help-xref-stack'."
 651   (let (item position method args)
 652     (with-current-buffer buffer
 653       (push (cons (point) help-xref-stack-item) help-xref-forward-stack)
 654       (when help-xref-stack
 655         (setq item (pop help-xref-stack)
 656               ;; Clear the current item so that it won't get pushed
 657               ;; by the function we're about to call.  TODO: We could also
 658               ;; push it onto a "forward" stack and add a `forw' button.
 659               help-xref-stack-item nil
 660               position (car item)
 661               method (cadr item)
 662               args (cddr item))))
 663     (apply method args)
 664     (with-current-buffer buffer
 665       (if (get-buffer-window buffer)
 666           (set-window-point (get-buffer-window buffer) position)
 667         (goto-char position)))))
 668
 669 (defun help-xref-go-forward (buffer)
 670   "From BUFFER, go forward to next help buffer."
 671   (let (item position method args)
 672     (with-current-buffer buffer
 673       (push (cons (point) help-xref-stack-item) help-xref-stack)
 674       (when help-xref-forward-stack
 675         (setq item (pop help-xref-forward-stack)
 676               ;; Clear the current item so that it won't get pushed
 677               ;; by the function we're about to call.  TODO: We could also
 678               ;; push it onto a "forward" stack and add a `forw' button.
 679               help-xref-stack-item nil
 680               position (car item)
 681               method (cadr item)
 682               args (cddr item))))
 683     (apply method args)
 684     (with-current-buffer buffer
 685       (if (get-buffer-window buffer)
 686           (set-window-point (get-buffer-window buffer) position)
 687         (goto-char position)))))
 688
 689 (defun help-go-back ()
 690   "Go back to previous topic in this help buffer."
 691   (interactive)
 692   (if help-xref-stack
 693       (help-xref-go-back (current-buffer))
 694     (error "No previous help buffer")))
 695
 696 (defun help-go-forward ()
 697   "Go back to next topic in this help buffer."
 698   (interactive)
 699   (if help-xref-forward-stack
 700       (help-xref-go-forward (current-buffer))
 701     (error "No next help buffer")))
 702
 703 (defun help-do-xref (pos function args)
 704   "Call the help cross-reference function FUNCTION with args ARGS.
 705 Things are set up properly so that the resulting help-buffer has
 706 a proper [back] button."
 707   ;; There is a reference at point.  Follow it.
 708   (let ((help-xref-following t))
 709     (apply function args)))
 710
 711 ;; The doc string is meant to explain what buttons do.
 712 (defun help-follow-mouse ()
 713   "Follow the cross-reference that you click on."
 714   (interactive)
 715   (error "No cross-reference here"))
 716
 717 ;; The doc string is meant to explain what buttons do.
 718 (defun help-follow ()
 719   "Follow cross-reference at point.
 720
 721 For the cross-reference format, see `help-make-xrefs'."
 722   (interactive)
 723   (error "No cross-reference here"))
 724
 725 (defun help-follow-symbol (&optional pos)
 726   "In help buffer, show docs for symbol at POS, defaulting to point.
 727 Show all docs for that symbol as either a variable, function or face."
 728   (interactive "d")
 729   (unless pos
 730     (setq pos (point)))
 731   ;; check if the symbol under point is a function, variable or face
 732   (let ((sym
 733          (intern
 734           (save-excursion
 735             (goto-char pos) (skip-syntax-backward "w_")
 736             (buffer-substring (point)
 737                               (progn (skip-syntax-forward "w_")
 738                                      (point)))))))
 739     (when (or (boundp sym)
 740               (get sym 'variable-documentation)
 741               (fboundp sym) (facep sym))
 742       (help-do-xref pos #'help-xref-interned (list sym)))))
 743
 744 (defun help-insert-string (string)
 745   "Insert STRING to the help buffer and install xref info for it.
 746 This function can be used to restore the old contents of the help buffer
 747 when going back to the previous topic in the xref stack.  It is needed
 748 in case when it is impossible to recompute the old contents of the
 749 help buffer by other means."
 750   (setq help-xref-stack-item (list #'help-insert-string string))
 751   (with-output-to-temp-buffer (help-buffer)
 752     (insert string)))
 753
 754 (provide 'help-mode)
 755
 756 ;; arch-tag: 850954ae-3725-4cb4-8e91-0bf6d52d6b0b
 757 ;;; help-mode.el ends here