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