lisp/help-mode.el

   1 ;;; help-mode.el --- `help-mode' used by *Help* buffers
   2
   3 ;; Copyright (C) 1985-1986, 1993-1994, 1998-2012
   4 ;;   Free Software Foundation, Inc.
   5
   6 ;; Maintainer: FSF
   7 ;; Keywords: help, internal
   8 ;; Package: emacs
   9
  10 ;; This file is part of GNU Emacs.
  11
  12 ;; GNU Emacs is free software: you can redistribute it and/or modify
  13 ;; it under the terms of the GNU General Public License as published by
  14 ;; the Free Software Foundation, either version 3 of the License, or
  15 ;; (at your option) any later version.
  16
  17 ;; GNU Emacs is distributed in the hope that it will be useful,
  18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20 ;; GNU General Public License for more details.
  21
  22 ;; You should have received a copy of the GNU General Public License
  23 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  24
  25 ;;; Commentary:
  26
  27 ;; Defines `help-mode', which is the mode used by *Help* buffers, and
  28 ;; associated support machinery, such as adding hyperlinks, etc.,
  29
  30 ;;; Code:
  31
  32 (require 'button)
  33 (require 'view)
  34 (eval-when-compile (require 'easymenu))
  35
  36 (defvar help-mode-map
  37   (let ((map (make-sparse-keymap)))
  38     (set-keymap-parent map (make-composed-keymap button-buffer-map
  39                                                  special-mode-map))
  40     (define-key map [mouse-2] 'help-follow-mouse)
  41     (define-key map "\C-c\C-b" 'help-go-back)
  42     (define-key map "\C-c\C-f" 'help-go-forward)
  43     (define-key map "\C-c\C-c" 'help-follow-symbol)
  44     (define-key map "\r" 'help-follow)
  45     map)
  46   "Keymap for help mode.")
  47
  48 (easy-menu-define help-mode-menu help-mode-map
  49   "Menu for Help Mode."
  50   '("Help-Mode"
  51     ["Show Help for Symbol" help-follow-symbol
  52      :help "Show the docs for the symbol at point"]
  53     ["Previous Topic" help-go-back
  54      :help "Go back to previous topic in this help buffer"]
  55     ["Next Topic" help-go-forward
  56      :help "Go back to next topic in this help buffer"]
  57     ["Move to Previous Button" backward-button
  58      :help "Move to the Next Button in the help buffer"]
  59     ["Move to Next Button" forward-button
  60       :help "Move to the Next Button in the help buffer"]))
  61
  62 (defvar help-xref-stack nil
  63   "A stack of ways by which to return to help buffers after following xrefs.
  64 Used by `help-follow' and `help-xref-go-back'.
  65 An element looks like (POSITION FUNCTION ARGS...).
  66 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  67 (put 'help-xref-stack 'permanent-local t)
  68 (make-variable-buffer-local 'help-xref-stack)
  69
  70 (defvar help-xref-forward-stack nil
  71   "A stack used to navigate help forwards after using the back button.
  72 Used by `help-follow' and `help-xref-go-forward'.
  73 An element looks like (POSITION FUNCTION ARGS...).
  74 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  75 (put 'help-xref-forward-stack 'permanent-local t)
  76 (make-variable-buffer-local 'help-xref-forward-stack)
  77
  78 (defvar help-xref-stack-item nil
  79   "An item for `help-follow' in this buffer to push onto `help-xref-stack'.
  80 The format is (FUNCTION ARGS...).")
  81 (put 'help-xref-stack-item 'permanent-local t)
  82 (make-variable-buffer-local 'help-xref-stack-item)
  83
  84 (defvar help-xref-stack-forward-item nil
  85   "An item for `help-go-back' to push onto `help-xref-forward-stack'.
  86 The format is (FUNCTION ARGS...).")
  87 (put 'help-xref-stack-forward-item 'permanent-local t)
  88 (make-variable-buffer-local 'help-xref-stack-forward-item)
  89
  90 (setq-default help-xref-stack nil help-xref-stack-item nil)
  91 (setq-default help-xref-forward-stack nil help-xref-forward-stack-item nil)
  92
  93 (defcustom help-mode-hook nil
  94   "Hook run by `help-mode'."
  95   :type 'hook
  96   :group 'help)
  97 \f
  98 ;; Button types used by help
  99
 100 (define-button-type 'help-xref
 101   'follow-link t
 102   'action #'help-button-action)
 103
 104 (defun help-button-action (button)
 105   "Call BUTTON's help function."
 106   (help-do-xref (button-start button)
 107                 (button-get button 'help-function)
 108                 (button-get button 'help-args)))
 109
 110 ;; These 6 calls to define-button-type were generated in a dolist
 111 ;; loop, but that is bad because it means these button types don't
 112 ;; have an easily found definition.
 113
 114 (define-button-type 'help-function
 115   :supertype 'help-xref
 116   'help-function 'describe-function
 117   'help-echo (purecopy "mouse-2, RET: describe this function"))
 118
 119 (define-button-type 'help-variable
 120   :supertype 'help-xref
 121   'help-function 'describe-variable
 122   'help-echo (purecopy "mouse-2, RET: describe this variable"))
 123
 124 (define-button-type 'help-face
 125   :supertype 'help-xref
 126   'help-function 'describe-face
 127   'help-echo (purecopy "mouse-2, RET: describe this face"))
 128
 129 (define-button-type 'help-coding-system
 130   :supertype 'help-xref
 131   'help-function 'describe-coding-system
 132   'help-echo (purecopy "mouse-2, RET: describe this coding system"))
 133
 134 (define-button-type 'help-input-method
 135   :supertype 'help-xref
 136   'help-function 'describe-input-method
 137   'help-echo (purecopy "mouse-2, RET: describe this input method"))
 138
 139 (define-button-type 'help-character-set
 140   :supertype 'help-xref
 141   'help-function 'describe-character-set
 142   'help-echo (purecopy "mouse-2, RET: describe this character set"))
 143
 144 ;; Make some more idiosyncratic button types.
 145
 146 (define-button-type 'help-symbol
 147   :supertype 'help-xref
 148   'help-function #'help-xref-interned
 149   'help-echo (purecopy "mouse-2, RET: describe this symbol"))
 150
 151 (define-button-type 'help-back
 152   :supertype 'help-xref
 153   'help-function #'help-xref-go-back
 154   'help-echo (purecopy "mouse-2, RET: go back to previous help buffer"))
 155
 156 (define-button-type 'help-forward
 157   :supertype 'help-xref
 158   'help-function #'help-xref-go-forward
 159   'help-echo (purecopy "mouse-2, RET: move forward to next help buffer"))
 160
 161 (define-button-type 'help-info-variable
 162   :supertype 'help-xref
 163   ;; the name of the variable is put before the argument to Info
 164   'help-function (lambda (_a v) (info v))
 165   'help-echo (purecopy "mouse-2, RET: read this Info node"))
 166
 167 (define-button-type 'help-info
 168   :supertype 'help-xref
 169   'help-function #'info
 170   'help-echo (purecopy "mouse-2, RET: read this Info node"))
 171
 172 (define-button-type 'help-url
 173   :supertype 'help-xref
 174   'help-function #'browse-url
 175   'help-echo (purecopy "mouse-2, RET: view this URL in a browser"))
 176
 177 (define-button-type 'help-customize-variable
 178   :supertype 'help-xref
 179   'help-function (lambda (v)
 180                    (customize-variable v))
 181   'help-echo (purecopy "mouse-2, RET: customize variable"))
 182
 183 (define-button-type 'help-customize-face
 184   :supertype 'help-xref
 185   'help-function (lambda (v)
 186                    (customize-face v))
 187   'help-echo (purecopy "mouse-2, RET: customize face"))
 188
 189 (define-button-type 'help-function-def
 190   :supertype 'help-xref
 191   'help-function (lambda (fun file)
 192                    (require 'find-func)
 193                    (when (eq file 'C-source)
 194                      (setq file
 195                            (help-C-file-name (indirect-function fun) 'fun)))
 196                    ;; Don't use find-function-noselect because it follows
 197                    ;; aliases (which fails for built-in functions).
 198                    (let ((location
 199                           (find-function-search-for-symbol fun nil file)))
 200                      (pop-to-buffer (car location))
 201                      (if (cdr location)
 202                          (goto-char (cdr location))
 203                        (message "Unable to find location in file"))))
 204   'help-echo (purecopy "mouse-2, RET: find function's definition"))
 205
 206 (define-button-type 'help-function-cmacro
 207   :supertype 'help-xref
 208   'help-function (lambda (fun file)
 209                    (setq file (locate-library file t))
 210                    (if (and file (file-readable-p file))
 211                        (progn
 212                          (pop-to-buffer (find-file-noselect file))
 213                          (goto-char (point-min))
 214                          (if (re-search-forward
 215                               (format "^[ \t]*(define-compiler-macro[ \t]+%s"
 216                                       (regexp-quote (symbol-name fun))) nil t)
 217                              (forward-line 0)
 218                            (message "Unable to find location in file")))
 219                      (message "Unable to find file")))
 220   'help-echo (purecopy "mouse-2, RET: find function's compiler macro"))
 221
 222 (define-button-type 'help-variable-def
 223   :supertype 'help-xref
 224   'help-function (lambda (var &optional file)
 225                    (when (eq file 'C-source)
 226                      (setq file (help-C-file-name var 'var)))
 227                    (let ((location (find-variable-noselect var file)))
 228                      (pop-to-buffer (car location))
 229                      (if (cdr location)
 230                        (goto-char (cdr location))
 231                        (message "Unable to find location in file"))))
 232   'help-echo (purecopy "mouse-2, RET: find variable's definition"))
 233
 234 (define-button-type 'help-face-def
 235   :supertype 'help-xref
 236   'help-function (lambda (fun file)
 237                    (require 'find-func)
 238                    ;; Don't use find-function-noselect because it follows
 239                    ;; aliases (which fails for built-in functions).
 240                    (let ((location
 241                           (find-function-search-for-symbol fun 'defface file)))
 242                      (pop-to-buffer (car location))
 243                      (if (cdr location)
 244                          (goto-char (cdr location))
 245                        (message "Unable to find location in file"))))
 246   'help-echo (purecopy "mouse-2, RET: find face's definition"))
 247
 248 (define-button-type 'help-package
 249   :supertype 'help-xref
 250   'help-function 'describe-package
 251   'help-echo (purecopy "mouse-2, RET: Describe package"))
 252
 253 (define-button-type 'help-package-def
 254   :supertype 'help-xref
 255   'help-function (lambda (file) (dired file))
 256   'help-echo (purecopy "mouse-2, RET: visit package directory"))
 257
 258 (define-button-type 'help-theme-def
 259   :supertype 'help-xref
 260   'help-function 'find-file
 261   'help-echo (purecopy "mouse-2, RET: visit theme file"))
 262
 263 (define-button-type 'help-theme-edit
 264   :supertype 'help-xref
 265   'help-function 'customize-create-theme
 266   'help-echo (purecopy "mouse-2, RET: edit this theme file"))
 267 \f
 268 ;;;###autoload
 269 (define-derived-mode help-mode special-mode "Help"
 270   "Major mode for viewing help text and navigating references in it.
 271 Entry to this mode runs the normal hook `help-mode-hook'.
 272 Commands:
 273 \\{help-mode-map}"
 274   (set (make-local-variable 'revert-buffer-function)
 275        'help-mode-revert-buffer))
 276
 277 ;;;###autoload
 278 (defun help-mode-setup ()
 279   (help-mode)
 280   (setq buffer-read-only nil))
 281
 282 ;;;###autoload
 283 (defun help-mode-finish ()
 284   (when (eq major-mode 'help-mode)
 285     ;; View mode's read-only status of existing *Help* buffer is lost
 286     ;; by with-output-to-temp-buffer.
 287     (toggle-read-only 1)
 288
 289     (save-excursion
 290       (goto-char (point-min))
 291       (let ((inhibit-read-only t))
 292         (when (re-search-forward "^This [^[:space:]]+ is advised.$" nil t)
 293           (put-text-property (match-beginning 0)
 294                              (match-end 0)
 295                              'face 'font-lock-warning-face))))
 296
 297     (help-make-xrefs (current-buffer))))
 298 \f
 299 ;; Grokking cross-reference information in doc strings and
 300 ;; hyperlinking it.
 301
 302 ;; This may have some scope for extension and the same or something
 303 ;; similar should be done for widget doc strings, which currently use
 304 ;; another mechanism.
 305
 306 (defvar help-back-label (purecopy "[back]")
 307   "Label to use by `help-make-xrefs' for the go-back reference.")
 308
 309 (defvar help-forward-label (purecopy "[forward]")
 310   "Label to use by `help-make-xrefs' for the go-forward reference.")
 311
 312 (defconst help-xref-symbol-regexp
 313   (purecopy (concat "\\(\\<\\(\\(variable\\|option\\)\\|"  ; Link to var
 314                     "\\(function\\|command\\)\\|"          ; Link to function
 315                     "\\(face\\)\\|"                        ; Link to face
 316                     "\\(symbol\\|program\\|property\\)\\|" ; Don't link
 317                     "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)"
 318                     "[ \t\n]+\\)?"
 319                     ;; Note starting with word-syntax character:
 320                     "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"))
 321   "Regexp matching doc string references to symbols.
 322
 323 The words preceding the quoted symbol can be used in doc strings to
 324 distinguish references to variables, functions and symbols.")
 325
 326 (defvar help-xref-mule-regexp nil
 327   "Regexp matching doc string references to MULE-related keywords.
 328
 329 It is usually nil, and is temporarily bound to an appropriate regexp
 330 when help commands related to multilingual environment (e.g.,
 331 `describe-coding-system') are invoked.")
 332
 333
 334 (defconst help-xref-info-regexp
 335   (purecopy "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+`\\([^']+\\)'")
 336   "Regexp matching doc string references to an Info node.")
 337
 338 (defconst help-xref-url-regexp
 339   (purecopy "\\<[Uu][Rr][Ll][ \t\n]+`\\([^']+\\)'")
 340   "Regexp matching doc string references to a URL.")
 341
 342 ;;;###autoload
 343 (defun help-setup-xref (item interactive-p)
 344   "Invoked from commands using the \"*Help*\" buffer to install some xref info.
 345
 346 ITEM is a (FUNCTION . ARGS) pair appropriate for recreating the help
 347 buffer after following a reference.  INTERACTIVE-P is non-nil if the
 348 calling command was invoked interactively.  In this case the stack of
 349 items for help buffer \"back\" buttons is cleared.
 350
 351 This should be called very early, before the output buffer is cleared,
 352 because we want to record the \"previous\" position of point so we can
 353 restore it properly when going back."
 354   (with-current-buffer (help-buffer)
 355     (when help-xref-stack-item
 356       (push (cons (point) help-xref-stack-item) help-xref-stack)
 357       (setq help-xref-forward-stack nil))
 358     (when interactive-p
 359       (let ((tail (nthcdr 10 help-xref-stack)))
 360         ;; Truncate the stack.
 361         (if tail (setcdr tail nil))))
 362     (setq help-xref-stack-item item)))
 363
 364 (defvar help-xref-following nil
 365   "Non-nil when following a help cross-reference.")
 366
 367 ;;;###autoload
 368 (defun help-buffer ()
 369   "Return the name of a buffer for inserting help.
 370 If `help-xref-following' is non-nil, this is the name of the
 371 current buffer.  Signal an error if this buffer is not derived
 372 from `help-mode'.
 373 Otherwise, return \"*Help*\", creating a buffer with that name if
 374 it does not already exist."
 375   (buffer-name                          ;for with-output-to-temp-buffer
 376    (if (not help-xref-following)
 377        (get-buffer-create "*Help*")
 378      (unless (derived-mode-p 'help-mode)
 379        (error "Current buffer is not in Help mode"))
 380      (current-buffer))))
 381
 382 ;;;###autoload
 383 (defun help-make-xrefs (&optional buffer)
 384   "Parse and hyperlink documentation cross-references in the given BUFFER.
 385
 386 Find cross-reference information in a buffer and activate such cross
 387 references for selection with `help-follow'.  Cross-references have
 388 the canonical form `...'  and the type of reference may be
 389 disambiguated by the preceding word(s) used in
 390 `help-xref-symbol-regexp'.  Faces only get cross-referenced if
 391 preceded or followed by the word `face'.  Variables without
 392 variable documentation do not get cross-referenced, unless
 393 preceded by the word `variable' or `option'.
 394
 395 If the variable `help-xref-mule-regexp' is non-nil, find also
 396 cross-reference information related to multilingual environment
 397 \(e.g., coding-systems).  This variable is also used to disambiguate
 398 the type of reference as the same way as `help-xref-symbol-regexp'.
 399
 400 A special reference `back' is made to return back through a stack of
 401 help buffers.  Variable `help-back-label' specifies the text for
 402 that."
 403   (interactive "b")
 404   (with-current-buffer (or buffer (current-buffer))
 405     (save-excursion
 406       (goto-char (point-min))
 407       ;; Skip the header-type info, though it might be useful to parse
 408       ;; it at some stage (e.g. "function in `library'").
 409       (forward-paragraph)
 410       (let ((old-modified (buffer-modified-p)))
 411         (let ((stab (syntax-table))
 412               (case-fold-search t)
 413               (inhibit-read-only t))
 414           (set-syntax-table emacs-lisp-mode-syntax-table)
 415           ;; The following should probably be abstracted out.
 416           (unwind-protect
 417               (progn
 418                 ;; Info references
 419                 (save-excursion
 420                   (while (re-search-forward help-xref-info-regexp nil t)
 421                     (let ((data (match-string 2)))
 422                       (save-match-data
 423                         (unless (string-match "^([^)]+)" data)
 424                           (setq data (concat "(emacs)" data)))
 425                         (setq data ;; possible newlines if para filled
 426                               (replace-regexp-in-string "[ \t\n]+" " " data t t)))
 427                       (help-xref-button 2 'help-info data))))
 428                 ;; URLs
 429                 (save-excursion
 430                   (while (re-search-forward help-xref-url-regexp nil t)
 431                     (let ((data (match-string 1)))
 432                       (help-xref-button 1 'help-url data))))
 433                 ;; Mule related keywords.  Do this before trying
 434                 ;; `help-xref-symbol-regexp' because some of Mule
 435                 ;; keywords have variable or function definitions.
 436                 (if help-xref-mule-regexp
 437                     (save-excursion
 438                       (while (re-search-forward help-xref-mule-regexp nil t)
 439                         (let* ((data (match-string 7))
 440                                (sym (intern-soft data)))
 441                           (cond
 442                            ((match-string 3) ; coding system
 443                             (and sym (coding-system-p sym)
 444                                  (help-xref-button 6 'help-coding-system sym)))
 445                            ((match-string 4) ; input method
 446                             (and (assoc data input-method-alist)
 447                                  (help-xref-button 7 'help-input-method data)))
 448                            ((or (match-string 5) (match-string 6)) ; charset
 449                             (and sym (charsetp sym)
 450                                  (help-xref-button 7 'help-character-set sym)))
 451                            ((assoc data input-method-alist)
 452                             (help-xref-button 7 'help-character-set data))
 453                            ((and sym (coding-system-p sym))
 454                             (help-xref-button 7 'help-coding-system sym))
 455                            ((and sym (charsetp sym))
 456                             (help-xref-button 7 'help-character-set sym)))))))
 457                 ;; Quoted symbols
 458                 (save-excursion
 459                   (while (re-search-forward help-xref-symbol-regexp nil t)
 460                     (let* ((data (match-string 8))
 461                            (sym (intern-soft data)))
 462                       (if sym
 463                           (cond
 464                            ((match-string 3) ; `variable' &c
 465                             (and (or (boundp sym) ; `variable' doesn't ensure
 466                                         ; it's actually bound
 467                                      (get sym 'variable-documentation))
 468                                  (help-xref-button 8 'help-variable sym)))
 469                            ((match-string 4) ; `function' &c
 470                             (and (fboundp sym) ; similarly
 471                                  (help-xref-button 8 'help-function sym)))
 472                            ((match-string 5) ; `face'
 473                             (and (facep sym)
 474                                  (help-xref-button 8 'help-face sym)))
 475                            ((match-string 6)) ; nothing for `symbol'
 476                            ((match-string 7)
 477                             ;; this used:
 478                             ;; #'(lambda (arg)
 479                             ;;     (let ((location
 480                             ;;            (find-function-noselect arg)))
 481                             ;;       (pop-to-buffer (car location))
 482                             ;;  (goto-char (cdr location))))
 483                             (help-xref-button 8 'help-function-def sym))
 484                            ((and
 485                              (facep sym)
 486                              (save-match-data (looking-at "[ \t\n]+face\\W")))
 487                             (help-xref-button 8 'help-face sym))
 488                            ((and (or (boundp sym)
 489                                      (get sym 'variable-documentation))
 490                                  (fboundp sym))
 491                             ;; We can't intuit whether to use the
 492                             ;; variable or function doc -- supply both.
 493                             (help-xref-button 8 'help-symbol sym))
 494                            ((and
 495                              (or (boundp sym)
 496                                  (get sym 'variable-documentation))
 497                              (or
 498                               (documentation-property
 499                                sym 'variable-documentation)
 500                               (condition-case nil
 501                                   (documentation-property
 502                                    (indirect-variable sym)
 503                                    'variable-documentation)
 504                                 (cyclic-variable-indirection nil))))
 505                             (help-xref-button 8 'help-variable sym))
 506                            ((fboundp sym)
 507                             (help-xref-button 8 'help-function sym)))))))
 508                 ;; An obvious case of a key substitution:
 509                 (save-excursion
 510                   (while (re-search-forward
 511                           ;; Assume command name is only word and symbol
 512                           ;; characters to get things like `use M-x foo->bar'.
 513                           ;; Command required to end with word constituent
 514                           ;; to avoid `.' at end of a sentence.
 515                           "\\<M-x\\s-+\\(\\sw\\(\\sw\\|\\s_\\)*\\sw\\)" nil t)
 516                     (let ((sym (intern-soft (match-string 1))))
 517                       (if (fboundp sym)
 518                           (help-xref-button 1 'help-function sym)))))
 519                 ;; Look for commands in whole keymap substitutions:
 520                 (save-excursion
 521                   ;; Make sure to find the first keymap.
 522                   (goto-char (point-min))
 523                   ;; Find a header and the column at which the command
 524                   ;; name will be found.
 525
 526                   ;; If the keymap substitution isn't the last thing in
 527                   ;; the doc string, and if there is anything on the same
 528                   ;; line after it, this code won't recognize the end of it.
 529                   (while (re-search-forward "^key +binding\n\\(-+ +\\)-+\n\n"
 530                                             nil t)
 531                     (let ((col (- (match-end 1) (match-beginning 1))))
 532                       (while
 533                           (and (not (eobp))
 534                                ;; Stop at a pair of blank lines.
 535                                (not (looking-at "\n\\s-*\n")))
 536                         ;; Skip a single blank line.
 537                         (and (eolp) (forward-line))
 538                         (end-of-line)
 539                         (skip-chars-backward "^ \t\n")
 540                         (if (and (>= (current-column) col)
 541                                  (looking-at "\\(\\sw\\|\\s_\\)+$"))
 542                             (let ((sym (intern-soft (match-string 0))))
 543                               (if (fboundp sym)
 544                                   (help-xref-button 0 'help-function sym))))
 545                         (forward-line))))))
 546             (set-syntax-table stab))
 547           ;; Delete extraneous newlines at the end of the docstring
 548           (goto-char (point-max))
 549           (while (and (not (bobp)) (bolp))
 550             (delete-char -1))
 551           (insert "\n")
 552           (when (or help-xref-stack help-xref-forward-stack)
 553             (insert "\n"))
 554           ;; Make a back-reference in this buffer if appropriate.
 555           (when help-xref-stack
 556             (help-insert-xref-button help-back-label 'help-back
 557                                      (current-buffer)))
 558           ;; Make a forward-reference in this buffer if appropriate.
 559           (when help-xref-forward-stack
 560             (when help-xref-stack
 561               (insert "\t"))
 562             (help-insert-xref-button help-forward-label 'help-forward
 563                                      (current-buffer)))
 564           (when (or help-xref-stack help-xref-forward-stack)
 565             (insert "\n")))
 566         (set-buffer-modified-p old-modified)))))
 567
 568 ;;;###autoload
 569 (defun help-xref-button (match-number type &rest args)
 570   "Make a hyperlink for cross-reference text previously matched.
 571 MATCH-NUMBER is the subexpression of interest in the last matched
 572 regexp.  TYPE is the type of button to use.  Any remaining arguments are
 573 passed to the button's help-function when it is invoked.
 574 See `help-make-xrefs'."
 575   ;; Don't mung properties we've added specially in some instances.
 576   (unless (button-at (match-beginning match-number))
 577     (make-text-button (match-beginning match-number)
 578                       (match-end match-number)
 579                       'type type 'help-args args)))
 580
 581 ;;;###autoload
 582 (defun help-insert-xref-button (string type &rest args)
 583   "Insert STRING and make a hyperlink from cross-reference text on it.
 584 TYPE is the type of button to use.  Any remaining arguments are passed
 585 to the button's help-function when it is invoked.
 586 See `help-make-xrefs'."
 587   (unless (button-at (point))
 588     (insert-text-button string 'type type 'help-args args)))
 589
 590 ;;;###autoload
 591 (defun help-xref-on-pp (from to)
 592   "Add xrefs for symbols in `pp's output between FROM and TO."
 593   (if (> (- to from) 5000) nil
 594     (with-syntax-table emacs-lisp-mode-syntax-table
 595       (save-excursion
 596         (save-restriction
 597           (narrow-to-region from to)
 598           (goto-char (point-min))
 599           (condition-case nil
 600               (while (not (eobp))
 601                 (cond
 602                  ((looking-at "\"") (forward-sexp 1))
 603                  ((looking-at "#<") (search-forward ">" nil 'move))
 604                  ((looking-at "\\(\\(\\sw\\|\\s_\\)+\\)")
 605                   (let* ((sym (intern-soft (match-string 1)))
 606                          (type (cond ((fboundp sym) 'help-function)
 607                                      ((or (memq sym '(t nil))
 608                                           (keywordp sym))
 609                                       nil)
 610                                      ((and sym
 611                                            (or (boundp sym)
 612                                                (get sym
 613                                                     'variable-documentation)))
 614                                       'help-variable))))
 615                     (when type (help-xref-button 1 type sym)))
 616                   (goto-char (match-end 1)))
 617                  (t (forward-char 1))))
 618             (error nil)))))))
 619
 620 \f
 621 ;; Additional functions for (re-)creating types of help buffers.
 622 (defun help-xref-interned (symbol)
 623   "Follow a hyperlink which appeared to be an arbitrary interned SYMBOL.
 624 Both variable, function and face documentation are extracted into a single
 625 help buffer."
 626   (with-current-buffer (help-buffer)
 627     ;; Push the previous item on the stack before clobbering the output buffer.
 628     (help-setup-xref nil nil)
 629     (let ((facedoc (when (facep symbol)
 630                      ;; Don't record the current entry in the stack.
 631                      (setq help-xref-stack-item nil)
 632                      (describe-face symbol)))
 633           (fdoc (when (fboundp symbol)
 634                   ;; Don't record the current entry in the stack.
 635                   (setq help-xref-stack-item nil)
 636                   (describe-function symbol)))
 637           (sdoc (when (or (boundp symbol)
 638                           (get symbol 'variable-documentation))
 639                   ;; Don't record the current entry in the stack.
 640                   (setq help-xref-stack-item nil)
 641                   (describe-variable symbol))))
 642       (cond
 643        (sdoc
 644         ;; We now have a help buffer on the variable.
 645         ;; Insert the function and face text before it.
 646         (when (or fdoc facedoc)
 647           (goto-char (point-min))
 648           (let ((inhibit-read-only t))
 649             (when fdoc
 650               (insert fdoc "\n\n")
 651               (when facedoc
 652                 (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
 653                         " is also a " "face." "\n\n")))
 654             (when facedoc
 655               (insert facedoc "\n\n"))
 656             (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
 657                     " is also a " "variable." "\n\n"))
 658           ;; Don't record the `describe-variable' item in the stack.
 659           (setq help-xref-stack-item nil)
 660           (help-setup-xref (list #'help-xref-interned symbol) nil)))
 661        (fdoc
 662         ;; We now have a help buffer on the function.
 663         ;; Insert face text before it.
 664         (when facedoc
 665           (goto-char (point-max))
 666           (let ((inhibit-read-only t))
 667             (insert "\n\n" (make-string 30 ?-) "\n\n" (symbol-name symbol)
 668                     " is also a " "face." "\n\n" facedoc))
 669           ;; Don't record the `describe-function' item in the stack.
 670           (setq help-xref-stack-item nil)
 671           (help-setup-xref (list #'help-xref-interned symbol) nil)))))))
 672
 673 \f
 674 ;; Navigation/hyperlinking with xrefs
 675
 676 (defun help-xref-go-back (buffer)
 677   "From BUFFER, go back to previous help buffer text using `help-xref-stack'."
 678   (let (item position method args)
 679     (with-current-buffer buffer
 680       (push (cons (point) help-xref-stack-item) help-xref-forward-stack)
 681       (when help-xref-stack
 682         (setq item (pop help-xref-stack)
 683               ;; Clear the current item so that it won't get pushed
 684               ;; by the function we're about to call.  TODO: We could also
 685               ;; push it onto a "forward" stack and add a `forw' button.
 686               help-xref-stack-item nil
 687               position (car item)
 688               method (cadr item)
 689               args (cddr item))))
 690     (apply method args)
 691     (with-current-buffer buffer
 692       (if (get-buffer-window buffer)
 693           (set-window-point (get-buffer-window buffer) position)
 694         (goto-char position)))))
 695
 696 (defun help-xref-go-forward (buffer)
 697   "From BUFFER, go forward to next help buffer."
 698   (let (item position method args)
 699     (with-current-buffer buffer
 700       (push (cons (point) help-xref-stack-item) help-xref-stack)
 701       (when help-xref-forward-stack
 702         (setq item (pop help-xref-forward-stack)
 703               ;; Clear the current item so that it won't get pushed
 704               ;; by the function we're about to call.  TODO: We could also
 705               ;; push it onto a "forward" stack and add a `forw' button.
 706               help-xref-stack-item nil
 707               position (car item)
 708               method (cadr item)
 709               args (cddr item))))
 710     (apply method args)
 711     (with-current-buffer buffer
 712       (if (get-buffer-window buffer)
 713           (set-window-point (get-buffer-window buffer) position)
 714         (goto-char position)))))
 715
 716 (defun help-go-back ()
 717   "Go back to previous topic in this help buffer."
 718   (interactive)
 719   (if help-xref-stack
 720       (help-xref-go-back (current-buffer))
 721     (error "No previous help buffer")))
 722
 723 (defun help-go-forward ()
 724   "Go back to next topic in this help buffer."
 725   (interactive)
 726   (if help-xref-forward-stack
 727       (help-xref-go-forward (current-buffer))
 728     (error "No next help buffer")))
 729
 730 (defun help-do-xref (_pos function args)
 731   "Call the help cross-reference function FUNCTION with args ARGS.
 732 Things are set up properly so that the resulting help-buffer has
 733 a proper [back] button."
 734   ;; There is a reference at point.  Follow it.
 735   (let ((help-xref-following t))
 736     (apply function args)))
 737
 738 ;; The doc string is meant to explain what buttons do.
 739 (defun help-follow-mouse ()
 740   "Follow the cross-reference that you click on."
 741   (interactive)
 742   (error "No cross-reference here"))
 743
 744 ;; The doc string is meant to explain what buttons do.
 745 (defun help-follow ()
 746   "Follow cross-reference at point.
 747
 748 For the cross-reference format, see `help-make-xrefs'."
 749   (interactive)
 750   (error "No cross-reference here"))
 751
 752 (defun help-follow-symbol (&optional pos)
 753   "In help buffer, show docs for symbol at POS, defaulting to point.
 754 Show all docs for that symbol as either a variable, function or face."
 755   (interactive "d")
 756   (unless pos
 757     (setq pos (point)))
 758   ;; check if the symbol under point is a function, variable or face
 759   (let ((sym
 760          (intern
 761           (save-excursion
 762             (goto-char pos) (skip-syntax-backward "w_")
 763             (buffer-substring (point)
 764                               (progn (skip-syntax-forward "w_")
 765                                      (point)))))))
 766     (when (or (boundp sym)
 767               (get sym 'variable-documentation)
 768               (fboundp sym) (facep sym))
 769       (help-do-xref pos #'help-xref-interned (list sym)))))
 770
 771 (defun help-mode-revert-buffer (_ignore-auto noconfirm)
 772   (when (or noconfirm (yes-or-no-p "Revert help buffer? "))
 773     (let ((pos (point))
 774           (item help-xref-stack-item)
 775           ;; Pretend there is no current item to add to the history.
 776           (help-xref-stack-item nil)
 777           ;; Use the current buffer.
 778           (help-xref-following t))
 779       (apply (car item) (cdr item))
 780       (goto-char pos))))
 781
 782 (defun help-insert-string (string)
 783   "Insert STRING to the help buffer and install xref info for it.
 784 This function can be used to restore the old contents of the help buffer
 785 when going back to the previous topic in the xref stack.  It is needed
 786 in case when it is impossible to recompute the old contents of the
 787 help buffer by other means."
 788   (setq help-xref-stack-item (list #'help-insert-string string))
 789   (with-output-to-temp-buffer (help-buffer)
 790     (insert string)))
 791
 792 (provide 'help-mode)
 793
 794 ;;; help-mode.el ends here