lisp/help-mode.el

   1 ;;; help-mode.el --- `help-mode' used by *Help* buffers
   2
   3 ;; Copyright (C) 1985-1986, 1993-1994, 1998-2017 Free Software
   4 ;; Foundation, Inc.
   5
   6 ;; Maintainer: emacs-devel@gnu.org
   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 'cl-lib)
  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 "l" 'help-go-back)
  42     (define-key map "r" 'help-go-forward)
  43     (define-key map "\C-c\C-b" 'help-go-back)
  44     (define-key map "\C-c\C-f" 'help-go-forward)
  45     (define-key map [XF86Back] 'help-go-back)
  46     (define-key map [XF86Forward] 'help-go-forward)
  47     (define-key map "\C-c\C-c" 'help-follow-symbol)
  48     (define-key map "\r" 'help-follow)
  49     map)
  50   "Keymap for help mode.")
  51
  52 (easy-menu-define help-mode-menu help-mode-map
  53   "Menu for Help Mode."
  54   '("Help-Mode"
  55     ["Show Help for Symbol" help-follow-symbol
  56      :help "Show the docs for the symbol at point"]
  57     ["Previous Topic" help-go-back
  58      :help "Go back to previous topic in this help buffer"]
  59     ["Next Topic" help-go-forward
  60      :help "Go back to next topic in this help buffer"]
  61     ["Move to Previous Button" backward-button
  62      :help "Move to the Next Button in the help buffer"]
  63     ["Move to Next Button" forward-button
  64       :help "Move to the Next Button in the help buffer"]))
  65
  66 (defvar help-xref-stack nil
  67   "A stack of ways by which to return to help buffers after following xrefs.
  68 Used by `help-follow' and `help-xref-go-back'.
  69 An element looks like (POSITION FUNCTION ARGS...).
  70 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  71 (put 'help-xref-stack 'permanent-local t)
  72 (make-variable-buffer-local 'help-xref-stack)
  73
  74 (defvar help-xref-forward-stack nil
  75   "A stack used to navigate help forwards after using the back button.
  76 Used by `help-follow' and `help-xref-go-forward'.
  77 An element looks like (POSITION FUNCTION ARGS...).
  78 To use the element, do (apply FUNCTION ARGS) then goto the point.")
  79 (put 'help-xref-forward-stack 'permanent-local t)
  80 (make-variable-buffer-local 'help-xref-forward-stack)
  81
  82 (defvar help-xref-stack-item nil
  83   "An item for `help-follow' in this buffer to push onto `help-xref-stack'.
  84 The format is (FUNCTION ARGS...).")
  85 (put 'help-xref-stack-item 'permanent-local t)
  86 (make-variable-buffer-local 'help-xref-stack-item)
  87
  88 (defvar help-xref-stack-forward-item nil
  89   "An item for `help-go-back' to push onto `help-xref-forward-stack'.
  90 The format is (FUNCTION ARGS...).")
  91 (put 'help-xref-stack-forward-item 'permanent-local t)
  92 (make-variable-buffer-local 'help-xref-stack-forward-item)
  93
  94 (setq-default help-xref-stack nil help-xref-stack-item nil)
  95 (setq-default help-xref-forward-stack nil help-xref-forward-stack-item nil)
  96
  97 (defcustom help-mode-hook nil
  98   "Hook run by `help-mode'."
  99   :type 'hook
 100   :group 'help)
 101 \f
 102 ;; Button types used by help
 103
 104 (define-button-type 'help-xref
 105   'follow-link t
 106   'action #'help-button-action)
 107
 108 (defun help-button-action (button)
 109   "Call BUTTON's help function."
 110   (help-do-xref nil
 111                 (button-get button 'help-function)
 112                 (button-get button 'help-args)))
 113
 114 ;; These 6 calls to define-button-type were generated in a dolist
 115 ;; loop, but that is bad because it means these button types don't
 116 ;; have an easily found definition.
 117
 118 (define-button-type 'help-function
 119   :supertype 'help-xref
 120   'help-function 'describe-function
 121   'help-echo (purecopy "mouse-2, RET: describe this function"))
 122
 123 (define-button-type 'help-variable
 124   :supertype 'help-xref
 125   'help-function 'describe-variable
 126   'help-echo (purecopy "mouse-2, RET: describe this variable"))
 127
 128 (define-button-type 'help-face
 129   :supertype 'help-xref
 130   'help-function 'describe-face
 131   'help-echo (purecopy "mouse-2, RET: describe this face"))
 132
 133 (define-button-type 'help-coding-system
 134   :supertype 'help-xref
 135   'help-function 'describe-coding-system
 136   'help-echo (purecopy "mouse-2, RET: describe this coding system"))
 137
 138 (define-button-type 'help-input-method
 139   :supertype 'help-xref
 140   'help-function 'describe-input-method
 141   'help-echo (purecopy "mouse-2, RET: describe this input method"))
 142
 143 (define-button-type 'help-character-set
 144   :supertype 'help-xref
 145   'help-function 'describe-character-set
 146   'help-echo (purecopy "mouse-2, RET: describe this character set"))
 147
 148 ;; Make some more idiosyncratic button types.
 149
 150 (define-button-type 'help-symbol
 151   :supertype 'help-xref
 152   'help-function #'describe-symbol
 153   'help-echo (purecopy "mouse-2, RET: describe this symbol"))
 154
 155 (define-button-type 'help-back
 156   :supertype 'help-xref
 157   'help-function #'help-xref-go-back
 158   'help-echo (purecopy "mouse-2, RET: go back to previous help buffer"))
 159
 160 (define-button-type 'help-forward
 161   :supertype 'help-xref
 162   'help-function #'help-xref-go-forward
 163   'help-echo (purecopy "mouse-2, RET: move forward to next help buffer"))
 164
 165 (define-button-type 'help-info-variable
 166   :supertype 'help-xref
 167   ;; the name of the variable is put before the argument to Info
 168   'help-function (lambda (_a v) (info v))
 169   'help-echo (purecopy "mouse-2, RET: read this Info node"))
 170
 171 (define-button-type 'help-info
 172   :supertype 'help-xref
 173   'help-function #'info
 174   'help-echo (purecopy "mouse-2, RET: read this Info node"))
 175
 176 (define-button-type 'help-url
 177   :supertype 'help-xref
 178   'help-function #'browse-url
 179   'help-echo (purecopy "mouse-2, RET: view this URL in a browser"))
 180
 181 (define-button-type 'help-customize-variable
 182   :supertype 'help-xref
 183   'help-function (lambda (v)
 184                    (customize-variable v))
 185   'help-echo (purecopy "mouse-2, RET: customize variable"))
 186
 187 (define-button-type 'help-customize-face
 188   :supertype 'help-xref
 189   'help-function (lambda (v)
 190                    (customize-face v))
 191   'help-echo (purecopy "mouse-2, RET: customize face"))
 192
 193 (define-button-type 'help-function-def
 194   :supertype 'help-xref
 195   'help-function (lambda (fun file &optional type)
 196                    (require 'find-func)
 197                    (when (eq file 'C-source)
 198                      (setq file
 199                            (help-C-file-name (indirect-function fun) 'fun)))
 200                    ;; Don't use find-function-noselect because it follows
 201                    ;; aliases (which fails for built-in functions).
 202                    (let ((location
 203                           (find-function-search-for-symbol fun type file)))
 204                      (pop-to-buffer (car location))
 205                          (run-hooks 'find-function-after-hook)
 206                      (if (cdr location)
 207                          (goto-char (cdr location))
 208                        (message "Unable to find location in file"))))
 209   'help-echo (purecopy "mouse-2, RET: find function's definition"))
 210
 211 (define-button-type 'help-function-cmacro ; FIXME: Obsolete since 24.4.
 212   :supertype 'help-xref
 213   'help-function (lambda (fun file)
 214                    (setq file (locate-library file t))
 215                    (if (and file (file-readable-p file))
 216                        (progn
 217                          (pop-to-buffer (find-file-noselect file))
 218                          (goto-char (point-min))
 219                          (if (re-search-forward
 220                               (format "^[ \t]*(\\(cl-\\)?define-compiler-macro[ \t]+%s"
 221                                       (regexp-quote (symbol-name fun)))
 222                               nil t)
 223                              (forward-line 0)
 224                            (message "Unable to find location in file")))
 225                      (message "Unable to find file")))
 226   'help-echo (purecopy "mouse-2, RET: find function's compiler macro"))
 227
 228 (define-button-type 'help-variable-def
 229   :supertype 'help-xref
 230   'help-function (lambda (var &optional file)
 231                    (when (eq file 'C-source)
 232                      (setq file (help-C-file-name var 'var)))
 233                    (let ((location (find-variable-noselect var file)))
 234                      (pop-to-buffer (car location))
 235                      (run-hooks 'find-function-after-hook)
 236                      (if (cdr location)
 237                        (goto-char (cdr location))
 238                        (message "Unable to find location in file"))))
 239   'help-echo (purecopy "mouse-2, RET: find variable's definition"))
 240
 241 (define-button-type 'help-face-def
 242   :supertype 'help-xref
 243   'help-function (lambda (fun file)
 244                    (require 'find-func)
 245                    ;; Don't use find-function-noselect because it follows
 246                    ;; aliases (which fails for built-in functions).
 247                    (let ((location
 248                           (find-function-search-for-symbol fun 'defface file)))
 249                      (pop-to-buffer (car location))
 250                      (if (cdr location)
 251                          (goto-char (cdr location))
 252                        (message "Unable to find location in file"))))
 253   'help-echo (purecopy "mouse-2, RET: find face's definition"))
 254
 255 (define-button-type 'help-package
 256   :supertype 'help-xref
 257   'help-function 'describe-package
 258   'help-echo (purecopy "mouse-2, RET: Describe package"))
 259
 260 (define-button-type 'help-package-def
 261   :supertype 'help-xref
 262   'help-function (lambda (file) (dired file))
 263   'help-echo (purecopy "mouse-2, RET: visit package directory"))
 264
 265 (define-button-type 'help-theme-def
 266   :supertype 'help-xref
 267   'help-function 'find-file
 268   'help-echo (purecopy "mouse-2, RET: visit theme file"))
 269
 270 (define-button-type 'help-theme-edit
 271   :supertype 'help-xref
 272   'help-function 'customize-create-theme
 273   'help-echo (purecopy "mouse-2, RET: edit this theme file"))
 274
 275 (define-button-type 'help-dir-local-var-def
 276   :supertype 'help-xref
 277   'help-function (lambda (_var &optional file)
 278                    ;; FIXME: this should go to the point where the
 279                    ;; local variable was defined.
 280                    (find-file file))
 281   'help-echo (purecopy "mouse-2, RET: open directory-local variables file"))
 282
 283 \f
 284 (defvar bookmark-make-record-function)
 285
 286 ;;;###autoload
 287 (define-derived-mode help-mode special-mode "Help"
 288   "Major mode for viewing help text and navigating references in it.
 289 Entry to this mode runs the normal hook `help-mode-hook'.
 290 Commands:
 291 \\{help-mode-map}"
 292   (set (make-local-variable 'revert-buffer-function)
 293        'help-mode-revert-buffer)
 294   (set (make-local-variable 'bookmark-make-record-function)
 295        'help-bookmark-make-record))
 296
 297 ;;;###autoload
 298 (defun help-mode-setup ()
 299   "Enter Help Mode in the current buffer."
 300   (help-mode)
 301   (setq buffer-read-only nil))
 302
 303 ;;;###autoload
 304 (defun help-mode-finish ()
 305   "Finalize Help Mode setup in current buffer."
 306   (when (derived-mode-p 'help-mode)
 307     (setq buffer-read-only t)
 308     (help-make-xrefs (current-buffer))))
 309 \f
 310 ;; Grokking cross-reference information in doc strings and
 311 ;; hyperlinking it.
 312
 313 ;; This may have some scope for extension and the same or something
 314 ;; similar should be done for widget doc strings, which currently use
 315 ;; another mechanism.
 316
 317 (defvar help-back-label (purecopy "[back]")
 318   "Label to use by `help-make-xrefs' for the go-back reference.")
 319
 320 (defvar help-forward-label (purecopy "[forward]")
 321   "Label to use by `help-make-xrefs' for the go-forward reference.")
 322
 323 (defconst help-xref-symbol-regexp
 324   (purecopy (concat "\\(\\<\\(\\(variable\\|option\\)\\|"  ; Link to var
 325                     "\\(function\\|command\\|call\\)\\|"   ; Link to function
 326                     "\\(face\\)\\|"                        ; Link to face
 327                     "\\(symbol\\|program\\|property\\)\\|" ; Don't link
 328                     "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)"
 329                     "[ \t\n]+\\)?"
 330                     ;; Note starting with word-syntax character:
 331                     "['`‘]\\(\\sw\\(\\sw\\|\\s_\\)+\\|`\\)['’]"))
 332   "Regexp matching doc string references to symbols.
 333
 334 The words preceding the quoted symbol can be used in doc strings to
 335 distinguish references to variables, functions and symbols.")
 336
 337 (defvar help-xref-mule-regexp nil
 338   "Regexp matching doc string references to MULE-related keywords.
 339
 340 It is usually nil, and is temporarily bound to an appropriate regexp
 341 when help commands related to multilingual environment (e.g.,
 342 `describe-coding-system') are invoked.")
 343
 344
 345 (defconst help-xref-info-regexp
 346   (purecopy
 347    "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+['`‘]\\([^'’]+\\)['’]")
 348   "Regexp matching doc string references to an Info node.")
 349
 350 (defconst help-xref-url-regexp
 351   (purecopy "\\<[Uu][Rr][Ll][ \t\n]+['`‘]\\([^'’]+\\)['’]")
 352   "Regexp matching doc string references to a URL.")
 353
 354 ;;;###autoload
 355 (defun help-setup-xref (item interactive-p)
 356   "Invoked from commands using the \"*Help*\" buffer to install some xref info.
 357
 358 ITEM is a (FUNCTION . ARGS) pair appropriate for recreating the help
 359 buffer after following a reference.  INTERACTIVE-P is non-nil if the
 360 calling command was invoked interactively.  In this case the stack of
 361 items for help buffer \"back\" buttons is cleared.
 362
 363 This should be called very early, before the output buffer is cleared,
 364 because we want to record the \"previous\" position of point so we can
 365 restore it properly when going back."
 366   (with-current-buffer (help-buffer)
 367     (when help-xref-stack-item
 368       (push (cons (point) help-xref-stack-item) help-xref-stack)
 369       (setq help-xref-forward-stack nil))
 370     (when interactive-p
 371       (let ((tail (nthcdr 10 help-xref-stack)))
 372         ;; Truncate the stack.
 373         (if tail (setcdr tail nil))))
 374     (setq help-xref-stack-item item)))
 375
 376 (defvar help-xref-following nil
 377   "Non-nil when following a help cross-reference.")
 378
 379 ;;;###autoload
 380 (defun help-buffer ()
 381   "Return the name of a buffer for inserting help.
 382 If `help-xref-following' is non-nil, this is the name of the
 383 current buffer.  Signal an error if this buffer is not derived
 384 from `help-mode'.
 385 Otherwise, return \"*Help*\", creating a buffer with that name if
 386 it does not already exist."
 387   (buffer-name                          ;for with-output-to-temp-buffer
 388    (if (not help-xref-following)
 389        (get-buffer-create "*Help*")
 390      (unless (derived-mode-p 'help-mode)
 391        (error "Current buffer is not in Help mode"))
 392      (current-buffer))))
 393
 394 (defvar describe-symbol-backends
 395   `((nil ,#'fboundp ,(lambda (s _b _f) (describe-function s)))
 396     (nil
 397      ,(lambda (symbol)
 398         (or (and (boundp symbol) (not (keywordp symbol)))
 399             (get symbol 'variable-documentation)))
 400      ,#'describe-variable)
 401     ("face" ,#'facep ,(lambda (s _b _f) (describe-face s)))))
 402
 403 ;;;###autoload
 404 (defun help-make-xrefs (&optional buffer)
 405   "Parse and hyperlink documentation cross-references in the given BUFFER.
 406
 407 Find cross-reference information in a buffer and activate such cross
 408 references for selection with `help-follow'.  Cross-references have
 409 the canonical form `...'  and the type of reference may be
 410 disambiguated by the preceding word(s) used in
 411 `help-xref-symbol-regexp'.  Faces only get cross-referenced if
 412 preceded or followed by the word `face'.  Variables without
 413 variable documentation do not get cross-referenced, unless
 414 preceded by the word `variable' or `option'.
 415
 416 If the variable `help-xref-mule-regexp' is non-nil, find also
 417 cross-reference information related to multilingual environment
 418 \(e.g., coding-systems).  This variable is also used to disambiguate
 419 the type of reference as the same way as `help-xref-symbol-regexp'.
 420
 421 A special reference `back' is made to return back through a stack of
 422 help buffers.  Variable `help-back-label' specifies the text for
 423 that."
 424   (interactive "b")
 425   (with-current-buffer (or buffer (current-buffer))
 426     (save-excursion
 427       (goto-char (point-min))
 428       ;; Skip the header-type info, though it might be useful to parse
 429       ;; it at some stage (e.g. "function in `library'").
 430       (forward-paragraph)
 431       (let ((old-modified (buffer-modified-p)))
 432         (let ((stab (syntax-table))
 433               (case-fold-search t)
 434               (inhibit-read-only t))
 435           (set-syntax-table emacs-lisp-mode-syntax-table)
 436           ;; The following should probably be abstracted out.
 437           (unwind-protect
 438               (progn
 439                 ;; Info references
 440                 (save-excursion
 441                   (while (re-search-forward help-xref-info-regexp nil t)
 442                     (let ((data (match-string 2)))
 443                       (save-match-data
 444                         (unless (string-match "^([^)]+)" data)
 445                           (setq data (concat "(emacs)" data)))
 446                         (setq data ;; possible newlines if para filled
 447                               (replace-regexp-in-string "[ \t\n]+" " " data t t)))
 448                       (help-xref-button 2 'help-info data))))
 449                 ;; URLs
 450                 (save-excursion
 451                   (while (re-search-forward help-xref-url-regexp nil t)
 452                     (let ((data (match-string 1)))
 453                       (help-xref-button 1 'help-url data))))
 454                 ;; Mule related keywords.  Do this before trying
 455                 ;; `help-xref-symbol-regexp' because some of Mule
 456                 ;; keywords have variable or function definitions.
 457                 (if help-xref-mule-regexp
 458                     (save-excursion
 459                       (while (re-search-forward help-xref-mule-regexp nil t)
 460                         (let* ((data (match-string 7))
 461                                (sym (intern-soft data)))
 462                           (cond
 463                            ((match-string 3) ; coding system
 464                             (and sym (coding-system-p sym)
 465                                  (help-xref-button 6 'help-coding-system sym)))
 466                            ((match-string 4) ; input method
 467                             (and (assoc data input-method-alist)
 468                                  (help-xref-button 7 'help-input-method data)))
 469                            ((or (match-string 5) (match-string 6)) ; charset
 470                             (and sym (charsetp sym)
 471                                  (help-xref-button 7 'help-character-set sym)))
 472                            ((assoc data input-method-alist)
 473                             (help-xref-button 7 'help-character-set data))
 474                            ((and sym (coding-system-p sym))
 475                             (help-xref-button 7 'help-coding-system sym))
 476                            ((and sym (charsetp sym))
 477                             (help-xref-button 7 'help-character-set sym)))))))
 478                 ;; Quoted symbols
 479                 (save-excursion
 480                   (while (re-search-forward help-xref-symbol-regexp nil t)
 481                     (let* ((data (match-string 8))
 482                            (sym (intern-soft data)))
 483                       (if sym
 484                           (cond
 485                            ((match-string 3) ; `variable' &c
 486                             (and (or (boundp sym) ; `variable' doesn't ensure
 487                                         ; it's actually bound
 488                                      (get sym 'variable-documentation))
 489                                  (help-xref-button 8 'help-variable sym)))
 490                            ((match-string 4) ; `function' &c
 491                             (and (fboundp sym) ; similarly
 492                                  (help-xref-button 8 'help-function sym)))
 493                            ((match-string 5) ; `face'
 494                             (and (facep sym)
 495                                  (help-xref-button 8 'help-face sym)))
 496                            ((match-string 6)) ; nothing for `symbol'
 497                            ((match-string 7)
 498                             ;; this used:
 499                             ;; #'(lambda (arg)
 500                             ;;     (let ((location
 501                             ;;            (find-function-noselect arg)))
 502                             ;;       (pop-to-buffer (car location))
 503                             ;;  (goto-char (cdr location))))
 504                             (help-xref-button 8 'help-function-def sym))
 505                            ((cl-some (lambda (x) (funcall (nth 1 x) sym))
 506                                      describe-symbol-backends)
 507                             (help-xref-button 8 'help-symbol 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-p "\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           (ignore-errors
 600             (while (not (eobp))
 601               (cond
 602                ((looking-at-p "\"") (forward-sexp 1))
 603                ((looking-at-p "#<") (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
 619 \f
 620 ;; Additional functions for (re-)creating types of help buffers.
 621
 622 ;;;###autoload
 623 (define-obsolete-function-alias 'help-xref-interned 'describe-symbol "25.1")
 624
 625 \f
 626 ;; Navigation/hyperlinking with xrefs
 627
 628 (defun help-xref-go-back (buffer)
 629   "From BUFFER, go back to previous help buffer text using `help-xref-stack'."
 630   (let (item position method args)
 631     (with-current-buffer buffer
 632       (push (cons (point) help-xref-stack-item) help-xref-forward-stack)
 633       (when help-xref-stack
 634         (setq item (pop help-xref-stack)
 635               ;; Clear the current item so that it won't get pushed
 636               ;; by the function we're about to call.  TODO: We could also
 637               ;; push it onto a "forward" stack and add a `forw' button.
 638               help-xref-stack-item nil
 639               position (car item)
 640               method (cadr item)
 641               args (cddr item))))
 642     (apply method args)
 643     (with-current-buffer buffer
 644       (if (get-buffer-window buffer)
 645           (set-window-point (get-buffer-window buffer) position)
 646         (goto-char position)))))
 647
 648 (defun help-xref-go-forward (buffer)
 649   "From BUFFER, go forward to next help buffer."
 650   (let (item position method args)
 651     (with-current-buffer buffer
 652       (push (cons (point) help-xref-stack-item) help-xref-stack)
 653       (when help-xref-forward-stack
 654         (setq item (pop help-xref-forward-stack)
 655               ;; Clear the current item so that it won't get pushed
 656               ;; by the function we're about to call.  TODO: We could also
 657               ;; push it onto a "forward" stack and add a `forw' button.
 658               help-xref-stack-item nil
 659               position (car item)
 660               method (cadr item)
 661               args (cddr item))))
 662     (apply method args)
 663     (with-current-buffer buffer
 664       (if (get-buffer-window buffer)
 665           (set-window-point (get-buffer-window buffer) position)
 666         (goto-char position)))))
 667
 668 (defun help-go-back ()
 669   "Go back to previous topic in this help buffer."
 670   (interactive)
 671   (if help-xref-stack
 672       (help-xref-go-back (current-buffer))
 673     (user-error "No previous help buffer")))
 674
 675 (defun help-go-forward ()
 676   "Go to the next topic in this help buffer."
 677   (interactive)
 678   (if help-xref-forward-stack
 679       (help-xref-go-forward (current-buffer))
 680     (user-error "No next help buffer")))
 681
 682 (defun help-do-xref (_pos function args)
 683   "Call the help cross-reference function FUNCTION with args ARGS.
 684 Things are set up properly so that the resulting help-buffer has
 685 a proper [back] button."
 686   ;; There is a reference at point.  Follow it.
 687   (let ((help-xref-following t))
 688     (apply function (if (eq function 'info)
 689                         (append args (list (generate-new-buffer-name "*info*"))) args))))
 690
 691 ;; The doc string is meant to explain what buttons do.
 692 (defun help-follow-mouse ()
 693   "Follow the cross-reference that you click on."
 694   (interactive)
 695   (error "No cross-reference here"))
 696
 697 ;; The doc string is meant to explain what buttons do.
 698 (defun help-follow ()
 699   "Follow cross-reference at point.
 700
 701 For the cross-reference format, see `help-make-xrefs'."
 702   (interactive)
 703   (user-error "No cross-reference here"))
 704
 705 (defun help-follow-symbol (&optional pos)
 706   "In help buffer, show docs for symbol at POS, defaulting to point.
 707 Show all docs for that symbol as either a variable, function or face."
 708   (interactive "d")
 709   (unless pos
 710     (setq pos (point)))
 711   ;; check if the symbol under point is a function, variable or face
 712   (let ((sym
 713          (intern
 714           (save-excursion
 715             (goto-char pos) (skip-syntax-backward "w_")
 716             (buffer-substring (point)
 717                               (progn (skip-syntax-forward "w_")
 718                                      (point)))))))
 719     (when (or (boundp sym)
 720               (get sym 'variable-documentation)
 721               (fboundp sym) (facep sym))
 722       (help-do-xref pos #'describe-symbol (list sym)))))
 723
 724 (defun help-mode-revert-buffer (_ignore-auto noconfirm)
 725   (when (or noconfirm (yes-or-no-p "Revert help buffer? "))
 726     (let ((pos (point))
 727           (item help-xref-stack-item)
 728           ;; Pretend there is no current item to add to the history.
 729           (help-xref-stack-item nil)
 730           ;; Use the current buffer.
 731           (help-xref-following t))
 732       (apply (car item) (cdr item))
 733       (goto-char pos))))
 734
 735 (defun help-insert-string (string)
 736   "Insert STRING to the help buffer and install xref info for it.
 737 This function can be used to restore the old contents of the help buffer
 738 when going back to the previous topic in the xref stack.  It is needed
 739 in case when it is impossible to recompute the old contents of the
 740 help buffer by other means."
 741   (setq help-xref-stack-item (list #'help-insert-string string))
 742   (with-output-to-temp-buffer (help-buffer)
 743     (insert string)))
 744
 745 \f
 746 ;; Bookmark support
 747
 748 (declare-function bookmark-prop-get "bookmark" (bookmark prop))
 749 (declare-function bookmark-make-record-default "bookmark"
 750                   (&optional no-file no-context posn))
 751
 752 (defun help-bookmark-make-record ()
 753   "Create and return a help-mode bookmark record.
 754 Implements `bookmark-make-record-function' for help-mode buffers."
 755   (unless (car help-xref-stack-item)
 756     (error "Cannot create bookmark - help command not known"))
 757   `(,@(bookmark-make-record-default 'NO-FILE 'NO-CONTEXT)
 758       (help-fn     . ,(car help-xref-stack-item))
 759       (help-args   . ,(cdr help-xref-stack-item))
 760       (position    . ,(point))
 761       (handler     . help-bookmark-jump)))
 762
 763 ;;;###autoload
 764 (defun help-bookmark-jump (bookmark)
 765   "Jump to help-mode bookmark BOOKMARK.
 766 Handler function for record returned by `help-bookmark-make-record'.
 767 BOOKMARK is a bookmark name or a bookmark record."
 768   (let ((help-fn    (bookmark-prop-get bookmark 'help-fn))
 769         (help-args  (bookmark-prop-get bookmark 'help-args))
 770         (position   (bookmark-prop-get bookmark 'position)))
 771     (apply help-fn help-args)
 772     (pop-to-buffer "*Help*")
 773     (goto-char position)))
 774
 775
 776 (provide 'help-mode)
 777
 778 ;;; help-mode.el ends here