lisp/help.el

   1 ;;; help.el --- help commands for Emacs
   2
   3 ;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: FSF
   6 ;; Keywords: help, internal
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software; you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation; either version 2, or (at your option)
  13 ;; any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  22 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  23 ;; Boston, MA 02111-1307, USA.
  24
  25 ;;; Commentary:
  26
  27 ;; This code implements GNU Emacs' on-line help system, the one invoked by
  28 ;; `M-x help-for-help'.
  29
  30 ;;; Code:
  31
  32 ;; Get the macro make-help-screen when this is compiled,
  33 ;; or run interpreted, but not when the compiled code is loaded.
  34 (eval-when-compile (require 'help-macro))
  35 (eval-when-compile (require 'view))
  36
  37 (defvar help-map (make-sparse-keymap)
  38   "Keymap for characters following the Help key.")
  39
  40 (defvar help-mode-map (make-sparse-keymap)
  41   "Keymap for help mode.")
  42
  43 (define-key global-map (char-to-string help-char) 'help-command)
  44 (define-key global-map [help] 'help-command)
  45 (define-key global-map [f1] 'help-command)
  46 (fset 'help-command help-map)
  47
  48 (define-key help-map (char-to-string help-char) 'help-for-help)
  49 (define-key help-map [help] 'help-for-help)
  50 (define-key help-map [f1] 'help-for-help)
  51 (define-key help-map "?" 'help-for-help)
  52
  53 (define-key help-map "\C-c" 'describe-copying)
  54 (define-key help-map "\C-d" 'describe-distribution)
  55 (define-key help-map "\C-w" 'describe-no-warranty)
  56 (define-key help-map "\C-p" 'describe-project)
  57 (define-key help-map "a" 'apropos-command)
  58
  59 (define-key help-map "b" 'describe-bindings)
  60
  61 (define-key help-map "c" 'describe-key-briefly)
  62 (define-key help-map "k" 'describe-key)
  63
  64 (define-key help-map "d" 'describe-function)
  65 (define-key help-map "f" 'describe-function)
  66
  67 (define-key help-map "F" 'view-emacs-FAQ)
  68
  69 (define-key help-map "i" 'info)
  70 (define-key help-map "4i" 'info-other-window)
  71 (define-key help-map "\C-f" 'Info-goto-emacs-command-node)
  72 (define-key help-map "\C-k" 'Info-goto-emacs-key-command-node)
  73 (define-key help-map "\C-i" 'info-lookup-symbol)
  74
  75 (define-key help-map "l" 'view-lossage)
  76
  77 (define-key help-map "m" 'describe-mode)
  78
  79 (define-key help-map "\C-n" 'view-emacs-news)
  80 (define-key help-map "n" 'view-emacs-news)
  81
  82 (define-key help-map "p" 'finder-by-keyword)
  83 (autoload 'finder-by-keyword "finder"
  84   "Find packages matching a given keyword." t)
  85
  86 (define-key help-map "s" 'describe-syntax)
  87
  88 (define-key help-map "t" 'help-with-tutorial)
  89
  90 (define-key help-map "w" 'where-is)
  91
  92 (define-key help-map "v" 'describe-variable)
  93
  94 (define-key help-map "q" 'help-quit)
  95
  96 (define-key help-mode-map [mouse-2] 'help-follow-mouse)
  97 (define-key help-mode-map "\C-c\C-b" 'help-go-back)
  98 (define-key help-mode-map "\C-c\C-c" 'help-follow)
  99 (define-key help-mode-map "\t" 'help-next-ref)
 100 (define-key help-mode-map [backtab] 'help-previous-ref)
 101 (define-key help-mode-map [(shift tab)] 'help-previous-ref)
 102 ;; Documentation only, since we use minor-mode-overriding-map-alist.
 103 (define-key help-mode-map "\r" 'help-follow)
 104
 105 ;; Font-locking is incompatible with the new xref stuff.
 106 ;(defvar help-font-lock-keywords
 107 ;  (eval-when-compile
 108 ;    (let ((name-char "[-+a-zA-Z0-9_*]") (sym-char "[-+a-zA-Z0-9_:*]"))
 109 ;      (list
 110 ;       ;;
 111 ;       ;; The symbol itself.
 112 ;       (list (concat "\\`\\(" name-char "+\\)\\(\\(:\\)\\|\\('\\)\\)")
 113 ;            '(1 (if (match-beginning 3)
 114 ;                    font-lock-function-name-face
 115 ;                  font-lock-variable-name-face)))
 116 ;       ;;
 117 ;       ;; Words inside `' which tend to be symbol names.
 118 ;       (list (concat "`\\(" sym-char sym-char "+\\)'")
 119 ;            1 'font-lock-constant-face t)
 120 ;       ;;
 121 ;       ;; CLisp `:' keywords as references.
 122 ;       (list (concat "\\<:" sym-char "+\\>") 0 'font-lock-builtin-face t))))
 123 ;  "Default expressions to highlight in Help mode.")
 124
 125 (defvar help-xref-stack nil
 126   "A stack of ways by which to return to help buffers after following xrefs.
 127 Used by `help-follow' and `help-xref-go-back'.
 128 An element looks like (POSITION FUNCTION ARGS...).
 129 To use the element, do (apply FUNCTION ARGS) then (goto-char POSITION).")
 130 (put 'help-xref-stack 'permanent-local t)
 131
 132 (defvar help-xref-stack-item nil
 133   "An item for `help-follow' in this buffer to push onto `help-xref-stack'.
 134 The format is (FUNCTION ARGS...).")
 135 (put 'help-xref-stack-item 'permanent-local t)
 136
 137 (setq-default help-xref-stack nil help-xref-stack-item nil)
 138
 139 (defun help-mode ()
 140   "Major mode for viewing help text and navigating references in it.
 141 Entry to this mode runs the normal hook `help-mode-hook'.
 142 Commands:
 143 \\{help-mode-map}"
 144   (interactive)
 145   (kill-all-local-variables)
 146   (use-local-map help-mode-map)
 147   (setq mode-name "Help")
 148   (setq major-mode 'help-mode)
 149   (make-local-variable 'font-lock-defaults)
 150   (setq font-lock-defaults nil)         ; font-lock would defeat xref
 151   (view-mode)
 152   (make-local-variable 'view-no-disable-on-exit)
 153   (setq view-no-disable-on-exit t)
 154   ;; `help-make-xrefs' would be run here if not invoked from
 155   ;; `help-mode-maybe'.
 156   (run-hooks 'help-mode-hook))
 157
 158 (defun help-mode-setup ()
 159   (help-mode)
 160   (setq buffer-read-only nil))
 161
 162 (add-hook 'temp-buffer-setup-hook 'help-mode-setup)
 163
 164 (defun help-mode-finish ()
 165   (when (eq major-mode 'help-mode)
 166     ;; View mode's read-only status of existing *Help* buffer is lost
 167     ;; by with-output-to-temp-buffer.
 168     (toggle-read-only 1)
 169     (help-make-xrefs (current-buffer)))
 170   (setq view-return-to-alist
 171         (list (cons (selected-window) help-return-method))))
 172
 173 (add-hook 'temp-buffer-show-hook 'help-mode-finish)
 174
 175 (defun help-quit ()
 176   "Just exit from the Help command's command loop."
 177   (interactive)
 178   nil)
 179
 180 (defun help-with-tutorial (&optional arg)
 181   "Select the Emacs learn-by-doing tutorial.
 182 If there is a tutorial version written in the language
 183 of the selected language environment, that version is used.
 184 If there's no tutorial in that language, `TUTORIAL' is selected.
 185 With arg, you are asked to choose which language."
 186   (interactive "P")
 187   (let ((lang (if arg
 188                   (read-language-name 'tutorial "Language: " "English")
 189                 (if (get-language-info current-language-environment 'tutorial)
 190                     current-language-environment
 191                   "English")))
 192         file filename)
 193     (setq filename (get-language-info lang 'tutorial))
 194     (setq file (expand-file-name (concat "~/" filename)))
 195     (delete-other-windows)
 196     (if (get-file-buffer file)
 197         (switch-to-buffer (get-file-buffer file))
 198       (switch-to-buffer (create-file-buffer file))
 199       (setq buffer-file-name file)
 200       (setq default-directory (expand-file-name "~/"))
 201       (setq buffer-auto-save-file-name nil)
 202       (insert-file-contents (expand-file-name filename data-directory))
 203       (goto-char (point-min))
 204       (search-forward "\n<<")
 205       (beginning-of-line)
 206       (delete-region (point) (progn (end-of-line) (point)))
 207       (let ((n (- (window-height (selected-window))
 208                   (count-lines (point-min) (point))
 209                   6)))
 210         (if (< n 12)
 211             (newline n)
 212           ;; Some people get confused by the large gap.
 213           (newline (/ n 2))
 214           (insert "[Middle of page left blank for didactic purposes.  "
 215                   "Text continues below]")
 216           (newline (- n (/ n 2)))))
 217       (goto-char (point-min))
 218       (set-buffer-modified-p nil))))
 219
 220 (defun mode-line-key-binding (key)
 221   "Value is the binding of KEY in the mode line or nil if none."
 222   (let (string-info defn)
 223     (when (and (eq 'mode-line (aref key 0))
 224                (consp (setq string-info (nth 4 (event-start (aref key 1))))))
 225     (let* ((string (car string-info))
 226            (pos (cdr string-info))
 227            (local-map (and (> pos 0)
 228                            (< pos (length string))
 229                            (get-text-property pos 'local-map string))))
 230       (setq defn (and local-map (lookup-key local-map key)))))
 231     defn))
 232
 233 (defun describe-key-briefly (key &optional insert)
 234   "Print the name of the function KEY invokes.  KEY is a string.
 235 If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
 236   (interactive "kDescribe key briefly: \nP")
 237   (save-excursion
 238     (let ((modifiers (event-modifiers (aref key 0)))
 239           (standard-output (if insert (current-buffer) t))
 240           window position)
 241       ;; For a mouse button event, go to the button it applies to
 242       ;; to get the right key bindings.  And go to the right place
 243       ;; in case the keymap depends on where you clicked.
 244       (if (or (memq 'click modifiers) (memq 'down modifiers)
 245               (memq 'drag modifiers))
 246           (setq window (posn-window (event-start (aref key 0)))
 247                 position (posn-point (event-start (aref key 0)))))
 248       (if (windowp window)
 249           (progn
 250             (set-buffer (window-buffer window))
 251             (goto-char position)))
 252       ;; Ok, now look up the key and name the command.
 253       (let ((defn (or (mode-line-key-binding key)
 254                       (key-binding key)))
 255             (key-desc (key-description key)))
 256         (if (or (null defn) (integerp defn))
 257             (princ (format "%s is undefined" key-desc))
 258           (princ (format (if insert
 259                              "`%s' (`%s')"
 260                            (if (windowp window)
 261                                "%s at that spot runs the command %s"
 262                              "%s runs the command %s"))
 263                          key-desc
 264                          (if (symbolp defn) defn (prin1-to-string defn)))))))))
 265
 266 (defvar help-return-method nil
 267   "What to do to \"exit\" the help buffer.
 268 This is a list
 269  (WINDOW . t)              delete the selected window, go to WINDOW.
 270  (WINDOW . quit-window)    do quit-window, then select WINDOW.
 271  (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")
 272
 273 (defun print-help-return-message (&optional function)
 274   "Display or return message saying how to restore windows after help command.
 275 Computes a message and applies the optional argument FUNCTION to it.
 276 If FUNCTION is nil, applies `message' to it, thus printing it."
 277   (and (not (get-buffer-window standard-output))
 278        (let ((first-message
 279               (cond ((special-display-p (buffer-name standard-output))
 280                      (setq help-return-method (cons (selected-window) t))
 281                      ;; If the help output buffer is a special display buffer,
 282                      ;; don't say anything about how to get rid of it.
 283                      ;; First of all, the user will do that with the window
 284                      ;; manager, not with Emacs.
 285                      ;; Secondly, the buffer has not been displayed yet,
 286                      ;; so we don't know whether its frame will be selected.
 287                      nil)
 288                     ((not (one-window-p t))
 289                      (setq help-return-method
 290                            (cons (selected-window) 'quit-window))
 291                      "Type \\[switch-to-buffer-other-window] RET to restore the other window.")
 292                     (pop-up-windows
 293                      (setq help-return-method (cons (selected-window) t))
 294                      "Type \\[delete-other-windows] to remove help window.")
 295                     (t
 296                      (setq help-return-method
 297                            (list (selected-window) (window-buffer)
 298                                  (window-start) (window-point)))
 299                      "Type \\[switch-to-buffer] RET to remove help window."))))
 300          (funcall (or function 'message)
 301                   (concat
 302                    (if first-message
 303                        (substitute-command-keys first-message)
 304                      "")
 305                    (if first-message "  " "")
 306                    ;; If the help buffer will go in a separate frame,
 307                    ;; it's no use mentioning a command to scroll, so don't.
 308                    (if (special-display-p (buffer-name standard-output))
 309                        nil
 310                      (if (same-window-p (buffer-name standard-output))
 311                          ;; Say how to scroll this window.
 312                          (substitute-command-keys
 313                           "\\[scroll-up] to scroll the help.")
 314                        ;; Say how to scroll some other window.
 315                        (substitute-command-keys
 316                         "\\[scroll-other-window] to scroll the help."))))))))
 317
 318 (defun describe-key (key)
 319   "Display documentation of the function invoked by KEY.  KEY is a string."
 320   (interactive "kDescribe key: ")
 321   (save-excursion
 322     (let ((modifiers (event-modifiers (aref key 0)))
 323           window position)
 324       ;; For a mouse button event, go to the button it applies to
 325       ;; to get the right key bindings.  And go to the right place
 326       ;; in case the keymap depends on where you clicked.
 327       (if (or (memq 'click modifiers) (memq 'down modifiers)
 328               (memq 'drag modifiers))
 329           (setq window (posn-window (event-start (aref key 0)))
 330                 position (posn-point (event-start (aref key 0)))))
 331       (if (windowp window)
 332           (progn
 333             (set-buffer (window-buffer window))
 334             (goto-char position)))
 335       (let ((defn (or (mode-line-key-binding key) (key-binding key))))
 336         (if (or (null defn) (integerp defn))
 337             (message "%s is undefined" (key-description key))
 338           (with-output-to-temp-buffer "*Help*"
 339             (princ (key-description key))
 340             (if (windowp window)
 341                 (princ " at that spot"))
 342             (princ " runs the command ")
 343             (prin1 defn)
 344             (princ "\n   which is ")
 345             (describe-function-1 defn nil (interactive-p))
 346             (print-help-return-message)))))))
 347
 348 (defun describe-mode ()
 349   "Display documentation of current major mode and minor modes.
 350 The major mode description comes first, followed by the minor modes,
 351 each on a separate page.
 352
 353 For this to work correctly for a minor mode, the mode's indicator variable
 354 \(listed in `minor-mode-alist') must also be a function whose documentation
 355 describes the minor mode."
 356   (interactive)
 357   (with-output-to-temp-buffer "*Help*"
 358     (when minor-mode-alist
 359       (princ "The major mode is described first.
 360 For minor modes, see following pages.\n\n"))
 361     (princ mode-name)
 362     (princ " mode:\n")
 363     (princ (documentation major-mode))
 364     (help-setup-xref (list #'help-xref-mode (current-buffer)) (interactive-p))
 365     (let ((minor-modes minor-mode-alist))
 366       (while minor-modes
 367         (let* ((minor-mode (car (car minor-modes)))
 368                (indicator (car (cdr (car minor-modes)))))
 369           ;; Document a minor mode if it is listed in minor-mode-alist,
 370           ;; bound locally in this buffer, non-nil, and has a function
 371           ;; definition.
 372           (if (and (symbol-value minor-mode)
 373                    (fboundp minor-mode))
 374               (let ((pretty-minor-mode minor-mode))
 375                 (if (string-match "-mode$" (symbol-name minor-mode))
 376                     (setq pretty-minor-mode
 377                           (capitalize
 378                            (substring (symbol-name minor-mode)
 379                                       0 (match-beginning 0)))))
 380                 (while (and indicator (symbolp indicator)
 381                             (boundp indicator)
 382                             (not (eq indicator (symbol-value indicator))))
 383                   (setq indicator (symbol-value indicator)))
 384                 (princ "\n\f\n")
 385                 (princ (format "%s minor mode (%s):\n"
 386                                pretty-minor-mode
 387                                (if indicator
 388                                    (format "indicator%s" indicator)
 389                                  "no indicator")))
 390                 (princ (documentation minor-mode)))))
 391         (setq minor-modes (cdr minor-modes))))
 392     (print-help-return-message)))
 393
 394 ;; So keyboard macro definitions are documented correctly
 395 (fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))
 396
 397 (defun describe-distribution ()
 398   "Display info on how to obtain the latest version of GNU Emacs."
 399   (interactive)
 400   (find-file-read-only
 401    (expand-file-name "DISTRIB" data-directory)))
 402
 403 (defun describe-copying ()
 404   "Display info on how you may redistribute copies of GNU Emacs."
 405   (interactive)
 406   (find-file-read-only
 407    (expand-file-name "COPYING" data-directory))
 408   (goto-char (point-min)))
 409
 410 (defun describe-project ()
 411   "Display info on the GNU project."
 412   (interactive)
 413   (find-file-read-only
 414    (expand-file-name "GNU" data-directory))
 415   (goto-char (point-min)))
 416
 417 (defun describe-no-warranty ()
 418   "Display info on all the kinds of warranty Emacs does NOT have."
 419   (interactive)
 420   (describe-copying)
 421   (let (case-fold-search)
 422     (search-forward "NO WARRANTY")
 423     (recenter 0)))
 424
 425 (defun describe-prefix-bindings ()
 426   "Describe the bindings of the prefix used to reach this command.
 427 The prefix described consists of all but the last event
 428 of the key sequence that ran this command."
 429   (interactive)
 430   (let* ((key (this-command-keys)))
 431     (describe-bindings
 432      (if (stringp key)
 433          (substring key 0 (1- (length key)))
 434        (let ((prefix (make-vector (1- (length key)) nil))
 435              (i 0))
 436          (while (< i (length prefix))
 437            (aset prefix i (aref key i))
 438            (setq i (1+ i)))
 439          prefix)))))
 440 ;; Make C-h after a prefix, when not specifically bound,
 441 ;; run describe-prefix-bindings.
 442 (setq prefix-help-command 'describe-prefix-bindings)
 443
 444 (defun view-emacs-news (&optional arg)
 445   "Display info on recent changes to Emacs.
 446 With numeric argument display information on correspondingly older changes."
 447   (interactive "P")
 448   (let* ((arg (if arg (prefix-numeric-value arg) 0)))
 449     (find-file-read-only
 450      (expand-file-name (concat (make-string arg ?O) "NEWS")
 451                        data-directory))))
 452
 453 (defun view-emacs-FAQ ()
 454   "Display the Emacs Frequently Asked Questions (FAQ) file."
 455   (interactive)
 456 ;;;  (find-file-read-only (expand-file-name "FAQ" data-directory))
 457   (info "(emacs-faq)"))
 458
 459 (defun view-lossage ()
 460   "Display last 100 input keystrokes."
 461   (interactive)
 462   (with-output-to-temp-buffer "*Help*"
 463     (princ (mapconcat (function (lambda (key)
 464                                   (if (or (integerp key)
 465                                           (symbolp key)
 466                                           (listp key))
 467                                       (single-key-description key)
 468                                     (prin1-to-string key nil))))
 469                       (recent-keys)
 470                       " "))
 471     (save-excursion
 472       (set-buffer standard-output)
 473       (goto-char (point-min))
 474       (while (progn (move-to-column 50) (not (eobp)))
 475         (search-forward " " nil t)
 476         (insert "\n"))
 477       (setq help-xref-stack nil
 478             help-xref-stack-item nil))
 479     (print-help-return-message)))
 480
 481 (defalias 'help 'help-for-help)
 482 (make-help-screen help-for-help
 483   "a b c C f F C-f i I k C-k l L m n p s t v w C-c C-d C-n C-p C-w; ? for help:"
 484   "You have typed %THIS-KEY%, the help character.  Type a Help option:
 485 \(Use SPC or DEL to scroll through this text.  Type \\<help-map>\\[help-quit] to exit the Help command.)
 486
 487 a  command-apropos.  Give a substring, and see a list of commands
 488         (functions interactively callable) that contain
 489         that substring.  See also the  apropos  command.
 490 b  describe-bindings.  Display table of all key bindings.
 491 c  describe-key-briefly.  Type a command key sequence;
 492         it prints the function name that sequence runs.
 493 C  describe-coding-system.  This describes either a specific coding system
 494         (if you type its name) or the coding systems currently in use
 495         (if you type just RET).
 496 f  describe-function.  Type a function name and get documentation of it.
 497 C-f Info-goto-emacs-command-node.  Type a function name;
 498         it takes you to the Info node for that command.
 499 i  info. The  info  documentation reader.
 500 I  describe-input-method.  Describe a specific input method (if you type
 501         its name) or the current input method (if you type just RET).
 502 C-i  info-lookup-symbol.  Display the definition of a specific symbol
 503         as found in the manual for the language this buffer is written in.
 504 k  describe-key.  Type a command key sequence;
 505         it displays the full documentation.
 506 C-k Info-goto-emacs-key-command-node.  Type a command key sequence;
 507         it takes you to the Info node for the command bound to that key.
 508 l  view-lossage.  Show last 100 characters you typed.
 509 L  describe-language-environment.  This describes either the a
 510         specific language environment (if you type its name)
 511         or the current language environment (if you type just RET).
 512 m  describe-mode.  Print documentation of current minor modes,
 513         and the current major mode, including their special commands.
 514 n  view-emacs-news.  Display news of recent Emacs changes.
 515 p  finder-by-keyword. Find packages matching a given topic keyword.
 516 s  describe-syntax.  Display contents of syntax table, plus explanations
 517 t  help-with-tutorial.  Select the Emacs learn-by-doing tutorial.
 518 v  describe-variable.  Type name of a variable;
 519         it displays the variable's documentation and value.
 520 w  where-is.  Type command name; it prints which keystrokes
 521         invoke that command.
 522
 523 F  Display the frequently asked questions file.
 524 h  Display the HELLO file which illustrates various scripts.
 525 C-c Display Emacs copying permission (General Public License).
 526 C-d Display Emacs ordering information.
 527 C-n Display news of recent Emacs changes.
 528 C-p Display information about the GNU project.
 529 C-w Display information on absence of warranty for GNU Emacs."
 530   help-map)
 531
 532 (defun function-called-at-point ()
 533   "Return a function around point or else called by the list containing point.
 534 If that doesn't give a function, return nil."
 535   (let ((stab (syntax-table)))
 536     (set-syntax-table emacs-lisp-mode-syntax-table)
 537     (unwind-protect
 538         (or (condition-case ()
 539                 (save-excursion
 540                   (or (not (zerop (skip-syntax-backward "_w")))
 541                       (eq (char-syntax (following-char)) ?w)
 542                       (eq (char-syntax (following-char)) ?_)
 543                       (forward-sexp -1))
 544                   (skip-chars-forward "'")
 545                   (let ((obj (read (current-buffer))))
 546                     (and (symbolp obj) (fboundp obj) obj)))
 547               (error nil))
 548             (condition-case ()
 549                 (save-excursion
 550                   (save-restriction
 551                     (narrow-to-region (max (point-min) (- (point) 1000)) (point-max))
 552                     ;; Move up to surrounding paren, then after the open.
 553                     (backward-up-list 1)
 554                     (forward-char 1)
 555                     ;; If there is space here, this is probably something
 556                     ;; other than a real Lisp function call, so ignore it.
 557                     (if (looking-at "[ \t]")
 558                         (error "Probably not a Lisp function call"))
 559                     (let (obj)
 560                       (setq obj (read (current-buffer)))
 561                       (and (symbolp obj) (fboundp obj) obj))))
 562               (error nil)))
 563       (set-syntax-table stab))))
 564
 565 (defvar symbol-file-load-history-loaded nil
 566   "Non-nil means we have loaded the file `fns-VERSION.el' in `exec-directory'.
 567 That file records the part of `load-history' for preloaded files,
 568 which is cleared out before dumping to make Emacs smaller.")
 569
 570 (defun symbol-file (function)
 571   "Return the input source from which FUNCTION was loaded.
 572 The value is normally a string that was passed to `load':
 573 either an absolute file name, or a library name
 574 \(with no directory name and no `.el' or `.elc' at the end).
 575 It can also be nil, if the definition is not associated with any file."
 576   (unless symbol-file-load-history-loaded
 577     (load (expand-file-name
 578            ;; fns-XX.YY.ZZ.el does not work on DOS filesystem.
 579            (if (eq system-type 'ms-dos)
 580                "fns.el"
 581              (format "fns-%s.el" emacs-version))
 582            exec-directory)
 583           ;; The file name fns-%s.el already has a .el extension.
 584           nil nil t)
 585     (setq symbol-file-load-history-loaded t))
 586   (let ((files load-history)
 587         file functions)
 588     (while files
 589       (if (memq function (cdr (car files)))
 590           (setq file (car (car files)) files nil))
 591       (setq files (cdr files)))
 592     file))
 593
 594 (defun describe-function (function)
 595   "Display the full documentation of FUNCTION (a symbol)."
 596   (interactive
 597    (let ((fn (function-called-at-point))
 598          (enable-recursive-minibuffers t)
 599          val)
 600      (setq val (completing-read (if fn
 601                                     (format "Describe function (default %s): " fn)
 602                                   "Describe function: ")
 603                                 obarray 'fboundp t nil nil (symbol-name fn)))
 604      (list (if (equal val "")
 605                fn (intern val)))))
 606   (if function
 607       (with-output-to-temp-buffer "*Help*"
 608         (prin1 function)
 609         ;; Use " is " instead of a colon so that
 610         ;; it is easier to get out the function name using forward-sexp.
 611         (princ " is ")
 612         (describe-function-1 function nil (interactive-p))
 613         (print-help-return-message)
 614         (save-excursion
 615           (set-buffer standard-output)
 616           ;; Return the text we displayed.
 617           (buffer-string)))
 618     (message "You didn't specify a function")))
 619
 620 (defun describe-function-1 (function parens interactive-p)
 621   (let* ((def (if (symbolp function)
 622                   (symbol-function function)
 623                 function))
 624          file-name string need-close
 625          (beg (if (commandp def) "an interactive " "a ")))
 626     (setq string
 627           (cond ((or (stringp def)
 628                      (vectorp def))
 629                  "a keyboard macro")
 630                 ((subrp def)
 631                  (concat beg "built-in function"))
 632                 ((byte-code-function-p def)
 633                  (concat beg "compiled Lisp function"))
 634                 ((symbolp def)
 635                  (while (symbolp (symbol-function def))
 636                    (setq def (symbol-function def)))
 637                  (format "an alias for `%s'" def))
 638                 ((eq (car-safe def) 'lambda)
 639                  (concat beg "Lisp function"))
 640                 ((eq (car-safe def) 'macro)
 641                  "a Lisp macro")
 642                 ((eq (car-safe def) 'mocklisp)
 643                  "a mocklisp function")
 644                 ((eq (car-safe def) 'autoload)
 645                  (setq file-name (nth 1 def))
 646                  (format "%s autoloaded %s"
 647                          (if (commandp def) "an interactive" "an")
 648                          (if (eq (nth 4 def) 'keymap) "keymap"
 649                            (if (nth 4 def) "Lisp macro" "Lisp function"))
 650                          ))
 651                 ;; perhaps use keymapp here instead
 652                 ((eq (car-safe def) 'keymap)
 653                  (let ((is-full nil)
 654                        (elts (cdr-safe def)))
 655                    (while elts
 656                      (if (char-table-p (car-safe elts))
 657                          (setq is-full t
 658                                elts nil))
 659                      (setq elts (cdr-safe elts)))
 660                    (if is-full
 661                        "a full keymap"
 662                      "a sparse keymap")))
 663                 (t "")))
 664     (when (and parens (not (equal string "")))
 665       (setq need-close t)
 666       (princ "("))
 667     (princ string)
 668     (with-current-buffer "*Help*"
 669       (save-excursion
 670         (save-match-data
 671           (if (re-search-backward "alias for `\\([^`']+\\)'" nil t)
 672               (help-xref-button 1 #'describe-function def)))))
 673     (or file-name
 674         (setq file-name (symbol-file function)))
 675     (if file-name
 676         (progn
 677           (princ " in `")
 678           ;; We used to add .el to the file name,
 679           ;; but that's completely wrong when the user used load-file.
 680           (princ file-name)
 681           (princ "'")
 682           ;; Make a hyperlink to the library.
 683           (with-current-buffer "*Help*"
 684             (save-excursion
 685               (re-search-backward "`\\([^`']+\\)'" nil t)
 686               (help-xref-button 1 #'(lambda (arg)
 687                                       (let ((location
 688                                              (find-function-noselect arg)))
 689                                         (pop-to-buffer (car location))
 690                                         (goto-char (cdr location))))
 691                                 function)))))
 692     (if need-close (princ ")"))
 693     (princ ".")
 694     (terpri)
 695     ;; Handle symbols aliased to other symbols.
 696     (setq def (indirect-function def))
 697     ;; If definition is a macro, find the function inside it.
 698     (if (eq (car-safe def) 'macro)
 699         (setq def (cdr def)))
 700     (let ((arglist (cond ((byte-code-function-p def)
 701                           (car (append def nil)))
 702                          ((eq (car-safe def) 'lambda)
 703                           (nth 1 def))
 704                          (t t))))
 705       (if (listp arglist)
 706           (progn
 707             (princ (cons (if (symbolp function) function "anonymous")
 708                          (mapcar (lambda (arg)
 709                                    (if (memq arg '(&optional &rest))
 710                                        arg
 711                                      (intern (upcase (symbol-name arg)))))
 712                                  arglist)))
 713             (terpri))))
 714     (let ((doc (documentation function)))
 715       (if doc
 716           (progn (terpri)
 717                  (princ doc)
 718                  (help-setup-xref (list #'describe-function function) interactive-p))
 719         (princ "not documented")))))
 720
 721 (defun variable-at-point ()
 722   "Return the bound variable symbol found around point.
 723 Return 0 if there is no such symbol."
 724   (condition-case ()
 725       (let ((stab (syntax-table)))
 726         (unwind-protect
 727             (save-excursion
 728               (set-syntax-table emacs-lisp-mode-syntax-table)
 729               (or (not (zerop (skip-syntax-backward "_w")))
 730                   (eq (char-syntax (following-char)) ?w)
 731                   (eq (char-syntax (following-char)) ?_)
 732                   (forward-sexp -1))
 733               (skip-chars-forward "'")
 734               (let ((obj (read (current-buffer))))
 735                 (or (and (symbolp obj) (boundp obj) obj)
 736                     0)))
 737           (set-syntax-table stab)))
 738     (error 0)))
 739
 740 (defun describe-variable (variable)
 741   "Display the full documentation of VARIABLE (a symbol).
 742 Returns the documentation as a string, also."
 743   (interactive
 744    (let ((v (variable-at-point))
 745          (enable-recursive-minibuffers t)
 746          val)
 747      (setq val (completing-read (if (symbolp v)
 748                                     (format "Describe variable (default %s): " v)
 749                                   "Describe variable: ")
 750                                 obarray 'boundp t nil nil
 751                                 (if (symbolp v) (symbol-name v))))
 752      (list (if (equal val "")
 753                v (intern val)))))
 754   (if (symbolp variable)
 755       (let (valvoid)
 756         (with-output-to-temp-buffer "*Help*"
 757           (prin1 variable)
 758           (if (not (boundp variable))
 759               (progn
 760                 (princ " is void")
 761                 (terpri)
 762                 (setq valvoid t))
 763             (princ "'s value is ")
 764             (terpri)
 765             (pp (symbol-value variable))
 766             (terpri))
 767           (if (local-variable-p variable)
 768               (progn
 769                 (princ (format "Local in buffer %s; " (buffer-name)))
 770                 (if (not (default-boundp variable))
 771                     (princ "globally void")
 772                   (princ "global value is ")
 773                   (terpri)
 774                   (pp (default-value variable)))
 775                 (terpri)))
 776           (terpri)
 777           (save-current-buffer
 778             (set-buffer standard-output)
 779             (if (> (count-lines (point-min) (point-max)) 10)
 780                 (progn
 781                   (goto-char (point-min))
 782                   (if valvoid
 783                       (forward-line 1)
 784                     (forward-sexp 1)
 785                     (delete-region (point) (progn (end-of-line) (point)))
 786                     (insert "'s value is shown below.\n\n")
 787                     (save-excursion
 788                       (insert "\n\nValue:"))))))
 789           (princ "Documentation:")
 790           (terpri)
 791           (let ((doc (documentation-property variable 'variable-documentation)))
 792             (princ (or doc "not documented as a variable.")))
 793           (help-setup-xref (list #'describe-variable variable) (interactive-p))
 794
 795           ;; Make a link to customize if this variable can be customized.
 796           ;; Note, it is not reliable to test only for a custom-type property
 797           ;; because those are only present after the var's definition
 798           ;; has been loaded.
 799           (if (or (get variable 'custom-type) ; after defcustom
 800                   (get variable 'custom-loads) ; from loaddefs.el
 801                   (get variable 'standard-value)) ; from cus-start.el
 802               (let ((customize-label "customize"))
 803                 (terpri)
 804                 (terpri)
 805                 (princ (concat "You can " customize-label " this variable."))
 806                 (with-current-buffer "*Help*"
 807                   (save-excursion
 808                     (re-search-backward
 809                      (concat "\\(" customize-label "\\)") nil t)
 810                     (help-xref-button 1 #'(lambda (v)
 811                                             (customize-variable v)) variable)
 812                     ))))
 813           ;; Make a hyperlink to the library if appropriate.  (Don't
 814           ;; change the format of the buffer's initial line in case
 815           ;; anything expects the current format.)
 816           (let ((file-name (symbol-file variable)))
 817             (when file-name
 818               (princ "\n\nDefined in `")
 819               (princ file-name)
 820               (princ "'.")
 821               (with-current-buffer "*Help*"
 822                 (save-excursion
 823                   (re-search-backward "`\\([^`']+\\)'" nil t)
 824                   (help-xref-button 1 (lambda (arg)
 825                                         (let ((location
 826                                                (find-variable-noselect arg)))
 827                                           (pop-to-buffer (car location))
 828                                           (goto-char (cdr location))))
 829                                     variable)))))
 830
 831           (print-help-return-message)
 832           (save-excursion
 833             (set-buffer standard-output)
 834             ;; Return the text we displayed.
 835             (buffer-string))))
 836     (message "You did not specify a variable")))
 837
 838 (defun describe-bindings (&optional prefix buffer)
 839   "Show a list of all defined keys, and their definitions.
 840 We put that list in a buffer, and display the buffer.
 841
 842 The optional argument PREFIX, if non-nil, should be a key sequence;
 843 then we display only bindings that start with that prefix.
 844 The optional argument BUFFER specifies which buffer's bindings
 845 to display (default, the current buffer)."
 846   (interactive "P")
 847   (or buffer (setq buffer (current-buffer)))
 848   (with-current-buffer buffer
 849     (describe-bindings-internal nil prefix))
 850   (with-current-buffer "*Help*"
 851     (help-setup-xref (list #'describe-bindings prefix buffer)
 852                      (interactive-p))))
 853
 854 (defun where-is (definition &optional insert)
 855   "Print message listing key sequences that invoke the command DEFINITION.
 856 Argument is a command definition, usually a symbol with a function definition.
 857 If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
 858   (interactive
 859    (let ((fn (function-called-at-point))
 860          (enable-recursive-minibuffers t)
 861          val)
 862      (setq val (completing-read (if fn
 863                                     (format "Where is command (default %s): " fn)
 864                                   "Where is command: ")
 865                                 obarray 'fboundp t))
 866      (list (if (equal val "")
 867                fn (intern val))
 868            current-prefix-arg)))
 869   (let* ((keys (where-is-internal definition overriding-local-map nil nil))
 870          (keys1 (mapconcat 'key-description keys ", "))
 871          (standard-output (if insert (current-buffer) t)))
 872     (if insert
 873         (if (> (length keys1) 0)
 874             (princ (format "%s (%s)" keys1 definition))
 875           (princ (format "M-x %s RET" definition)))
 876       (if (> (length keys1) 0)
 877           (princ (format "%s is on %s" definition keys1))
 878         (princ (format "%s is not on any key" definition)))))
 879   nil)
 880
 881 (defun locate-library (library &optional nosuffix path interactive-call)
 882   "Show the precise file name of Emacs library LIBRARY.
 883 This command searches the directories in `load-path' like `M-x load-library'
 884 to find the file that `M-x load-library RET LIBRARY RET' would load.
 885 Optional second arg NOSUFFIX non-nil means don't add suffixes `.elc' or `.el'
 886 to the specified name LIBRARY.
 887
 888 If the optional third arg PATH is specified, that list of directories
 889 is used instead of `load-path'.
 890
 891 When called from a program, the file name is normaly returned as a
 892 string.  When run interactively, the argument INTERACTIVE-CALL is t,
 893 and the file name is displayed in the echo area."
 894   (interactive (list (read-string "Locate library: ")
 895                      nil nil
 896                      t))
 897   (let (result)
 898     (catch 'answer
 899       (mapcar
 900        (lambda (dir)
 901          (mapcar
 902           (lambda (suf)
 903             (let ((try (expand-file-name (concat library suf) dir)))
 904               (and (file-readable-p try)
 905                    (null (file-directory-p try))
 906                    (progn
 907                      (setq result try)
 908                      (throw 'answer try)))))
 909           (if nosuffix
 910               '("")
 911             '(".elc" ".el" "")
 912 ;;; load doesn't handle this yet.
 913 ;;;         (let ((basic '(".elc" ".el" ""))
 914 ;;;               (compressed '(".Z" ".gz" "")))
 915 ;;;           ;; If autocompression mode is on,
 916 ;;;           ;; consider all combinations of library suffixes
 917 ;;;           ;; and compression suffixes.
 918 ;;;           (if (rassq 'jka-compr-handler file-name-handler-alist)
 919 ;;;               (apply 'nconc
 920 ;;;                      (mapcar (lambda (compelt)
 921 ;;;                                (mapcar (lambda (baselt)
 922 ;;;                                          (concat baselt compelt))
 923 ;;;                                        basic))
 924 ;;;                              compressed))
 925 ;;;             basic))
 926             )))
 927        (or path load-path)))
 928     (and interactive-call
 929          (if result
 930              (message "Library is file %s" result)
 931            (message "No library %s in search path" library)))
 932     result))
 933
 934 \f
 935 ;;; Grokking cross-reference information in doc strings and
 936 ;;; hyperlinking it.
 937
 938 ;; This may have some scope for extension and the same or something
 939 ;; similar should be done for widget doc strings, which currently use
 940 ;; another mechanism.
 941
 942 (defcustom help-highlight-p t
 943   "*If non-nil, `help-make-xrefs' highlight cross-references.
 944 Under a window system it highlights them with face defined by
 945 `help-highlight-face'."
 946  :group 'help
 947  :version "20.3"
 948  :type 'boolean)
 949
 950 (defcustom help-highlight-face 'underline
 951   "Face used by `help-make-xrefs' to highlight cross-references.
 952 Must be previously-defined."
 953   :group 'help
 954   :version "20.3"
 955   :type 'face)
 956
 957 (defvar help-back-label "[back]"
 958   "Label to use by `help-make-xrefs' for the go-back reference.")
 959
 960 (defvar help-xref-symbol-regexp
 961   (concat "\\(\\<\\(\\(variable\\|option\\)\\|"
 962           "\\(function\\|command\\)\\|"
 963           "\\(symbol\\)\\)\\s-+\\)?"
 964           ;; Note starting with word-syntax character:
 965           "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'")
 966   "Regexp matching doc string references to symbols.
 967
 968 The words preceding the quoted symbol can be used in doc strings to
 969 distinguish references to variables, functions and symbols.")
 970
 971 (defvar help-xref-info-regexp
 972   "\\<[Ii]nfo[ \t\n]+node[ \t\n]+`\\([^']+\\)'"
 973   "Regexp matching doc string references to an Info node.")
 974
 975 (defun help-setup-xref (item interactive-p)
 976   "Invoked from commands using the \"*Help*\" buffer to install some xref info.
 977
 978 ITEM is a (FUNCTION . ARGS) pair appropriate for recreating the help
 979 buffer after following a reference.  INTERACTIVE-P is non-nil if the
 980 calling command was invoked interactively.  In this case the stack of
 981 items for help buffer \"back\" buttons is cleared."
 982   (if interactive-p
 983       (setq help-xref-stack nil))
 984   (setq help-xref-stack-item item))
 985
 986 (defun help-make-xrefs (&optional buffer)
 987   "Parse and hyperlink documentation cross-references in the given BUFFER.
 988
 989 Find cross-reference information in a buffer and, if
 990 `help-highlight-p' is non-nil, highlight it with face defined by
 991 `help-highlight-face'; activate such cross references for selection
 992 with `help-follow'.  Cross-references have the canonical form `...'
 993 and the type of reference may be disambiguated by the preceding
 994 word(s) used in `help-xref-symbol-regexp'.
 995
 996 A special reference `back' is made to return back through a stack of
 997 help buffers.  Variable `help-back-label' specifies the text for
 998 that."
 999   (interactive "b")
1000   (save-excursion
1001     (set-buffer (or buffer (current-buffer)))
1002     (goto-char (point-min))
1003     ;; Skip the header-type info, though it might be useful to parse
1004     ;; it at some stage (e.g. "function in `library'").
1005     (forward-paragraph)
1006     (let ((old-modified (buffer-modified-p)))
1007       (let ((stab (syntax-table))
1008             (case-fold-search t)
1009             (inhibit-read-only t))
1010         (set-syntax-table emacs-lisp-mode-syntax-table)
1011         ;; The following should probably be abstracted out.
1012         (unwind-protect
1013             (progn
1014               ;; Info references
1015               (save-excursion
1016                 (while (re-search-forward help-xref-info-regexp nil t)
1017                   (let ((data (match-string 1)))
1018                     (save-match-data
1019                       (unless (string-match "^([^)]+)" data)
1020                         (setq data (concat "(emacs)" data))))
1021                     (help-xref-button 1 #'info data))))
1022               ;; Quoted symbols
1023               (save-excursion
1024                 (while (re-search-forward help-xref-symbol-regexp nil t)
1025                   (let* ((data (match-string 6))
1026                          (sym (intern-soft data)))
1027                     (if sym
1028                         (cond
1029                          ((match-string 3) ; `variable' &c
1030                           (and (boundp sym) ; `variable' doesn't ensure
1031                                         ; it's actually bound
1032                                (help-xref-button 6 #'describe-variable sym)))
1033                          ((match-string 4) ; `function' &c
1034                           (and (fboundp sym) ; similarly
1035                                (help-xref-button 6 #'describe-function sym)))
1036                          ((match-string 5)) ; nothing for symbol
1037                          ((or (boundp sym) (fboundp sym))
1038                           ;; We can't intuit whether to use the
1039                           ;; variable or function doc -- supply both.
1040                           (help-xref-button 6 #'help-xref-interned sym)))))))
1041               ;; An obvious case of a key substitution:
1042               (save-excursion
1043                 (while (re-search-forward
1044                         ;; Assume command name is only word characters
1045                         ;; and dashes to get things like `use M-x foo.'.
1046                         "\\<M-x\\s-+\\(\\sw\\(\\sw\\|-\\)+\\)" nil t)
1047                   (let ((sym (intern-soft (match-string 1))))
1048                     (if (fboundp sym)
1049                         (help-xref-button 1 #'describe-function sym)))))
1050               ;; Look for commands in whole keymap substitutions:
1051               (save-excursion
1052                 ;; Make sure to find the first keymap.
1053                 (goto-char (point-min))
1054                 ;; Find a header and the column at which the command
1055                 ;; name will be found.
1056                 (while (re-search-forward "^key +binding\n\\(-+ +\\)-+\n\n"
1057                                           nil t)
1058                   (let ((col (- (match-end 1) (match-beginning 1))))
1059                     (while
1060                         ;; Ignore single blank lines in table, but not
1061                         ;; double ones, which should terminate it.
1062                         (and (not (looking-at "\n\\s-*\n"))
1063                              (progn
1064                                (and (eolp) (forward-line))
1065                                (end-of-line)
1066                                (skip-chars-backward "^\t\n")
1067                                (if (and (>= (current-column) col)
1068                                         (looking-at "\\(\\sw\\|-\\)+$"))
1069                                    (let ((sym (intern-soft (match-string 0))))
1070                                      (if (fboundp sym)
1071                                          (help-xref-button
1072                                           0 #'describe-function sym))))
1073                                (zerop (forward-line)))))))))
1074           (set-syntax-table stab))
1075         ;; Make a back-reference in this buffer if appropriate.
1076         (when help-xref-stack
1077           (goto-char (point-max))
1078           (save-excursion
1079             (insert "\n\n" help-back-label))
1080           ;; Just to provide the match data:
1081           (looking-at (concat "\n\n\\(" (regexp-quote help-back-label) "\\)"))
1082           (help-xref-button 1 #'help-xref-go-back (current-buffer))))
1083       ;; View mode steals RET from us.
1084       (set (make-local-variable 'minor-mode-overriding-map-alist)
1085            (list (cons 'view-mode
1086                        (let ((map (make-sparse-keymap)))
1087                          (set-keymap-parent map view-mode-map)
1088                          (define-key map "\r" 'help-follow)
1089                          map))))
1090       (set-buffer-modified-p old-modified))))
1091
1092 (defun help-xref-button (match-number function data)
1093   "Make a hyperlink for cross-reference text previously matched.
1094
1095 MATCH-NUMBER is the subexpression of interest in the last matched
1096 regexp.  FUNCTION is a function to invoke when the button is
1097 activated, applied to DATA.  DATA may be a single value or a list.
1098 See `help-make-xrefs'."
1099   ;; Don't mung properties we've added specially in some instances.
1100   (unless (get-text-property (match-beginning match-number) 'help-xref)
1101     (add-text-properties (match-beginning match-number)
1102                          (match-end match-number)
1103                          (list 'mouse-face 'highlight
1104                                'help-xref (cons function
1105                                                 (if (listp data)
1106                                                     data
1107                                                   (list data)))))
1108     (if help-highlight-p
1109         (put-text-property (match-beginning match-number)
1110                            (match-end match-number)
1111                            'face help-highlight-face))))
1112
1113 \f
1114 ;; Additional functions for (re-)creating types of help buffers.
1115 (defun help-xref-interned (symbol)
1116   "Follow a hyperlink which appeared to be an arbitrary interned SYMBOL.
1117
1118 Both variable and function documentation are extracted into a single
1119 help buffer."
1120   (let ((fdoc (when (fboundp symbol) (describe-function symbol))))
1121     (when (or (boundp symbol) (not fdoc))
1122       (describe-variable symbol)
1123       ;; We now have a help buffer on the variable.  Insert the function
1124       ;; text before it.
1125       (when fdoc
1126         (with-current-buffer "*Help*"
1127           (goto-char (point-min))
1128           (let ((inhibit-read-only t))
1129             (insert fdoc "\n\n" (symbol-name symbol) " is also a variable.\n\n"))
1130           (help-setup-xref (list #'help-xref-interned symbol) nil))))))
1131
1132 (defun help-xref-mode (buffer)
1133   "Do a `describe-mode' for the specified BUFFER."
1134   (save-excursion
1135     (set-buffer buffer)
1136     (describe-mode)))
1137 \f
1138 ;;; Navigation/hyperlinking with xrefs
1139
1140 (defun help-follow-mouse (click)
1141   "Follow the cross-reference that you click on."
1142   (interactive "e")
1143   (let* ((start (event-start click))
1144          (window (car start))
1145          (pos (car (cdr start))))
1146     (with-current-buffer (window-buffer window)
1147       (help-follow pos))))
1148
1149 (defun help-xref-go-back (buffer)
1150   "From BUFFER, go back to previous help buffer text using `help-xref-stack'."
1151   (let (item position method args)
1152     (with-current-buffer buffer
1153       (when help-xref-stack
1154         (setq help-xref-stack (cdr help-xref-stack)) ; due to help-follow
1155         (setq item (car help-xref-stack)
1156               position (car item)
1157               method (cadr item)
1158               args (cddr item))
1159         (setq help-xref-stack (cdr help-xref-stack))))
1160     (apply method args)
1161     (goto-char position)))
1162
1163 (defun help-go-back ()
1164   "Invoke the [back] button (if any) in the Help mode buffer."
1165   (interactive)
1166   (help-follow (1- (point-max))))
1167
1168 (defun help-follow (&optional pos)
1169   "Follow cross-reference at POS, defaulting to point.
1170
1171 For the cross-reference format, see `help-make-xrefs'."
1172   (interactive "d")
1173   (unless pos
1174     (setq pos (point)))
1175   (let* ((help-data
1176           (or (and (not (= pos (point-max)))
1177                    (get-text-property pos 'help-xref))
1178               (and (not (= pos (point-min)))
1179                    (get-text-property (1- pos) 'help-xref))
1180               ;; check if the symbol under point is a function or variable
1181               (let ((sym
1182                      (intern
1183                       (save-excursion
1184                         (goto-char pos) (skip-syntax-backward "w_")
1185                         (buffer-substring (point)
1186                                           (progn (skip-syntax-forward "w_")
1187                                                  (point)))))))
1188                 (when (or (boundp sym) (fboundp sym))
1189                   (list #'help-xref-interned sym)))))
1190          (method (car help-data))
1191          (args (cdr help-data)))
1192     (when help-data
1193       (setq help-xref-stack (cons (cons (point) help-xref-stack-item)
1194                                   help-xref-stack))
1195       (setq help-xref-stack-item nil)
1196       ;; There is a reference at point.  Follow it.
1197       (apply method args))))
1198
1199 ;; For tabbing through buffer.
1200 (defun help-next-ref ()
1201   "Find the next help cross-reference in the buffer."
1202   (interactive)
1203   (let (pos)
1204     (while (not pos)
1205       (if (get-text-property (point) 'help-xref) ; move off reference
1206            (goto-char (or (next-single-property-change (point) 'help-xref)
1207                           (point))))
1208       (cond ((setq pos (next-single-property-change (point) 'help-xref))
1209              (if pos (goto-char pos)))
1210             ((bobp)
1211              (message "No cross references in the buffer.")
1212              (setq pos t))
1213             (t                          ; be circular
1214              (goto-char (point-min)))))))
1215
1216 (defun help-previous-ref ()
1217   "Find the previous help cross-reference in the buffer."
1218   (interactive)
1219   (let (pos)
1220     (while (not pos)
1221       (if (get-text-property (point) 'help-xref) ; move off reference
1222           (goto-char (or (previous-single-property-change (point) 'help-xref)
1223                          (point))))
1224       (cond ((setq pos (previous-single-property-change (point) 'help-xref))
1225              (if pos (goto-char pos)))
1226             ((bobp)
1227              (message "No cross references in the buffer.")
1228              (setq pos t))
1229             (t                          ; be circular
1230              (goto-char (point-max)))))))
1231
1232 \f
1233 ;;; Automatic resizing of temporary buffers.
1234
1235 (defcustom temp-buffer-resize-mode nil
1236   "Non-nil means resize windows displaying temporary buffers.
1237 This makes the window the right height for its contents, but never
1238 more than `temp-buffer-max-height' nor less than `window-min-height'.
1239 This applies to `help', `apropos' and `completion' buffers, and some others.
1240
1241 Setting this variable directly does not take effect;
1242 use either \\[customize] or the function `temp-buffer-resize-mode'."
1243   :get (lambda (symbol)
1244          (and (memq 'resize-temp-buffer-window temp-buffer-show-hook) t))
1245   :set (lambda (symbol value)
1246          (temp-buffer-resize-mode (if value 1 -1)))
1247   :initialize 'custom-initialize-default
1248   :type 'boolean
1249   :group 'help
1250   :version "20.4")
1251
1252 (defcustom temp-buffer-max-height (lambda (buffer) (/ (- (frame-height) 2) 2))
1253   "*Maximum height of a window displaying a temporary buffer.
1254 This is the maximum height (in text lines) which `resize-temp-buffer-window'
1255 will give to a window displaying a temporary buffer.
1256 It can also be a function which will be called with the object corresponding
1257 to the buffer to be displayed as argument and should return an integer
1258 positive number."
1259   :type '(choice integer function)
1260   :group 'help
1261   :version "20.4")
1262
1263 (defun temp-buffer-resize-mode (arg)
1264   "Toggle the mode which that makes windows smaller for temporary buffers.
1265 With prefix argument ARG, turn the resizing of windows displaying temporary
1266 buffers on if ARG is positive or off otherwise.
1267 See the documentation of the variable `temp-buffer-resize-mode' for
1268 more information."
1269   (interactive "P")
1270   (let ((turn-it-on
1271          (if (null arg)
1272              (not (memq 'resize-temp-buffer-window temp-buffer-show-hook))
1273            (> (prefix-numeric-value arg) 0))))
1274     (if turn-it-on
1275         (progn
1276           ;; `help-mode-maybe' may add a `back' button and thus increase the
1277           ;; text size, so `resize-temp-buffer-window' must be run *after* it.
1278           (add-hook 'temp-buffer-show-hook 'resize-temp-buffer-window 'append)
1279           (setq temp-buffer-resize-mode t))
1280       (remove-hook 'temp-buffer-show-hook 'resize-temp-buffer-window)
1281       (setq temp-buffer-resize-mode nil))))
1282
1283 (defun resize-temp-buffer-window ()
1284   "Resize the current window to fit its contents.
1285 Will not make it higher than `temp-buffer-max-height' nor smaller than
1286 `window-min-height'.  Do nothing if it is the only window on its frame, if it
1287 is not as wide as the frame or if some of the window's contents are scrolled
1288 out of view."
1289   (unless (or (one-window-p 'nomini)
1290               (not (pos-visible-in-window-p (point-min)))
1291               (/=  (frame-width) (window-width)))
1292     (let* ((max-height (if (functionp temp-buffer-max-height)
1293                            (funcall temp-buffer-max-height (current-buffer))
1294                          temp-buffer-max-height))
1295            (win-height (1- (window-height)))
1296            (min-height (1- window-min-height))
1297            (text-height (window-buffer-height(selected-window)))
1298            (new-height (max (min text-height max-height) min-height)))
1299       (enlarge-window (- new-height win-height)))))
1300
1301 ;;; help.el ends here