lisp/help.el

   1 ;;; help.el --- help commands for Emacs
   2
   3 ;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999, 2000, 2001, 2002
   4 ;;   Free Software Foundation, Inc.
   5
   6 ;; Maintainer: FSF
   7 ;; Keywords: help, internal
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software; you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation; either version 2, or (at your option)
  14 ;; any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  24 ;; Boston, MA 02111-1307, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; This code implements GNU Emacs' on-line help system, the one invoked by
  29 ;; `M-x help-for-help'.
  30
  31 ;;; Code:
  32
  33 ;; Get the macro make-help-screen when this is compiled,
  34 ;; or run interpreted, but not when the compiled code is loaded.
  35 (eval-when-compile (require 'help-macro))
  36
  37 ;; This makes `with-output-to-temp-buffer' buffers use `help-mode'.
  38 (add-hook 'temp-buffer-setup-hook 'help-mode-setup)
  39 (add-hook 'temp-buffer-show-hook 'help-mode-finish)
  40
  41 (defvar help-map (make-sparse-keymap)
  42   "Keymap for characters following the Help key.")
  43
  44 (define-key global-map (char-to-string help-char) 'help-command)
  45 (define-key global-map [help] 'help-command)
  46 (define-key global-map [f1] 'help-command)
  47 (fset 'help-command help-map)
  48
  49 (define-key help-map (char-to-string help-char) 'help-for-help)
  50 (define-key help-map [help] 'help-for-help)
  51 (define-key help-map [f1] 'help-for-help)
  52 (define-key help-map "?" 'help-for-help)
  53
  54 (define-key help-map "\C-c" 'describe-copying)
  55 (define-key help-map "\C-d" 'describe-distribution)
  56 (define-key help-map "\C-e" 'view-emacs-problems)
  57 (define-key help-map "\C-f" 'view-emacs-FAQ)
  58 (define-key help-map "\C-m" 'view-order-manuals)
  59 (define-key help-map "\C-n" 'view-emacs-news)
  60 (define-key help-map "\C-p" 'describe-project)
  61 (define-key help-map "\C-t" 'view-todo)
  62 (define-key help-map "\C-w" 'describe-no-warranty)
  63
  64 ;; This does not fit the pattern, but it is natural given the C-\ command.
  65 (define-key help-map "\C-\\" 'describe-input-method)
  66
  67 (define-key help-map "C" 'describe-coding-system)
  68 (define-key help-map "F" 'Info-goto-emacs-command-node)
  69 (define-key help-map "I" 'describe-input-method)
  70 (define-key help-map "K" 'Info-goto-emacs-key-command-node)
  71 (define-key help-map "L" 'describe-language-environment)
  72 (define-key help-map "S" 'info-lookup-symbol)
  73
  74 (define-key help-map "a" 'apropos-command)
  75
  76 (define-key help-map "b" 'describe-bindings)
  77
  78 (define-key help-map "c" 'describe-key-briefly)
  79
  80 (define-key help-map "e" 'view-echo-area-messages)
  81
  82 (define-key help-map "f" 'describe-function)
  83
  84 (define-key help-map "h" 'view-hello-file)
  85
  86 (define-key help-map "i" 'info)
  87 (define-key help-map "4i" 'info-other-window)
  88
  89 (define-key help-map "k" 'describe-key)
  90
  91 (define-key help-map "l" 'view-lossage)
  92
  93 (define-key help-map "m" 'describe-mode)
  94
  95 (define-key help-map "n" 'view-emacs-news)
  96
  97 (define-key help-map "p" 'finder-by-keyword)
  98 (autoload 'finder-by-keyword "finder"
  99   "Find packages matching a given keyword." t)
 100
 101 (define-key help-map "r" 'info-emacs-manual)
 102
 103 (define-key help-map "s" 'describe-syntax)
 104
 105 (define-key help-map "t" 'help-with-tutorial)
 106
 107 (define-key help-map "w" 'where-is)
 108
 109 (define-key help-map "v" 'describe-variable)
 110
 111 (define-key help-map "q" 'help-quit)
 112
 113 \f
 114 (defun help-quit ()
 115   "Just exit from the Help command's command loop."
 116   (interactive)
 117   nil)
 118
 119 (defvar help-return-method nil
 120   "What to do to \"exit\" the help buffer.
 121 This is a list
 122  (WINDOW . t)              delete the selected window, go to WINDOW.
 123  (WINDOW . quit-window)    do quit-window, then select WINDOW.
 124  (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")
 125
 126 (defun print-help-return-message (&optional function)
 127   "Display or return message saying how to restore windows after help command.
 128 This function assumes that `standard-output' is the help buffer.
 129 It computes a message, and applies the optional argument FUNCTION to it.
 130 If FUNCTION is nil, it applies `message', thus displaying the message."
 131   (and (not (get-buffer-window standard-output))
 132        (let ((first-message
 133               (cond ((special-display-p (buffer-name standard-output))
 134                      (setq help-return-method (cons (selected-window) t))
 135                      ;; If the help output buffer is a special display buffer,
 136                      ;; don't say anything about how to get rid of it.
 137                      ;; First of all, the user will do that with the window
 138                      ;; manager, not with Emacs.
 139                      ;; Secondly, the buffer has not been displayed yet,
 140                      ;; so we don't know whether its frame will be selected.
 141                      nil)
 142                     (display-buffer-reuse-frames
 143                      (setq help-return-method (cons (selected-window)
 144                                                     'quit-window))
 145                      nil)
 146                     ((not (one-window-p t))
 147                      (setq help-return-method
 148                            (cons (selected-window) 'quit-window))
 149                      "Type \\[switch-to-buffer-other-window] RET to restore the other window.")
 150                     (pop-up-windows
 151                      (setq help-return-method (cons (selected-window) t))
 152                      "Type \\[delete-other-windows] to remove help window.")
 153                     (t
 154                      (setq help-return-method
 155                            (list (selected-window) (window-buffer)
 156                                  (window-start) (window-point)))
 157                      "Type \\[switch-to-buffer] RET to remove help window."))))
 158          (funcall (or function 'message)
 159                   (concat
 160                    (if first-message
 161                        (substitute-command-keys first-message))
 162                    (if first-message "  ")
 163                    ;; If the help buffer will go in a separate frame,
 164                    ;; it's no use mentioning a command to scroll, so don't.
 165                    (if (special-display-p (buffer-name standard-output))
 166                        nil
 167                      (if (same-window-p (buffer-name standard-output))
 168                          ;; Say how to scroll this window.
 169                          (substitute-command-keys
 170                           "\\[scroll-up] to scroll the help.")
 171                        ;; Say how to scroll some other window.
 172                        (substitute-command-keys
 173                         "\\[scroll-other-window] to scroll the help."))))))))
 174
 175 ;; So keyboard macro definitions are documented correctly
 176 (fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))
 177
 178 (defalias 'help 'help-for-help)
 179 (make-help-screen help-for-help
 180   "a b c C e f F i I k C-k l L m p s t v w C-c C-d C-f C-n C-p C-t C-w or ? :"
 181   "You have typed %THIS-KEY%, the help character.  Type a Help option:
 182 \(Use SPC or DEL to scroll through this text.  Type \\<help-map>\\[help-quit] to exit the Help command.)
 183
 184 a  command-apropos.  Give a substring, and see a list of commands
 185         (functions interactively callable) that contain
 186         that substring.  See also the  apropos  command.
 187 b  describe-bindings.  Display table of all key bindings.
 188 c  describe-key-briefly.  Type a command key sequence;
 189         it prints the function name that sequence runs.
 190 C  describe-coding-system.  This describes either a specific coding system
 191         (if you type its name) or the coding systems currently in use
 192         (if you type just RET).
 193 e  view-echo-area-messages.  Show the `*Messages*' buffer.
 194 f  describe-function.  Type a function name and get documentation of it.
 195 F  Info-goto-emacs-command-node.  Type a function name;
 196         it takes you to the Info node for that command.
 197 h  Display the HELLO file which illustrates various scripts.
 198 i  info. The  info  documentation reader.
 199 I  describe-input-method.  Describe a specific input method (if you type
 200         its name) or the current input method (if you type just RET).
 201 k  describe-key.  Type a command key sequence;
 202         it displays the full documentation.
 203 K Info-goto-emacs-key-command-node.  Type a command key sequence;
 204         it takes you to the Info node for the command bound to that key.
 205 l  view-lossage.  Show last 100 characters you typed.
 206 L  describe-language-environment.  This describes either a
 207         specific language environment (if you type its name)
 208         or the current language environment (if you type just RET).
 209 m  describe-mode.  Print documentation of current minor modes,
 210         and the current major mode, including their special commands.
 211 p  finder-by-keyword. Find packages matching a given topic keyword.
 212 s  describe-syntax.  Display contents of syntax table, plus explanations.
 213 S  info-lookup-symbol.  Display the definition of a specific symbol
 214         as found in the manual for the language this buffer is written in.
 215 t  help-with-tutorial.  Select the Emacs learn-by-doing tutorial.
 216 v  describe-variable.  Type name of a variable;
 217         it displays the variable's documentation and value.
 218 w  where-is.  Type command name; it prints which keystrokes
 219         invoke that command.
 220
 221 C-c Display Emacs copying permission (GNU General Public License).
 222 C-d Display Emacs ordering information.
 223 C-e Display info about Emacs problems.
 224 C-f Display the Emacs FAQ.
 225 C-m Display how to order printed Emacs manuals.
 226 C-n Display news of recent Emacs changes.
 227 C-p Display information about the GNU project.
 228 C-t Display the Emacs TODO list.
 229 C-w Display information on absence of warranty for GNU Emacs."
 230   help-map)
 231
 232 \f
 233
 234 (defun function-called-at-point ()
 235   "Return a function around point or else called by the list containing point.
 236 If that doesn't give a function, return nil."
 237   (with-syntax-table emacs-lisp-mode-syntax-table
 238     (or (condition-case ()
 239             (save-excursion
 240               (or (not (zerop (skip-syntax-backward "_w")))
 241                   (eq (char-syntax (following-char)) ?w)
 242                   (eq (char-syntax (following-char)) ?_)
 243                   (forward-sexp -1))
 244               (skip-chars-forward "'")
 245               (let ((obj (read (current-buffer))))
 246                 (and (symbolp obj) (fboundp obj) obj)))
 247           (error nil))
 248         (condition-case ()
 249             (save-excursion
 250               (save-restriction
 251                 (narrow-to-region (max (point-min)
 252                                        (- (point) 1000)) (point-max))
 253                 ;; Move up to surrounding paren, then after the open.
 254                 (backward-up-list 1)
 255                 (forward-char 1)
 256                 ;; If there is space here, this is probably something
 257                 ;; other than a real Lisp function call, so ignore it.
 258                 (if (looking-at "[ \t]")
 259                     (error "Probably not a Lisp function call"))
 260                 (let ((obj (read (current-buffer))))
 261                   (and (symbolp obj) (fboundp obj) obj))))
 262           (error nil)))))
 263
 264 \f
 265 ;;; `User' help functions
 266
 267 (defun describe-distribution ()
 268   "Display info on how to obtain the latest version of GNU Emacs."
 269   (interactive)
 270   (view-file (expand-file-name "DISTRIB" data-directory)))
 271
 272 (defun describe-copying ()
 273   "Display info on how you may redistribute copies of GNU Emacs."
 274   (interactive)
 275   (view-file (expand-file-name "COPYING" data-directory))
 276   (goto-char (point-min)))
 277
 278 (defun describe-project ()
 279   "Display info on the GNU project."
 280   (interactive)
 281   (view-file (expand-file-name "THE-GNU-PROJECT" data-directory))
 282   (goto-char (point-min)))
 283
 284 (defun describe-no-warranty ()
 285   "Display info on all the kinds of warranty Emacs does NOT have."
 286   (interactive)
 287   (describe-copying)
 288   (let (case-fold-search)
 289     (search-forward "NO WARRANTY")
 290     (recenter 0)))
 291
 292 (defun describe-prefix-bindings ()
 293   "Describe the bindings of the prefix used to reach this command.
 294 The prefix described consists of all but the last event
 295 of the key sequence that ran this command."
 296   (interactive)
 297   (let* ((key (this-command-keys)))
 298     (describe-bindings
 299      (if (stringp key)
 300          (substring key 0 (1- (length key)))
 301        (let ((prefix (make-vector (1- (length key)) nil))
 302              (i 0))
 303          (while (< i (length prefix))
 304            (aset prefix i (aref key i))
 305            (setq i (1+ i)))
 306          prefix)))))
 307 ;; Make C-h after a prefix, when not specifically bound,
 308 ;; run describe-prefix-bindings.
 309 (setq prefix-help-command 'describe-prefix-bindings)
 310
 311 (defun view-emacs-news (&optional arg)
 312   "Display info on recent changes to Emacs.
 313 With numeric argument, display information on correspondingly older changes."
 314   (interactive "P")
 315   (let* ((arg (if arg (prefix-numeric-value arg) 0))
 316          (file (cond ((eq arg 0) "NEWS")
 317                      ((eq arg 1) "ONEWS")
 318                      (t
 319                       (nth (- arg 2)
 320                            (nreverse (directory-files data-directory
 321                                                       nil "^ONEWS\\.[0-9]+$"
 322                                                       nil)))))))
 323     (if file
 324         (view-file (expand-file-name file data-directory))
 325       (error "No such old news"))))
 326
 327 (defun view-todo (&optional arg)
 328   "Display the Emacs TODO list."
 329   (interactive "P")
 330   (view-file (expand-file-name "TODO" data-directory)))
 331
 332 (defun view-echo-area-messages ()
 333   "View the log of recent echo-area messages: the `*Messages*' buffer.
 334 The number of messages retained in that buffer
 335 is specified by the variable `message-log-max'."
 336   (interactive)
 337   (switch-to-buffer (get-buffer-create "*Messages*")))
 338
 339 (defun view-order-manuals ()
 340   "Display the Emacs ORDERS file."
 341   (interactive)
 342   (view-file (expand-file-name "ORDERS" data-directory))
 343   (goto-address))
 344
 345 (defun view-emacs-FAQ ()
 346   "Display the Emacs Frequently Asked Questions (FAQ) file."
 347   (interactive)
 348   ;; (find-file-read-only (expand-file-name "FAQ" data-directory))
 349   (info "(efaq)"))
 350
 351 (defun view-emacs-problems ()
 352   "Display info on known problems with Emacs and possible workarounds."
 353   (interactive)
 354   (view-file (expand-file-name "PROBLEMS" data-directory)))
 355
 356 (defun view-lossage ()
 357   "Display last 100 input keystrokes.
 358
 359 To record all your input on a file, use `open-dribble-file'."
 360   (interactive)
 361   (help-setup-xref (list #'view-lossage) (interactive-p))
 362   (with-output-to-temp-buffer (help-buffer)
 363     (princ (mapconcat (lambda (key)
 364                         (if (or (integerp key) (symbolp key) (listp key))
 365                             (single-key-description key)
 366                           (prin1-to-string key nil)))
 367                       (recent-keys)
 368                       " "))
 369     (with-current-buffer standard-output
 370       (goto-char (point-min))
 371       (while (progn (move-to-column 50) (not (eobp)))
 372         (search-forward " " nil t)
 373         (insert "\n")))
 374     (print-help-return-message)))
 375
 376 \f
 377 ;; Key bindings
 378
 379 (defun describe-bindings (&optional prefix buffer)
 380   "Show a list of all defined keys, and their definitions.
 381 We put that list in a buffer, and display the buffer.
 382
 383 The optional argument PREFIX, if non-nil, should be a key sequence;
 384 then we display only bindings that start with that prefix.
 385 The optional argument BUFFER specifies which buffer's bindings
 386 to display (default, the current buffer)."
 387   (interactive)
 388   (or buffer (setq buffer (current-buffer)))
 389   (help-setup-xref (list #'describe-bindings prefix buffer) (interactive-p))
 390   (with-current-buffer buffer
 391     (describe-bindings-internal nil prefix)))
 392
 393 ;; This function used to be in keymap.c.
 394 (defun describe-bindings-internal (&optional menus prefix)
 395   "Show a list of all defined keys, and their definitions.
 396 We put that list in a buffer, and display the buffer.
 397
 398 The optional argument MENUS, if non-nil, says to mention menu bindings.
 399 \(Ordinarily these are omitted from the output.)
 400 The optional argument PREFIX, if non-nil, should be a key sequence;
 401 then we display only bindings that start with that prefix."
 402   (interactive)
 403   (let ((buf (current-buffer)))
 404     (with-output-to-temp-buffer "*Help*"
 405       (with-current-buffer standard-output
 406         (describe-buffer-bindings buf prefix menus)))))
 407
 408 (defun where-is (definition &optional insert)
 409   "Print message listing key sequences that invoke the command DEFINITION.
 410 Argument is a command definition, usually a symbol with a function definition.
 411 If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
 412   (interactive
 413    (let ((fn (function-called-at-point))
 414          (enable-recursive-minibuffers t)
 415          val)
 416      (setq val (completing-read
 417                 (if fn
 418                     (format "Where is command (default %s): " fn)
 419                   "Where is command: ")
 420                 obarray 'commandp t))
 421      (list (if (equal val "") fn (intern val)) current-prefix-arg)))
 422   (let ((func (indirect-function definition))
 423         (defs nil)
 424         (standard-output (if insert (current-buffer) t)))
 425     (mapatoms (lambda (symbol)
 426                 (and (fboundp symbol)
 427                      (not (eq symbol definition))
 428                      (eq func (condition-case ()
 429                                   (indirect-function symbol)
 430                                 (error symbol)))
 431                      (push symbol defs))))
 432     (princ (mapconcat
 433             #'(lambda (symbol)
 434                 (let* ((remapped (command-remapping symbol))
 435                        (keys (where-is-internal
 436                               symbol overriding-local-map nil nil remapped))
 437                        (keys (mapconcat 'key-description keys ", ")))
 438                   (if insert
 439                       (if (> (length keys) 0)
 440                           (if remapped
 441                               (format "%s (%s) (remapped from %s)"
 442                                       keys remapped symbol)
 443                             (format "%s (%s)" keys symbol))
 444                         (format "M-x %s RET" symbol))
 445                     (if (> (length keys) 0)
 446                         (if remapped
 447                             (format "%s is remapped to %s which is on %s"
 448                                     definition symbol keys)
 449                           (format "%s is on %s" symbol keys))
 450                       (format "%s is not on any key" symbol)))))
 451             (cons definition defs)
 452             ";\nand ")))
 453   nil)
 454
 455 (defun string-key-binding (key)
 456   "Value is the binding of KEY in a string.
 457 If KEY is an event on a string, and that string has a `local-map'
 458 or `keymap' property, return the binding of KEY in the string's keymap."
 459   (let* ((defn nil)
 460          (start (when (vectorp key)
 461                   (if (memq (aref key 0)
 462                             '(mode-line header-line left-margin right-margin))
 463                       (event-start (aref key 1))
 464                     (and (consp (aref key 0))
 465                          (event-start (aref key 0))))))
 466          (string-info (and (consp start) (nth 4 start))))
 467     (when string-info
 468       (let* ((string (car string-info))
 469              (pos (cdr string-info))
 470              (local-map (and (>= pos 0)
 471                              (< pos (length string))
 472                              (or (get-text-property pos 'local-map string)
 473                                  (get-text-property pos 'keymap string)))))
 474         (setq defn (and local-map (lookup-key local-map key)))))
 475     defn))
 476
 477 (defun help-key-description (key untranslated)
 478   (let ((string (key-description key)))
 479     (if (or (not untranslated)
 480             (and (eq (aref untranslated 0) ?\e) (not (eq (aref key 0) ?\e))))
 481         string
 482       (let ((otherstring (key-description untranslated)))
 483         (if (equal string otherstring)
 484             string
 485           (format "%s (translated from %s)" string otherstring))))))
 486
 487 (defun describe-key-briefly (key &optional insert untranslated)
 488   "Print the name of the function KEY invokes.  KEY is a string.
 489 If INSERT (the prefix arg) is non-nil, insert the message in the buffer.
 490 If non-nil UNTRANSLATED is a vector of the untranslated events.
 491 It can also be a number in which case the untranslated events from
 492 the last key hit are used."
 493   (interactive "kDescribe key briefly: \nP\np")
 494   (if (numberp untranslated)
 495       (setq untranslated (this-single-command-raw-keys)))
 496   (save-excursion
 497     (let ((modifiers (event-modifiers (aref key 0)))
 498           (standard-output (if insert (current-buffer) t))
 499           window position)
 500       ;; For a mouse button event, go to the button it applies to
 501       ;; to get the right key bindings.  And go to the right place
 502       ;; in case the keymap depends on where you clicked.
 503       (if (or (memq 'click modifiers) (memq 'down modifiers)
 504               (memq 'drag modifiers))
 505           (setq window (posn-window (event-start (aref key 0)))
 506                 position (posn-point (event-start (aref key 0)))))
 507       (if (windowp window)
 508           (progn
 509             (set-buffer (window-buffer window))
 510             (goto-char position)))
 511       ;; Ok, now look up the key and name the command.
 512       (let ((defn (or (string-key-binding key)
 513                       (key-binding key)))
 514             (key-desc (help-key-description key untranslated)))
 515         (if (or (null defn) (integerp defn) (equal defn 'undefined))
 516             (princ (format "%s is undefined" key-desc))
 517           (princ (format (if (windowp window)
 518                              "%s at that spot runs the command %s"
 519                            "%s runs the command %s")
 520                          key-desc
 521                          (if (symbolp defn) defn (prin1-to-string defn)))))))))
 522
 523
 524 (defun describe-key (key &optional untranslated)
 525   "Display documentation of the function invoked by KEY.
 526 KEY should be a key sequence--when calling from a program,
 527 pass a string or a vector.
 528 If non-nil UNTRANSLATED is a vector of the untranslated events.
 529 It can also be a number in which case the untranslated events from
 530 the last key hit are used."
 531   (interactive "kDescribe key: \np")
 532   (if (numberp untranslated)
 533       (setq untranslated (this-single-command-raw-keys)))
 534   (save-excursion
 535     (let ((modifiers (event-modifiers (aref key 0)))
 536           window position)
 537       ;; For a mouse button event, go to the button it applies to
 538       ;; to get the right key bindings.  And go to the right place
 539       ;; in case the keymap depends on where you clicked.
 540       (if (or (memq 'click modifiers) (memq 'down modifiers)
 541               (memq 'drag modifiers))
 542           (setq window (posn-window (event-start (aref key 0)))
 543                 position (posn-point (event-start (aref key 0)))))
 544       (when (windowp window)
 545             (set-buffer (window-buffer window))
 546         (goto-char position))
 547       (let ((defn (or (string-key-binding key) (key-binding key))))
 548         (if (or (null defn) (integerp defn) (equal defn 'undefined))
 549             (message "%s is undefined" (help-key-description key untranslated))
 550           (help-setup-xref (list #'describe-function defn) (interactive-p))
 551           (with-output-to-temp-buffer (help-buffer)
 552             (princ (help-key-description key untranslated))
 553             (if (windowp window)
 554                 (princ " at that spot"))
 555             (princ " runs the command ")
 556             (prin1 defn)
 557             (princ "\n   which is ")
 558             (describe-function-1 defn)
 559             (print-help-return-message)))))))
 560
 561 \f
 562 (defun describe-mode (&optional buffer)
 563   "Display documentation of current major mode and minor modes.
 564 The major mode description comes first, followed by the minor modes,
 565 each on a separate page.
 566 For this to work correctly for a minor mode, the mode's indicator variable
 567 \(listed in `minor-mode-alist') must also be a function whose documentation
 568 describes the minor mode."
 569   (interactive)
 570   (help-setup-xref (list #'describe-mode (or buffer (current-buffer)))
 571                    (interactive-p))
 572   ;; For the sake of help-do-xref and help-xref-go-back,
 573   ;; don't switch buffers before calling `help-buffer'.
 574   (with-output-to-temp-buffer (help-buffer)
 575     (save-excursion
 576       (when buffer (set-buffer buffer))
 577       (when minor-mode-alist
 578         (princ "The major mode is described first.
 579 For minor modes, see following pages.\n\n"))
 580       (princ mode-name)
 581       (princ " mode:\n")
 582       (princ (documentation major-mode))
 583       (let ((minor-modes minor-mode-alist))
 584         (while minor-modes
 585           (let* ((minor-mode (car (car minor-modes)))
 586                  (indicator (car (cdr (car minor-modes)))))
 587             ;; Document a minor mode if it is listed in minor-mode-alist,
 588             ;; bound locally in this buffer, non-nil, and has a function
 589             ;; definition.
 590             (if (and (boundp minor-mode)
 591                      (symbol-value minor-mode)
 592                      (fboundp minor-mode))
 593                 (let ((pretty-minor-mode minor-mode))
 594                   (if (string-match "\\(-minor\\)?-mode\\'"
 595                                     (symbol-name minor-mode))
 596                       (setq pretty-minor-mode
 597                             (capitalize
 598                              (substring (symbol-name minor-mode)
 599                                         0 (match-beginning 0)))))
 600                   (while (and indicator (symbolp indicator)
 601                               (boundp indicator)
 602                               (not (eq indicator (symbol-value indicator))))
 603                     (setq indicator (symbol-value indicator)))
 604                   (princ "\n\f\n")
 605                   (princ (format "%s minor mode (%s):\n"
 606                                  pretty-minor-mode
 607                                  (if indicator
 608                                      (format "indicator%s" indicator)
 609                                    "no indicator")))
 610                   (princ (documentation minor-mode)))))
 611           (setq minor-modes (cdr minor-modes))))
 612       (print-help-return-message))))
 613
 614 (defun describe-minor-mode (minor-mode)
 615   "Display documentation of a minor mode given as MINOR-MODE."
 616   (interactive (list (intern (completing-read
 617                               "Minor mode: "
 618                               (delete nil (mapcar
 619                                            (function (lambda (x)
 620                                                        (if (eval (car x))
 621                                                            (symbol-name (car x)))))
 622                                            minor-mode-alist))))))
 623   (if (fboundp minor-mode)
 624       (describe-function minor-mode)
 625     (describe-variable minor-mode)))
 626
 627 (defun describe-minor-mode-from-indicator (indicator)
 628   "Display documentation of a minor mode specified by INDICATOR."
 629   (interactive (list
 630                 (completing-read
 631                  "Minor mode indicator: "
 632                  (delete nil
 633                          (mapcar
 634                           #'(lambda (x)
 635                               (if (eval (car x))
 636                                   (let ((i (expand-minor-mode-indicator-object (cadr x))))
 637                                     (if (and (< 0 (length i))
 638                                              (string= " " (substring i 0 1)))
 639                                         (substring i 1)
 640                                       i))))
 641                           minor-mode-alist)))))
 642   (let ((minor-mode (lookup-minor-mode-from-indicator indicator)))
 643     (if minor-mode
 644         (describe-minor-mode minor-mode)
 645       (error "Cannot find minor mode for `%s'" indicator))))
 646
 647 (defun lookup-minor-mode-from-indicator (indicator)
 648   "Return a minor mode symbol from its indicator on the modeline."
 649   (if (and (< 0 (length indicator))
 650            (not (string= " " (substring indicator 0 1))))
 651       (setq indicator (concat " " indicator)))
 652   (let ((minor-modes minor-mode-alist)
 653         result)
 654     (while minor-modes
 655       (let* ((minor-mode (car (car minor-modes)))
 656              (anindicator (car (cdr (car minor-modes)))))
 657         (setq anindicator (expand-minor-mode-indicator-object anindicator))
 658         (if (and (stringp anindicator)
 659                  (string= anindicator indicator))
 660             (setq result minor-mode
 661                   minor-modes nil)
 662           (setq minor-modes (cdr minor-modes)))))
 663     result))
 664
 665 (defun expand-minor-mode-indicator-object (obj)
 666   "Expand OBJ that represents a minor-mode indicator.
 667 cdr part of a `minor-mode-alist' element(indicator object) is the
 668 indicator of minor mode that is in car part.  Normally indicator
 669 object is a string. However, in some case it is more compound object
 670 like cons cell. This function tries to make the compound object a string."
 671   ;; copied from describe-mode
 672   (while (and obj (symbolp obj)
 673               (boundp obj)
 674               (not (eq obj (symbol-value obj))))
 675     (setq obj (symbol-value obj)))
 676   (when (and (consp obj)
 677              (keywordp (car obj))
 678              (eq :eval (car obj)))
 679     (setq obj (eval (cadr obj))))
 680   obj)
 681
 682 \f
 683 ;;; Automatic resizing of temporary buffers.
 684
 685 (defcustom temp-buffer-max-height (lambda (buffer) (/ (- (frame-height) 2) 2))
 686   "*Maximum height of a window displaying a temporary buffer.
 687 This is the maximum height (in text lines) which `resize-temp-buffer-window'
 688 will give to a window displaying a temporary buffer.
 689 It can also be a function which will be called with the object corresponding
 690 to the buffer to be displayed as argument and should return an integer
 691 positive number."
 692   :type '(choice integer function)
 693   :group 'help
 694   :version "20.4")
 695
 696 (define-minor-mode temp-buffer-resize-mode
 697   "Toggle the mode which makes windows smaller for temporary buffers.
 698 With prefix argument ARG, turn the resizing of windows displaying temporary
 699 buffers on if ARG is positive or off otherwise.
 700 This makes the window the right height for its contents, but never
 701 more than `temp-buffer-max-height' nor less than `window-min-height'.
 702 This applies to `help', `apropos' and `completion' buffers, and some others."
 703   :global t :group 'help
 704   (if temp-buffer-resize-mode
 705       ;; `help-make-xrefs' may add a `back' button and thus increase the
 706       ;; text size, so `resize-temp-buffer-window' must be run *after* it.
 707       (add-hook 'temp-buffer-show-hook 'resize-temp-buffer-window 'append)
 708     (remove-hook 'temp-buffer-show-hook 'resize-temp-buffer-window)))
 709
 710 (defun resize-temp-buffer-window ()
 711   "Resize the current window to fit its contents.
 712 Will not make it higher than `temp-buffer-max-height' nor smaller than
 713 `window-min-height'.  Do nothing if it is the only window on its frame, if it
 714 is not as wide as the frame or if some of the window's contents are scrolled
 715 out of view."
 716   (unless (or (one-window-p 'nomini)
 717               (not (pos-visible-in-window-p (point-min)))
 718               (/=  (frame-width) (window-width)))
 719     (fit-window-to-buffer
 720      (selected-window)
 721      (if (functionp temp-buffer-max-height)
 722          (funcall temp-buffer-max-height (current-buffer))
 723        temp-buffer-max-height))))
 724
 725 ;; Provide this for the sake of define-minor-mode which generates
 726 ;; defcustoms which require 'help'.
 727 (provide 'help)
 728
 729 ;;; help.el ends here