lisp/help.el

   1 ;;; help.el --- help commands for Emacs
   2
   3 ;; Copyright (C) 1985-1986, 1993-1994, 1998-2012 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: FSF
   6 ;; Keywords: help, internal
   7 ;; Package: emacs
   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 3 of the License, or
  14 ;; (at your option) 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.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; This code implements GNU Emacs's on-line help system, the one invoked by
  27 ;; `M-x help-for-help'.
  28
  29 ;;; Code:
  30
  31 ;; Get the macro make-help-screen when this is compiled,
  32 ;; or run interpreted, but not when the compiled code is loaded.
  33 (eval-when-compile (require 'help-macro))
  34
  35 ;; This makes `with-output-to-temp-buffer' buffers use `help-mode'.
  36 (add-hook 'temp-buffer-setup-hook 'help-mode-setup)
  37 (add-hook 'temp-buffer-show-hook 'help-mode-finish)
  38
  39 ;; `help-window-point-marker' is a marker you can move to a valid
  40 ;; position of the buffer shown in the help window in order to override
  41 ;; the standard positioning mechanism (`point-min') chosen by
  42 ;; `with-output-to-temp-buffer'.  `with-help-window' has this point
  43 ;; nowhere before exiting.  Currently used by `view-lossage' to assert
  44 ;; that the last keystrokes are always visible.
  45 (defvar help-window-point-marker (make-marker)
  46   "Marker to override default `window-point' in help windows.")
  47
  48 (defvar help-map
  49   (let ((map (make-sparse-keymap)))
  50     (define-key map (char-to-string help-char) 'help-for-help)
  51     (define-key map [help] 'help-for-help)
  52     (define-key map [f1] 'help-for-help)
  53     (define-key map "." 'display-local-help)
  54     (define-key map "?" 'help-for-help)
  55
  56     (define-key map "\C-a" 'about-emacs)
  57     (define-key map "\C-c" 'describe-copying)
  58     (define-key map "\C-d" 'view-emacs-debugging)
  59     (define-key map "\C-e" 'view-external-packages)
  60     (define-key map "\C-f" 'view-emacs-FAQ)
  61     (define-key map "\C-m" 'view-order-manuals)
  62     (define-key map "\C-n" 'view-emacs-news)
  63     (define-key map "\C-o" 'describe-distribution)
  64     (define-key map "\C-p" 'view-emacs-problems)
  65     (define-key map "\C-t" 'view-emacs-todo)
  66     (define-key map "\C-w" 'describe-no-warranty)
  67
  68     ;; This does not fit the pattern, but it is natural given the C-\ command.
  69     (define-key map "\C-\\" 'describe-input-method)
  70
  71     (define-key map "C" 'describe-coding-system)
  72     (define-key map "F" 'Info-goto-emacs-command-node)
  73     (define-key map "I" 'describe-input-method)
  74     (define-key map "K" 'Info-goto-emacs-key-command-node)
  75     (define-key map "L" 'describe-language-environment)
  76     (define-key map "S" 'info-lookup-symbol)
  77
  78     (define-key map "a" 'apropos-command)
  79     (define-key map "b" 'describe-bindings)
  80     (define-key map "c" 'describe-key-briefly)
  81     (define-key map "d" 'apropos-documentation)
  82     (define-key map "e" 'view-echo-area-messages)
  83     (define-key map "f" 'describe-function)
  84     (define-key map "g" 'describe-gnu-project)
  85     (define-key map "h" 'view-hello-file)
  86
  87     (define-key map "i" 'info)
  88     (define-key map "4i" 'info-other-window)
  89
  90     (define-key map "k" 'describe-key)
  91     (define-key map "l" 'view-lossage)
  92     (define-key map "m" 'describe-mode)
  93     (define-key map "n" 'view-emacs-news)
  94     (define-key map "p" 'finder-by-keyword)
  95     (define-key map "P" 'describe-package)
  96     (define-key map "r" 'info-emacs-manual)
  97     (define-key map "s" 'describe-syntax)
  98     (define-key map "t" 'help-with-tutorial)
  99     (define-key map "w" 'where-is)
 100     (define-key map "v" 'describe-variable)
 101     (define-key map "q" 'help-quit)
 102     map)
 103   "Keymap for characters following the Help key.")
 104
 105 (define-key global-map (char-to-string help-char) 'help-command)
 106 (define-key global-map [help] 'help-command)
 107 (define-key global-map [f1] 'help-command)
 108 (fset 'help-command help-map)
 109
 110 ;; insert-button makes the action nil if it is not store somewhere
 111 (defvar help-button-cache nil)
 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 (and possibly its frame,
 123                            see `quit-window'), go to WINDOW.
 124  (WINDOW . quit-window)    do quit-window, then select WINDOW.
 125  (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")
 126
 127 (define-obsolete-function-alias 'print-help-return-message 'help-print-return-message "23.2")
 128 (defun help-print-return-message (&optional function)
 129   "Display or return message saying how to restore windows after help command.
 130 This function assumes that `standard-output' is the help buffer.
 131 It computes a message, and applies the optional argument FUNCTION to it.
 132 If FUNCTION is nil, it applies `message', thus displaying the message.
 133 In addition, this function sets up `help-return-method', which see, that
 134 specifies what to do when the user exits the help buffer."
 135   (and (not (get-buffer-window standard-output))
 136        (let ((first-message
 137               (cond ((or
 138                       pop-up-frames
 139                       (special-display-p (buffer-name standard-output)))
 140                      (setq help-return-method (cons (selected-window) t))
 141                      ;; If the help output buffer is a special display buffer,
 142                      ;; don't say anything about how to get rid of it.
 143                      ;; First of all, the user will do that with the window
 144                      ;; manager, not with Emacs.
 145                      ;; Secondly, the buffer has not been displayed yet,
 146                      ;; so we don't know whether its frame will be selected.
 147                      nil)
 148                     ((not (one-window-p t))
 149                      (setq help-return-method
 150                            (cons (selected-window) 'quit-window))
 151                      "Type \\[display-buffer] RET to restore the other window.")
 152                     (pop-up-windows
 153                      (setq help-return-method (cons (selected-window) t))
 154                      "Type \\[delete-other-windows] to remove help window.")
 155                     (t
 156                      (setq help-return-method
 157                            (list (selected-window) (window-buffer)
 158                                  (window-start) (window-point)))
 159                      "Type \\[switch-to-buffer] RET to remove help window."))))
 160          (funcall (or function 'message)
 161                   (concat
 162                    (if first-message
 163                        (substitute-command-keys first-message))
 164                    (if first-message "  ")
 165                    ;; If the help buffer will go in a separate frame,
 166                    ;; it's no use mentioning a command to scroll, so don't.
 167                    (if (or pop-up-windows
 168                            (special-display-p (buffer-name standard-output)))
 169                        nil
 170                      (if (same-window-p (buffer-name standard-output))
 171                          ;; Say how to scroll this window.
 172                          (substitute-command-keys
 173                           "\\[scroll-up] to scroll the help.")
 174                        ;; Say how to scroll some other window.
 175                        (substitute-command-keys
 176                         "\\[scroll-other-window] to scroll the help."))))))))
 177
 178 ;; So keyboard macro definitions are documented correctly
 179 (fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))
 180
 181 (defalias 'help 'help-for-help-internal)
 182 ;; find-function can find this.
 183 (defalias 'help-for-help 'help-for-help-internal)
 184 ;; It can't find this, but nobody will look.
 185 (make-help-screen help-for-help-internal
 186   (purecopy "Type a help option: [abcCdefFgiIkKlLmnprstvw.] C-[cdefmnoptw] or ?")
 187   ;; Don't purecopy this one, because it's not evaluated (it's
 188   ;; directly used as a docstring in a function definition, so it'll
 189   ;; be moved to the DOC file anyway: no need for purecopying it).
 190   "You have typed %THIS-KEY%, the help character.  Type a Help option:
 191 \(Use SPC or DEL to scroll through this text.  Type \\<help-map>\\[help-quit] to exit the Help command.)
 192
 193 a PATTERN   Show commands whose name matches the PATTERN (a list of words
 194               or a regexp).  See also the `apropos' command.
 195 b           Display all key bindings.
 196 c KEYS      Display the command name run by the given key sequence.
 197 C CODING    Describe the given coding system, or RET for current ones.
 198 d PATTERN   Show a list of functions, variables, and other items whose
 199               documentation matches the PATTERN (a list of words or a regexp).
 200 e           Go to the *Messages* buffer which logs echo-area messages.
 201 f FUNCTION  Display documentation for the given function.
 202 F COMMAND   Show the on-line manual's section that describes the command.
 203 g           Display information about the GNU project.
 204 h           Display the HELLO file which illustrates various scripts.
 205 i           Start the Info documentation reader: read on-line manuals.
 206 I METHOD    Describe a specific input method, or RET for current.
 207 k KEYS      Display the full documentation for the key sequence.
 208 K KEYS      Show the on-line manual's section for the command bound to KEYS.
 209 l           Show last 300 input keystrokes (lossage).
 210 L LANG-ENV  Describes a specific language environment, or RET for current.
 211 m           Display documentation of current minor modes and current major mode,
 212               including their special commands.
 213 n           Display news of recent Emacs changes.
 214 p TOPIC     Find packages matching a given topic keyword.
 215 r           Display the Emacs manual in Info mode.
 216 s           Display contents of current syntax table, plus explanations.
 217 S SYMBOL    Show the section for the given symbol in the on-line manual
 218               for the programming language used in this buffer.
 219 t           Start the Emacs learn-by-doing tutorial.
 220 v VARIABLE  Display the given variable's documentation and value.
 221 w COMMAND   Display which keystrokes invoke the given command (where-is).
 222 .           Display any available local help at point in the echo area.
 223
 224 C-a         Information about Emacs.
 225 C-c         Emacs copying permission (GNU General Public License).
 226 C-d         Instructions for debugging GNU Emacs.
 227 C-e         External packages and information about Emacs.
 228 C-f         Emacs FAQ.
 229 C-m         How to order printed Emacs manuals.
 230 C-n         News of recent Emacs changes.
 231 C-o         Emacs ordering and distribution information.
 232 C-p         Info about known Emacs problems.
 233 C-t         Emacs TODO list.
 234 C-w         Information on absence of warranty for GNU Emacs."
 235   help-map)
 236
 237 \f
 238
 239 (defun function-called-at-point ()
 240   "Return a function around point or else called by the list containing point.
 241 If that doesn't give a function, return nil."
 242   (with-syntax-table emacs-lisp-mode-syntax-table
 243     (or (condition-case ()
 244             (save-excursion
 245               (or (not (zerop (skip-syntax-backward "_w")))
 246                   (eq (char-syntax (following-char)) ?w)
 247                   (eq (char-syntax (following-char)) ?_)
 248                   (forward-sexp -1))
 249               (skip-chars-forward "'")
 250               (let ((obj (read (current-buffer))))
 251                 (and (symbolp obj) (fboundp obj) obj)))
 252           (error nil))
 253         (condition-case ()
 254             (save-excursion
 255               (save-restriction
 256                 (narrow-to-region (max (point-min)
 257                                        (- (point) 1000)) (point-max))
 258                 ;; Move up to surrounding paren, then after the open.
 259                 (backward-up-list 1)
 260                 (forward-char 1)
 261                 ;; If there is space here, this is probably something
 262                 ;; other than a real Lisp function call, so ignore it.
 263                 (if (looking-at "[ \t]")
 264                     (error "Probably not a Lisp function call"))
 265                 (let ((obj (read (current-buffer))))
 266                   (and (symbolp obj) (fboundp obj) obj))))
 267           (error nil))
 268         (let* ((str (find-tag-default))
 269                (sym (if str (intern-soft str))))
 270           (if (and sym (fboundp sym))
 271               sym
 272             (save-match-data
 273               (when (and str (string-match "\\`\\W*\\(.*?\\)\\W*\\'" str))
 274                 (setq sym (intern-soft (match-string 1 str)))
 275                 (and (fboundp sym) sym))))))))
 276
 277 \f
 278 ;;; `User' help functions
 279
 280 (defun view-help-file (file &optional dir)
 281   (view-file (expand-file-name file (or dir data-directory)))
 282   (goto-address-mode 1)
 283   (goto-char (point-min)))
 284
 285 (defun describe-distribution ()
 286   "Display info on how to obtain the latest version of GNU Emacs."
 287   (interactive)
 288   (view-help-file "DISTRIB"))
 289
 290 (defun describe-copying ()
 291   "Display info on how you may redistribute copies of GNU Emacs."
 292   (interactive)
 293   (view-help-file "COPYING"))
 294
 295 (defun describe-gnu-project ()
 296   "Display info on the GNU project."
 297   (interactive)
 298   (view-help-file "THE-GNU-PROJECT"))
 299
 300 (define-obsolete-function-alias 'describe-project 'describe-gnu-project "22.2")
 301
 302 (defun describe-no-warranty ()
 303   "Display info on all the kinds of warranty Emacs does NOT have."
 304   (interactive)
 305   (describe-copying)
 306   (let (case-fold-search)
 307     (search-forward "Disclaimer of Warranty")
 308     (forward-line 0)
 309     (recenter 0)))
 310
 311 (defun describe-prefix-bindings ()
 312   "Describe the bindings of the prefix used to reach this command.
 313 The prefix described consists of all but the last event
 314 of the key sequence that ran this command."
 315   (interactive)
 316   (let ((key (this-command-keys)))
 317     (describe-bindings
 318      (if (stringp key)
 319          (substring key 0 (1- (length key)))
 320        (let ((prefix (make-vector (1- (length key)) nil))
 321              (i 0))
 322          (while (< i (length prefix))
 323            (aset prefix i (aref key i))
 324            (setq i (1+ i)))
 325          prefix)))))
 326 ;; Make C-h after a prefix, when not specifically bound,
 327 ;; run describe-prefix-bindings.
 328 (setq prefix-help-command 'describe-prefix-bindings)
 329
 330 (defun view-emacs-news (&optional version)
 331   "Display info on recent changes to Emacs.
 332 With argument, display info only for the selected version."
 333   (interactive "P")
 334   (unless version
 335     (setq version emacs-major-version))
 336   (when (consp version)
 337     (let* ((all-versions
 338             (let (res)
 339               (mapc
 340                (lambda (file)
 341                  (with-temp-buffer
 342                    (insert-file-contents
 343                     (expand-file-name file data-directory))
 344                    (while (re-search-forward
 345                            (if (member file '("NEWS.18" "NEWS.1-17"))
 346                                "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
 347                              "^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t)
 348                      (setq res (cons (match-string-no-properties 1) res)))))
 349                (cons "NEWS"
 350                      (directory-files data-directory nil
 351                                       "^NEWS\\.[0-9][-0-9]*$" nil)))
 352               (sort (delete-dups res) (lambda (a b) (string< b a)))))
 353            (current (car all-versions)))
 354       (setq version (completing-read
 355                      (format "Read NEWS for the version (default %s): " current)
 356                      all-versions nil nil nil nil current))
 357       (if (integerp (string-to-number version))
 358           (setq version (string-to-number version))
 359         (unless (or (member version all-versions)
 360                     (<= (string-to-number version) (string-to-number current)))
 361           (error "No news about version %s" version)))))
 362   (when (integerp version)
 363     (cond ((<= version 12)
 364            (setq version (format "1.%d" version)))
 365           ((<= version 18)
 366            (setq version (format "%d" version)))
 367           ((> version emacs-major-version)
 368            (error "No news about Emacs %d (yet)" version))))
 369   (let* ((vn (if (stringp version)
 370                  (string-to-number version)
 371                version))
 372          (file (cond
 373                 ((>= vn emacs-major-version) "NEWS")
 374                 ((< vn 18) "NEWS.1-17")
 375                 (t (format "NEWS.%d" vn))))
 376          res)
 377     (view-file (expand-file-name file data-directory))
 378     (widen)
 379     (goto-char (point-min))
 380     (when (stringp version)
 381       (when (re-search-forward
 382              (concat (if (< vn 19)
 383                          "Changes in Emacs[ \t]*"
 384                        "^\* [^0-9\n]*") version "$")
 385              nil t)
 386         (beginning-of-line)
 387         (narrow-to-region
 388          (point)
 389          (save-excursion
 390            (while (and (setq res
 391                              (re-search-forward
 392                               (if (< vn 19)
 393                                   "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
 394                                 "^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t))
 395                        (equal (match-string-no-properties 1) version)))
 396            (or res (goto-char (point-max)))
 397            (beginning-of-line)
 398            (point)))))))
 399
 400 (defun view-emacs-todo (&optional _arg)
 401   "Display the Emacs TODO list."
 402   (interactive "P")
 403   (view-help-file "TODO"))
 404
 405 (define-obsolete-function-alias 'view-todo 'view-emacs-todo "22.2")
 406
 407
 408 (defun view-echo-area-messages ()
 409   "View the log of recent echo-area messages: the `*Messages*' buffer.
 410 The number of messages retained in that buffer
 411 is specified by the variable `message-log-max'."
 412   (interactive)
 413   (switch-to-buffer (get-buffer-create "*Messages*")))
 414
 415 (defun view-order-manuals ()
 416   "Display the Emacs ORDERS file."
 417   (interactive)
 418   (view-help-file "ORDERS"))
 419
 420 (defun view-emacs-FAQ ()
 421   "Display the Emacs Frequently Asked Questions (FAQ) file."
 422   (interactive)
 423   ;; (find-file-read-only (expand-file-name "FAQ" data-directory))
 424   (info "(efaq)"))
 425
 426 (defun view-emacs-problems ()
 427   "Display info on known problems with Emacs and possible workarounds."
 428   (interactive)
 429   (view-help-file "PROBLEMS"))
 430
 431 (defun view-emacs-debugging ()
 432   "Display info on how to debug Emacs problems."
 433   (interactive)
 434   (view-help-file "DEBUG"))
 435
 436 (defun view-external-packages ()
 437   "Display external packages and information about Emacs."
 438   (interactive)
 439   (view-help-file "MORE.STUFF"))
 440
 441 (defun view-lossage ()
 442   "Display last 300 input keystrokes.
 443
 444 To record all your input on a file, use `open-dribble-file'."
 445   (interactive)
 446   (help-setup-xref (list #'view-lossage)
 447                    (called-interactively-p 'interactive))
 448   (with-help-window (help-buffer)
 449     (princ (mapconcat (lambda (key)
 450                         (if (or (integerp key) (symbolp key) (listp key))
 451                             (single-key-description key)
 452                           (prin1-to-string key nil)))
 453                       (recent-keys)
 454                       " "))
 455     (with-current-buffer standard-output
 456       (goto-char (point-min))
 457       (while (progn (move-to-column 50) (not (eobp)))
 458         (when (search-forward " " nil t)
 459           (delete-char -1))
 460         (insert "\n"))
 461       ;; jidanni wants to see the last keystrokes immediately.
 462       (set-marker help-window-point-marker (point)))))
 463
 464 \f
 465 ;; Key bindings
 466
 467 (defun describe-bindings (&optional prefix buffer)
 468   "Show a list of all defined keys, and their definitions.
 469 We put that list in a buffer, and display the buffer.
 470
 471 The optional argument PREFIX, if non-nil, should be a key sequence;
 472 then we display only bindings that start with that prefix.
 473 The optional argument BUFFER specifies which buffer's bindings
 474 to display (default, the current buffer).  BUFFER can be a buffer
 475 or a buffer name."
 476   (interactive)
 477   (or buffer (setq buffer (current-buffer)))
 478   (help-setup-xref (list #'describe-bindings prefix buffer)
 479                    (called-interactively-p 'interactive))
 480   (with-current-buffer buffer
 481     (describe-bindings-internal nil prefix)))
 482
 483 ;; This function used to be in keymap.c.
 484 (defun describe-bindings-internal (&optional menus prefix)
 485   "Show a list of all defined keys, and their definitions.
 486 We put that list in a buffer, and display the buffer.
 487
 488 The optional argument MENUS, if non-nil, says to mention menu bindings.
 489 \(Ordinarily these are omitted from the output.)
 490 The optional argument PREFIX, if non-nil, should be a key sequence;
 491 then we display only bindings that start with that prefix."
 492   (let ((buf (current-buffer)))
 493     (with-help-window "*Help*"
 494       (with-current-buffer standard-output
 495         (describe-buffer-bindings buf prefix menus)))))
 496
 497 (defun where-is (definition &optional insert)
 498   "Print message listing key sequences that invoke the command DEFINITION.
 499 Argument is a command definition, usually a symbol with a function definition.
 500 If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
 501   (interactive
 502    (let ((fn (function-called-at-point))
 503          (enable-recursive-minibuffers t)
 504          val)
 505      (setq val (completing-read
 506                 (if fn
 507                     (format "Where is command (default %s): " fn)
 508                   "Where is command: ")
 509                 obarray 'commandp t))
 510      (list (if (equal val "") fn (intern val)) current-prefix-arg)))
 511   (unless definition (error "No command"))
 512   (let ((func (indirect-function definition))
 513         (defs nil)
 514         (standard-output (if insert (current-buffer) standard-output)))
 515     ;; In DEFS, find all symbols that are aliases for DEFINITION.
 516     (mapatoms (lambda (symbol)
 517                 (and (fboundp symbol)
 518                      (not (eq symbol definition))
 519                      (eq func (condition-case ()
 520                                   (indirect-function symbol)
 521                                 (error symbol)))
 522                      (push symbol defs))))
 523     ;; Look at all the symbols--first DEFINITION,
 524     ;; then its aliases.
 525     (dolist (symbol (cons definition defs))
 526       (let* ((remapped (command-remapping symbol))
 527              (keys (where-is-internal
 528                     symbol overriding-local-map nil nil remapped))
 529              (keys (mapconcat 'key-description keys ", "))
 530              string)
 531         (setq string
 532               (if insert
 533                   (if (> (length keys) 0)
 534                       (if remapped
 535                           (format "%s (%s) (remapped from %s)"
 536                                   keys remapped symbol)
 537                         (format "%s (%s)" keys symbol))
 538                     (format "M-x %s RET" symbol))
 539                 (if (> (length keys) 0)
 540                     (if remapped
 541                         (format "%s is remapped to %s which is on %s"
 542                                 symbol remapped keys)
 543                       (format "%s is on %s" symbol keys))
 544                   ;; If this is the command the user asked about,
 545                   ;; and it is not on any key, say so.
 546                   ;; For other symbols, its aliases, say nothing
 547                   ;; about them unless they are on keys.
 548                   (if (eq symbol definition)
 549                       (format "%s is not on any key" symbol)))))
 550         (when string
 551           (unless (eq symbol definition)
 552             (princ ";\n its alias "))
 553           (princ string)))))
 554   nil)
 555
 556 (defun help-key-description (key untranslated)
 557   (let ((string (key-description key)))
 558     (if (or (not untranslated)
 559             (and (eq (aref untranslated 0) ?\e) (not (eq (aref key 0) ?\e))))
 560         string
 561       (let ((otherstring (key-description untranslated)))
 562         (if (equal string otherstring)
 563             string
 564           (format "%s (translated from %s)" string otherstring))))))
 565
 566 (defun describe-key-briefly (&optional key insert untranslated)
 567   "Print the name of the function KEY invokes.  KEY is a string.
 568 If INSERT (the prefix arg) is non-nil, insert the message in the buffer.
 569 If non-nil, UNTRANSLATED is a vector of the untranslated events.
 570 It can also be a number in which case the untranslated events from
 571 the last key hit are used.
 572
 573 If KEY is a menu item or a tool-bar button that is disabled, this command
 574 temporarily enables it to allow getting help on disabled items and buttons."
 575   (interactive
 576    (let ((enable-disabled-menus-and-buttons t)
 577          (cursor-in-echo-area t)
 578          saved-yank-menu)
 579      (unwind-protect
 580          (let (key)
 581            ;; If yank-menu is empty, populate it temporarily, so that
 582            ;; "Select and Paste" menu can generate a complete event.
 583            (when (null (cdr yank-menu))
 584              (setq saved-yank-menu (copy-sequence yank-menu))
 585              (menu-bar-update-yank-menu "(any string)" nil))
 586            (setq key (read-key-sequence "Describe key (or click or menu item): "))
 587            ;; If KEY is a down-event, read and discard the
 588            ;; corresponding up-event.  Note that there are also
 589            ;; down-events on scroll bars and mode lines: the actual
 590            ;; event then is in the second element of the vector.
 591            (and (vectorp key)
 592                 (let ((last-idx (1- (length key))))
 593                   (and (eventp (aref key last-idx))
 594                        (memq 'down (event-modifiers (aref key last-idx)))))
 595                 (read-event))
 596            (list
 597             key
 598             (if current-prefix-arg (prefix-numeric-value current-prefix-arg))
 599             1))
 600        ;; Put yank-menu back as it was, if we changed it.
 601        (when saved-yank-menu
 602          (setq yank-menu (copy-sequence saved-yank-menu))
 603          (fset 'yank-menu (cons 'keymap yank-menu))))))
 604   (if (numberp untranslated)
 605       (setq untranslated (this-single-command-raw-keys)))
 606   (let* ((event (if (and (symbolp (aref key 0))
 607                          (> (length key) 1)
 608                          (consp (aref key 1)))
 609                     (aref key 1)
 610                   (aref key 0)))
 611          (modifiers (event-modifiers event))
 612          (standard-output (if insert (current-buffer) standard-output))
 613          (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
 614                             (memq 'drag modifiers)) " at that spot" ""))
 615          (defn (key-binding key t))
 616          key-desc)
 617     ;; Handle the case where we faked an entry in "Select and Paste" menu.
 618     (if (and (eq defn nil)
 619              (stringp (aref key (1- (length key))))
 620              (eq (key-binding (substring key 0 -1)) 'yank-menu))
 621         (setq defn 'menu-bar-select-yank))
 622     ;; Don't bother user with strings from (e.g.) the select-paste menu.
 623     (if (stringp (aref key (1- (length key))))
 624         (aset key (1- (length key)) "(any string)"))
 625     (if (and (> (length untranslated) 0)
 626              (stringp (aref untranslated (1- (length untranslated)))))
 627         (aset untranslated (1- (length untranslated)) "(any string)"))
 628     ;; Now describe the key, perhaps as changed.
 629     (setq key-desc (help-key-description key untranslated))
 630     (if (or (null defn) (integerp defn) (equal defn 'undefined))
 631         (princ (format "%s%s is undefined" key-desc mouse-msg))
 632       (princ (format "%s%s runs the command %S" key-desc mouse-msg defn)))))
 633
 634 (defun describe-key (&optional key untranslated up-event)
 635   "Display documentation of the function invoked by KEY.
 636 KEY can be any kind of a key sequence; it can include keyboard events,
 637 mouse events, and/or menu events.  When calling from a program,
 638 pass KEY as a string or a vector.
 639
 640 If non-nil, UNTRANSLATED is a vector of the corresponding untranslated events.
 641 It can also be a number, in which case the untranslated events from
 642 the last key sequence entered are used.
 643 UP-EVENT is the up-event that was discarded by reading KEY, or nil.
 644
 645 If KEY is a menu item or a tool-bar button that is disabled, this command
 646 temporarily enables it to allow getting help on disabled items and buttons."
 647   (interactive
 648    (let ((enable-disabled-menus-and-buttons t)
 649          (cursor-in-echo-area t)
 650          saved-yank-menu)
 651      (unwind-protect
 652          (let (key)
 653            ;; If yank-menu is empty, populate it temporarily, so that
 654            ;; "Select and Paste" menu can generate a complete event.
 655            (when (null (cdr yank-menu))
 656              (setq saved-yank-menu (copy-sequence yank-menu))
 657              (menu-bar-update-yank-menu "(any string)" nil))
 658            (setq key (read-key-sequence "Describe key (or click or menu item): "))
 659            (list
 660             key
 661             (prefix-numeric-value current-prefix-arg)
 662             ;; If KEY is a down-event, read and include the
 663             ;; corresponding up-event.  Note that there are also
 664             ;; down-events on scroll bars and mode lines: the actual
 665             ;; event then is in the second element of the vector.
 666             (and (vectorp key)
 667                  (let ((last-idx (1- (length key))))
 668                    (and (eventp (aref key last-idx))
 669                         (memq 'down (event-modifiers (aref key last-idx)))))
 670                  (or (and (eventp (aref key 0))
 671                           (memq 'down (event-modifiers (aref key 0)))
 672                           ;; However, for the C-down-mouse-2 popup
 673                           ;; menu, there is no subsequent up-event.  In
 674                           ;; this case, the up-event is the next
 675                           ;; element in the supplied vector.
 676                           (= (length key) 1))
 677                      (and (> (length key) 1)
 678                           (eventp (aref key 1))
 679                           (memq 'down (event-modifiers (aref key 1)))))
 680                  (read-event))))
 681        ;; Put yank-menu back as it was, if we changed it.
 682        (when saved-yank-menu
 683          (setq yank-menu (copy-sequence saved-yank-menu))
 684          (fset 'yank-menu (cons 'keymap yank-menu))))))
 685   (if (numberp untranslated)
 686       (setq untranslated (this-single-command-raw-keys)))
 687   (let* ((event (aref key (if (and (symbolp (aref key 0))
 688                                    (> (length key) 1)
 689                                    (consp (aref key 1)))
 690                               1
 691                             0)))
 692          (modifiers (event-modifiers event))
 693          (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
 694                             (memq 'drag modifiers)) " at that spot" ""))
 695          (defn (key-binding key t))
 696          defn-up defn-up-tricky ev-type
 697          mouse-1-remapped mouse-1-tricky)
 698
 699     ;; Handle the case where we faked an entry in "Select and Paste" menu.
 700     (when (and (eq defn nil)
 701                (stringp (aref key (1- (length key))))
 702                (eq (key-binding (substring key 0 -1)) 'yank-menu))
 703       (setq defn 'menu-bar-select-yank))
 704     (if (or (null defn) (integerp defn) (equal defn 'undefined))
 705         (message "%s%s is undefined"
 706                  (help-key-description key untranslated) mouse-msg)
 707       (help-setup-xref (list #'describe-function defn)
 708                        (called-interactively-p 'interactive))
 709       ;; Don't bother user with strings from (e.g.) the select-paste menu.
 710       (when (stringp (aref key (1- (length key))))
 711         (aset key (1- (length key)) "(any string)"))
 712       (when (and untranslated
 713                  (stringp (aref untranslated (1- (length untranslated)))))
 714         (aset untranslated (1- (length untranslated))
 715               "(any string)"))
 716       ;; Need to do this before erasing *Help* buffer in case event
 717       ;; is a mouse click in an existing *Help* buffer.
 718       (when up-event
 719         (setq ev-type (event-basic-type up-event))
 720         (let ((sequence (vector up-event)))
 721           (when (and (eq ev-type 'mouse-1)
 722                      mouse-1-click-follows-link
 723                      (not (eq mouse-1-click-follows-link 'double))
 724                      (setq mouse-1-remapped
 725                            (mouse-on-link-p (event-start up-event))))
 726             (setq mouse-1-tricky (and (integerp mouse-1-click-follows-link)
 727                                       (> mouse-1-click-follows-link 0)))
 728             (cond ((stringp mouse-1-remapped)
 729                    (setq sequence mouse-1-remapped))
 730                   ((vectorp mouse-1-remapped)
 731                    (setcar up-event (elt mouse-1-remapped 0)))
 732                   (t (setcar up-event 'mouse-2))))
 733           (setq defn-up (key-binding sequence nil nil (event-start up-event)))
 734           (when mouse-1-tricky
 735             (setq sequence (vector up-event))
 736             (aset sequence 0 'mouse-1)
 737             (setq defn-up-tricky (key-binding sequence nil nil (event-start up-event))))))
 738       (with-help-window (help-buffer)
 739         (princ (help-key-description key untranslated))
 740         (princ (format "\
 741 %s runs the command %S, which is "
 742                        mouse-msg defn))
 743         (describe-function-1 defn)
 744         (when up-event
 745           (unless (or (null defn-up)
 746                       (integerp defn-up)
 747                       (equal defn-up 'undefined))
 748             (princ (format "
 749
 750 ----------------- up-event %s----------------
 751
 752 %s%s%s runs the command %S, which is "
 753                            (if mouse-1-tricky "(short click) " "")
 754                            (key-description (vector up-event))
 755                            mouse-msg
 756                            (if mouse-1-remapped
 757                                " is remapped to <mouse-2>, which" "")
 758                            defn-up))
 759             (describe-function-1 defn-up))
 760           (unless (or (null defn-up-tricky)
 761                       (integerp defn-up-tricky)
 762                       (eq defn-up-tricky 'undefined))
 763             (princ (format "
 764
 765 ----------------- up-event (long click) ----------------
 766
 767 Pressing <%S>%s for longer than %d milli-seconds
 768 runs the command %S, which is "
 769                            ev-type mouse-msg
 770                            mouse-1-click-follows-link
 771                            defn-up-tricky))
 772             (describe-function-1 defn-up-tricky)))))))
 773 \f
 774 (defun describe-mode (&optional buffer)
 775   "Display documentation of current major mode and minor modes.
 776 A brief summary of the minor modes comes first, followed by the
 777 major mode description.  This is followed by detailed
 778 descriptions of the minor modes, each on a separate page.
 779
 780 For this to work correctly for a minor mode, the mode's indicator
 781 variable \(listed in `minor-mode-alist') must also be a function
 782 whose documentation describes the minor mode.
 783
 784 If called from Lisp with a non-nil BUFFER argument, display
 785 documentation for the major and minor modes of that buffer."
 786   (interactive "@")
 787   (unless buffer (setq buffer (current-buffer)))
 788   (help-setup-xref (list #'describe-mode buffer)
 789                    (called-interactively-p 'interactive))
 790   ;; For the sake of help-do-xref and help-xref-go-back,
 791   ;; don't switch buffers before calling `help-buffer'.
 792   (with-help-window (help-buffer)
 793     (with-current-buffer buffer
 794       (let (minor-modes)
 795         ;; Older packages do not register in minor-mode-list but only in
 796         ;; minor-mode-alist.
 797         (dolist (x minor-mode-alist)
 798           (setq x (car x))
 799           (unless (memq x minor-mode-list)
 800             (push x minor-mode-list)))
 801         ;; Find enabled minor mode we will want to mention.
 802         (dolist (mode minor-mode-list)
 803           ;; Document a minor mode if it is listed in minor-mode-alist,
 804           ;; non-nil, and has a function definition.
 805           (let ((fmode (or (get mode :minor-mode-function) mode)))
 806             (and (boundp mode) (symbol-value mode)
 807                  (fboundp fmode)
 808                  (let ((pretty-minor-mode
 809                         (if (string-match "\\(\\(-minor\\)?-mode\\)?\\'"
 810                                           (symbol-name fmode))
 811                             (capitalize
 812                              (substring (symbol-name fmode)
 813                                         0 (match-beginning 0)))
 814                           fmode)))
 815                    (push (list fmode pretty-minor-mode
 816                                (format-mode-line (assq mode minor-mode-alist)))
 817                          minor-modes)))))
 818         (setq minor-modes
 819               (sort minor-modes
 820                     (lambda (a b) (string-lessp (cadr a) (cadr b)))))
 821         (when minor-modes
 822           (princ "Enabled minor modes:\n")
 823           (make-local-variable 'help-button-cache)
 824           (with-current-buffer standard-output
 825             (dolist (mode minor-modes)
 826               (let ((mode-function (nth 0 mode))
 827                     (pretty-minor-mode (nth 1 mode))
 828                     (indicator (nth 2 mode)))
 829                 (add-text-properties 0 (length pretty-minor-mode)
 830                                      '(face bold) pretty-minor-mode)
 831                 (save-excursion
 832                   (goto-char (point-max))
 833                   (princ "\n\f\n")
 834                   (push (point-marker) help-button-cache)
 835                   ;; Document the minor modes fully.
 836                   (insert pretty-minor-mode)
 837                   (princ (format " minor mode (%s):\n"
 838                                  (if (zerop (length indicator))
 839                                      "no indicator"
 840                                    (format "indicator%s"
 841                                            indicator))))
 842                   (princ (documentation mode-function)))
 843                 (insert-button pretty-minor-mode
 844                                'action (car help-button-cache)
 845                                'follow-link t
 846                                'help-echo "mouse-2, RET: show full information")
 847                 (newline)))
 848             (forward-line -1)
 849             (fill-paragraph nil)
 850             (forward-line 1))
 851
 852           (princ "\n(Information about these minor modes follows the major mode info.)\n\n"))
 853         ;; Document the major mode.
 854         (let ((mode mode-name))
 855           (with-current-buffer standard-output
 856             (let ((start (point)))
 857               (insert (format-mode-line mode nil nil buffer))
 858               (add-text-properties start (point) '(face bold)))))
 859         (princ " mode")
 860         (let* ((mode major-mode)
 861                (file-name (find-lisp-object-file-name mode nil)))
 862           (when file-name
 863             (princ (concat " defined in `" (file-name-nondirectory file-name) "'"))
 864             ;; Make a hyperlink to the library.
 865             (with-current-buffer standard-output
 866               (save-excursion
 867                 (re-search-backward "`\\([^`']+\\)'" nil t)
 868                 (help-xref-button 1 'help-function-def mode file-name)))))
 869         (princ ":\n")
 870         (princ (documentation major-mode)))))
 871   ;; For the sake of IELM and maybe others
 872   nil)
 873
 874
 875 (defun describe-minor-mode (minor-mode)
 876   "Display documentation of a minor mode given as MINOR-MODE.
 877 MINOR-MODE can be a minor mode symbol or a minor mode indicator string
 878 appeared on the mode-line."
 879   (interactive (list (completing-read
 880                       "Minor mode: "
 881                               (nconc
 882                                (describe-minor-mode-completion-table-for-symbol)
 883                                (describe-minor-mode-completion-table-for-indicator)
 884                                ))))
 885   (if (symbolp minor-mode)
 886       (setq minor-mode (symbol-name minor-mode)))
 887   (let ((symbols (describe-minor-mode-completion-table-for-symbol))
 888         (indicators (describe-minor-mode-completion-table-for-indicator)))
 889     (cond
 890      ((member minor-mode symbols)
 891       (describe-minor-mode-from-symbol (intern minor-mode)))
 892      ((member minor-mode indicators)
 893       (describe-minor-mode-from-indicator minor-mode))
 894      (t
 895       (error "No such minor mode: %s" minor-mode)))))
 896
 897 ;; symbol
 898 (defun describe-minor-mode-completion-table-for-symbol ()
 899   ;; In order to list up all minor modes, minor-mode-list
 900   ;; is used here instead of minor-mode-alist.
 901   (delq nil (mapcar 'symbol-name minor-mode-list)))
 902
 903 (defun describe-minor-mode-from-symbol (symbol)
 904   "Display documentation of a minor mode given as a symbol, SYMBOL"
 905   (interactive (list (intern (completing-read
 906                               "Minor mode symbol: "
 907                               (describe-minor-mode-completion-table-for-symbol)))))
 908   (if (fboundp symbol)
 909       (describe-function symbol)
 910     (describe-variable symbol)))
 911
 912 ;; indicator
 913 (defun describe-minor-mode-completion-table-for-indicator ()
 914   (delq nil
 915         (mapcar (lambda (x)
 916                   (let ((i (format-mode-line x)))
 917                     ;; remove first space if existed
 918                     (cond
 919                      ((= 0 (length i))
 920                       nil)
 921                      ((eq (aref i 0) ?\s)
 922                       (substring i 1))
 923                      (t
 924                       i))))
 925                 minor-mode-alist)))
 926
 927 (defun describe-minor-mode-from-indicator (indicator)
 928   "Display documentation of a minor mode specified by INDICATOR.
 929 If you call this function interactively, you can give indicator which
 930 is currently activated with completion."
 931   (interactive (list
 932                 (completing-read
 933                  "Minor mode indicator: "
 934                  (describe-minor-mode-completion-table-for-indicator))))
 935   (let ((minor-mode (lookup-minor-mode-from-indicator indicator)))
 936     (if minor-mode
 937         (describe-minor-mode-from-symbol minor-mode)
 938       (error "Cannot find minor mode for `%s'" indicator))))
 939
 940 (defun lookup-minor-mode-from-indicator (indicator)
 941   "Return a minor mode symbol from its indicator on the mode line."
 942   ;; remove first space if existed
 943   (if (and (< 0 (length indicator))
 944            (eq (aref indicator 0) ?\s))
 945       (setq indicator (substring indicator 1)))
 946   (let ((minor-modes minor-mode-alist)
 947         result)
 948     (while minor-modes
 949       (let* ((minor-mode (car (car minor-modes)))
 950              (anindicator (format-mode-line
 951                            (car (cdr (car minor-modes))))))
 952         ;; remove first space if existed
 953         (if (and (stringp anindicator)
 954                  (> (length anindicator) 0)
 955                  (eq (aref anindicator 0) ?\s))
 956             (setq anindicator (substring anindicator 1)))
 957         (if (equal indicator anindicator)
 958             (setq result minor-mode
 959                   minor-modes nil)
 960           (setq minor-modes (cdr minor-modes)))))
 961     result))
 962 \f
 963 ;;; Automatic resizing of temporary buffers.
 964 (defcustom temp-buffer-max-height (lambda (buffer) (/ (- (frame-height) 2) 2))
 965   "Maximum height of a window displaying a temporary buffer.
 966 This is effective only when Temp Buffer Resize mode is enabled.
 967 The value is the maximum height (in lines) which
 968 `resize-temp-buffer-window' will give to a window displaying a
 969 temporary buffer.  It can also be a function to be called to
 970 choose the height for such a buffer.  It gets one argument, the
 971 buffer, and should return a positive integer.  At the time the
 972 function is called, the window to be resized is selected."
 973   :type '(choice integer function)
 974   :group 'help
 975   :version "20.4")
 976
 977 (define-minor-mode temp-buffer-resize-mode
 978   "Toggle auto-shrinking temp buffer windows (Temp Buffer Resize mode).
 979 With a prefix argument ARG, enable Temp Buffer Resize mode if ARG
 980 is positive, and disable it otherwise.  If called from Lisp,
 981 enable the mode if ARG is omitted or nil.
 982
 983 When Temp Buffer Resize mode is enabled, the windows in which we
 984 show a temporary buffer are automatically reduced in height to
 985 fit the buffer's contents, but never more than
 986 `temp-buffer-max-height' nor less than `window-min-height'.
 987
 988 This mode is used by `help', `apropos' and `completion' buffers,
 989 and some others."
 990   :global t :group 'help
 991   (if temp-buffer-resize-mode
 992       ;; `help-make-xrefs' may add a `back' button and thus increase the
 993       ;; text size, so `resize-temp-buffer-window' must be run *after* it.
 994       (add-hook 'temp-buffer-show-hook 'resize-temp-buffer-window 'append)
 995     (remove-hook 'temp-buffer-show-hook 'resize-temp-buffer-window)))
 996
 997 (defun resize-temp-buffer-window ()
 998   "Resize the selected window to fit its contents.
 999 Will not make it higher than `temp-buffer-max-height' nor smaller
1000 than `window-min-height'.  Do nothing if the selected window is
1001 not vertically combined or some of its contents are scrolled out
1002 of view."
1003   (when (and (pos-visible-in-window-p (point-min))
1004              (window-combined-p))
1005     (fit-window-to-buffer
1006      nil
1007      (if (functionp temp-buffer-max-height)
1008          (funcall temp-buffer-max-height (window-buffer))
1009        temp-buffer-max-height))))
1010
1011 ;;; Help windows.
1012 (defcustom help-window-select 'other
1013     "Non-nil means select help window for viewing.
1014 Choices are:
1015  never (nil) Select help window only if there is no other window
1016              on its frame.
1017  other       Select help window unless the selected window is the
1018              only other window on the help window's frame.
1019  always (t)  Always select the help window.
1020
1021 This option has effect if and only if the help window was created
1022 by `with-help-window'"
1023   :type '(choice (const :tag "never (nil)" nil)
1024                  (const :tag "other" other)
1025                  (const :tag "always (t)" t))
1026   :group 'help
1027   :version "23.1")
1028
1029 (defcustom help-enable-auto-load t
1030   "Whether Help commands can perform autoloading.
1031 If non-nil, whenever \\[describe-function] is called for an
1032 autoloaded function whose docstring contains any key substitution
1033 construct (see `substitute-command-keys'), the library is loaded,
1034 so that the documentation can show the right key bindings."
1035   :type 'boolean
1036   :group 'help
1037   :version "24.3")
1038
1039 (defun help-window-display-message (quit-part window &optional scroll)
1040   "Display message telling how to quit and scroll help window.
1041 QUIT-PART is a string telling how to quit the help window WINDOW.
1042 Optional argument SCROLL non-nil means tell how to scroll WINDOW.
1043 SCROLL equal `other' means tell how to scroll the \"other\"
1044 window."
1045   (let ((scroll-part
1046          (cond
1047           ;; If we don't have QUIT-PART we probably reuse a window
1048           ;; showing the same buffer so we don't show any message.
1049           ((not quit-part) nil)
1050           ((pos-visible-in-window-p
1051             (with-current-buffer (window-buffer window)
1052               (point-max)) window t)
1053            ;; Buffer end is at least partially visible, no need to talk
1054            ;; about scrolling.
1055            ".")
1056           ((eq scroll 'other)
1057            ", \\[scroll-other-window] to scroll help.")
1058           (scroll ", \\[scroll-up] to scroll help."))))
1059     (message "%s"
1060      (substitute-command-keys (concat quit-part scroll-part)))))
1061
1062 (defun help-window-setup (help-window)
1063   "Set up help window for `with-help-window'.
1064 HELP-WINDOW is the window used for displaying the help buffer."
1065   (let* ((help-buffer (when (window-live-p help-window)
1066                         (window-buffer help-window)))
1067          (help-setup (when (window-live-p help-window)
1068                        (car (window-parameter help-window 'quit-restore)))))
1069     (when help-buffer
1070       ;; Handle `help-window-point-marker'.
1071       (when (eq (marker-buffer help-window-point-marker) help-buffer)
1072         (set-window-point help-window help-window-point-marker)
1073         ;; Reset `help-window-point-marker'.
1074         (set-marker help-window-point-marker nil))
1075
1076       (cond
1077        ((or (eq help-window (selected-window))
1078             (and (or (eq help-window-select t)
1079                      (eq help-setup 'frame)
1080                      (and (eq help-window-select 'other)
1081                           (eq (window-frame help-window) (selected-frame))
1082                           (> (length (window-list nil 'no-mini)) 2)))
1083                  (select-window help-window)))
1084         ;; The help window is or gets selected ...
1085         (help-window-display-message
1086          (cond
1087           ((eq help-setup 'window)
1088            ;; ... and is new, ...
1089            "Type \"q\" to delete help window")
1090           ((eq help-setup 'frame)
1091            "Type \"q\" to delete help frame")
1092           ((eq help-setup 'other)
1093            ;; ... or displayed some other buffer before.
1094            "Type \"q\" to restore previous buffer"))
1095          help-window t))
1096        ((and (eq (window-frame help-window) (selected-frame))
1097              (= (length (window-list nil 'no-mini)) 2))
1098         ;; There are two windows on the help window's frame and the
1099         ;; other one is the selected one.
1100         (help-window-display-message
1101          (cond
1102           ((eq help-setup 'window)
1103            "Type \\[delete-other-windows] to delete the help window")
1104           ((eq help-setup 'other)
1105            "Type \"q\" in help window to restore its previous buffer"))
1106          help-window 'other))
1107        (t
1108         ;; The help window is not selected ...
1109         (help-window-display-message
1110          (cond
1111           ((eq help-setup 'window)
1112            ;; ... and is new, ...
1113            "Type \"q\" in help window to delete it")
1114           ((eq help-setup 'other)
1115            ;; ... or displayed some other buffer before.
1116            "Type \"q\" in help window to restore previous buffer"))
1117          help-window))))))
1118
1119 ;; `with-help-window' is a wrapper for `with-output-to-temp-buffer'
1120 ;; providing the following additional twists:
1121
1122 ;; (1) Issue more accurate messages telling how to scroll and quit the
1123 ;; help window.
1124
1125 ;; (2) An option (customizable via `help-window-select') to select the
1126 ;; help window automatically.
1127
1128 ;; (3) A marker (`help-window-point-marker') to move point in the help
1129 ;; window to an arbitrary buffer position.
1130
1131 ;; Note: It's usually always wrong to use `help-print-return-message' in
1132 ;; the body of `with-help-window'.
1133 (defmacro with-help-window (buffer-name &rest body)
1134   "Display buffer with name BUFFER-NAME in a help window evaluating BODY.
1135 Select help window if the actual value of the user option
1136 `help-window-select' says so.  Return last value in BODY."
1137   (declare (indent 1) (debug t))
1138   `(progn
1139      ;; Make `help-window-point-marker' point nowhere.  The only place
1140      ;; where this should be set to a buffer position is within BODY.
1141      (set-marker help-window-point-marker nil)
1142      (let* (help-window
1143             (temp-buffer-show-hook
1144              (cons (lambda () (setq help-window (selected-window)))
1145                    temp-buffer-show-hook)))
1146        ;; Return value returned by `with-output-to-temp-buffer'.
1147        (prog1
1148            (with-output-to-temp-buffer ,buffer-name
1149              (progn ,@body))
1150          (help-window-setup help-window)))))
1151
1152 ;; Called from C, on encountering `help-char' when reading a char.
1153 ;; Don't print to *Help*; that would clobber Help history.
1154 (defun help-form-show ()
1155   "Display the output of a non-nil `help-form'."
1156   (let ((msg (eval help-form)))
1157     (if (stringp msg)
1158         (with-output-to-temp-buffer " *Char Help*"
1159           (princ msg)))))
1160 \f
1161 (provide 'help)
1162
1163 ;;; help.el ends here