lisp/help.el

   1 ;;; help.el --- help commands for Emacs
   2
   3 ;; Copyright (C) 1985-1986, 1993-1994, 1998-2011
   4 ;;   Free Software Foundation, Inc.
   5
   6 ;; Maintainer: FSF
   7 ;; Keywords: help, internal
   8 ;; Package: emacs
   9
  10 ;; This file is part of GNU Emacs.
  11
  12 ;; GNU Emacs is free software: you can redistribute it and/or modify
  13 ;; it under the terms of the GNU General Public License as published by
  14 ;; the Free Software Foundation, either version 3 of the License, or
  15 ;; (at your option) any later version.
  16
  17 ;; GNU Emacs is distributed in the hope that it will be useful,
  18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20 ;; GNU General Public License for more details.
  21
  22 ;; You should have received a copy of the GNU General Public License
  23 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  24
  25 ;;; Commentary:
  26
  27 ;; 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
  36 ;; This makes `with-output-to-temp-buffer' buffers use `help-mode'.
  37 (add-hook 'temp-buffer-setup-hook 'help-mode-setup)
  38 (add-hook 'temp-buffer-show-hook 'help-mode-finish)
  39
  40 ;; The variable `help-window' below is used by `help-mode-finish' to
  41 ;; communicate the window displaying help (the "help window") to the
  42 ;; macro `with-help-window'.  The latter sets `help-window' to t before
  43 ;; invoking `with-output-to-temp-buffer'.  If and only if `help-window'
  44 ;; is eq to t, `help-mode-finish' (called by `temp-buffer-setup-hook')
  45 ;; sets `help-window' to the window selected by `display-buffer'.
  46 ;; Exiting `with-help-window' and calling `help-print-return-message'
  47 ;; reset `help-window' to nil.
  48 (defvar help-window nil
  49   "Window chosen for displaying help.")
  50
  51 ;; `help-window-point-marker' is a marker you can move to a valid
  52 ;; position of the buffer shown in the help window in order to override
  53 ;; the standard positioning mechanism (`point-min') chosen by
  54 ;; `with-output-to-temp-buffer'.  `with-help-window' has this point
  55 ;; nowhere before exiting.  Currently used by `view-lossage' to assert
  56 ;; that the last keystrokes are always visible.
  57 (defvar help-window-point-marker (make-marker)
  58   "Marker to override default `window-point' in help windows.")
  59
  60 (defvar help-map
  61   (let ((map (make-sparse-keymap)))
  62     (define-key map (char-to-string help-char) 'help-for-help)
  63     (define-key map [help] 'help-for-help)
  64     (define-key map [f1] 'help-for-help)
  65     (define-key map "." 'display-local-help)
  66     (define-key map "?" 'help-for-help)
  67
  68     (define-key map "\C-a" 'about-emacs)
  69     (define-key map "\C-c" 'describe-copying)
  70     (define-key map "\C-d" 'view-emacs-debugging)
  71     (define-key map "\C-e" 'view-external-packages)
  72     (define-key map "\C-f" 'view-emacs-FAQ)
  73     (define-key map "\C-m" 'view-order-manuals)
  74     (define-key map "\C-n" 'view-emacs-news)
  75     (define-key map "\C-o" 'describe-distribution)
  76     (define-key map "\C-p" 'view-emacs-problems)
  77     (define-key map "\C-t" 'view-emacs-todo)
  78     (define-key map "\C-w" 'describe-no-warranty)
  79
  80     ;; This does not fit the pattern, but it is natural given the C-\ command.
  81     (define-key map "\C-\\" 'describe-input-method)
  82
  83     (define-key map "C" 'describe-coding-system)
  84     (define-key map "F" 'Info-goto-emacs-command-node)
  85     (define-key map "I" 'describe-input-method)
  86     (define-key map "K" 'Info-goto-emacs-key-command-node)
  87     (define-key map "L" 'describe-language-environment)
  88     (define-key map "S" 'info-lookup-symbol)
  89
  90     (define-key map "a" 'apropos-command)
  91     (define-key map "b" 'describe-bindings)
  92     (define-key map "c" 'describe-key-briefly)
  93     (define-key map "d" 'apropos-documentation)
  94     (define-key map "e" 'view-echo-area-messages)
  95     (define-key map "f" 'describe-function)
  96     (define-key map "g" 'describe-gnu-project)
  97     (define-key map "h" 'view-hello-file)
  98
  99     (define-key map "i" 'info)
 100     (define-key map "4i" 'info-other-window)
 101
 102     (define-key map "k" 'describe-key)
 103     (define-key map "l" 'view-lossage)
 104     (define-key map "m" 'describe-mode)
 105     (define-key map "n" 'view-emacs-news)
 106     (define-key map "p" 'finder-by-keyword)
 107     (define-key map "P" 'describe-package)
 108     (define-key map "r" 'info-emacs-manual)
 109     (define-key map "s" 'describe-syntax)
 110     (define-key map "t" 'help-with-tutorial)
 111     (define-key map "w" 'where-is)
 112     (define-key map "v" 'describe-variable)
 113     (define-key map "q" 'help-quit)
 114     map)
 115   "Keymap for characters following the Help key.")
 116
 117 (define-key global-map (char-to-string help-char) 'help-command)
 118 (define-key global-map [help] 'help-command)
 119 (define-key global-map [f1] 'help-command)
 120 (fset 'help-command help-map)
 121
 122 ;; insert-button makes the action nil if it is not store somewhere
 123 (defvar help-button-cache nil)
 124
 125 \f
 126 (defun help-quit ()
 127   "Just exit from the Help command's command loop."
 128   (interactive)
 129   nil)
 130
 131 (defvar help-return-method nil
 132   "What to do to \"exit\" the help buffer.
 133 This is a list
 134  (WINDOW . t)              delete the selected window (and possibly its frame,
 135                            see `quit-window' and `View-quit'), go to WINDOW.
 136  (WINDOW . quit-window)    do quit-window, then select WINDOW.
 137  (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")
 138
 139 (define-obsolete-function-alias 'print-help-return-message 'help-print-return-message "23.2")
 140 (defun help-print-return-message (&optional function)
 141   "Display or return message saying how to restore windows after help command.
 142 This function assumes that `standard-output' is the help buffer.
 143 It computes a message, and applies the optional argument FUNCTION to it.
 144 If FUNCTION is nil, it applies `message', thus displaying the message.
 145 In addition, this function sets up `help-return-method', which see, that
 146 specifies what to do when the user exits the help buffer."
 147   (and (not (get-buffer-window standard-output))
 148        (let ((first-message
 149               (cond ((or
 150                       pop-up-frames
 151                       (special-display-p (buffer-name standard-output)))
 152                      (setq help-return-method (cons (selected-window) t))
 153                      ;; If the help output buffer is a special display buffer,
 154                      ;; don't say anything about how to get rid of it.
 155                      ;; First of all, the user will do that with the window
 156                      ;; manager, not with Emacs.
 157                      ;; Secondly, the buffer has not been displayed yet,
 158                      ;; so we don't know whether its frame will be selected.
 159                      nil)
 160                     (display-buffer-reuse-frames
 161                      (setq help-return-method (cons (selected-window)
 162                                                     'quit-window))
 163                      nil)
 164                     ((not (one-window-p t))
 165                      (setq help-return-method
 166                            (cons (selected-window) 'quit-window))
 167                      "Type \\[display-buffer] RET to restore the other window.")
 168                     (pop-up-windows
 169                      (setq help-return-method (cons (selected-window) t))
 170                      "Type \\[delete-other-windows] to remove help window.")
 171                     (t
 172                      (setq help-return-method
 173                            (list (selected-window) (window-buffer)
 174                                  (window-start) (window-point)))
 175                      "Type \\[switch-to-buffer] RET to remove help window."))))
 176          (funcall (or function 'message)
 177                   (concat
 178                    (if first-message
 179                        (substitute-command-keys first-message))
 180                    (if first-message "  ")
 181                    ;; If the help buffer will go in a separate frame,
 182                    ;; it's no use mentioning a command to scroll, so don't.
 183                    (if (or pop-up-windows
 184                            (special-display-p (buffer-name standard-output)))
 185                        nil
 186                      (if (same-window-p (buffer-name standard-output))
 187                          ;; Say how to scroll this window.
 188                          (substitute-command-keys
 189                           "\\[scroll-up] to scroll the help.")
 190                        ;; Say how to scroll some other window.
 191                        (substitute-command-keys
 192                         "\\[scroll-other-window] to scroll the help."))))))))
 193
 194 ;; So keyboard macro definitions are documented correctly
 195 (fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))
 196
 197 (defalias 'help 'help-for-help-internal)
 198 ;; find-function can find this.
 199 (defalias 'help-for-help 'help-for-help-internal)
 200 ;; It can't find this, but nobody will look.
 201 (make-help-screen help-for-help-internal
 202   (purecopy "Type a help option: [abcCdefFgiIkKlLmnprstvw.] C-[cdefmnoptw] or ?")
 203   ;; Don't purecopy this one, because it's not evaluated (it's
 204   ;; directly used as a docstring in a function definition, so it'll
 205   ;; be moved to the DOC file anyway: no need for purecopying it).
 206   "You have typed %THIS-KEY%, the help character.  Type a Help option:
 207 \(Use SPC or DEL to scroll through this text.  Type \\<help-map>\\[help-quit] to exit the Help command.)
 208
 209 a PATTERN   Show commands whose name matches the PATTERN (a list of words
 210               or a regexp).  See also the `apropos' command.
 211 b           Display all key bindings.
 212 c KEYS      Display the command name run by the given key sequence.
 213 C CODING    Describe the given coding system, or RET for current ones.
 214 d PATTERN   Show a list of functions, variables, and other items whose
 215               documentation matches the PATTERN (a list of words or a regexp).
 216 e           Go to the *Messages* buffer which logs echo-area messages.
 217 f FUNCTION  Display documentation for the given function.
 218 F COMMAND   Show the on-line manual's section that describes the command.
 219 g           Display information about the GNU project.
 220 h           Display the HELLO file which illustrates various scripts.
 221 i           Start the Info documentation reader: read on-line manuals.
 222 I METHOD    Describe a specific input method, or RET for current.
 223 k KEYS      Display the full documentation for the key sequence.
 224 K KEYS      Show the on-line manual's section for the command bound to KEYS.
 225 l           Show last 300 input keystrokes (lossage).
 226 L LANG-ENV  Describes a specific language environment, or RET for current.
 227 m           Display documentation of current minor modes and current major mode,
 228               including their special commands.
 229 n           Display news of recent Emacs changes.
 230 p TOPIC     Find packages matching a given topic keyword.
 231 r           Display the Emacs manual in Info mode.
 232 s           Display contents of current syntax table, plus explanations.
 233 S SYMBOL    Show the section for the given symbol in the on-line manual
 234               for the programming language used in this buffer.
 235 t           Start the Emacs learn-by-doing tutorial.
 236 v VARIABLE  Display the given variable's documentation and value.
 237 w COMMAND   Display which keystrokes invoke the given command (where-is).
 238 .           Display any available local help at point in the echo area.
 239
 240 C-a         Information about Emacs.
 241 C-c         Emacs copying permission (GNU General Public License).
 242 C-d         Instructions for debugging GNU Emacs.
 243 C-e         External packages and information about Emacs.
 244 C-f         Emacs FAQ.
 245 C-m         How to order printed Emacs manuals.
 246 C-n         News of recent Emacs changes.
 247 C-o         Emacs ordering and distribution information.
 248 C-p         Info about known Emacs problems.
 249 C-t         Emacs TODO list.
 250 C-w         Information on absence of warranty for GNU Emacs."
 251   help-map)
 252
 253 \f
 254
 255 (defun function-called-at-point ()
 256   "Return a function around point or else called by the list containing point.
 257 If that doesn't give a function, return nil."
 258   (with-syntax-table emacs-lisp-mode-syntax-table
 259     (or (condition-case ()
 260             (save-excursion
 261               (or (not (zerop (skip-syntax-backward "_w")))
 262                   (eq (char-syntax (following-char)) ?w)
 263                   (eq (char-syntax (following-char)) ?_)
 264                   (forward-sexp -1))
 265               (skip-chars-forward "'")
 266               (let ((obj (read (current-buffer))))
 267                 (and (symbolp obj) (fboundp obj) obj)))
 268           (error nil))
 269         (condition-case ()
 270             (save-excursion
 271               (save-restriction
 272                 (narrow-to-region (max (point-min)
 273                                        (- (point) 1000)) (point-max))
 274                 ;; Move up to surrounding paren, then after the open.
 275                 (backward-up-list 1)
 276                 (forward-char 1)
 277                 ;; If there is space here, this is probably something
 278                 ;; other than a real Lisp function call, so ignore it.
 279                 (if (looking-at "[ \t]")
 280                     (error "Probably not a Lisp function call"))
 281                 (let ((obj (read (current-buffer))))
 282                   (and (symbolp obj) (fboundp obj) obj))))
 283           (error nil))
 284         (let* ((str (find-tag-default))
 285                (sym (if str (intern-soft str))))
 286           (if (and sym (fboundp sym))
 287               sym
 288             (save-match-data
 289               (when (and str (string-match "\\`\\W*\\(.*?\\)\\W*\\'" str))
 290                 (setq sym (intern-soft (match-string 1 str)))
 291                 (and (fboundp sym) sym))))))))
 292
 293 \f
 294 ;;; `User' help functions
 295
 296 (defun view-help-file (file &optional dir)
 297   (view-file (expand-file-name file (or dir data-directory)))
 298   (goto-address-mode 1)
 299   (goto-char (point-min)))
 300
 301 (defun describe-distribution ()
 302   "Display info on how to obtain the latest version of GNU Emacs."
 303   (interactive)
 304   (view-help-file "DISTRIB"))
 305
 306 (defun describe-copying ()
 307   "Display info on how you may redistribute copies of GNU Emacs."
 308   (interactive)
 309   (view-help-file "COPYING"))
 310
 311 (defun describe-gnu-project ()
 312   "Display info on the GNU project."
 313   (interactive)
 314   (view-help-file "THE-GNU-PROJECT"))
 315
 316 (define-obsolete-function-alias 'describe-project 'describe-gnu-project "22.2")
 317
 318 (defun describe-no-warranty ()
 319   "Display info on all the kinds of warranty Emacs does NOT have."
 320   (interactive)
 321   (describe-copying)
 322   (let (case-fold-search)
 323     (search-forward "Disclaimer of Warranty")
 324     (forward-line 0)
 325     (recenter 0)))
 326
 327 (defun describe-prefix-bindings ()
 328   "Describe the bindings of the prefix used to reach this command.
 329 The prefix described consists of all but the last event
 330 of the key sequence that ran this command."
 331   (interactive)
 332   (let ((key (this-command-keys)))
 333     (describe-bindings
 334      (if (stringp key)
 335          (substring key 0 (1- (length key)))
 336        (let ((prefix (make-vector (1- (length key)) nil))
 337              (i 0))
 338          (while (< i (length prefix))
 339            (aset prefix i (aref key i))
 340            (setq i (1+ i)))
 341          prefix)))))
 342 ;; Make C-h after a prefix, when not specifically bound,
 343 ;; run describe-prefix-bindings.
 344 (setq prefix-help-command 'describe-prefix-bindings)
 345
 346 (defun view-emacs-news (&optional version)
 347   "Display info on recent changes to Emacs.
 348 With argument, display info only for the selected version."
 349   (interactive "P")
 350   (unless version
 351     (setq version emacs-major-version))
 352   (when (consp version)
 353     (let* ((all-versions
 354             (let (res)
 355               (mapc
 356                (lambda (file)
 357                  (with-temp-buffer
 358                    (insert-file-contents
 359                     (expand-file-name file data-directory))
 360                    (while (re-search-forward
 361                            (if (member file '("NEWS.18" "NEWS.1-17"))
 362                                "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
 363                              "^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t)
 364                      (setq res (cons (match-string-no-properties 1) res)))))
 365                (cons "NEWS"
 366                      (directory-files data-directory nil
 367                                       "^NEWS\\.[0-9][-0-9]*$" nil)))
 368               (sort (delete-dups res) (lambda (a b) (string< b a)))))
 369            (current (car all-versions)))
 370       (setq version (completing-read
 371                      (format "Read NEWS for the version (default %s): " current)
 372                      all-versions nil nil nil nil current))
 373       (if (integerp (string-to-number version))
 374           (setq version (string-to-number version))
 375         (unless (or (member version all-versions)
 376                     (<= (string-to-number version) (string-to-number current)))
 377           (error "No news about version %s" version)))))
 378   (when (integerp version)
 379     (cond ((<= version 12)
 380            (setq version (format "1.%d" version)))
 381           ((<= version 18)
 382            (setq version (format "%d" version)))
 383           ((> version emacs-major-version)
 384            (error "No news about Emacs %d (yet)" version))))
 385   (let* ((vn (if (stringp version)
 386                  (string-to-number version)
 387                version))
 388          (file (cond
 389                 ((>= vn emacs-major-version) "NEWS")
 390                 ((< vn 18) "NEWS.1-17")
 391                 (t (format "NEWS.%d" vn))))
 392          res)
 393     (view-file (expand-file-name file data-directory))
 394     (widen)
 395     (goto-char (point-min))
 396     (when (stringp version)
 397       (when (re-search-forward
 398              (concat (if (< vn 19)
 399                          "Changes in Emacs[ \t]*"
 400                        "^\* [^0-9\n]*") version "$")
 401              nil t)
 402         (beginning-of-line)
 403         (narrow-to-region
 404          (point)
 405          (save-excursion
 406            (while (and (setq res
 407                              (re-search-forward
 408                               (if (< vn 19)
 409                                   "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
 410                                 "^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t))
 411                        (equal (match-string-no-properties 1) version)))
 412            (or res (goto-char (point-max)))
 413            (beginning-of-line)
 414            (point)))))))
 415
 416 (defun view-emacs-todo (&optional _arg)
 417   "Display the Emacs TODO list."
 418   (interactive "P")
 419   (view-help-file "TODO"))
 420
 421 (define-obsolete-function-alias 'view-todo 'view-emacs-todo "22.2")
 422
 423
 424 (defun view-echo-area-messages ()
 425   "View the log of recent echo-area messages: the `*Messages*' buffer.
 426 The number of messages retained in that buffer
 427 is specified by the variable `message-log-max'."
 428   (interactive)
 429   (switch-to-buffer (get-buffer-create "*Messages*")))
 430
 431 (defun view-order-manuals ()
 432   "Display the Emacs ORDERS file."
 433   (interactive)
 434   (view-help-file "ORDERS"))
 435
 436 (defun view-emacs-FAQ ()
 437   "Display the Emacs Frequently Asked Questions (FAQ) file."
 438   (interactive)
 439   ;; (find-file-read-only (expand-file-name "FAQ" data-directory))
 440   (info "(efaq)"))
 441
 442 (defun view-emacs-problems ()
 443   "Display info on known problems with Emacs and possible workarounds."
 444   (interactive)
 445   (view-help-file "PROBLEMS"))
 446
 447 (defun view-emacs-debugging ()
 448   "Display info on how to debug Emacs problems."
 449   (interactive)
 450   (view-help-file "DEBUG"))
 451
 452 (defun view-external-packages ()
 453   "Display external packages and information about Emacs."
 454   (interactive)
 455   (view-help-file "MORE.STUFF"))
 456
 457 (defun view-lossage ()
 458   "Display last 300 input keystrokes.
 459
 460 To record all your input on a file, use `open-dribble-file'."
 461   (interactive)
 462   (help-setup-xref (list #'view-lossage)
 463                    (called-interactively-p 'interactive))
 464   (with-help-window (help-buffer)
 465     (princ (mapconcat (lambda (key)
 466                         (if (or (integerp key) (symbolp key) (listp key))
 467                             (single-key-description key)
 468                           (prin1-to-string key nil)))
 469                       (recent-keys)
 470                       " "))
 471     (with-current-buffer standard-output
 472       (goto-char (point-min))
 473       (while (progn (move-to-column 50) (not (eobp)))
 474         (when (search-forward " " nil t)
 475           (delete-char -1))
 476         (insert "\n"))
 477       ;; jidanni wants to see the last keystrokes immediately.
 478       (set-marker help-window-point-marker (point)))))
 479
 480 \f
 481 ;; Key bindings
 482
 483 (defun describe-bindings (&optional prefix buffer)
 484   "Show a list of all defined keys, and their definitions.
 485 We put that list in a buffer, and display the buffer.
 486
 487 The optional argument PREFIX, if non-nil, should be a key sequence;
 488 then we display only bindings that start with that prefix.
 489 The optional argument BUFFER specifies which buffer's bindings
 490 to display (default, the current buffer).  BUFFER can be a buffer
 491 or a buffer name."
 492   (interactive)
 493   (or buffer (setq buffer (current-buffer)))
 494   (help-setup-xref (list #'describe-bindings prefix buffer)
 495                    (called-interactively-p 'interactive))
 496   (with-current-buffer buffer
 497     (describe-bindings-internal nil prefix)))
 498
 499 ;; This function used to be in keymap.c.
 500 (defun describe-bindings-internal (&optional menus prefix)
 501   "Show a list of all defined keys, and their definitions.
 502 We put that list in a buffer, and display the buffer.
 503
 504 The optional argument MENUS, if non-nil, says to mention menu bindings.
 505 \(Ordinarily these are omitted from the output.)
 506 The optional argument PREFIX, if non-nil, should be a key sequence;
 507 then we display only bindings that start with that prefix."
 508   (let ((buf (current-buffer)))
 509     (with-help-window "*Help*"
 510       (with-current-buffer standard-output
 511         (describe-buffer-bindings buf prefix menus)))))
 512
 513 (defun where-is (definition &optional insert)
 514   "Print message listing key sequences that invoke the command DEFINITION.
 515 Argument is a command definition, usually a symbol with a function definition.
 516 If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
 517   (interactive
 518    (let ((fn (function-called-at-point))
 519          (enable-recursive-minibuffers t)
 520          val)
 521      (setq val (completing-read
 522                 (if fn
 523                     (format "Where is command (default %s): " fn)
 524                   "Where is command: ")
 525                 obarray 'commandp t))
 526      (list (if (equal val "") fn (intern val)) current-prefix-arg)))
 527   (unless definition (error "No command"))
 528   (let ((func (indirect-function definition))
 529         (defs nil)
 530         (standard-output (if insert (current-buffer) t)))
 531     ;; In DEFS, find all symbols that are aliases for DEFINITION.
 532     (mapatoms (lambda (symbol)
 533                 (and (fboundp symbol)
 534                      (not (eq symbol definition))
 535                      (eq func (condition-case ()
 536                                   (indirect-function symbol)
 537                                 (error symbol)))
 538                      (push symbol defs))))
 539     ;; Look at all the symbols--first DEFINITION,
 540     ;; then its aliases.
 541     (dolist (symbol (cons definition defs))
 542       (let* ((remapped (command-remapping symbol))
 543              (keys (where-is-internal
 544                     symbol overriding-local-map nil nil remapped))
 545              (keys (mapconcat 'key-description keys ", "))
 546              string)
 547         (setq string
 548               (if insert
 549                   (if (> (length keys) 0)
 550                       (if remapped
 551                           (format "%s (%s) (remapped from %s)"
 552                                   keys remapped symbol)
 553                         (format "%s (%s)" keys symbol))
 554                     (format "M-x %s RET" symbol))
 555                 (if (> (length keys) 0)
 556                     (if remapped
 557                         (format "%s is remapped to %s which is on %s"
 558                                 symbol remapped keys)
 559                       (format "%s is on %s" symbol keys))
 560                   ;; If this is the command the user asked about,
 561                   ;; and it is not on any key, say so.
 562                   ;; For other symbols, its aliases, say nothing
 563                   ;; about them unless they are on keys.
 564                   (if (eq symbol definition)
 565                       (format "%s is not on any key" symbol)))))
 566         (when string
 567           (unless (eq symbol definition)
 568             (princ ";\n its alias "))
 569           (princ string)))))
 570   nil)
 571
 572 (defun help-key-description (key untranslated)
 573   (let ((string (key-description key)))
 574     (if (or (not untranslated)
 575             (and (eq (aref untranslated 0) ?\e) (not (eq (aref key 0) ?\e))))
 576         string
 577       (let ((otherstring (key-description untranslated)))
 578         (if (equal string otherstring)
 579             string
 580           (format "%s (translated from %s)" string otherstring))))))
 581
 582 (defun describe-key-briefly (&optional key insert untranslated)
 583   "Print the name of the function KEY invokes.  KEY is a string.
 584 If INSERT (the prefix arg) is non-nil, insert the message in the buffer.
 585 If non-nil, UNTRANSLATED is a vector of the untranslated events.
 586 It can also be a number in which case the untranslated events from
 587 the last key hit are used.
 588
 589 If KEY is a menu item or a tool-bar button that is disabled, this command
 590 temporarily enables it to allow getting help on disabled items and buttons."
 591   (interactive
 592    (let ((enable-disabled-menus-and-buttons t)
 593          (cursor-in-echo-area t)
 594          saved-yank-menu)
 595      (unwind-protect
 596          (let (key)
 597            ;; If yank-menu is empty, populate it temporarily, so that
 598            ;; "Select and Paste" menu can generate a complete event.
 599            (when (null (cdr yank-menu))
 600              (setq saved-yank-menu (copy-sequence yank-menu))
 601              (menu-bar-update-yank-menu "(any string)" nil))
 602            (setq key (read-key-sequence "Describe key (or click or menu item): "))
 603            ;; If KEY is a down-event, read and discard the
 604            ;; corresponding up-event.  Note that there are also
 605            ;; down-events on scroll bars and mode lines: the actual
 606            ;; event then is in the second element of the vector.
 607            (and (vectorp key)
 608                 (let ((last-idx (1- (length key))))
 609                   (and (eventp (aref key last-idx))
 610                        (memq 'down (event-modifiers (aref key last-idx)))))
 611                 (read-event))
 612            (list
 613             key
 614             (if current-prefix-arg (prefix-numeric-value current-prefix-arg))
 615             1))
 616        ;; Put yank-menu back as it was, if we changed it.
 617        (when saved-yank-menu
 618          (setq yank-menu (copy-sequence saved-yank-menu))
 619          (fset 'yank-menu (cons 'keymap yank-menu))))))
 620   (if (numberp untranslated)
 621       (setq untranslated (this-single-command-raw-keys)))
 622   (let* ((event (if (and (symbolp (aref key 0))
 623                          (> (length key) 1)
 624                          (consp (aref key 1)))
 625                     (aref key 1)
 626                   (aref key 0)))
 627          (modifiers (event-modifiers event))
 628          (standard-output (if insert (current-buffer) t))
 629          (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
 630                             (memq 'drag modifiers)) " at that spot" ""))
 631          (defn (key-binding key t))
 632          key-desc)
 633     ;; Handle the case where we faked an entry in "Select and Paste" menu.
 634     (if (and (eq defn nil)
 635              (stringp (aref key (1- (length key))))
 636              (eq (key-binding (substring key 0 -1)) 'yank-menu))
 637         (setq defn 'menu-bar-select-yank))
 638     ;; Don't bother user with strings from (e.g.) the select-paste menu.
 639     (if (stringp (aref key (1- (length key))))
 640         (aset key (1- (length key)) "(any string)"))
 641     (if (and (> (length untranslated) 0)
 642              (stringp (aref untranslated (1- (length untranslated)))))
 643         (aset untranslated (1- (length untranslated)) "(any string)"))
 644     ;; Now describe the key, perhaps as changed.
 645     (setq key-desc (help-key-description key untranslated))
 646     (if (or (null defn) (integerp defn) (equal defn 'undefined))
 647         (princ (format "%s%s is undefined" key-desc mouse-msg))
 648       (princ (format "%s%s runs the command %S" key-desc mouse-msg defn)))))
 649
 650 (defun describe-key (&optional key untranslated up-event)
 651   "Display documentation of the function invoked by KEY.
 652 KEY can be any kind of a key sequence; it can include keyboard events,
 653 mouse events, and/or menu events.  When calling from a program,
 654 pass KEY as a string or a vector.
 655
 656 If non-nil, UNTRANSLATED is a vector of the corresponding untranslated events.
 657 It can also be a number, in which case the untranslated events from
 658 the last key sequence entered are used.
 659 UP-EVENT is the up-event that was discarded by reading KEY, or nil.
 660
 661 If KEY is a menu item or a tool-bar button that is disabled, this command
 662 temporarily enables it to allow getting help on disabled items and buttons."
 663   (interactive
 664    (let ((enable-disabled-menus-and-buttons t)
 665          (cursor-in-echo-area t)
 666          saved-yank-menu)
 667      (unwind-protect
 668          (let (key)
 669            ;; If yank-menu is empty, populate it temporarily, so that
 670            ;; "Select and Paste" menu can generate a complete event.
 671            (when (null (cdr yank-menu))
 672              (setq saved-yank-menu (copy-sequence yank-menu))
 673              (menu-bar-update-yank-menu "(any string)" nil))
 674            (setq key (read-key-sequence "Describe key (or click or menu item): "))
 675            (list
 676             key
 677             (prefix-numeric-value current-prefix-arg)
 678             ;; If KEY is a down-event, read and include the
 679             ;; corresponding up-event.  Note that there are also
 680             ;; down-events on scroll bars and mode lines: the actual
 681             ;; event then is in the second element of the vector.
 682             (and (vectorp key)
 683                  (let ((last-idx (1- (length key))))
 684                    (and (eventp (aref key last-idx))
 685                         (memq 'down (event-modifiers (aref key last-idx)))))
 686                  (or (and (eventp (aref key 0))
 687                           (memq 'down (event-modifiers (aref key 0)))
 688                           ;; However, for the C-down-mouse-2 popup
 689                           ;; menu, there is no subsequent up-event.  In
 690                           ;; this case, the up-event is the next
 691                           ;; element in the supplied vector.
 692                           (= (length key) 1))
 693                      (and (> (length key) 1)
 694                           (eventp (aref key 1))
 695                           (memq 'down (event-modifiers (aref key 1)))))
 696                  (read-event))))
 697        ;; Put yank-menu back as it was, if we changed it.
 698        (when saved-yank-menu
 699          (setq yank-menu (copy-sequence saved-yank-menu))
 700          (fset 'yank-menu (cons 'keymap yank-menu))))))
 701   (if (numberp untranslated)
 702       (setq untranslated (this-single-command-raw-keys)))
 703   (let* ((event (aref key (if (and (symbolp (aref key 0))
 704                                    (> (length key) 1)
 705                                    (consp (aref key 1)))
 706                               1
 707                             0)))
 708          (modifiers (event-modifiers event))
 709          (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
 710                             (memq 'drag modifiers)) " at that spot" ""))
 711          (defn (key-binding key t))
 712          defn-up defn-up-tricky ev-type
 713          mouse-1-remapped mouse-1-tricky)
 714
 715     ;; Handle the case where we faked an entry in "Select and Paste" menu.
 716     (when (and (eq defn nil)
 717                (stringp (aref key (1- (length key))))
 718                (eq (key-binding (substring key 0 -1)) 'yank-menu))
 719       (setq defn 'menu-bar-select-yank))
 720     (if (or (null defn) (integerp defn) (equal defn 'undefined))
 721         (message "%s%s is undefined"
 722                  (help-key-description key untranslated) mouse-msg)
 723       (help-setup-xref (list #'describe-function defn)
 724                        (called-interactively-p 'interactive))
 725       ;; Don't bother user with strings from (e.g.) the select-paste menu.
 726       (when (stringp (aref key (1- (length key))))
 727         (aset key (1- (length key)) "(any string)"))
 728       (when (and untranslated
 729                  (stringp (aref untranslated (1- (length untranslated)))))
 730         (aset untranslated (1- (length untranslated))
 731               "(any string)"))
 732       ;; Need to do this before erasing *Help* buffer in case event
 733       ;; is a mouse click in an existing *Help* buffer.
 734       (when up-event
 735         (setq ev-type (event-basic-type up-event))
 736         (let ((sequence (vector up-event)))
 737           (when (and (eq ev-type 'mouse-1)
 738                      mouse-1-click-follows-link
 739                      (not (eq mouse-1-click-follows-link 'double))
 740                      (setq mouse-1-remapped
 741                            (mouse-on-link-p (event-start up-event))))
 742             (setq mouse-1-tricky (and (integerp mouse-1-click-follows-link)
 743                                       (> mouse-1-click-follows-link 0)))
 744             (cond ((stringp mouse-1-remapped)
 745                    (setq sequence mouse-1-remapped))
 746                   ((vectorp mouse-1-remapped)
 747                    (setcar up-event (elt mouse-1-remapped 0)))
 748                   (t (setcar up-event 'mouse-2))))
 749           (setq defn-up (key-binding sequence nil nil (event-start up-event)))
 750           (when mouse-1-tricky
 751             (setq sequence (vector up-event))
 752             (aset sequence 0 'mouse-1)
 753             (setq defn-up-tricky (key-binding sequence nil nil (event-start up-event))))))
 754       (with-help-window (help-buffer)
 755         (princ (help-key-description key untranslated))
 756         (princ (format "\
 757 %s runs the command %S, which is "
 758                        mouse-msg defn))
 759         (describe-function-1 defn)
 760         (when up-event
 761           (unless (or (null defn-up)
 762                       (integerp defn-up)
 763                       (equal defn-up 'undefined))
 764             (princ (format "
 765
 766 ----------------- up-event %s----------------
 767
 768 %s%s%s runs the command %S, which is "
 769                            (if mouse-1-tricky "(short click) " "")
 770                            (key-description (vector up-event))
 771                            mouse-msg
 772                            (if mouse-1-remapped
 773                                " is remapped to <mouse-2>, which" "")
 774                            defn-up))
 775             (describe-function-1 defn-up))
 776           (unless (or (null defn-up-tricky)
 777                       (integerp defn-up-tricky)
 778                       (eq defn-up-tricky 'undefined))
 779             (princ (format "
 780
 781 ----------------- up-event (long click) ----------------
 782
 783 Pressing <%S>%s for longer than %d milli-seconds
 784 runs the command %S, which is "
 785                            ev-type mouse-msg
 786                            mouse-1-click-follows-link
 787                            defn-up-tricky))
 788             (describe-function-1 defn-up-tricky)))))))
 789 \f
 790 (defun describe-mode (&optional buffer)
 791   "Display documentation of current major mode and minor modes.
 792 A brief summary of the minor modes comes first, followed by the
 793 major mode description.  This is followed by detailed
 794 descriptions of the minor modes, each on a separate page.
 795
 796 For this to work correctly for a minor mode, the mode's indicator
 797 variable \(listed in `minor-mode-alist') must also be a function
 798 whose documentation describes the minor mode."
 799   (interactive "@")
 800   (unless buffer (setq buffer (current-buffer)))
 801   (help-setup-xref (list #'describe-mode buffer)
 802                    (called-interactively-p 'interactive))
 803   ;; For the sake of help-do-xref and help-xref-go-back,
 804   ;; don't switch buffers before calling `help-buffer'.
 805   (with-help-window (help-buffer)
 806     (with-current-buffer buffer
 807       (let (minor-modes)
 808         ;; Older packages do not register in minor-mode-list but only in
 809         ;; minor-mode-alist.
 810         (dolist (x minor-mode-alist)
 811           (setq x (car x))
 812           (unless (memq x minor-mode-list)
 813             (push x minor-mode-list)))
 814         ;; Find enabled minor mode we will want to mention.
 815         (dolist (mode minor-mode-list)
 816           ;; Document a minor mode if it is listed in minor-mode-alist,
 817           ;; non-nil, and has a function definition.
 818           (let ((fmode (or (get mode :minor-mode-function) mode)))
 819             (and (boundp mode) (symbol-value mode)
 820                  (fboundp fmode)
 821                  (let ((pretty-minor-mode
 822                         (if (string-match "\\(\\(-minor\\)?-mode\\)?\\'"
 823                                           (symbol-name fmode))
 824                             (capitalize
 825                              (substring (symbol-name fmode)
 826                                         0 (match-beginning 0)))
 827                           fmode)))
 828                    (push (list fmode pretty-minor-mode
 829                                (format-mode-line (assq mode minor-mode-alist)))
 830                          minor-modes)))))
 831         (setq minor-modes
 832               (sort minor-modes
 833                     (lambda (a b) (string-lessp (cadr a) (cadr b)))))
 834         (when minor-modes
 835           (princ "Enabled minor modes:\n")
 836           (make-local-variable 'help-button-cache)
 837           (with-current-buffer standard-output
 838             (dolist (mode minor-modes)
 839               (let ((mode-function (nth 0 mode))
 840                     (pretty-minor-mode (nth 1 mode))
 841                     (indicator (nth 2 mode)))
 842                 (add-text-properties 0 (length pretty-minor-mode)
 843                                      '(face bold) pretty-minor-mode)
 844                 (save-excursion
 845                   (goto-char (point-max))
 846                   (princ "\n\f\n")
 847                   (push (point-marker) help-button-cache)
 848                   ;; Document the minor modes fully.
 849                   (insert pretty-minor-mode)
 850                   (princ (format " minor mode (%s):\n"
 851                                  (if (zerop (length indicator))
 852                                      "no indicator"
 853                                    (format "indicator%s"
 854                                            indicator))))
 855                   (princ (documentation mode-function)))
 856                 (insert-button pretty-minor-mode
 857                                'action (car help-button-cache)
 858                                'follow-link t
 859                                'help-echo "mouse-2, RET: show full information")
 860                 (newline)))
 861             (forward-line -1)
 862             (fill-paragraph nil)
 863             (forward-line 1))
 864
 865           (princ "\n(Information about these minor modes follows the major mode info.)\n\n"))
 866         ;; Document the major mode.
 867         (let ((mode mode-name))
 868           (with-current-buffer standard-output
 869             (let ((start (point)))
 870               (insert (format-mode-line mode nil nil buffer))
 871               (add-text-properties start (point) '(face bold)))))
 872         (princ " mode")
 873         (let* ((mode major-mode)
 874                (file-name (find-lisp-object-file-name mode nil)))
 875           (when file-name
 876             (princ (concat " defined in `" (file-name-nondirectory file-name) "'"))
 877             ;; Make a hyperlink to the library.
 878             (with-current-buffer standard-output
 879               (save-excursion
 880                 (re-search-backward "`\\([^`']+\\)'" nil t)
 881                 (help-xref-button 1 'help-function-def mode file-name)))))
 882         (princ ":\n")
 883         (princ (documentation major-mode)))))
 884   ;; For the sake of IELM and maybe others
 885   nil)
 886
 887
 888 (defun describe-minor-mode (minor-mode)
 889   "Display documentation of a minor mode given as MINOR-MODE.
 890 MINOR-MODE can be a minor mode symbol or a minor mode indicator string
 891 appeared on the mode-line."
 892   (interactive (list (completing-read
 893                       "Minor mode: "
 894                               (nconc
 895                                (describe-minor-mode-completion-table-for-symbol)
 896                                (describe-minor-mode-completion-table-for-indicator)
 897                                ))))
 898   (if (symbolp minor-mode)
 899       (setq minor-mode (symbol-name minor-mode)))
 900   (let ((symbols (describe-minor-mode-completion-table-for-symbol))
 901         (indicators (describe-minor-mode-completion-table-for-indicator)))
 902     (cond
 903      ((member minor-mode symbols)
 904       (describe-minor-mode-from-symbol (intern minor-mode)))
 905      ((member minor-mode indicators)
 906       (describe-minor-mode-from-indicator minor-mode))
 907      (t
 908       (error "No such minor mode: %s" minor-mode)))))
 909
 910 ;; symbol
 911 (defun describe-minor-mode-completion-table-for-symbol ()
 912   ;; In order to list up all minor modes, minor-mode-list
 913   ;; is used here instead of minor-mode-alist.
 914   (delq nil (mapcar 'symbol-name minor-mode-list)))
 915
 916 (defun describe-minor-mode-from-symbol (symbol)
 917   "Display documentation of a minor mode given as a symbol, SYMBOL"
 918   (interactive (list (intern (completing-read
 919                               "Minor mode symbol: "
 920                               (describe-minor-mode-completion-table-for-symbol)))))
 921   (if (fboundp symbol)
 922       (describe-function symbol)
 923     (describe-variable symbol)))
 924
 925 ;; indicator
 926 (defun describe-minor-mode-completion-table-for-indicator ()
 927   (delq nil
 928         (mapcar (lambda (x)
 929                   (let ((i (format-mode-line x)))
 930                     ;; remove first space if existed
 931                     (cond
 932                      ((= 0 (length i))
 933                       nil)
 934                      ((eq (aref i 0) ?\s)
 935                       (substring i 1))
 936                      (t
 937                       i))))
 938                 minor-mode-alist)))
 939
 940 (defun describe-minor-mode-from-indicator (indicator)
 941   "Display documentation of a minor mode specified by INDICATOR.
 942 If you call this function interactively, you can give indicator which
 943 is currently activated with completion."
 944   (interactive (list
 945                 (completing-read
 946                  "Minor mode indicator: "
 947                  (describe-minor-mode-completion-table-for-indicator))))
 948   (let ((minor-mode (lookup-minor-mode-from-indicator indicator)))
 949     (if minor-mode
 950         (describe-minor-mode-from-symbol minor-mode)
 951       (error "Cannot find minor mode for `%s'" indicator))))
 952
 953 (defun lookup-minor-mode-from-indicator (indicator)
 954   "Return a minor mode symbol from its indicator on the modeline."
 955   ;; remove first space if existed
 956   (if (and (< 0 (length indicator))
 957            (eq (aref indicator 0) ?\s))
 958       (setq indicator (substring indicator 1)))
 959   (let ((minor-modes minor-mode-alist)
 960         result)
 961     (while minor-modes
 962       (let* ((minor-mode (car (car minor-modes)))
 963              (anindicator (format-mode-line
 964                            (car (cdr (car minor-modes))))))
 965         ;; remove first space if existed
 966         (if (and (stringp anindicator)
 967                  (> (length anindicator) 0)
 968                  (eq (aref anindicator 0) ?\s))
 969             (setq anindicator (substring anindicator 1)))
 970         (if (equal indicator anindicator)
 971             (setq result minor-mode
 972                   minor-modes nil)
 973           (setq minor-modes (cdr minor-modes)))))
 974     result))
 975 \f
 976 ;;; Automatic resizing of temporary buffers.
 977 (defcustom temp-buffer-max-height (lambda (buffer) (/ (- (frame-height) 2) 2))
 978   "Maximum height of a window displaying a temporary buffer.
 979 This is effective only when Temp Buffer Resize mode is enabled.
 980 The value is the maximum height (in lines) which
 981 `resize-temp-buffer-window' will give to a window displaying a
 982 temporary buffer.  It can also be a function to be called to
 983 choose the height for such a buffer.  It gets one argumemt, the
 984 buffer, and should return a positive integer.  At the time the
 985 function is called, the window to be resized is selected."
 986   :type '(choice integer function)
 987   :group 'help
 988   :version "20.4")
 989
 990 (define-minor-mode temp-buffer-resize-mode
 991   "Toggle mode which makes windows smaller for temporary buffers.
 992 With prefix argument ARG, turn the resizing of windows displaying
 993 temporary buffers on if ARG is positive or off otherwise.
 994
 995 This mode makes a window the right height for its contents, but
 996 never more than `temp-buffer-max-height' nor less than
 997 `window-min-height'.
 998
 999 This mode is used by `help', `apropos' and `completion' buffers,
1000 and some others."
1001   :global t :group 'help
1002   (if temp-buffer-resize-mode
1003       ;; `help-make-xrefs' may add a `back' button and thus increase the
1004       ;; text size, so `resize-temp-buffer-window' must be run *after* it.
1005       (add-hook 'temp-buffer-show-hook 'resize-temp-buffer-window 'append)
1006     (remove-hook 'temp-buffer-show-hook 'resize-temp-buffer-window)))
1007
1008 (defun resize-temp-buffer-window ()
1009   "Resize the selected window to fit its contents.
1010 Will not make it higher than `temp-buffer-max-height' nor smaller
1011 than `window-min-height'.  Do nothing if the selected window is
1012 not vertically combined or some of its contents are scrolled out
1013 of view."
1014   (when (and (pos-visible-in-window-p (point-min))
1015              (window-iso-combined-p))
1016     (fit-window-to-buffer
1017      nil
1018      (if (functionp temp-buffer-max-height)
1019          (funcall temp-buffer-max-height (window-buffer))
1020        temp-buffer-max-height))))
1021
1022 ;;; Help windows.
1023 (defcustom help-window-select 'other
1024     "Non-nil means select help window for viewing.
1025 Choices are:
1026  never (nil) Select help window only if there is no other window
1027              on its frame.
1028  other       Select help window unless the selected window is the
1029              only other window on the help window's frame.
1030  always (t)  Always select the help window.
1031
1032 This option has effect if and only if the help window was created
1033 by `with-help-window'"
1034   :type '(choice (const :tag "never (nil)" nil)
1035                  (const :tag "other" other)
1036                  (const :tag "always (t)" t))
1037   :group 'help
1038   :version "23.1")
1039
1040 (defun help-window-display-message (quit-part window &optional scroll)
1041   "Display message telling how to quit and scroll help window.
1042 QUIT-PART is a string telling how to quit the help window WINDOW.
1043 Optional argument SCROLL non-nil means tell how to scroll WINDOW.
1044 SCROLL equal `other' means tell how to scroll the \"other\"
1045 window."
1046   (let ((scroll-part
1047          (cond
1048           ;; If we don't have QUIT-PART we probably reuse a window
1049           ;; showing the same buffer so we don't show any message.
1050           ((not quit-part) nil)
1051           ((pos-visible-in-window-p
1052             (with-current-buffer (window-buffer window)
1053               (point-max)) window t)
1054            ;; Buffer end is at least partially visible, no need to talk
1055            ;; about scrolling.
1056            ".")
1057           ((eq scroll 'other)
1058            ", \\[scroll-other-window] to scroll help.")
1059           (scroll ", \\[scroll-up] to scroll help."))))
1060     (message "%s"
1061      (substitute-command-keys (concat quit-part scroll-part)))))
1062
1063 (defun help-window-setup ()
1064   "Set up help window for `with-help-window'.
1065 This relies on `display-buffer-window' being correctly set up by
1066 `display-buffer'."
1067   (let* ((help-window (car-safe display-buffer-window))
1068          (help-buffer (when (window-live-p help-window)
1069                         (window-buffer help-window)))
1070          (help-value (cdr-safe display-buffer-window)))
1071     (when help-buffer
1072       ;; Handle `help-window-point-marker'.
1073       (when (eq (marker-buffer help-window-point-marker) help-buffer)
1074         (set-window-point help-window help-window-point-marker)
1075         ;; Reset `help-window-point-marker'.
1076         (set-marker help-window-point-marker nil))
1077
1078       (cond
1079        ((or (eq help-window (selected-window))
1080             (and (or (eq help-window-select t)
1081                      (and (eq help-window-select 'other)
1082                           (eq (window-frame help-window) (selected-frame))
1083                           (> (length (window-list nil 'no-mini)) 2)))
1084                  (select-window help-window)))
1085         ;; The help window is or gets selected ...
1086         (help-window-display-message
1087          (cond
1088           ((eq help-value 'new-window)
1089            ;; ... and is new, ...
1090            "Type \"q\" to delete this window")
1091           ((eq help-value 'new-frame)
1092            ;; ... is on a new frame ...
1093            "Type \"q\" to delete this frame")
1094           ((eq help-value 'reuse-other-window)
1095            ;; ... or displayed some other buffer before.
1096            "Type \"q\" to restore previous buffer"))
1097          help-window t))
1098        ((and (eq (window-frame help-window) (selected-frame))
1099              (= (length (window-list nil 'no-mini)) 2))
1100         ;; There are two windows on the help window's frame and the
1101         ;; other one is the selected one.
1102         (help-window-display-message
1103          (cond
1104           ((eq help-value 'new-window)
1105            "Type \\[delete-other-windows] to delete the help window")
1106           ((eq help-value 'reuse-other-window)
1107            "Type \"q\" in other window to quit"))
1108          help-window 'other))
1109        (t
1110         ;; Not much to say here.
1111         (help-window-display-message
1112          "Type \"q\" in help window to quit" help-window))))))
1113
1114 ;; `with-help-window' is a wrapper for `with-output-to-temp-buffer'
1115 ;; providing the following additional twists:
1116
1117 ;; (1) Issue more accurate messages telling how to scroll and quit the
1118 ;; help window.
1119
1120 ;; (2) An option (customizable via `help-window-select') to select the
1121 ;; help window automatically.
1122
1123 ;; (3) A marker (`help-window-point-marker') to move point in the help
1124 ;; window to an arbitrary buffer position.
1125
1126 ;; Note: It's usually always wrong to use `help-print-return-message' in
1127 ;; the body of `with-help-window'.
1128 (defmacro with-help-window (buffer-name &rest body)
1129   "Display buffer with name BUFFER-NAME in a help window evaluating BODY.
1130 Select help window if the actual value of the user option
1131 `help-window-select' says so.  Return last value in BODY.
1132
1133 You can specify where and how to show the buffer by binding the
1134 variable `temp-buffer-show-specifiers' to an appropriate value."
1135   (declare (indent 1) (debug t))
1136   `(progn
1137      ;; Reset `display-buffer-window': `display-buffer' is
1138      ;; supposed to set this to the window displaying the buffer plus
1139      ;; some additional information.
1140      (setq display-buffer-window nil)
1141      ;; Make `help-window-point-marker' point nowhere.  The only place
1142      ;; where this should be set to a buffer position is within BODY.
1143      (set-marker help-window-point-marker nil)
1144      (prog1
1145          ;; Return value returned by `with-output-to-temp-buffer'.
1146          (with-output-to-temp-buffer ,buffer-name
1147            (progn ,@body))
1148        (when display-buffer-window (help-window-setup)))))
1149
1150 ;; Called from C, on encountering `help-char' when reading a char.
1151 ;; Don't print to *Help*; that would clobber Help history.
1152 (defun help-form-show ()
1153   "Display the output of a non-nil `help-form'."
1154   (let ((msg (eval help-form)))
1155     (if (stringp msg)
1156         (with-output-to-temp-buffer " *Char Help*"
1157           (princ msg)))))
1158 \f
1159 (provide 'help)
1160
1161 ;;; help.el ends here