emacs/lisp/help.el

;;; help.el --- help commands for Emacs

;; Copyright (C) 1985-1986, 1993-1994, 1998-2011
;;   Free Software Foundation, Inc.

;; Maintainer: FSF
;; Keywords: help, internal
;; Package: emacs

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This code implements GNU Emacs' on-line help system, the one invoked by
;; `M-x help-for-help'.

;;; Code:

;; Get the macro make-help-screen when this is compiled,
;; or run interpreted, but not when the compiled code is loaded.
(eval-when-compile (require 'help-macro))

;; This makes `with-output-to-temp-buffer' buffers use `help-mode'.
(add-hook 'temp-buffer-setup-hook 'help-mode-setup)
(add-hook 'temp-buffer-show-hook 'help-mode-finish)

;; `help-window-point-marker' is a marker you can move to a valid
;; position of the buffer shown in the help window in order to override
;; the standard positioning mechanism (`point-min') chosen by
;; `with-output-to-temp-buffer'.  `with-help-window' has this point
;; nowhere before exiting.  Currently used by `view-lossage' to assert
;; that the last keystrokes are always visible.
(defvar help-window-point-marker (make-marker)
  "Marker to override default `window-point' in help windows.")

(defvar help-map
  (let ((map (make-sparse-keymap)))
    (define-key map (char-to-string help-char) 'help-for-help)
    (define-key map [help] 'help-for-help)
    (define-key map [f1] 'help-for-help)
    (define-key map "." 'display-local-help)
    (define-key map "?" 'help-for-help)

    (define-key map "\C-a" 'about-emacs)
    (define-key map "\C-c" 'describe-copying)
    (define-key map "\C-d" 'view-emacs-debugging)
    (define-key map "\C-e" 'view-external-packages)
    (define-key map "\C-f" 'view-emacs-FAQ)
    (define-key map "\C-m" 'view-order-manuals)
    (define-key map "\C-n" 'view-emacs-news)
    (define-key map "\C-o" 'describe-distribution)
    (define-key map "\C-p" 'view-emacs-problems)
    (define-key map "\C-t" 'view-emacs-todo)
    (define-key map "\C-w" 'describe-no-warranty)

    ;; This does not fit the pattern, but it is natural given the C-\ command.
    (define-key map "\C-\\" 'describe-input-method)

    (define-key map "C" 'describe-coding-system)
    (define-key map "F" 'Info-goto-emacs-command-node)
    (define-key map "I" 'describe-input-method)
    (define-key map "K" 'Info-goto-emacs-key-command-node)
    (define-key map "L" 'describe-language-environment)
    (define-key map "S" 'info-lookup-symbol)

    (define-key map "a" 'apropos-command)
    (define-key map "b" 'describe-bindings)
    (define-key map "c" 'describe-key-briefly)
    (define-key map "d" 'apropos-documentation)
    (define-key map "e" 'view-echo-area-messages)
    (define-key map "f" 'describe-function)
    (define-key map "g" 'describe-gnu-project)
    (define-key map "h" 'view-hello-file)

    (define-key map "i" 'info)
    (define-key map "4i" 'info-other-window)

    (define-key map "k" 'describe-key)
    (define-key map "l" 'view-lossage)
    (define-key map "m" 'describe-mode)
    (define-key map "n" 'view-emacs-news)
    (define-key map "p" 'finder-by-keyword)
    (define-key map "P" 'describe-package)
    (define-key map "r" 'info-emacs-manual)
    (define-key map "s" 'describe-syntax)
    (define-key map "t" 'help-with-tutorial)
    (define-key map "w" 'where-is)
    (define-key map "v" 'describe-variable)
    (define-key map "q" 'help-quit)
    map)
  "Keymap for characters following the Help key.")

(define-key global-map (char-to-string help-char) 'help-command)
(define-key global-map [help] 'help-command)
(define-key global-map [f1] 'help-command)
(fset 'help-command help-map)

;; insert-button makes the action nil if it is not store somewhere
(defvar help-button-cache nil)


(defun help-quit ()
  "Just exit from the Help command's command loop."
  (interactive)
  nil)

(defvar help-return-method nil
  "What to do to \"exit\" the help buffer.
This is a list
 (WINDOW . t)              delete the selected window (and possibly its frame,
                           see `quit-window'), go to WINDOW.
 (WINDOW . quit-window)    do quit-window, then select WINDOW.
 (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")

(define-obsolete-function-alias 'print-help-return-message 'help-print-return-message "23.2")
(defun help-print-return-message (&optional function)
  "Display or return message saying how to restore windows after help command.
This function assumes that `standard-output' is the help buffer.
It computes a message, and applies the optional argument FUNCTION to it.
If FUNCTION is nil, it applies `message', thus displaying the message.
In addition, this function sets up `help-return-method', which see, that
specifies what to do when the user exits the help buffer."
  (and (not (get-buffer-window standard-output))
       (let ((first-message
	      (cond ((or
		      pop-up-frames
		      (special-display-p (buffer-name standard-output)))
		     (setq help-return-method (cons (selected-window) t))
		     ;; If the help output buffer is a special display buffer,
		     ;; don't say anything about how to get rid of it.
		     ;; First of all, the user will do that with the window
		     ;; manager, not with Emacs.
		     ;; Secondly, the buffer has not been displayed yet,
		     ;; so we don't know whether its frame will be selected.
		     nil)
		    (display-buffer-reuse-frames
		     (setq help-return-method (cons (selected-window)
						    'quit-window))
		     nil)
		    ((not (one-window-p t))
		     (setq help-return-method
			   (cons (selected-window) 'quit-window))
		     "Type \\[display-buffer] RET to restore the other window.")
		    (pop-up-windows
		     (setq help-return-method (cons (selected-window) t))
		     "Type \\[delete-other-windows] to remove help window.")
		    (t
		     (setq help-return-method
			   (list (selected-window) (window-buffer)
				 (window-start) (window-point)))
		     "Type \\[switch-to-buffer] RET to remove help window."))))
	 (funcall (or function 'message)
		  (concat
		   (if first-message
		       (substitute-command-keys first-message))
		   (if first-message "  ")
		   ;; If the help buffer will go in a separate frame,
		   ;; it's no use mentioning a command to scroll, so don't.
		   (if (or pop-up-windows
			   (special-display-p (buffer-name standard-output)))
		       nil
		     (if (same-window-p (buffer-name standard-output))
			 ;; Say how to scroll this window.
			 (substitute-command-keys
			  "\\[scroll-up] to scroll the help.")
		       ;; Say how to scroll some other window.
		       (substitute-command-keys
			"\\[scroll-other-window] to scroll the help."))))))))

;; So keyboard macro definitions are documented correctly
(fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))

(defalias 'help 'help-for-help-internal)
;; find-function can find this.
(defalias 'help-for-help 'help-for-help-internal)
;; It can't find this, but nobody will look.
(make-help-screen help-for-help-internal
  (purecopy "Type a help option: [abcCdefFgiIkKlLmnprstvw.] C-[cdefmnoptw] or ?")
  ;; Don't purecopy this one, because it's not evaluated (it's
  ;; directly used as a docstring in a function definition, so it'll
  ;; be moved to the DOC file anyway: no need for purecopying it).
  "You have typed %THIS-KEY%, the help character.  Type a Help option:
\(Use SPC or DEL to scroll through this text.  Type \\<help-map>\\[help-quit] to exit the Help command.)

a PATTERN   Show commands whose name matches the PATTERN (a list of words
              or a regexp).  See also the `apropos' command.
b           Display all key bindings.
c KEYS      Display the command name run by the given key sequence.
C CODING    Describe the given coding system, or RET for current ones.
d PATTERN   Show a list of functions, variables, and other items whose
              documentation matches the PATTERN (a list of words or a regexp).
e           Go to the *Messages* buffer which logs echo-area messages.
f FUNCTION  Display documentation for the given function.
F COMMAND   Show the on-line manual's section that describes the command.
g           Display information about the GNU project.
h           Display the HELLO file which illustrates various scripts.
i           Start the Info documentation reader: read on-line manuals.
I METHOD    Describe a specific input method, or RET for current.
k KEYS      Display the full documentation for the key sequence.
K KEYS      Show the on-line manual's section for the command bound to KEYS.
l           Show last 300 input keystrokes (lossage).
L LANG-ENV  Describes a specific language environment, or RET for current.
m           Display documentation of current minor modes and current major mode,
              including their special commands.
n           Display news of recent Emacs changes.
p TOPIC     Find packages matching a given topic keyword.
r           Display the Emacs manual in Info mode.
s           Display contents of current syntax table, plus explanations.
S SYMBOL    Show the section for the given symbol in the on-line manual
              for the programming language used in this buffer.
t           Start the Emacs learn-by-doing tutorial.
v VARIABLE  Display the given variable's documentation and value.
w COMMAND   Display which keystrokes invoke the given command (where-is).
.           Display any available local help at point in the echo area.

C-a         Information about Emacs.
C-c         Emacs copying permission (GNU General Public License).
C-d         Instructions for debugging GNU Emacs.
C-e         External packages and information about Emacs.
C-f         Emacs FAQ.
C-m         How to order printed Emacs manuals.
C-n         News of recent Emacs changes.
C-o         Emacs ordering and distribution information.
C-p         Info about known Emacs problems.
C-t         Emacs TODO list.
C-w         Information on absence of warranty for GNU Emacs."
  help-map)



(defun function-called-at-point ()
  "Return a function around point or else called by the list containing point.
If that doesn't give a function, return nil."
  (with-syntax-table emacs-lisp-mode-syntax-table
    (or (condition-case ()
            (save-excursion
              (or (not (zerop (skip-syntax-backward "_w")))
                  (eq (char-syntax (following-char)) ?w)
                  (eq (char-syntax (following-char)) ?_)
                  (forward-sexp -1))
              (skip-chars-forward "'")
              (let ((obj (read (current-buffer))))
                (and (symbolp obj) (fboundp obj) obj)))
          (error nil))
        (condition-case ()
            (save-excursion
              (save-restriction
                (narrow-to-region (max (point-min)
                                       (- (point) 1000)) (point-max))
                ;; Move up to surrounding paren, then after the open.
                (backward-up-list 1)
                (forward-char 1)
                ;; If there is space here, this is probably something
                ;; other than a real Lisp function call, so ignore it.
                (if (looking-at "[ \t]")
                    (error "Probably not a Lisp function call"))
                (let ((obj (read (current-buffer))))
                  (and (symbolp obj) (fboundp obj) obj))))
          (error nil))
        (let* ((str (find-tag-default))
               (sym (if str (intern-soft str))))
          (if (and sym (fboundp sym))
              sym
            (save-match-data
              (when (and str (string-match "\\`\\W*\\(.*?\\)\\W*\\'" str))
                (setq sym (intern-soft (match-string 1 str)))
                (and (fboundp sym) sym))))))))


;;; `User' help functions

(defun view-help-file (file &optional dir)
  (view-file (expand-file-name file (or dir data-directory)))
  (goto-address-mode 1)
  (goto-char (point-min)))

(defun describe-distribution ()
  "Display info on how to obtain the latest version of GNU Emacs."
  (interactive)
  (view-help-file "DISTRIB"))

(defun describe-copying ()
  "Display info on how you may redistribute copies of GNU Emacs."
  (interactive)
  (view-help-file "COPYING"))

(defun describe-gnu-project ()
  "Display info on the GNU project."
  (interactive)
  (view-help-file "THE-GNU-PROJECT"))

(define-obsolete-function-alias 'describe-project 'describe-gnu-project "22.2")

(defun describe-no-warranty ()
  "Display info on all the kinds of warranty Emacs does NOT have."
  (interactive)
  (describe-copying)
  (let (case-fold-search)
    (search-forward "Disclaimer of Warranty")
    (forward-line 0)
    (recenter 0)))

(defun describe-prefix-bindings ()
  "Describe the bindings of the prefix used to reach this command.
The prefix described consists of all but the last event
of the key sequence that ran this command."
  (interactive)
  (let ((key (this-command-keys)))
    (describe-bindings
     (if (stringp key)
	 (substring key 0 (1- (length key)))
       (let ((prefix (make-vector (1- (length key)) nil))
	     (i 0))
	 (while (< i (length prefix))
	   (aset prefix i (aref key i))
	   (setq i (1+ i)))
	 prefix)))))
;; Make C-h after a prefix, when not specifically bound,
;; run describe-prefix-bindings.
(setq prefix-help-command 'describe-prefix-bindings)

(defun view-emacs-news (&optional version)
  "Display info on recent changes to Emacs.
With argument, display info only for the selected version."
  (interactive "P")
  (unless version
    (setq version emacs-major-version))
  (when (consp version)
    (let* ((all-versions
	    (let (res)
	      (mapc
	       (lambda (file)
		 (with-temp-buffer
		   (insert-file-contents
		    (expand-file-name file data-directory))
		   (while (re-search-forward
			   (if (member file '("NEWS.18" "NEWS.1-17"))
			       "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
			     "^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t)
		     (setq res (cons (match-string-no-properties 1) res)))))
	       (cons "NEWS"
		     (directory-files data-directory nil
				      "^NEWS\\.[0-9][-0-9]*$" nil)))
	      (sort (delete-dups res) (lambda (a b) (string< b a)))))
	   (current (car all-versions)))
      (setq version (completing-read
		     (format "Read NEWS for the version (default %s): " current)
		     all-versions nil nil nil nil current))
      (if (integerp (string-to-number version))
	  (setq version (string-to-number version))
	(unless (or (member version all-versions)
		    (<= (string-to-number version) (string-to-number current)))
	  (error "No news about version %s" version)))))
  (when (integerp version)
    (cond ((<= version 12)
	   (setq version (format "1.%d" version)))
	  ((<= version 18)
	   (setq version (format "%d" version)))
	  ((> version emacs-major-version)
	   (error "No news about Emacs %d (yet)" version))))
  (let* ((vn (if (stringp version)
		 (string-to-number version)
	       version))
	 (file (cond
		((>= vn emacs-major-version) "NEWS")
		((< vn 18) "NEWS.1-17")
		(t (format "NEWS.%d" vn))))
	 res)
    (view-file (expand-file-name file data-directory))
    (widen)
    (goto-char (point-min))
    (when (stringp version)
      (when (re-search-forward
	     (concat (if (< vn 19)
			 "Changes in Emacs[ \t]*"
		       "^\* [^0-9\n]*") version "$")
	     nil t)
	(beginning-of-line)
	(narrow-to-region
	 (point)
	 (save-excursion
	   (while (and (setq res
			     (re-search-forward
			      (if (< vn 19)
				  "Changes in \\(?:Emacs\\|version\\)?[ \t]*\\([0-9]+\\(?:\\.[0-9]+\\)?\\)"
				"^\* [^0-9\n]*\\([0-9]+\\.[0-9]+\\)") nil t))
		       (equal (match-string-no-properties 1) version)))
	   (or res (goto-char (point-max)))
	   (beginning-of-line)
	   (point)))))))

(defun view-emacs-todo (&optional _arg)
  "Display the Emacs TODO list."
  (interactive "P")
  (view-help-file "TODO"))

(define-obsolete-function-alias 'view-todo 'view-emacs-todo "22.2")


(defun view-echo-area-messages ()
  "View the log of recent echo-area messages: the `*Messages*' buffer.
The number of messages retained in that buffer
is specified by the variable `message-log-max'."
  (interactive)
  (switch-to-buffer (get-buffer-create "*Messages*")))

(defun view-order-manuals ()
  "Display the Emacs ORDERS file."
  (interactive)
  (view-help-file "ORDERS"))

(defun view-emacs-FAQ ()
  "Display the Emacs Frequently Asked Questions (FAQ) file."
  (interactive)
  ;; (find-file-read-only (expand-file-name "FAQ" data-directory))
  (info "(efaq)"))

(defun view-emacs-problems ()
  "Display info on known problems with Emacs and possible workarounds."
  (interactive)
  (view-help-file "PROBLEMS"))

(defun view-emacs-debugging ()
  "Display info on how to debug Emacs problems."
  (interactive)
  (view-help-file "DEBUG"))

(defun view-external-packages ()
  "Display external packages and information about Emacs."
  (interactive)
  (view-help-file "MORE.STUFF"))

(defun view-lossage ()
  "Display last 300 input keystrokes.

To record all your input on a file, use `open-dribble-file'."
  (interactive)
  (help-setup-xref (list #'view-lossage)
		   (called-interactively-p 'interactive))
  (with-help-window (help-buffer)
    (princ (mapconcat (lambda (key)
			(if (or (integerp key) (symbolp key) (listp key))
			    (single-key-description key)
			  (prin1-to-string key nil)))
		      (recent-keys)
		      " "))
    (with-current-buffer standard-output
      (goto-char (point-min))
      (while (progn (move-to-column 50) (not (eobp)))
        (when (search-forward " " nil t)
          (delete-char -1))
        (insert "\n"))
      ;; jidanni wants to see the last keystrokes immediately.
      (set-marker help-window-point-marker (point)))))


;; Key bindings

(defun describe-bindings (&optional prefix buffer)
  "Show a list of all defined keys, and their definitions.
We put that list in a buffer, and display the buffer.

The optional argument PREFIX, if non-nil, should be a key sequence;
then we display only bindings that start with that prefix.
The optional argument BUFFER specifies which buffer's bindings
to display (default, the current buffer).  BUFFER can be a buffer
or a buffer name."
  (interactive)
  (or buffer (setq buffer (current-buffer)))
  (help-setup-xref (list #'describe-bindings prefix buffer)
		   (called-interactively-p 'interactive))
  (with-current-buffer buffer
    (describe-bindings-internal nil prefix)))

;; This function used to be in keymap.c.
(defun describe-bindings-internal (&optional menus prefix)
  "Show a list of all defined keys, and their definitions.
We put that list in a buffer, and display the buffer.

The optional argument MENUS, if non-nil, says to mention menu bindings.
\(Ordinarily these are omitted from the output.)
The optional argument PREFIX, if non-nil, should be a key sequence;
then we display only bindings that start with that prefix."
  (let ((buf (current-buffer)))
    (with-help-window "*Help*"
      (with-current-buffer standard-output
	(describe-buffer-bindings buf prefix menus)))))

(defun where-is (definition &optional insert)
  "Print message listing key sequences that invoke the command DEFINITION.
Argument is a command definition, usually a symbol with a function definition.
If INSERT (the prefix arg) is non-nil, insert the message in the buffer."
  (interactive
   (let ((fn (function-called-at-point))
	 (enable-recursive-minibuffers t)
	 val)
     (setq val (completing-read
		(if fn
		    (format "Where is command (default %s): " fn)
		  "Where is command: ")
		obarray 'commandp t))
     (list (if (equal val "") fn (intern val)) current-prefix-arg)))
  (unless definition (error "No command"))
  (let ((func (indirect-function definition))
        (defs nil)
        (standard-output (if insert (current-buffer) standard-output)))
    ;; In DEFS, find all symbols that are aliases for DEFINITION.
    (mapatoms (lambda (symbol)
		(and (fboundp symbol)
		     (not (eq symbol definition))
		     (eq func (condition-case ()
				  (indirect-function symbol)
				(error symbol)))
		     (push symbol defs))))
    ;; Look at all the symbols--first DEFINITION,
    ;; then its aliases.
    (dolist (symbol (cons definition defs))
      (let* ((remapped (command-remapping symbol))
	     (keys (where-is-internal
		    symbol overriding-local-map nil nil remapped))
	     (keys (mapconcat 'key-description keys ", "))
	     string)
	(setq string
	      (if insert
		  (if (> (length keys) 0)
		      (if remapped
			  (format "%s (%s) (remapped from %s)"
				  keys remapped symbol)
			(format "%s (%s)" keys symbol))
		    (format "M-x %s RET" symbol))
		(if (> (length keys) 0)
		    (if remapped
			(format "%s is remapped to %s which is on %s"
				symbol remapped keys)
		      (format "%s is on %s" symbol keys))
		  ;; If this is the command the user asked about,
		  ;; and it is not on any key, say so.
		  ;; For other symbols, its aliases, say nothing
		  ;; about them unless they are on keys.
		  (if (eq symbol definition)
		      (format "%s is not on any key" symbol)))))
	(when string
	  (unless (eq symbol definition)
	    (princ ";\n its alias "))
	  (princ string)))))
  nil)

(defun help-key-description (key untranslated)
  (let ((string (key-description key)))
    (if (or (not untranslated)
	    (and (eq (aref untranslated 0) ?\e) (not (eq (aref key 0) ?\e))))
	string
      (let ((otherstring (key-description untranslated)))
	(if (equal string otherstring)
	    string
	  (format "%s (translated from %s)" string otherstring))))))

(defun describe-key-briefly (&optional key insert untranslated)
  "Print the name of the function KEY invokes.  KEY is a string.
If INSERT (the prefix arg) is non-nil, insert the message in the buffer.
If non-nil, UNTRANSLATED is a vector of the untranslated events.
It can also be a number in which case the untranslated events from
the last key hit are used.

If KEY is a menu item or a tool-bar button that is disabled, this command
temporarily enables it to allow getting help on disabled items and buttons."
  (interactive
   (let ((enable-disabled-menus-and-buttons t)
	 (cursor-in-echo-area t)
	 saved-yank-menu)
     (unwind-protect
	 (let (key)
	   ;; If yank-menu is empty, populate it temporarily, so that
	   ;; "Select and Paste" menu can generate a complete event.
	   (when (null (cdr yank-menu))
	     (setq saved-yank-menu (copy-sequence yank-menu))
	     (menu-bar-update-yank-menu "(any string)" nil))
	   (setq key (read-key-sequence "Describe key (or click or menu item): "))
	   ;; If KEY is a down-event, read and discard the
	   ;; corresponding up-event.  Note that there are also
	   ;; down-events on scroll bars and mode lines: the actual
	   ;; event then is in the second element of the vector.
	   (and (vectorp key)
		(let ((last-idx (1- (length key))))
		  (and (eventp (aref key last-idx))
		       (memq 'down (event-modifiers (aref key last-idx)))))
		(read-event))
	   (list
	    key
	    (if current-prefix-arg (prefix-numeric-value current-prefix-arg))
	    1))
       ;; Put yank-menu back as it was, if we changed it.
       (when saved-yank-menu
	 (setq yank-menu (copy-sequence saved-yank-menu))
	 (fset 'yank-menu (cons 'keymap yank-menu))))))
  (if (numberp untranslated)
      (setq untranslated (this-single-command-raw-keys)))
  (let* ((event (if (and (symbolp (aref key 0))
			 (> (length key) 1)
			 (consp (aref key 1)))
		    (aref key 1)
		  (aref key 0)))
	 (modifiers (event-modifiers event))
	 (standard-output (if insert (current-buffer) standard-output))
	 (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
			    (memq 'drag modifiers)) " at that spot" ""))
	 (defn (key-binding key t))
	 key-desc)
    ;; Handle the case where we faked an entry in "Select and Paste" menu.
    (if (and (eq defn nil)
	     (stringp (aref key (1- (length key))))
	     (eq (key-binding (substring key 0 -1)) 'yank-menu))
	(setq defn 'menu-bar-select-yank))
    ;; Don't bother user with strings from (e.g.) the select-paste menu.
    (if (stringp (aref key (1- (length key))))
	(aset key (1- (length key)) "(any string)"))
    (if (and (> (length untranslated) 0)
	     (stringp (aref untranslated (1- (length untranslated)))))
	(aset untranslated (1- (length untranslated)) "(any string)"))
    ;; Now describe the key, perhaps as changed.
    (setq key-desc (help-key-description key untranslated))
    (if (or (null defn) (integerp defn) (equal defn 'undefined))
	(princ (format "%s%s is undefined" key-desc mouse-msg))
      (princ (format "%s%s runs the command %S" key-desc mouse-msg defn)))))

(defun describe-key (&optional key untranslated up-event)
  "Display documentation of the function invoked by KEY.
KEY can be any kind of a key sequence; it can include keyboard events,
mouse events, and/or menu events.  When calling from a program,
pass KEY as a string or a vector.

If non-nil, UNTRANSLATED is a vector of the corresponding untranslated events.
It can also be a number, in which case the untranslated events from
the last key sequence entered are used.
UP-EVENT is the up-event that was discarded by reading KEY, or nil.

If KEY is a menu item or a tool-bar button that is disabled, this command
temporarily enables it to allow getting help on disabled items and buttons."
  (interactive
   (let ((enable-disabled-menus-and-buttons t)
	 (cursor-in-echo-area t)
	 saved-yank-menu)
     (unwind-protect
	 (let (key)
	   ;; If yank-menu is empty, populate it temporarily, so that
	   ;; "Select and Paste" menu can generate a complete event.
	   (when (null (cdr yank-menu))
	     (setq saved-yank-menu (copy-sequence yank-menu))
	     (menu-bar-update-yank-menu "(any string)" nil))
	   (setq key (read-key-sequence "Describe key (or click or menu item): "))
	   (list
	    key
	    (prefix-numeric-value current-prefix-arg)
	    ;; If KEY is a down-event, read and include the
	    ;; corresponding up-event.  Note that there are also
	    ;; down-events on scroll bars and mode lines: the actual
	    ;; event then is in the second element of the vector.
	    (and (vectorp key)
		 (let ((last-idx (1- (length key))))
		   (and (eventp (aref key last-idx))
			(memq 'down (event-modifiers (aref key last-idx)))))
		 (or (and (eventp (aref key 0))
			  (memq 'down (event-modifiers (aref key 0)))
			  ;; However, for the C-down-mouse-2 popup
			  ;; menu, there is no subsequent up-event.  In
			  ;; this case, the up-event is the next
			  ;; element in the supplied vector.
			  (= (length key) 1))
		     (and (> (length key) 1)
			  (eventp (aref key 1))
			  (memq 'down (event-modifiers (aref key 1)))))
		 (read-event))))
       ;; Put yank-menu back as it was, if we changed it.
       (when saved-yank-menu
	 (setq yank-menu (copy-sequence saved-yank-menu))
	 (fset 'yank-menu (cons 'keymap yank-menu))))))
  (if (numberp untranslated)
      (setq untranslated (this-single-command-raw-keys)))
  (let* ((event (aref key (if (and (symbolp (aref key 0))
				   (> (length key) 1)
				   (consp (aref key 1)))
			      1
			    0)))
	 (modifiers (event-modifiers event))
	 (mouse-msg (if (or (memq 'click modifiers) (memq 'down modifiers)
			    (memq 'drag modifiers)) " at that spot" ""))
	 (defn (key-binding key t))
	 defn-up defn-up-tricky ev-type
	 mouse-1-remapped mouse-1-tricky)

    ;; Handle the case where we faked an entry in "Select and Paste" menu.
    (when (and (eq defn nil)
	       (stringp (aref key (1- (length key))))
	       (eq (key-binding (substring key 0 -1)) 'yank-menu))
      (setq defn 'menu-bar-select-yank))
    (if (or (null defn) (integerp defn) (equal defn 'undefined))
	(message "%s%s is undefined"
		 (help-key-description key untranslated) mouse-msg)
      (help-setup-xref (list #'describe-function defn)
		       (called-interactively-p 'interactive))
      ;; Don't bother user with strings from (e.g.) the select-paste menu.
      (when (stringp (aref key (1- (length key))))
	(aset key (1- (length key)) "(any string)"))
      (when (and untranslated
		 (stringp (aref untranslated (1- (length untranslated)))))
	(aset untranslated (1- (length untranslated))
	      "(any string)"))
      ;; Need to do this before erasing *Help* buffer in case event
      ;; is a mouse click in an existing *Help* buffer.
      (when up-event
	(setq ev-type (event-basic-type up-event))
	(let ((sequence (vector up-event)))
	  (when (and (eq ev-type 'mouse-1)
		     mouse-1-click-follows-link
		     (not (eq mouse-1-click-follows-link 'double))
		     (setq mouse-1-remapped
			   (mouse-on-link-p (event-start up-event))))
	    (setq mouse-1-tricky (and (integerp mouse-1-click-follows-link)
				      (> mouse-1-click-follows-link 0)))
	    (cond ((stringp mouse-1-remapped)
		   (setq sequence mouse-1-remapped))
		  ((vectorp mouse-1-remapped)
		   (setcar up-event (elt mouse-1-remapped 0)))
		  (t (setcar up-event 'mouse-2))))
	  (setq defn-up (key-binding sequence nil nil (event-start up-event)))
	  (when mouse-1-tricky
	    (setq sequence (vector up-event))
	    (aset sequence 0 'mouse-1)
	    (setq defn-up-tricky (key-binding sequence nil nil (event-start up-event))))))
      (with-help-window (help-buffer)
	(princ (help-key-description key untranslated))
	(princ (format "\
%s runs the command %S, which is "
		       mouse-msg defn))
	(describe-function-1 defn)
	(when up-event
	  (unless (or (null defn-up)
		      (integerp defn-up)
		      (equal defn-up 'undefined))
	    (princ (format "

----------------- up-event %s----------------

%s%s%s runs the command %S, which is "
			   (if mouse-1-tricky "(short click) " "")
			   (key-description (vector up-event))
			   mouse-msg
			   (if mouse-1-remapped
                               " is remapped to <mouse-2>, which" "")
			   defn-up))
	    (describe-function-1 defn-up))
	  (unless (or (null defn-up-tricky)
		      (integerp defn-up-tricky)
		      (eq defn-up-tricky 'undefined))
	    (princ (format "

----------------- up-event (long click) ----------------

Pressing <%S>%s for longer than %d milli-seconds
runs the command %S, which is "
			   ev-type mouse-msg
			   mouse-1-click-follows-link
			   defn-up-tricky))
	    (describe-function-1 defn-up-tricky)))))))

(defun describe-mode (&optional buffer)
  "Display documentation of current major mode and minor modes.
A brief summary of the minor modes comes first, followed by the
major mode description.  This is followed by detailed
descriptions of the minor modes, each on a separate page.

For this to work correctly for a minor mode, the mode's indicator
variable \(listed in `minor-mode-alist') must also be a function
whose documentation describes the minor mode."
  (interactive "@")
  (unless buffer (setq buffer (current-buffer)))
  (help-setup-xref (list #'describe-mode buffer)
		   (called-interactively-p 'interactive))
  ;; For the sake of help-do-xref and help-xref-go-back,
  ;; don't switch buffers before calling `help-buffer'.
  (with-help-window (help-buffer)
    (with-current-buffer buffer
      (let (minor-modes)
	;; Older packages do not register in minor-mode-list but only in
	;; minor-mode-alist.
	(dolist (x minor-mode-alist)
	  (setq x (car x))
	  (unless (memq x minor-mode-list)
	    (push x minor-mode-list)))
	;; Find enabled minor mode we will want to mention.
	(dolist (mode minor-mode-list)
	  ;; Document a minor mode if it is listed in minor-mode-alist,
	  ;; non-nil, and has a function definition.
	  (let ((fmode (or (get mode :minor-mode-function) mode)))
	    (and (boundp mode) (symbol-value mode)
		 (fboundp fmode)
		 (let ((pretty-minor-mode
			(if (string-match "\\(\\(-minor\\)?-mode\\)?\\'"
					  (symbol-name fmode))
			    (capitalize
			     (substring (symbol-name fmode)
					0 (match-beginning 0)))
			  fmode)))
		   (push (list fmode pretty-minor-mode
			       (format-mode-line (assq mode minor-mode-alist)))
			 minor-modes)))))
	(setq minor-modes
	      (sort minor-modes
		    (lambda (a b) (string-lessp (cadr a) (cadr b)))))
	(when minor-modes
	  (princ "Enabled minor modes:\n")
	  (make-local-variable 'help-button-cache)
	  (with-current-buffer standard-output
	    (dolist (mode minor-modes)
	      (let ((mode-function (nth 0 mode))
		    (pretty-minor-mode (nth 1 mode))
		    (indicator (nth 2 mode)))
		(add-text-properties 0 (length pretty-minor-mode)
				     '(face bold) pretty-minor-mode)
		(save-excursion
		  (goto-char (point-max))
		  (princ "\n\f\n")
		  (push (point-marker) help-button-cache)
		  ;; Document the minor modes fully.
		  (insert pretty-minor-mode)
		  (princ (format " minor mode (%s):\n"
				 (if (zerop (length indicator))
				     "no indicator"
				   (format "indicator%s"
					   indicator))))
		  (princ (documentation mode-function)))
		(insert-button pretty-minor-mode
			       'action (car help-button-cache)
			       'follow-link t
			       'help-echo "mouse-2, RET: show full information")
		(newline)))
	    (forward-line -1)
	    (fill-paragraph nil)
	    (forward-line 1))

	  (princ "\n(Information about these minor modes follows the major mode info.)\n\n"))
	;; Document the major mode.
	(let ((mode mode-name))
	  (with-current-buffer standard-output
            (let ((start (point)))
              (insert (format-mode-line mode nil nil buffer))
              (add-text-properties start (point) '(face bold)))))
	(princ " mode")
	(let* ((mode major-mode)
	       (file-name (find-lisp-object-file-name mode nil)))
	  (when file-name
	    (princ (concat " defined in `" (file-name-nondirectory file-name) "'"))
	    ;; Make a hyperlink to the library.
	    (with-current-buffer standard-output
	      (save-excursion
		(re-search-backward "`\\([^`']+\\)'" nil t)
		(help-xref-button 1 'help-function-def mode file-name)))))
	(princ ":\n")
	(princ (documentation major-mode)))))
  ;; For the sake of IELM and maybe others
  nil)


(defun describe-minor-mode (minor-mode)
  "Display documentation of a minor mode given as MINOR-MODE.
MINOR-MODE can be a minor mode symbol or a minor mode indicator string
appeared on the mode-line."
  (interactive (list (completing-read
		      "Minor mode: "
			      (nconc
			       (describe-minor-mode-completion-table-for-symbol)
			       (describe-minor-mode-completion-table-for-indicator)
			       ))))
  (if (symbolp minor-mode)
      (setq minor-mode (symbol-name minor-mode)))
  (let ((symbols (describe-minor-mode-completion-table-for-symbol))
	(indicators (describe-minor-mode-completion-table-for-indicator)))
    (cond
     ((member minor-mode symbols)
      (describe-minor-mode-from-symbol (intern minor-mode)))
     ((member minor-mode indicators)
      (describe-minor-mode-from-indicator minor-mode))
     (t
      (error "No such minor mode: %s" minor-mode)))))

;; symbol
(defun describe-minor-mode-completion-table-for-symbol ()
  ;; In order to list up all minor modes, minor-mode-list
  ;; is used here instead of minor-mode-alist.
  (delq nil (mapcar 'symbol-name minor-mode-list)))

(defun describe-minor-mode-from-symbol (symbol)
  "Display documentation of a minor mode given as a symbol, SYMBOL"
  (interactive (list (intern (completing-read
			      "Minor mode symbol: "
			      (describe-minor-mode-completion-table-for-symbol)))))
  (if (fboundp symbol)
      (describe-function symbol)
    (describe-variable symbol)))

;; indicator
(defun describe-minor-mode-completion-table-for-indicator ()
  (delq nil
	(mapcar (lambda (x)
		  (let ((i (format-mode-line x)))
		    ;; remove first space if existed
		    (cond
		     ((= 0 (length i))
		      nil)
		     ((eq (aref i 0) ?\s)
		      (substring i 1))
		     (t
		      i))))
		minor-mode-alist)))

(defun describe-minor-mode-from-indicator (indicator)
  "Display documentation of a minor mode specified by INDICATOR.
If you call this function interactively, you can give indicator which
is currently activated with completion."
  (interactive (list
		(completing-read
		 "Minor mode indicator: "
		 (describe-minor-mode-completion-table-for-indicator))))
  (let ((minor-mode (lookup-minor-mode-from-indicator indicator)))
    (if minor-mode
	(describe-minor-mode-from-symbol minor-mode)
      (error "Cannot find minor mode for `%s'" indicator))))

(defun lookup-minor-mode-from-indicator (indicator)
  "Return a minor mode symbol from its indicator on the modeline."
  ;; remove first space if existed
  (if (and (< 0 (length indicator))
	   (eq (aref indicator 0) ?\s))
      (setq indicator (substring indicator 1)))
  (let ((minor-modes minor-mode-alist)
	result)
    (while minor-modes
      (let* ((minor-mode (car (car minor-modes)))
	     (anindicator (format-mode-line
			   (car (cdr (car minor-modes))))))
	;; remove first space if existed
	(if (and (stringp anindicator)
		 (> (length anindicator) 0)
		 (eq (aref anindicator 0) ?\s))
	    (setq anindicator (substring anindicator 1)))
	(if (equal indicator anindicator)
	    (setq result minor-mode
		  minor-modes nil)
	  (setq minor-modes (cdr minor-modes)))))
    result))

;;; Automatic resizing of temporary buffers.
(defcustom temp-buffer-max-height (lambda (buffer) (/ (- (frame-height) 2) 2))
  "Maximum height of a window displaying a temporary buffer.
This is effective only when Temp Buffer Resize mode is enabled.
The value is the maximum height (in lines) which
`resize-temp-buffer-window' will give to a window displaying a
temporary buffer.  It can also be a function to be called to
choose the height for such a buffer.  It gets one argument, the
buffer, and should return a positive integer.  At the time the
function is called, the window to be resized is selected."
  :type '(choice integer function)
  :group 'help
  :version "20.4")

(define-minor-mode temp-buffer-resize-mode
  "Toggle auto-shrinking temp buffer windows (Temp Buffer Resize mode).
With a prefix argument ARG, enable Temp Buffer Resize mode if ARG
is positive, and disable it otherwise.  If called from Lisp,
enable the mode if ARG is omitted or nil.

When Temp Buffer Resize mode is enabled, the windows in which we
show a temporary buffer are automatically reduced in height to
fit the buffer's contents, but never more than
`temp-buffer-max-height' nor less than `window-min-height'.

This mode is used by `help', `apropos' and `completion' buffers,
and some others."
  :global t :group 'help
  (if temp-buffer-resize-mode
      ;; `help-make-xrefs' may add a `back' button and thus increase the
      ;; text size, so `resize-temp-buffer-window' must be run *after* it.
      (add-hook 'temp-buffer-show-hook 'resize-temp-buffer-window 'append)
    (remove-hook 'temp-buffer-show-hook 'resize-temp-buffer-window)))

(defun resize-temp-buffer-window ()
  "Resize the selected window to fit its contents.
Will not make it higher than `temp-buffer-max-height' nor smaller
than `window-min-height'.  Do nothing if the selected window is
not vertically combined or some of its contents are scrolled out
of view."
  (when (and (pos-visible-in-window-p (point-min))
	     (window-combined-p))
    (fit-window-to-buffer
     nil
     (if (functionp temp-buffer-max-height)
	 (funcall temp-buffer-max-height (window-buffer))
       temp-buffer-max-height))))

;;; Help windows.
(defcustom help-window-select 'other
    "Non-nil means select help window for viewing.
Choices are:
 never (nil) Select help window only if there is no other window
             on its frame.
 other       Select help window unless the selected window is the
             only other window on the help window's frame.
 always (t)  Always select the help window.

This option has effect if and only if the help window was created
by `with-help-window'"
  :type '(choice (const :tag "never (nil)" nil)
		 (const :tag "other" other)
		 (const :tag "always (t)" t))
  :group 'help
  :version "23.1")

(defun help-window-display-message (quit-part window &optional scroll)
  "Display message telling how to quit and scroll help window.
QUIT-PART is a string telling how to quit the help window WINDOW.
Optional argument SCROLL non-nil means tell how to scroll WINDOW.
SCROLL equal `other' means tell how to scroll the \"other\"
window."
  (let ((scroll-part
	 (cond
	  ;; If we don't have QUIT-PART we probably reuse a window
	  ;; showing the same buffer so we don't show any message.
	  ((not quit-part) nil)
	  ((pos-visible-in-window-p
	    (with-current-buffer (window-buffer window)
	      (point-max)) window t)
	   ;; Buffer end is at least partially visible, no need to talk
	   ;; about scrolling.
	   ".")
	  ((eq scroll 'other)
	   ", \\[scroll-other-window] to scroll help.")
	  (scroll ", \\[scroll-up] to scroll help."))))
    (message "%s"
     (substitute-command-keys (concat quit-part scroll-part)))))

(defun help-window-setup (help-window)
  "Set up help window for `with-help-window'.
HELP-WINDOW is the window used for displaying the help buffer."
  (let* ((help-buffer (when (window-live-p help-window)
			(window-buffer help-window)))
	 (help-setup (when (window-live-p help-window)
		       (car (window-parameter help-window 'quit-restore)))))
    (when help-buffer
      ;; Handle `help-window-point-marker'.
      (when (eq (marker-buffer help-window-point-marker) help-buffer)
	(set-window-point help-window help-window-point-marker)
	;; Reset `help-window-point-marker'.
	(set-marker help-window-point-marker nil))

      (cond
       ((or (eq help-window (selected-window))
	    (and (or (eq help-window-select t)
		     (eq help-setup 'frame)
		     (and (eq help-window-select 'other)
			  (eq (window-frame help-window) (selected-frame))
			  (> (length (window-list nil 'no-mini)) 2)))
		 (select-window help-window)))
	;; The help window is or gets selected ...
	(help-window-display-message
	 (cond
	  ((eq help-setup 'window)
	   ;; ... and is new, ...
	   "Type \"q\" to delete help window")
	  ((eq help-setup 'frame)
	   "Type \"q\" to delete help frame")
	  ((eq help-setup 'other)
	   ;; ... or displayed some other buffer before.
	   "Type \"q\" to restore previous buffer"))
	 help-window t))
       ((and (eq (window-frame help-window) (selected-frame))
	     (= (length (window-list nil 'no-mini)) 2))
	;; There are two windows on the help window's frame and the
	;; other one is the selected one.
	(help-window-display-message
	 (cond
	  ((eq help-setup 'window)
	   "Type \\[delete-other-windows] to delete the help window")
	  ((eq help-setup 'other)
	   "Type \"q\" in help window to restore its previous buffer"))
	 help-window 'other))
       (t
	;; The help window is not selected ...
	(help-window-display-message
	 (cond
	  ((eq help-setup 'window)
	   ;; ... and is new, ...
	   "Type \"q\" in help window to delete it")
	  ((eq help-setup 'other)
	   ;; ... or displayed some other buffer before.
	   "Type \"q\" in help window to restore previous buffer"))
	 help-window))))))

;; `with-help-window' is a wrapper for `with-output-to-temp-buffer'
;; providing the following additional twists:

;; (1) Issue more accurate messages telling how to scroll and quit the
;; help window.

;; (2) An option (customizable via `help-window-select') to select the
;; help window automatically.

;; (3) A marker (`help-window-point-marker') to move point in the help
;; window to an arbitrary buffer position.

;; Note: It's usually always wrong to use `help-print-return-message' in
;; the body of `with-help-window'.
(defmacro with-help-window (buffer-name &rest body)
  "Display buffer with name BUFFER-NAME in a help window evaluating BODY.
Select help window if the actual value of the user option
`help-window-select' says so.  Return last value in BODY."
  (declare (indent 1) (debug t))
  `(progn
     ;; Make `help-window-point-marker' point nowhere.  The only place
     ;; where this should be set to a buffer position is within BODY.
     (set-marker help-window-point-marker nil)
     (let* (help-window
            (temp-buffer-show-hook
             (cons (lambda () (setq help-window (selected-window)))
                   temp-buffer-show-hook)))
       ;; Return value returned by `with-output-to-temp-buffer'.
       (prog1
	   (with-output-to-temp-buffer ,buffer-name
	     (progn ,@body))
	 (help-window-setup help-window)))))

;; Called from C, on encountering `help-char' when reading a char.
;; Don't print to *Help*; that would clobber Help history.
(defun help-form-show ()
  "Display the output of a non-nil `help-form'."
  (let ((msg (eval help-form)))
    (if (stringp msg)
	(with-output-to-temp-buffer " *Char Help*"
	  (princ msg)))))

(provide 'help)

;;; help.el ends here