* NEWS: explain new behavior and arguments of `key-binding' and

[bpt/emacs.git] / lisp / help.el

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

;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999, 2000, 2001, 2002,
;;   2003, 2004, 2005, 2006 Free Software Foundation, Inc.

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

;; 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 2, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; 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)

(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-c" 'describe-copying)
    (define-key map "\C-d" 'describe-distribution)
    (define-key map "\C-e" 'view-emacs-problems)
    (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-p" 'describe-project)
    (define-key map "\C-t" 'view-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 "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 "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)

(autoload 'finder-by-keyword "finder"
  "Find packages matching a given keyword." t)

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

\f
(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' and `View-quit'), go to WINDOW.
 (WINDOW . quit-window)    do quit-window, then select WINDOW.
 (WINDOW BUF START POINT)  display BUF at START, POINT, then select WINDOW.")

(defun print-help-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
  "a b c C e f F i I k C-k l L m p r s t v w C-c C-d C-f C-n C-p C-t C-w . or ? :"
  "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  command-apropos.  Type a list of words or a regexp; it shows a list of
        commands whose names match.  See also the  apropos  command.
b  describe-bindings.  Display a table of all key bindings.
c  describe-key-briefly.  Type a key sequence;
	it displays the command name run by that key sequence.
C  describe-coding-system.  Type the name of the coding system to describe,
        or just RET to describe the ones currently in use.
d  apropos-documentation.  Type a pattern (a list of words or a regexp), and
	it shows a list of functions, variables, and other items whose
	documentation matches that pattern.  See also the apropos command.
e  view-echo-area-messages.  Go to the buffer that logs echo-area messages.
f  describe-function.  Type a function name and you see its documentation.
F  Info-goto-emacs-command-node.  Type a command name;
	it goes to the on-line manual's section that describes the command.
h  Display the HELLO file which illustrates various scripts.
i  info.  The Info documentation reader: read on-line manuals.
I  describe-input-method.  Describe a specific input method (if you type
	its name) or the current input method (if you type just RET).
k  describe-key.  Type a key sequence;
	it displays the full documentation for that key sequence.
K  Info-goto-emacs-key-command-node.  Type a key sequence;
	it goes to the on-line manual's section that describes
	the command bound to that key.
l  view-lossage.  Show last 100 characters you typed.
L  describe-language-environment.  This describes either a
	specific language environment (if you type its name)
	or the current language environment (if you type just RET).
m  describe-mode.  Display documentation of current minor modes,
	and the current major mode, including their special commands.
n  view-emacs-news.  Display news of recent Emacs changes.
p  finder-by-keyword. Find packages matching a given topic keyword.
r  info-emacs-manual.  Display the Emacs manual in Info mode.
s  describe-syntax.  Display contents of syntax table, plus explanations.
S  info-lookup-symbol.  Type a symbol; it goes to that symbol in the
        on-line manual for the programming language used in this buffer.
t  help-with-tutorial.  Select the Emacs learn-by-doing tutorial.
v  describe-variable.  Type name of a variable;
	it displays the variable's documentation and value.
w  where-is.  Type a command name; it displays which keystrokes
	invoke that command.
.  display-local-help.  Display any available local help at point
        in the echo area.

C-c Display Emacs copying permission (GNU General Public License).
C-d Display Emacs ordering information.
C-e Display info about Emacs problems.
C-f Display the Emacs FAQ.
C-m Display how to order printed Emacs manuals.
C-n Display news of recent Emacs changes.
C-p Display information about the GNU project.
C-t Display the Emacs TODO list.
C-w Display information on absence of warranty for GNU Emacs."
  help-map)

\f

(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."
  (or (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)))))))

\f
;;; `User' help functions

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

(defun describe-copying ()
  "Display info on how you may redistribute copies of GNU Emacs."
  (interactive)
  (view-file (expand-file-name "COPYING" data-directory))
  (goto-char (point-min)))

(defun describe-project ()
  "Display info on the GNU project."
  (interactive)
  (view-file (expand-file-name "THE-GNU-PROJECT" data-directory))
  (goto-char (point-min)))

(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 "NO WARRANTY")
    (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)
	      (mapcar
	       (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-todo (&optional arg)
  "Display the Emacs TODO list."
  (interactive "P")
  (view-file (expand-file-name "TODO" data-directory)))

(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-file (expand-file-name "ORDERS" data-directory))
  (goto-address))

(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-file (expand-file-name "PROBLEMS" data-directory)))

(defun view-lossage ()
  "Display last 100 input keystrokes.

To record all your input on a file, use `open-dribble-file'."
  (interactive)
  (help-setup-xref (list #'view-lossage) (interactive-p))
  (with-output-to-temp-buffer (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")))
    (print-help-return-message)))

\f
;; 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) (interactive-p))
  (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."
  (interactive)
  (let ((buf (current-buffer)))
    (with-output-to-temp-buffer "*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)))
  (let ((func (indirect-function definition))
        (defs nil)
        (standard-output (if insert (current-buffer) t)))
    ;; 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.
	   (if (and (vectorp key)
		    (eventp (elt key 0))
		    (memq 'down (event-modifiers (elt key 0))))
	       (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)))
  (save-excursion
    (let ((modifiers (event-modifiers (aref key 0)))
	  (standard-output (if insert (current-buffer) t))
	  window position)
      ;; For a mouse button event, go to the button it applies to
      ;; to get the right key bindings.  And go to the right place
      ;; in case the keymap depends on where you clicked.
      (if (or (memq 'click modifiers) (memq 'down modifiers)
	      (memq 'drag modifiers))
	  (setq window (posn-window (event-start (aref key 0)))
		position (posn-point (event-start (aref key 0)))))
      (if (windowp window)
	  (progn
	    (set-buffer (window-buffer window))
	    (goto-char position)))
      ;; Ok, now look up the key and name the command.
      (let ((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 is undefined" key-desc))
	  (princ (format (if (windowp window)
			     "%s at that spot runs the command %s"
			   "%s runs the command %s")
			 key-desc
			 (if (symbolp defn) defn (prin1-to-string 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 the corresponding up-event
	    ;; and use it as the third argument.
	    (if (and (vectorp key)
		     (eventp (elt key 0))
		     (memq 'down (event-modifiers (elt key 0))))
		(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)))
  (save-excursion
    (let ((modifiers (event-modifiers (aref key 0)))
	  window position)
      ;; For a mouse button event, go to the button it applies to
      ;; to get the right key bindings.  And go to the right place
      ;; in case the keymap depends on where you clicked.
      (if (or (memq 'click modifiers) (memq 'down modifiers)
	      (memq 'drag modifiers))
	  (setq window (posn-window (event-start (aref key 0)))
		position (posn-point (event-start (aref key 0)))))
      (when (windowp window)
	    (set-buffer (window-buffer window))
	(goto-char position))
      (let ((defn (key-binding key t)))
	;; 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))
	(if (or (null defn) (integerp defn) (equal defn 'undefined))
	    (message "%s is undefined" (help-key-description key untranslated))
	  (help-setup-xref (list #'describe-function defn) (interactive-p))
	  ;; 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 untranslated
		   (stringp (aref untranslated (1- (length untranslated)))))
	      (aset untranslated (1- (length untranslated))
		    "(any string)"))
	  (with-output-to-temp-buffer (help-buffer)
	    (princ (help-key-description key untranslated))
	    (if (windowp window)
		(princ " at that spot"))
	    (princ " runs the command ")
	    (prin1 defn)
	    (princ "\n   which is ")
	    (describe-function-1 defn)
	    (when up-event
	      (let ((type (event-basic-type up-event))
		    (hdr "\n\n-------------- up event ---------------\n\n")
		    defn sequence
		    mouse-1-tricky mouse-1-remapped)
		(setq sequence (vector up-event))
		(when (and (eq type 'mouse-1)
			   (windowp window)
			   mouse-1-click-follows-link
			   (not (eq mouse-1-click-follows-link 'double))
			   (setq mouse-1-remapped
				 (with-current-buffer (window-buffer window)
				   (mouse-on-link-p (posn-point
						     (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 (key-binding sequence))
		(unless (or (null defn) (integerp defn) (equal defn 'undefined))
		  (princ (if mouse-1-tricky
			     "\n\n----------------- up-event (short click) ----------------\n\n"
			   hdr))
		  (setq hdr nil)
		  (princ (symbol-name type))
		  (if (windowp window)
		      (princ " at that spot"))
		  (if mouse-1-remapped
		      (princ " is remapped to <mouse-2>\n  which" ))
		  (princ " runs the command ")
		  (prin1 defn)
		  (princ "\n   which is ")
		  (describe-function-1 defn))
		(when mouse-1-tricky
		  (setcar up-event 'mouse-1)
		  (setq defn (key-binding (vector up-event)))
		  (unless (or (null defn) (integerp defn) (eq defn 'undefined))
		    (princ (or hdr
			       "\n\n----------------- up-event (long click) ----------------\n\n"))
		    (princ "Pressing mouse-1")
		    (if (windowp window)
			(princ " at that spot"))
		    (princ (format " for longer than %d milli-seconds\n"
				   mouse-1-click-follows-link))
		    (princ " runs the command ")
		    (prin1 defn)
		    (princ "\n   which is ")
		    (describe-function-1 defn)))))
	    (print-help-return-message)))))))
\f
(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)
		   (interactive-p))
  ;; For the sake of help-do-xref and help-xref-go-back,
  ;; don't switch buffers before calling `help-buffer'.
  (with-output-to-temp-buffer (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))
              (add-text-properties start (point) '(face bold)))))
	(princ " mode:\n")
	(princ (documentation major-mode)))
      (print-help-return-message))))


(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) ?\ )
		      (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) ?\ ))
      (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) ?\ ))
	    (setq anindicator (substring anindicator 1)))
	(if (equal indicator anindicator)
	    (setq result minor-mode
		  minor-modes nil)
	  (setq minor-modes (cdr minor-modes)))))
    result))

\f
;;; 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 argumemt, the buffer, and should return a positive integer."
  :type '(choice integer function)
  :group 'help
  :version "20.4")

(define-minor-mode temp-buffer-resize-mode
  "Toggle the mode which makes windows smaller for temporary buffers.
With prefix argument ARG, turn the resizing of windows displaying temporary
buffers on if ARG is positive or off otherwise.
This makes the window the right height for its contents, but never
more than `temp-buffer-max-height' nor less than `window-min-height'.
This applies to `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 current window to fit its contents.
Will not make it higher than `temp-buffer-max-height' nor smaller than
`window-min-height'.  Do nothing if it is the only window on its frame, if it
is not as wide as the frame or if some of the window's contents are scrolled
out of view."
  (unless (or (one-window-p 'nomini)
              (not (pos-visible-in-window-p (point-min)))
              (/=  (frame-width) (window-width)))
    (fit-window-to-buffer
     (selected-window)
     (if (functionp temp-buffer-max-height)
	 (funcall temp-buffer-max-height (current-buffer))
       temp-buffer-max-height))))

\f
(provide 'help)

;; arch-tag: cf427352-27e9-49b7-9a6f-741ebab02423
;;; help.el ends here