path: root/lisp/help-mode.el

;;; help-mode.el --- `help-mode' used by *Help* buffers

;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999, 2000, 2001
;;   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., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Defines `help-mode', which is the mode used by *Help* buffers, and
;; associated support machinery, such as adding hyperlinks, etc.,

;;; Code:

(require 'button)
(eval-when-compile (require 'view))

(defvar help-mode-map (make-sparse-keymap)
  "Keymap for help mode.")

(set-keymap-parent help-mode-map button-buffer-map)

(define-key help-mode-map "\C-c\C-b" 'help-go-back)
(define-key help-mode-map "\C-c\C-c" 'help-follow)
;; Documentation only, since we use minor-mode-overriding-map-alist.
(define-key help-mode-map "\r" 'help-follow)

(defvar help-xref-stack nil
  "A stack of ways by which to return to help buffers after following xrefs.
Used by `help-follow' and `help-xref-go-back'.
An element looks like (POSITION FUNCTION ARGS...), where POSITION is
`(POINT . BUFFER-NAME)'.
To use the element, do (apply FUNCTION ARGS) then goto the point in
the named buffer.")
(put 'help-xref-stack 'permanent-local t)

(defvar help-xref-stack-item nil
  "An item for `help-follow' in this buffer to push onto `help-xref-stack'.
The format is (FUNCTION ARGS...).")
(put 'help-xref-stack-item 'permanent-local t)

(setq-default help-xref-stack nil help-xref-stack-item nil)



;; Button types used by help

;; Make some button types that all use the same naming conventions
(dolist (help-type '("function" "variable" "face"
		     "coding-system" "input-method" "character-set"))
  (define-button-type (intern (purecopy (concat "help-" help-type)))
    'help-function (intern (concat "describe-" help-type))
    'help-echo (purecopy (concat "mouse-2, RET: describe this " help-type))
    'action #'help-button-action))

;; make some more ideosyncratic button types

(define-button-type 'help-symbol
  'help-function #'help-xref-interned
  'help-echo (purecopy "mouse-2, RET: describe this symbol")
  'action #'help-button-action)

(define-button-type 'help-back
  'help-function #'help-xref-go-back
  'help-echo (purecopy "mouse-2, RET: go back to previous help buffer")
  'action #'help-button-action)

(define-button-type 'help-info
  'help-function #'info
  'help-echo (purecopy"mouse-2, RET: read this Info node")
  'action #'help-button-action)

(define-button-type 'help-customize-variable
  'help-function (lambda (v)
		   (if help-xref-stack
		       (pop help-xref-stack))
		   (customize-variable v))
  'help-echo (purecopy "mouse-2, RET: customize variable")
  'action #'help-button-action)

(define-button-type 'help-function-def
  'help-function (lambda (fun file)
		   (require 'find-func)
		  ;; Don't use find-function-noselect because it follows
		   ;; aliases (which fails for built-in functions).
		   (let* ((location (find-function-search-for-symbol
				     fun nil file)))
		     (pop-to-buffer (car location))
		     (goto-char (cdr location))))
  'help-echo (purecopy "mouse-2, RET: find function's definition")
  'action #'help-button-action)

(define-button-type 'help-variable-def
  'help-function (lambda (var &optional file)
		   (let ((location
			  (find-variable-noselect var file)))
		     (pop-to-buffer (car location))
		     (goto-char (cdr location))))
  'help-echo (purecopy"mouse-2, RET: find variable's definition")
  'action #'help-button-action)

(defun help-button-action (button)
  "Call BUTTON's help function."
  (help-do-xref (button-start button)
		(button-get button 'help-function)
		(button-get button 'help-args)))


;;;###autoload
(define-derived-mode help-mode nil "Help"
  "Major mode for viewing help text and navigating references in it.
Entry to this mode runs the normal hook `help-mode-hook'.
Commands:
\\{help-mode-map}"
  (setq font-lock-defaults nil)         ; font-lock would defeat xref
  (view-mode)
  (make-local-variable 'view-no-disable-on-exit)
  (setq view-no-disable-on-exit t))

;;;###autoload
(defun help-mode-setup ()
  (help-mode)
  (setq buffer-read-only nil))

;;;###autoload
(defun help-mode-finish ()
  (when (eq major-mode 'help-mode)
    ;; View mode's read-only status of existing *Help* buffer is lost
    ;; by with-output-to-temp-buffer.
    (toggle-read-only 1)
    (help-make-xrefs (current-buffer)))
  (setq view-return-to-alist
	(list (cons (selected-window) help-return-method))))


;;; Grokking cross-reference information in doc strings and
;;; hyperlinking it.

;; This may have some scope for extension and the same or something
;; similar should be done for widget doc strings, which currently use
;; another mechanism.

(defcustom help-highlight-p t
  "*If non-nil, `help-make-xrefs' highlight cross-references.
Under a window system it highlights them with face defined by
`help-highlight-face'."
 :group 'help
 :version "20.3"
 :type 'boolean)

(defcustom help-highlight-face 'underline
  "Face used by `help-make-xrefs' to highlight cross-references.
Must be previously-defined."
  :group 'help
  :version "20.3"
  :type 'face)

(defvar help-back-label (purecopy "[back]")
  "Label to use by `help-make-xrefs' for the go-back reference.")

(defconst help-xref-symbol-regexp
  (purecopy (concat "\\(\\<\\(\\(variable\\|option\\)\\|"
		    "\\(function\\|command\\)\\|"
		    "\\(face\\)\\|"
		    "\\(symbol\\)\\|"
		    "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)\\s-+\\)?"
		    ;; Note starting with word-syntax character:
		    "`\\(\\sw\\(\\sw\\|\\s_\\)+\\)'"))
  "Regexp matching doc string references to symbols.

The words preceding the quoted symbol can be used in doc strings to
distinguish references to variables, functions and symbols.")

(defconst help-xref-mule-regexp nil
  "Regexp matching doc string references to MULE-related keywords.

It is usually nil, and is temporarily bound to an appropriate regexp
when help commands related to multilingual environment (e.g.,
`describe-coding-system') are invoked.")


(defconst help-xref-info-regexp
  (purecopy "\\<[Ii]nfo[ \t\n]+node[ \t\n]+`\\([^']+\\)'")
  "Regexp matching doc string references to an Info node.")

;;;###autoload
(defun help-setup-xref (item interactive-p)
  "Invoked from commands using the \"*Help*\" buffer to install some xref info.

ITEM is a (FUNCTION . ARGS) pair appropriate for recreating the help
buffer after following a reference.  INTERACTIVE-P is non-nil if the
calling command was invoked interactively.  In this case the stack of
items for help buffer \"back\" buttons is cleared."
  (if interactive-p
      (setq help-xref-stack nil))
  (setq help-xref-stack-item item))

(defvar help-xref-following nil
  "Non-nil when following a help cross-reference.")

;;;###autoload
(defun help-make-xrefs (&optional buffer)
  "Parse and hyperlink documentation cross-references in the given BUFFER.

Find cross-reference information in a buffer and, if
`help-highlight-p' is non-nil, highlight it with face defined by
`help-highlight-face'; activate such cross references for selection
with `help-follow'.  Cross-references have the canonical form `...'
and the type of reference may be disambiguated by the preceding
word(s) used in `help-xref-symbol-regexp'.

If the variable `help-xref-mule-regexp' is non-nil, find also
cross-reference information related to multilingual environment
\(e.g., coding-systems).  This variable is also used to disambiguate
the type of reference as the same way as `help-xref-symbol-regexp'.

A special reference `back' is made to return back through a stack of
help buffers.  Variable `help-back-label' specifies the text for
that."
  (interactive "b")
  (save-excursion
    (set-buffer (or buffer (current-buffer)))
    (goto-char (point-min))
    ;; Skip the header-type info, though it might be useful to parse
    ;; it at some stage (e.g. "function in `library'").
    (forward-paragraph)
    (let ((old-modified (buffer-modified-p)))
      (let ((stab (syntax-table))
            (case-fold-search t)
            (inhibit-read-only t))
        (set-syntax-table emacs-lisp-mode-syntax-table)
        ;; The following should probably be abstracted out.
        (unwind-protect
            (progn
              ;; Info references
              (save-excursion
                (while (re-search-forward help-xref-info-regexp nil t)
                  (let ((data (match-string 1)))
		    (save-match-data
		      (unless (string-match "^([^)]+)" data)
			(setq data (concat "(emacs)" data))))
		    (help-xref-button 1 'help-info data))))
	      ;; Mule related keywords.  Do this before trying
	      ;; `help-xref-symbol-regexp' because some of Mule
	      ;; keywords have variable or function definitions.
	      (if help-xref-mule-regexp
		  (save-excursion
		    (while (re-search-forward help-xref-mule-regexp nil t)
		      (let* ((data (match-string 7))
			     (sym (intern-soft data)))
			(cond
			 ((match-string 3) ; coding system
			  (and sym (coding-system-p sym)
			       (help-xref-button 6 'help-coding-system sym)))
			 ((match-string 4) ; input method
			  (and (assoc data input-method-alist)
			       (help-xref-button 7 'help-input-method data)))
			 ((or (match-string 5) (match-string 6)) ; charset
			  (and sym (charsetp sym)
			       (help-xref-button 7 'help-character-set sym)))
			 ((assoc data input-method-alist)
			  (help-xref-button 7 'help-character-set data))
			 ((and sym (coding-system-p sym))
			  (help-xref-button 7 'help-coding-system sym))
			 ((and sym (charsetp sym))
			  (help-xref-button 7 'help-character-set sym)))))))
              ;; Quoted symbols
              (save-excursion
                (while (re-search-forward help-xref-symbol-regexp nil t)
                  (let* ((data (match-string 8))
                         (sym (intern-soft data)))
                    (if sym
                        (cond
                         ((match-string 3) ; `variable' &c
                          (and (boundp sym) ; `variable' doesn't ensure
                                        ; it's actually bound
                               (help-xref-button 8 'help-variable sym)))
                         ((match-string 4) ; `function' &c
                          (and (fboundp sym) ; similarly
                               (help-xref-button 8 'help-function sym)))
			 ((match-string 5) ; `face'
			  (and (facep sym)
			       (help-xref-button 8 'help-face sym)))
                         ((match-string 6)) ; nothing for `symbol'
			 ((match-string 7)
;; this used:
;; 			   #'(lambda (arg)
;; 			       (let ((location
;; 				      (find-function-noselect arg)))
;; 				 (pop-to-buffer (car location))
;; 				 (goto-char (cdr location))))
			  (help-xref-button 8 'help-function-def sym))
                         ((and (boundp sym) (fboundp sym))
                          ;; We can't intuit whether to use the
                          ;; variable or function doc -- supply both.
                          (help-xref-button 8 'help-symbol sym))
                         ((boundp sym)
			  (help-xref-button 8 'help-variable sym))
			 ((fboundp sym)
			  (help-xref-button 8 'help-function sym))
			 ((facep sym)
			  (help-xref-button 8 'help-face sym)))))))
              ;; An obvious case of a key substitution:
              (save-excursion
                (while (re-search-forward
			;; Assume command name is only word characters
			;; and dashes to get things like `use M-x foo.'.
                        "\\<M-x\\s-+\\(\\sw\\(\\sw\\|-\\)+\\)" nil t)
                  (let ((sym (intern-soft (match-string 1))))
                    (if (fboundp sym)
                        (help-xref-button 1 'help-function sym)))))
              ;; Look for commands in whole keymap substitutions:
              (save-excursion
		;; Make sure to find the first keymap.
		(goto-char (point-min))
                ;; Find a header and the column at which the command
                ;; name will be found.
                (while (re-search-forward "^key +binding\n\\(-+ +\\)-+\n\n"
                                          nil t)
                  (let ((col (- (match-end 1) (match-beginning 1))))
                    (while
                        ;; Ignore single blank lines in table, but not
                        ;; double ones, which should terminate it.
                        (and (not (looking-at "\n\\s-*\n"))
                             (progn
			       (and (eolp) (forward-line))
			       (end-of-line)
			       (skip-chars-backward "^\t\n")
                               (if (and (>= (current-column) col)
					(looking-at "\\(\\sw\\|-\\)+$"))
                                   (let ((sym (intern-soft (match-string 0))))
                                     (if (fboundp sym)
                                         (help-xref-button 0 'help-function sym))))
			       (zerop (forward-line)))))))))
          (set-syntax-table stab))
	;; Delete extraneous newlines at the end of the docstring
	(goto-char (point-max))
	(while (and (not (bobp)) (bolp))
	  (delete-char -1))
        ;; Make a back-reference in this buffer if appropriate.
        (when (and help-xref-following help-xref-stack)
	  (insert "\n\n")
	  (help-insert-xref-button help-back-label 'help-back
				   (current-buffer))))
      ;; View mode steals RET from us.
      (set (make-local-variable 'minor-mode-overriding-map-alist)
           (list (cons 'view-mode
                       (let ((map (make-sparse-keymap)))
                         (set-keymap-parent map view-mode-map)
                         (define-key map "\r" 'help-follow)
                         map))))
      (set-buffer-modified-p old-modified))))

;;;###autoload
(defun help-xref-button (match-number type &rest args)
  "Make a hyperlink for cross-reference text previously matched.
MATCH-NUMBER is the subexpression of interest in the last matched
regexp.  TYPE is the type of button to use.  Any remaining arguments are
passed to the button's help-function when it is invoked.
See `help-make-xrefs'."
  ;; Don't mung properties we've added specially in some instances.
  (unless (button-at (match-beginning match-number))
    (make-text-button (match-beginning match-number)
		      (match-end match-number)
		      'type type 'help-args args)))

;;;###autoload
(defun help-insert-xref-button (string type &rest args)
  "Insert STRING and make a hyperlink from cross-reference text on it.
TYPE is the type of button to use.  Any remaining arguments are passed
to the button's help-function when it is invoked.
See `help-make-xrefs'."
  (unless (button-at (point))
    (insert-text-button string 'type type 'help-args args)))

;;;###autoload
(defun help-xref-on-pp (from to)
  "Add xrefs for symbols in `pp's output between FROM and TO."
  (let ((ost (syntax-table)))
    (unwind-protect
	(save-excursion
	  (save-restriction
	    (set-syntax-table emacs-lisp-mode-syntax-table)
	    (narrow-to-region from to)
	    (goto-char (point-min))
	    (while (not (eobp))
	      (cond
	       ((looking-at "\"") (forward-sexp 1))
	       ((looking-at "#<") (search-forward ">" nil 'move))
	       ((looking-at "\\(\\(\\sw\\|\\s_\\)+\\)")
		(let* ((sym (intern-soft (match-string 1)))
		       (type (cond ((fboundp sym) 'help-function)
				 ((or (memq sym '(t nil))
				      (keywordp sym))
				  nil)
				 ((and sym (boundp sym))
				  'help-variable))))
		  (when type (help-xref-button 1 type sym)))
		(goto-char (match-end 1)))
	       (t (forward-char 1))))))
      (set-syntax-table ost))))


;; Additional functions for (re-)creating types of help buffers.
(defun help-xref-interned (symbol)
  "Follow a hyperlink which appeared to be an arbitrary interned SYMBOL.

Both variable and function documentation are extracted into a single
help buffer."
  (let ((fdoc (when (fboundp symbol) (describe-function symbol)))
	(facedoc (when (facep symbol) (describe-face symbol))))
    (when (or (boundp symbol) (not fdoc))
      (describe-variable symbol)
      ;; We now have a help buffer on the variable.  Insert the function
      ;; text before it.
      (when (or fdoc facedoc)
	(with-current-buffer "*Help*"
	  (goto-char (point-min))
	  (let ((inhibit-read-only t))
	    (when fdoc
	      (insert fdoc "\n\n"))
	    (when facedoc
	      (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
		      " is also a " "face." "\n\n" facedoc "\n\n"))
	    (insert (make-string 30 ?-) "\n\n" (symbol-name symbol)
		    " is also a " "variable." "\n\n"))
	  (help-setup-xref (list #'help-xref-interned symbol) nil))))))


;;; Navigation/hyperlinking with xrefs

(defun help-xref-go-back (buffer)
  "From BUFFER, go back to previous help buffer text using `help-xref-stack'."
  (let (item position method args)
    (with-current-buffer buffer
      (when help-xref-stack
	(setq help-xref-stack (cdr help-xref-stack)) ; due to help-follow
	(setq item (pop help-xref-stack)
	      position (car item)
	      method (cadr item)
	      args (cddr item))))
    (apply method args)
    ;; We assume that the buffer we just recreated has the saved name,
    ;; which might not always be true.
    (when (get-buffer (cdr position))
      (with-current-buffer (cdr position)
	(goto-char (car position))))))

(defun help-go-back ()
  "Invoke the [back] button (if any) in the Help mode buffer."
  (interactive)
  (let ((back-button (button-at (1- (point-max)))))
    (if back-button
	(button-activate back-button)
      (error "No [back] button"))))

(defun help-do-xref (pos function args)
  "Call the help cross-reference function FUNCTION with args ARGS.
Things are set up properly so that the resulting help-buffer has
a proper [back] button."
  (setq help-xref-stack (cons (cons (cons pos (buffer-name))
				    help-xref-stack-item)
			      help-xref-stack))
  (setq help-xref-stack-item nil)
  ;; There is a reference at point.  Follow it.
  (let ((help-xref-following t))
    (apply function args)))

(defun help-follow (&optional pos)
  "Follow cross-reference at POS, defaulting to point.

For the cross-reference format, see `help-make-xrefs'."
  (interactive "d")
  (unless pos
    (setq pos (point)))
  (unless (push-button pos)
    ;; check if the symbol under point is a function or variable
    (let ((sym
	   (intern
	    (save-excursion
	      (goto-char pos) (skip-syntax-backward "w_")
	      (buffer-substring (point)
				(progn (skip-syntax-forward "w_")
				       (point)))))))
      (when (or (boundp sym) (fboundp sym))
	(help-do-xref pos #'help-xref-interned (list sym))))))


(provide 'help-mode)

;;; help-mode.el ends here