;;; help-fns.el --- Complex help functions -*- lexical-binding: t -*-

;; Copyright (C) 1985-1986, 1993-1994, 1998-2021 Free Software
;; Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This file contains those help commands which are complicated, and
;; which may not be used in every session.  For example
;; `describe-function' will probably be heavily used when doing elisp
;; programming, but not if just editing C files.  Simpler help commands
;; are in help.el

;;; Code:

(require 'cl-lib)
(require 'help-mode)
(require 'radix-tree)
(eval-when-compile (require 'subr-x))   ;For when-let.

(defvar help-fns-describe-function-functions nil
  "List of functions to run in help buffer in `describe-function'.
Those functions will be run after the header line and argument
list was inserted, and before the documentation will be inserted.
The functions will receive the function name as argument.
They can assume that a newline was output just before they were called,
and they should terminate any of their own output with a newline.
By convention they should indent their output by 2 spaces.")

(defvar help-fns-describe-variable-functions nil
  "List of functions to run in help buffer in `describe-variable'.
Those functions will be run after the header line and value was inserted,
and before the documentation will be inserted.
The functions will receive the variable name as argument.
They can assume that a newline was output just before they were called,
and they should terminate any of their own output with a newline.
By convention they should indent their output by 2 spaces.
Current buffer is the buffer in which we queried the variable,
and the output should go to `standard-output'.")

(defvar help-fns-describe-face-functions nil
  "List of functions to run in help buffer in `describe-face'.
The functions will be used (and take the same parameters) as
described in `help-fns-describe-variable-functions', except that
the functions are called with two parameters: The face and the
frame.")

;; Functions

(defvar help-definition-prefixes nil
  ;; FIXME: We keep `definition-prefixes' as a hash-table so as to
  ;; avoid pre-loading radix-tree and because it takes slightly less
  ;; memory.  But when we use this table it's more efficient to
  ;; represent it as a radix tree, since the main operation is to do
  ;; `radix-tree-prefixes'.  Maybe we should just bite the bullet and
  ;; use a radix tree for `definition-prefixes' (it's not *that*
  ;; costly, really).
  "Radix-tree representation replacing `definition-prefixes'.")

(defun help-definition-prefixes ()
  "Return the up-to-date radix-tree form of `definition-prefixes'."
  (when (> (hash-table-count definition-prefixes) 0)
    (maphash (lambda (prefix files)
               (let ((old (radix-tree-lookup help-definition-prefixes prefix)))
                 (setq help-definition-prefixes
                       (radix-tree-insert help-definition-prefixes
                                          prefix (append old files)))))
             definition-prefixes)
    (clrhash definition-prefixes))
  help-definition-prefixes)

(defun help--loaded-p (file)
  "Try and figure out if FILE has already been loaded."
  ;; FIXME: this regexp business is not good enough: for file
  ;; `toto', it will say `toto' is loaded when in reality it was
  ;; just cedet/semantic/toto that has been loaded.
  (or (let ((feature (intern-soft file)))
        (and feature (featurep feature)))
      (let* ((re (load-history-regexp file))
             (done nil))
        (dolist (x load-history)
          (and (stringp (car x)) (string-match-p re (car x)) (setq done t)))
        done)))

(defun help--load-prefixes (prefixes)
  (pcase-dolist (`(,prefix . ,files) prefixes)
    (setq help-definition-prefixes
          (radix-tree-insert help-definition-prefixes prefix nil))
    (dolist (file files)
      ;; FIXME: Should we scan help-definition-prefixes to remove
      ;; other prefixes of the same file?
      (unless (help--loaded-p file)
        (with-demoted-errors "while loading: %S"
          (load file 'noerror 'nomessage))))))


(define-obsolete-variable-alias 'help-enable-completion-auto-load
  'help-enable-completion-autoload "27.1")

(defcustom help-enable-completion-autoload t
  "Whether completion for Help commands can perform autoloading.
If non-nil, whenever invoking completion for `describe-function'
or `describe-variable' load files that might contain definitions
with the current prefix.  The files are chosen according to
`definition-prefixes'."
  :type 'boolean
  :group 'help
  :version "26.3")

(defun help--symbol-completion-table (string pred action)
  (when help-enable-completion-autoload
    (let ((prefixes (radix-tree-prefixes (help-definition-prefixes) string)))
      (help--load-prefixes prefixes)))
  (let ((prefix-completions
         (and help-enable-completion-autoload
              (mapcar #'intern (all-completions string definition-prefixes)))))
    (complete-with-action action obarray string
                          (if pred (lambda (sym)
                                     (or (funcall pred sym)
                                         (memq sym prefix-completions)))))))

(defvar describe-function-orig-buffer nil
  "Buffer that was current when `describe-function' was invoked.
Functions on `help-fns-describe-function-functions' can use this
to get buffer-local values.")

;;;###autoload
(defun describe-function (function)
  "Display the full documentation of FUNCTION (a symbol).
When called from lisp, FUNCTION may also be a function object."
  (interactive
   (let* ((fn (function-called-at-point))
          (enable-recursive-minibuffers t)
          (val (completing-read
                (if fn
                    (format "Describe function (default %s): " fn)
                  "Describe function: ")
                #'help--symbol-completion-table
                (lambda (f) (or (fboundp f) (get f 'function-documentation)))
                t nil nil
                (and fn (symbol-name fn)))))
     (unless (equal val "")
       (setq fn (intern val)))
     (unless (and fn (symbolp fn))
       (user-error "You didn't specify a function symbol"))
     (unless (or (fboundp fn) (get fn 'function-documentation))
       (user-error "Symbol's function definition is void: %s" fn))
     (list fn)))

  ;; We save describe-function-orig-buffer on the help xref stack, so
  ;; it is restored by the back/forward buttons.  'help-buffer'
  ;; expects (current-buffer) to be a help buffer when processing
  ;; those buttons, so we can't change the current buffer before
  ;; calling that.
  (let ((describe-function-orig-buffer
         (or describe-function-orig-buffer
             (current-buffer))))

    (help-setup-xref
     (list (lambda (function buffer)
             (let ((describe-function-orig-buffer
                    (if (buffer-live-p buffer) buffer)))
               (describe-function function)))
           function describe-function-orig-buffer)
     (called-interactively-p 'interactive))

    (save-excursion
      (with-help-window (help-buffer)
        (if (get function 'reader-construct)
            (princ function)
          (prin1 function))
        ;; Use " is " instead of a colon so that
        ;; it is easier to get out the function name using forward-sexp.
        (princ " is ")
        (describe-function-1 function)
        (with-current-buffer standard-output
          ;; Return the text we displayed.
          (buffer-string))))
    ))


;; Could be this, if we make symbol-file do the work below.
;; (defun help-C-file-name (subr-or-var kind)
;;   "Return the name of the C file where SUBR-OR-VAR is defined.
;; KIND should be `var' for a variable or `subr' for a subroutine."
;;   (symbol-file (if (symbolp subr-or-var) subr-or-var
;; 		 (subr-name subr-or-var))
;; 	       (if (eq kind 'var) 'defvar 'defun)))
;;;###autoload
(defun help-C-file-name (subr-or-var kind)
  "Return the name of the C file where SUBR-OR-VAR is defined.
KIND should be `var' for a variable or `subr' for a subroutine.
If we can't find the file name, nil is returned."
  (let ((docbuf (get-buffer-create " *DOC*"))
	(name (if (eq 'var kind)
		  (concat "V" (symbol-name subr-or-var))
		(concat "F" (subr-name (advice--cd*r subr-or-var))))))
    (with-current-buffer docbuf
      (goto-char (point-min))
      (if (eobp)
	  (insert-file-contents-literally
	   (expand-file-name internal-doc-file-name doc-directory)))
      (let ((file (catch 'loop
		    (while t
		      (let ((pnt (search-forward (concat "\^_" name "\n")
                                                 nil t)))
                        (if (not pnt)
                            (throw 'loop nil)
			  (re-search-backward "\^_S\\(.*\\)")
			  (let ((file (match-string 1)))
			    (if (member file build-files)
			        (throw 'loop file)
			      (goto-char pnt)))))))))
        (if (not file)
            nil
	  (if (string-match "^ns.*\\(\\.o\\|obj\\)\\'" file)
	      (setq file (replace-match ".m" t t file 1))
	    (if (string-match "\\.\\(o\\|obj\\)\\'" file)
	        (setq file (replace-match ".c" t t file))))
	  (if (string-match "\\.\\(c\\|m\\)\\'" file)
	      (concat "src/" file)
	    file))))))

(defcustom help-downcase-arguments nil
  "If non-nil, argument names in *Help* buffers are downcased."
  :type 'boolean
  :group 'help
  :version "23.2")

(defun help-highlight-arg (arg)
  "Highlight ARG as an argument name for a *Help* buffer.
Return ARG in face `help-argument-name'; ARG is also downcased
if the variable `help-downcase-arguments' is non-nil."
  (propertize (if help-downcase-arguments (downcase arg) arg)
	      'face 'help-argument-name))

(defun help-do-arg-highlight (doc args)
  (with-syntax-table (make-syntax-table emacs-lisp-mode-syntax-table)
    (modify-syntax-entry ?\- "w")
    (dolist (arg args)
      (setq doc (replace-regexp-in-string
                 ;; This is heuristic, but covers all common cases
                 ;; except ARG1-ARG2
                 (concat "\\<"                   ; beginning of word
                         "\\(?:[a-z-]*-\\)?"     ; for xxx-ARG
                         "\\("
                         (regexp-quote arg)
                         "\\)"
                         "\\(?:es\\|s\\|th\\)?"  ; for ARGth, ARGs
                         "\\(?:-[a-z0-9-]+\\)?"  ; for ARG-xxx, ARG-n
                         "\\(?:-[{([<`\"‘].*?\\)?"; for ARG-{x}, (x), <x>, [x], `x', ‘x’
                         "\\>")                  ; end of word
                 (help-highlight-arg arg)
                 doc t t 1)))
    doc))

(defun help-highlight-arguments (usage doc &rest args)
  (when (and usage (string-match "^(" usage))
    (with-temp-buffer
      (insert usage)
      (goto-char (point-min))
      (let ((case-fold-search nil)
            (next (not (or args (looking-at "\\["))))
            (opt nil))
        ;; Make a list of all arguments
        (skip-chars-forward "^ ")
        (while next
          (or opt (not (looking-at " &")) (setq opt t))
          (if (not (re-search-forward " \\([\\[(]*\\)\\([^] &).]+\\)" nil t))
              (setq next nil)
            (setq args (cons (match-string 2) args))
            (when (and opt (string= (match-string 1) "("))
              ;; A pesky CL-style optional argument with default value,
              ;; so let's skip over it
              (search-backward "(")
              (goto-char (scan-sexps (point) 1)))))
        ;; Highlight arguments in the USAGE string
        (setq usage (help-do-arg-highlight (buffer-string) args))
        ;; Highlight arguments in the DOC string
        (setq doc (and doc (help-do-arg-highlight doc args))))))
  ;; Return value is like the one from help-split-fundoc, but highlighted
  (cons usage doc))

;; The following function was compiled from the former functions
;; `describe-simplify-lib-file-name' and `find-source-lisp-file' with
;; some excerpts from `describe-function-1' and `describe-variable'.
;; The only additional twists provided are (1) locate the defining file
;; for autoloaded functions, and (2) give preference to files in the
;; "install directory" (directories found via `load-path') rather than
;; to files in the "compile directory" (directories found by searching
;; the loaddefs.el file).  We autoload it because it's also used by
;; `describe-face' (instead of `describe-simplify-lib-file-name').

;;;###autoload
(defun find-lisp-object-file-name (object type)
  "Guess the file that defined the Lisp object OBJECT, of type TYPE.
OBJECT should be a symbol associated with a function, variable, or face;
  alternatively, it can be a function definition.
If TYPE is `defvar', search for a variable definition.
If TYPE is `defface', search for a face definition.
If TYPE is not a symbol, search for a function definition.

The return value is the absolute name of a readable file where OBJECT is
defined.  If several such files exist, preference is given to a file
found via `load-path'.  The return value can also be `C-source', which
means that OBJECT is a function or variable defined in C.  If no
suitable file is found, return nil."
  (let* ((autoloaded (autoloadp type))
	 (file-name (or (and autoloaded (nth 1 type))
			(symbol-file
                         ;; FIXME: Why do we have this weird "If TYPE is the
                         ;; value returned by `symbol-function' for a function
                         ;; symbol" exception?
			 object (or (if (symbolp type) type) 'defun)))))
    (cond
     (autoloaded
      ;; An autoloaded function: Locate the file since `symbol-function'
      ;; has only returned a bare string here.
      (setq file-name
	    (locate-file file-name load-path '(".el" ".elc") 'readable)))
     ((and (stringp file-name)
	   (string-match "[.]*loaddefs.el\\'" file-name))
      ;; An autoloaded variable or face.  Visit loaddefs.el in a buffer
      ;; and try to extract the defining file.  The following form is
      ;; from `describe-function-1' and `describe-variable'.
      (let ((location
	     (condition-case nil
		 (find-function-search-for-symbol object nil file-name)
	       (error nil))))
	(when (cdr location)
	  (with-current-buffer (car location)
	    (goto-char (cdr location))
	    (when (re-search-backward
		   "^;;; Generated autoloads from \\(.*\\)" nil t)
	      (setq file-name
		    (locate-file
		     (file-name-sans-extension
		      (match-string-no-properties 1))
		     load-path '(".el" ".elc") 'readable))))))))

    (cond
     ((and (not file-name) (subrp type))
      ;; A built-in function.  The form is from `describe-function-1'.
      (if (get-buffer " *DOC*")
	  (help-C-file-name type 'subr)
	'C-source))
     ((and (not file-name) (symbolp object)
	   (integerp (get object 'variable-documentation)))
      ;; A variable defined in C.  The form is from `describe-variable'.
      (if (get-buffer " *DOC*")
	  (help-C-file-name object 'var)
	'C-source))
     ((not (stringp file-name))
      ;; If we don't have a file-name string by now, we lost.
      nil)
     ;; Now, `file-name' should have become an absolute file name.
     ;; For files loaded from ~/.foo.elc, try ~/.foo.
     ;; This applies to config files like ~/.emacs,
     ;; which people sometimes compile.
     ((let (fn)
	(and (string-match "\\`\\..*\\.elc\\'"
			   (file-name-nondirectory file-name))
	     (string-equal (file-name-directory file-name)
			   (file-name-as-directory (expand-file-name "~")))
	     (file-readable-p (setq fn (file-name-sans-extension file-name)))
	     fn)))
     ;; When the Elisp source file can be found in the install
     ;; directory, return the name of that file.
     ((let ((lib-name
	     (if (string-match "[.]elc\\'" file-name)
		 (substring-no-properties file-name 0 -1)
	       file-name)))
	(or (and (file-readable-p lib-name) lib-name)
	    ;; The library might be compressed.
	    (and (file-readable-p (concat lib-name ".gz")) lib-name))))
     ((let* ((lib-name (file-name-nondirectory file-name))
	     ;; The next form is from `describe-simplify-lib-file-name'.
	     (file-name
	      ;; Try converting the absolute file name to a library
	      ;; name, convert that back to a file name and see if we
	      ;; get the original one.  If so, they are equivalent.
	      (if (equal file-name (locate-file lib-name load-path '("")))
		  (if (string-match "[.]elc\\'" lib-name)
		      (substring-no-properties lib-name 0 -1)
		    lib-name)
		file-name))
	     (src-file (locate-library file-name t nil 'readable)))
	(and src-file (file-readable-p src-file) src-file))))))

(defun help-fns--key-bindings (function)
  (when (commandp function)
    (let ((pt2 (with-current-buffer standard-output (point)))
          (remapped (command-remapping function)))
      (unless (memq remapped '(ignore undefined))
        (let ((keys (where-is-internal
                     (or remapped function) overriding-local-map nil nil))
              non-modified-keys)
          (if (and (eq function 'self-insert-command)
                   (vectorp (car-safe keys))
                   (consp (aref (car keys) 0)))
              (princ "It is bound to many ordinary text characters.\n")
            ;; Which non-control non-meta keys run this command?
            (dolist (key keys)
              (if (member (event-modifiers (aref key 0)) '(nil (shift)))
                  (push key non-modified-keys)))
            (when remapped
              (princ "Its keys are remapped to ")
              (princ (if (symbolp remapped)
                         (format-message "`%s'" remapped)
		       "an anonymous command"))
              (princ ".\n"))

            (when keys
              (princ (if remapped
                         "Without this remapping, it would be bound to "
                       "It is bound to "))
              ;; If lots of ordinary text characters run this command,
              ;; don't mention them one by one.
              (if (< (length non-modified-keys) 10)
                  (princ (mapconcat #'key-description keys ", "))
                (dolist (key non-modified-keys)
                  (setq keys (delq key keys)))
                (if keys
                    (progn
                      (princ (mapconcat #'key-description keys ", "))
                      (princ ", and many ordinary text characters"))
                  (princ "many ordinary text characters"))))
            (when (or remapped keys non-modified-keys)
              (princ ".")
              (terpri)))))

      (with-current-buffer standard-output
        (fill-region-as-paragraph pt2 (point))
        (unless (looking-back "\n\n" (- (point) 2))
          (terpri))))))

(defun help-fns--compiler-macro (function)
  (let ((handler (function-get function 'compiler-macro)))
    (when handler
      (insert "  This function has a compiler macro")
      (if (symbolp handler)
          (progn
            (insert (format-message " `%s'" handler))
            (save-excursion
              (re-search-backward (substitute-command-keys "`\\([^`']+\\)'")
                                  nil t)
              (help-xref-button 1 'help-function handler)))
        ;; FIXME: Obsolete since 24.4.
        (let ((lib (get function 'compiler-macro-file)))
          (when (stringp lib)
            (insert (format-message " in `%s'" lib))
            (save-excursion
              (re-search-backward (substitute-command-keys "`\\([^`']+\\)'")
                                  nil t)
              (help-xref-button 1 'help-function-cmacro function lib)))))
      (insert ".\n"))))

(defun help-fns--signature (function doc real-def real-function buffer)
  "Insert usage at point and return docstring.  With highlighting."
  (if (keymapp function)
      doc                       ; If definition is a keymap, skip arglist note.
    (let* ((advertised (gethash real-def advertised-signature-table t))
           (arglist (if (listp advertised)
                        advertised (help-function-arglist real-def)))
           (usage (help-split-fundoc doc function)))
      (if usage (setq doc (cdr usage)))
      (let* ((use (cond
                   ((and usage (not (listp advertised))) (car usage))
                   ((listp arglist)
                    (help--make-usage-docstring function arglist))
                   ((stringp arglist) arglist)
                   ;; Maybe the arglist is in the docstring of a symbol
                   ;; this one is aliased to.
                   ((let ((fun real-function))
                      (while (and (symbolp fun)
                                  (setq fun (symbol-function fun))
                                  (not (setq usage (help-split-fundoc
                                                    (documentation fun)
                                                    function)))))
                      usage)
                    (car usage))
                   ((or (stringp real-def)
                        (vectorp real-def))
                    (format "\nMacro: %s"
                            (help--docstring-quote
                             (format-kbd-macro real-def))))
                   (t "[Missing arglist.  Please make a bug report.]")))
             ;; Insert "`X", not "(\` X)", when documenting `X.
             (use1 (replace-regexp-in-string
                    "\\`(\\\\=\\\\\\\\=` \\([^\n ]*\\))\\'"
                    "\\\\=`\\1" use t))
             (high (if buffer
                       (let (subst-use1 subst-doc)
                         (with-current-buffer buffer
                           (setq subst-use1 (substitute-command-keys use1))
                           (setq subst-doc (substitute-command-keys doc)))
                         (help-highlight-arguments subst-use1 subst-doc))
                     (cons use1 doc))))
        (let ((fill-begin (point))
              (high-usage (car high))
              (high-doc (cdr high)))
          (unless (and (symbolp function)
                       (get function 'reader-construct))
            (insert high-usage "\n"))
          (fill-region fill-begin (point))
          high-doc)))))

(defun help-fns--parent-mode (function)
  ;; If this is a derived mode, link to the parent.
  (let ((parent-mode (and (symbolp function)
                          (get function
                               'derived-mode-parent))))
    (when parent-mode
      (insert (substitute-command-keys "  Parent mode: `"))
      (let ((beg (point)))
        (insert (format "%s" parent-mode))
        (make-text-button beg (point)
                          'type 'help-function
                          'help-args (list parent-mode)))
      (insert (substitute-command-keys "'.\n")))))

(defun help-fns--obsolete (function)
  ;; Ignore lambda constructs, keyboard macros, etc.
  (let* ((obsolete (and (symbolp function)
			(get function 'byte-obsolete-info)))
         (use (car obsolete)))
    (when obsolete
      (insert "  This "
	      (if (eq (car-safe (symbol-function function)) 'macro)
		  "macro"
		"function")
	      " is obsolete")
      (when (nth 2 obsolete)
        (insert (format " since %s" (nth 2 obsolete))))
      (insert (cond ((stringp use) (concat ";\n  " use))
                    (use (format-message ";\n  use `%s' instead." use))
                    (t "."))
              "\n"))))

(add-hook 'help-fns-describe-function-functions
          #'help-fns--globalized-minor-mode)
(defun help-fns--globalized-minor-mode (function)
  (when (and (symbolp function)
             (get function 'globalized-minor-mode))
    (help-fns--customize-variable function " the global mode variable.")
    (terpri)))

;; We could use `symbol-file' but this is a wee bit more efficient.
(defun help-fns--autoloaded-p (function file)
  "Return non-nil if FUNCTION has previously been autoloaded.
FILE is the file where FUNCTION was probably defined."
  (let* ((file (file-name-sans-extension (file-truename file)))
	 (load-hist load-history)
	 (target (cons t function))
	 found)
    (while (and load-hist (not found))
      (and (stringp (caar load-hist))
	   (equal (file-name-sans-extension (caar load-hist)) file)
	   (setq found (member target (cdar load-hist))))
      (setq load-hist (cdr load-hist)))
    found))

(defun help-fns--interactive-only (function)
  "Insert some help blurb if FUNCTION should only be used interactively."
  ;; Ignore lambda constructs, keyboard macros, etc.
  (and (symbolp function)
       (not (eq (car-safe (symbol-function function)) 'macro))
       (let* ((interactive-only
               (or (get function 'interactive-only)
                   (if (boundp 'byte-compile-interactive-only-functions)
                       (memq function
                             byte-compile-interactive-only-functions)))))
         (when interactive-only
           (insert "  This function is for interactive use only"
                   ;; Cf byte-compile-form.
                   (cond ((stringp interactive-only)
                          (format ";\n  in Lisp code %s" interactive-only))
                         ((and (symbolp 'interactive-only)
                               (not (eq interactive-only t)))
                          (format-message ";\n  in Lisp code use `%s' instead."
                                          interactive-only))
                         (t "."))
                   "\n")))))

(add-hook 'help-fns-describe-function-functions #'help-fns--side-effects)
(defun help-fns--side-effects (function)
  (when (and (symbolp function)
             (or (function-get function 'pure)
                 (function-get function 'side-effect-free)))
    (insert "  This function does not change global state, "
            "including the match data.\n")))

(add-hook 'help-fns-describe-function-functions #'help-fns--disabled)
(defun help-fns--disabled (function)
  (when (and (symbolp function)
             (function-get function 'disabled))
    (insert "  This function is disabled.\n")))

(defun help-fns--first-release (symbol)
  "Return the likely first release that defined SYMBOL, or nil."
  ;; Code below relies on the etc/NEWS* files.
  ;; FIXME: Maybe we should also use the */ChangeLog* files when available.
  ;; FIXME: Maybe we should also look for announcements of the addition
  ;; of the *packages* in which the function is defined.
  (let* ((name (symbol-name symbol))
         (re (concat "\\_<" (regexp-quote name) "\\_>"))
         (news (directory-files data-directory t "\\`NEWS\\.[1-9]"))
         (place nil)
         (first nil))
    (with-temp-buffer
      (dolist (f news)
        (erase-buffer)
        (insert-file-contents f)
        (goto-char (point-min))
        (search-forward "\n*")
        (while (re-search-forward re nil t)
          (let ((pos (match-beginning 0)))
            (save-excursion
              ;; Almost all entries are of the form "* ... in Emacs NN.MM."
              ;; but there are also a few in the form "* Emacs NN.MM is a bug
              ;; fix release ...".
              (if (not (re-search-backward "^\\*.* Emacs \\([0-9.]+[0-9]\\)"
                                           nil t))
                  (message "Ref found in non-versioned section in %S"
                           (file-name-nondirectory f))
                (let ((version (match-string 1)))
                  (when (or (null first) (version< version first))
                    (setq place (list f pos))
                    (setq first version)))))))))
    (when first
      (make-text-button first nil 'type 'help-news 'help-args place))
    first))

(add-hook 'help-fns-describe-function-functions
          #'help-fns--mention-first-release)
(add-hook 'help-fns-describe-variable-functions
          #'help-fns--mention-first-release)
(defun help-fns--mention-first-release (object)
  (let ((first (if (symbolp object) (help-fns--first-release object))))
    (when first
      (with-current-buffer standard-output
        (insert (format "  Probably introduced at or before Emacs version %s.\n"
                        first))))))

(defun help-fns-short-filename (filename)
  (let* ((abbrev (abbreviate-file-name filename))
         (short abbrev))
    (dolist (dir load-path)
      (let ((rel (file-relative-name filename dir)))
        (if (< (length rel) (length short))
            (setq short rel)))
      (let ((rel (file-relative-name abbrev dir)))
        (if (< (length rel) (length short))
            (setq short rel))))
    short))

(defun help-fns--analyze-function (function)
  ;; FIXME: Document/explain the differences between FUNCTION,
  ;; REAL-FUNCTION, DEF, and REAL-DEF.
  "Return information about FUNCTION.
Returns a list of the form (REAL-FUNCTION DEF ALIASED REAL-DEF)."
  (let* ((advised (and (symbolp function)
		       (advice--p (advice--symbol-function function))))
	 ;; If the function is advised, use the symbol that has the
	 ;; real definition, if that symbol is already set up.
	 (real-function
	  (or (and advised
                   (advice--cd*r (advice--symbol-function function)))
	      function))
	 ;; Get the real definition, if any.
	 (def (if (symbolp real-function)
                  (cond ((symbol-function real-function))
                        ((get real-function 'function-documentation)
                         nil)
                        (t (signal 'void-function (list real-function))))
		real-function))
	 (aliased (and def
                       (or (symbolp def)
                           ;; Advised & aliased function.
                           (and advised (symbolp real-function)
                                (not (eq 'autoload (car-safe def))))
                           (and (subrp def)
                                (not (string= (subr-name def)
                                              (symbol-name function)))))))
	 (real-def (cond
                    ((and aliased (not (subrp def)))
                     (let ((f real-function))
                       (while (and (fboundp f)
                                   (symbolp (symbol-function f)))
                         (setq f (symbol-function f)))
                       f))
		    ((subrp def) (intern (subr-name def)))
                    (t def))))
    (list real-function def aliased real-def)))

(defun help-fns-function-description-header (function)
  "Print a line describing FUNCTION to `standard-output'."
  (pcase-let* ((`(,_real-function ,def ,aliased ,real-def)
                (help-fns--analyze-function function))
               (file-name (find-lisp-object-file-name function (if aliased 'defun
                                                                 def)))
               (beg (if (and (or (byte-code-function-p def)
                                 (keymapp def)
                                 (memq (car-safe def) '(macro lambda closure)))
                             (stringp file-name)
                             (help-fns--autoloaded-p function file-name))
                        (concat
                         "an autoloaded " (if (commandp def)
                                              "interactive "))
                      (if (commandp def) "an interactive " "a "))))

    ;; Print what kind of function-like object FUNCTION is.
    (princ (cond ((or (stringp def) (vectorp def))
		  "a keyboard macro")
		 ((and (symbolp function)
                       (get function 'reader-construct))
                  "a reader construct")
		 ;; Aliases are Lisp functions, so we need to check
		 ;; aliases before functions.
		 (aliased
		  (format-message "an alias for `%s'" real-def))
		 ((subrp def)
		  (concat beg (if (eq 'unevalled (cdr (subr-arity def)))
		                  "special form"
                                "built-in function")))
		 ((autoloadp def)
		  (format "an autoloaded %s"
                          (cond
			   ((commandp def) "interactive Lisp function")
			   ((eq (nth 4 def) 'keymap) "keymap")
			   ((nth 4 def) "Lisp macro")
                           (t "Lisp function"))))
		 ((or (eq (car-safe def) 'macro)
		      ;; For advised macros, def is a lambda
		      ;; expression or a byte-code-function-p, so we
		      ;; need to check macros before functions.
		      (macrop function))
		  (concat beg "Lisp macro"))
		 ((byte-code-function-p def)
		  (concat beg "compiled Lisp function"))
                 ((module-function-p def)
                  (concat beg "module function"))
		 ((eq (car-safe def) 'lambda)
		  (concat beg "Lisp function"))
		 ((eq (car-safe def) 'closure)
		  (concat beg "Lisp closure"))
		 ((keymapp def)
		  (let ((is-full nil)
			(elts (cdr-safe def)))
		    (while elts
		      (if (char-table-p (car-safe elts))
			  (setq is-full t
				elts nil))
		      (setq elts (cdr-safe elts)))
		    (concat beg (if is-full "keymap" "sparse keymap"))))
		 (t "")))

    (if (and aliased (not (fboundp real-def)))
	(princ ",\nwhich is not defined.  Please make a bug report.")
      (with-current-buffer standard-output
	(save-excursion
	  (save-match-data
	    (when (re-search-backward (substitute-command-keys
                                       "alias for `\\([^`']+\\)'")
                                      nil t)
	      (help-xref-button 1 'help-function real-def)))))

      (when file-name
	;; We used to add .el to the file name,
	;; but that's completely wrong when the user used load-file.
	(princ (format-message " in `%s'"
                               (if (eq file-name 'C-source)
                                   "C source code"
                                 (help-fns-short-filename file-name))))
	;; Make a hyperlink to the library.
	(with-current-buffer standard-output
	  (save-excursion
	    (re-search-backward (substitute-command-keys "`\\([^`']+\\)'")
                                nil t)
	    (help-xref-button 1 'help-function-def function file-name))))
      (princ "."))))

(defun help-fns--ensure-empty-line ()
  (unless (eolp) (insert "\n"))
  (unless (eq ?\n (char-before (1- (point)))) (insert "\n")))

;;;###autoload
(defun describe-function-1 (function)
  (let ((pt1 (with-current-buffer (help-buffer) (point))))
    (help-fns-function-description-header function)
    (with-current-buffer (help-buffer)
      (fill-region-as-paragraph (save-excursion (goto-char pt1) (forward-line 0) (point))
                                (point))))
  (terpri)(terpri)

  (pcase-let* ((`(,real-function ,def ,_aliased ,real-def)
                (help-fns--analyze-function function))
               (doc-raw (condition-case nil
                            ;; FIXME: Maybe `documentation' should return nil
                            ;; for invalid functions i.s.o. signaling an error.
                            (documentation function t)
                          ;; E.g. an alias for a not yet defined function.
                          ((invalid-function void-function) nil)))
               (key-bindings-buffer (current-buffer)))

    ;; If the function is autoloaded, and its docstring has
    ;; key substitution constructs, load the library.
    (and (autoloadp real-def) doc-raw
         help-enable-autoload
         (string-match "\\([^\\]=\\|[^=]\\|\\`\\)\\\\[[{<]" doc-raw)
         (autoload-do-load real-def))

    (help-fns--key-bindings function)
    (with-current-buffer standard-output
      (let ((doc (condition-case nil
                     ;; FIXME: Maybe `help-fns--signature' should return `doc'
                     ;; for invalid functions i.s.o. signaling an error.
                     (help-fns--signature
                      function doc-raw
                      (if (subrp def) (indirect-function real-def) real-def)
                      real-function key-bindings-buffer)
                   ;; E.g. an alias for a not yet defined function.
                   ((invalid-function void-function) doc-raw))))
        (help-fns--ensure-empty-line)
        (run-hook-with-args 'help-fns-describe-function-functions function)
        (help-fns--ensure-empty-line)
        (insert (or doc "Not documented.")))
      ;; Avoid asking the user annoying questions if she decides
      ;; to save the help buffer, when her locale's codeset
      ;; isn't UTF-8.
      (unless (memq text-quoting-style '(straight grave))
        (set-buffer-file-coding-system 'utf-8)))))

;; Add defaults to `help-fns-describe-function-functions'.
(add-hook 'help-fns-describe-function-functions #'help-fns--obsolete)
(add-hook 'help-fns-describe-function-functions #'help-fns--interactive-only)
(add-hook 'help-fns-describe-function-functions #'help-fns--parent-mode)
(add-hook 'help-fns-describe-function-functions #'help-fns--compiler-macro)


;; Variables

;;;###autoload
(defun variable-at-point (&optional any-symbol)
  "Return the bound variable symbol found at or before point.
Return 0 if there is no such symbol.
If ANY-SYMBOL is non-nil, don't insist the symbol be bound."
  (with-syntax-table emacs-lisp-mode-syntax-table
    (or (condition-case ()
	    (save-excursion
	      (skip-chars-forward "'")
	      (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) (boundp obj) obj)))
          (error nil))
        (let* ((str (find-tag-default))
               (sym (if str (intern-soft str))))
          (if (and sym (or any-symbol (boundp sym)))
              sym
            (save-match-data
              (when (and str (string-match "\\`\\W*\\(.*?\\)\\W*\\'" str))
                (setq sym (intern-soft (match-string 1 str)))
                (and (or any-symbol (boundp sym)) sym)))))
        0)))

(defun describe-variable-custom-version-info (variable &optional type)
  (let ((custom-version (get variable 'custom-version))
	(cpv (get variable 'custom-package-version))
        (type (or type "variable"))
	(output nil))
    (if custom-version
	(setq output
	      (format "This %s was introduced, or its default value was changed, in\nversion %s of Emacs.\n"
                      type custom-version))
      (when cpv
	(let* ((package (car-safe cpv))
	       (version (if (listp (cdr-safe cpv))
			    (car (cdr-safe cpv))
			  (cdr-safe cpv)))
	       (pkg-versions (assq package customize-package-emacs-version-alist))
	       (emacsv (cdr (assoc version pkg-versions))))
	  (if (and package version)
	      (setq output
		    (format (concat "This %s was introduced, or its default value was changed, in\nversion %s of the %s package"
				    (if emacsv
					(format " that is part of Emacs %s" emacsv))
				    ".\n")
			    type version package))))))
    output))

;;;###autoload
(defun describe-variable (variable &optional buffer frame)
  "Display the full documentation of VARIABLE (a symbol).
Returns the documentation as a string, also.
If VARIABLE has a buffer-local value in BUFFER or FRAME
\(default to the current buffer and current frame),
it is displayed along with the global value."
  (interactive
   (let ((v (variable-at-point))
	 (enable-recursive-minibuffers t)
         (orig-buffer (current-buffer))
	 val)
     (setq val (completing-read
                (if (symbolp v)
                    (format
                     "Describe variable (default %s): " v)
                  "Describe variable: ")
                #'help--symbol-completion-table
                (lambda (vv)
                  ;; In case the variable only exists in the buffer
                  ;; the command we switch back to that buffer before
                  ;; we examine the variable.
                  (with-current-buffer orig-buffer
                    (or (get vv 'variable-documentation)
                        (and (boundp vv) (not (keywordp vv))))))
                t nil nil
                (if (symbolp v) (symbol-name v))))
     (list (if (equal val "")
	       v (intern val)))))
  (let (file-name)
    (unless (buffer-live-p buffer) (setq buffer (current-buffer)))
    (unless (frame-live-p frame) (setq frame (selected-frame)))
    (if (not (symbolp variable))
	(message "You did not specify a variable")
      (save-excursion
	(let ((valvoid (not (with-current-buffer buffer (boundp variable))))
	      val val-start-pos locus)
	  ;; Extract the value before setting up the output buffer,
	  ;; in case `buffer' *is* the output buffer.
	  (unless valvoid
	    (with-selected-frame frame
	      (with-current-buffer buffer
		(setq val (symbol-value variable)
		      locus (variable-binding-locus variable)))))
	  (help-setup-xref (list #'describe-variable variable buffer)
			   (called-interactively-p 'interactive))
	  (with-help-window (help-buffer)
	    (with-current-buffer buffer
	      (prin1 variable)
	      (setq file-name (find-lisp-object-file-name variable 'defvar))

	      (princ (if file-name
		         (progn
		           (princ (format-message
                                   " is a variable defined in `%s'.\n"
                                   (if (eq file-name 'C-source)
                                       "C source code"
                                     (file-name-nondirectory file-name))))
		           (with-current-buffer standard-output
		             (save-excursion
			       (re-search-backward (substitute-command-keys
                                                    "`\\([^`']+\\)'")
                                                   nil t)
			       (help-xref-button 1 'help-variable-def
					         variable file-name)))
		           (if valvoid
			       "It is void as a variable."
                             "Its "))
                       (if valvoid
		           " is void as a variable."
                         (substitute-command-keys "'s ")))))
	    (unless valvoid
	      (with-current-buffer standard-output
		(setq val-start-pos (point))
		(princ "value is")
		(let ((line-beg (line-beginning-position))
		      (print-rep
		       (let ((rep
			      (let ((print-quoted t)
                                    (print-circle t))
				(cl-prin1-to-string val))))
			 (if (and (symbolp val) (not (booleanp val)))
			     (format-message "`%s'" rep)
			   rep))))
		  (if (< (+ (length print-rep) (point) (- line-beg)) 68)
		      (insert " " print-rep)
		    (terpri)
                    (let ((buf (current-buffer)))
                      (with-temp-buffer
                        (lisp-mode-variables nil)
                        (set-syntax-table emacs-lisp-mode-syntax-table)
                        (insert print-rep)
                        (pp-buffer)
                        (let ((pp-buffer (current-buffer)))
                          (with-current-buffer buf
                            (insert-buffer-substring pp-buffer)))))
                    ;; Remove trailing newline.
                    (and (= (char-before) ?\n) (delete-char -1)))
		  (let* ((sv (get variable 'standard-value))
			 (origval (and (consp sv)
				       (condition-case nil
					   (eval (car sv) t)
					 (error :help-eval-error))))
                         from)
		    (when (and (consp sv)
                               (not (equal origval val))
                               (not (equal origval :help-eval-error)))
		      (princ "\nOriginal value was \n")
		      (setq from (point))
		      (if (and (symbolp origval) (not (booleanp origval)))
			  (let* ((rep (cl-prin1-to-string origval))
				 (print-rep (format-message "`%s'" rep)))
			    (insert print-rep))
			(cl-prin1 origval))
                      (save-restriction
                        (narrow-to-region from (point))
                        (save-excursion (pp-buffer)))
		      (if (< (point) (+ from 20))
			  (delete-region (1- from) from)))))))
	    (terpri)
	    (when locus
	      (cond
               ((bufferp locus)
                (princ (format "Local in buffer %s; "
                               (buffer-name buffer))))
               ((terminal-live-p locus)
                (princ (format "It is a terminal-local variable; ")))
               (t
                (princ (format "It is local to %S" locus))))
	      (if (not (default-boundp variable))
		  (princ "globally void")
		(let ((global-val (default-value variable)))
		  (with-current-buffer standard-output
		    (princ "global value is ")
		    (if (eq val global-val)
			(princ "the same.")
		      (terpri)
		      ;; Fixme: pp can take an age if you happen to
		      ;; ask for a very large expression.  We should
		      ;; probably print it raw once and check it's a
		      ;; sensible size before prettyprinting.  -- fx
		      (let ((from (point)))
                        (cl-prin1 global-val)
                        (save-restriction
                          (narrow-to-region from (point))
                          (save-excursion (pp-buffer)))
			;; See previous comment for this function.
			;; (help-xref-on-pp from (point))
			(if (< (point) (+ from 20))
			    (delete-region (1- from) from)))))))
              (terpri))

	    ;; If the value is large, move it to the end.
	    (with-current-buffer standard-output
	      (when (> (count-lines (point-min) (point-max)) 10)
		;; Note that setting the syntax table like below
		;; makes forward-sexp move over a `'s' at the end
		;; of a symbol.
		(set-syntax-table emacs-lisp-mode-syntax-table)
		(goto-char val-start-pos)
		;; The line below previously read as
		;; (delete-region (point) (progn (end-of-line) (point)))
		;; which suppressed display of the buffer local value for
		;; large values.
		(when (looking-at "value is") (replace-match ""))
		(save-excursion
		  (insert "\n\nValue:")
		  (set (make-local-variable 'help-button-cache)
		       (point-marker)))
		(insert "value is shown ")
		(insert-button "below"
			       'action help-button-cache
			       'follow-link t
			       'help-echo "mouse-2, RET: show value")
		(insert ".\n")))
            (terpri)

            (let* ((alias (condition-case nil
                              (indirect-variable variable)
                            (error variable)))
                   (doc (or (documentation-property
                             variable 'variable-documentation)
                            (documentation-property
                             alias 'variable-documentation))))

              (with-current-buffer buffer
                (run-hook-with-args 'help-fns-describe-variable-functions
                                    variable))

              (with-current-buffer standard-output
                (help-fns--ensure-empty-line))
	      (princ "Documentation:\n")
	      (with-current-buffer standard-output
		(insert (or doc "Not documented as a variable."))))

	    (with-current-buffer standard-output
	      ;; Return the text we displayed.
	      (buffer-string))))))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--customize-variable)
(defun help-fns--customize-variable (variable &optional text)
  ;; Make a link to customize if this variable can be customized.
  (when (custom-variable-p variable)
    (let ((customize-label "customize"))
      (princ (concat "  You can " customize-label (or text " this variable.")))
      (with-current-buffer standard-output
	(save-excursion
	  (re-search-backward
	   (concat "\\(" customize-label "\\)") nil t)
	  (help-xref-button 1 'help-customize-variable variable)))
      (terpri))
    ;; Note variable's version or package version.
    (let ((output (describe-variable-custom-version-info variable)))
      (when output
	(terpri)
	(terpri)
	(princ output)))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-safe-local)
(defun help-fns--var-safe-local (variable)
  (let ((safe-var (get variable 'safe-local-variable)))
    (when safe-var
      (princ "  This variable is safe as a file local variable ")
      (princ "if its value\n  satisfies the predicate ")
      (princ (if (byte-code-function-p safe-var)
		 "which is a byte-compiled expression.\n"
	       (format-message "`%s'.\n" safe-var))))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-risky)
(defun help-fns--var-risky (variable)
  ;; Can be both risky and safe, eg auto-fill-function.
  (when (risky-local-variable-p variable)
    (princ "  This variable may be risky if used as a \
file-local variable.\n")
    (when (assq variable safe-local-variable-values)
      (princ (substitute-command-keys
              "  However, you have added it to \
`safe-local-variable-values'.\n")))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-ignored-local)
(defun help-fns--var-ignored-local (variable)
  (when (memq variable ignored-local-variables)
    (princ "  This variable is ignored as a file-local \
variable.\n")))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-file-local)
(defun help-fns--var-file-local (variable)
  (when (boundp variable)
    (let ((val (symbol-value variable)))
      (when (member (cons variable val)
                    file-local-variables-alist)
        (if (member (cons variable val)
                    dir-local-variables-alist)
	    (let ((file (and buffer-file-name
                             (not (file-remote-p buffer-file-name))
                             (dir-locals-find-file buffer-file-name)))
                  (is-directory nil))
	      (princ (substitute-command-keys
		      "  This variable's value is directory-local"))
              (when (consp file)       ; result from cache
                ;; If the cache element has an mtime, we
                ;; assume it came from a file.
                (if (nth 2 file)
                    ;; (car file) is a directory.
                    (setq file (dir-locals--all-files (car file)))
                  ;; Otherwise, assume it was set directly.
                  (setq file (car file)
                        is-directory t)))
              (if (null file)
                  (princ ".\n")
                (princ ", set ")
                (princ (substitute-command-keys
                        (cond
                         (is-directory "for the directory\n  `")
                         ;; Many files matched.
                         ((and (consp file) (cdr file))
                          (setq file (file-name-directory (car file)))
                          (format "by one of the\n  %s files in the directory\n  `"
                                  dir-locals-file))
                         (t (setq file (car file))
                            "by the file\n  `"))))
	        (with-current-buffer standard-output
	          (insert-text-button
	           file 'type 'help-dir-local-var-def
                   'help-args (list variable file)))
	        (princ (substitute-command-keys "'.\n"))))
          (princ (substitute-command-keys
	          "  This variable's value is file-local.\n")))))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-watchpoints)
(defun help-fns--var-watchpoints (variable)
  (let ((watchpoints (get-variable-watchers variable)))
    (when watchpoints
      (princ "  Calls these functions when changed: ")
      ;; FIXME: Turn function names into hyperlinks.
      (princ watchpoints)
      (terpri))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-obsolete)
(defun help-fns--var-obsolete (variable)
  (let* ((obsolete (get variable 'byte-obsolete-variable))
	 (use (car obsolete)))
    (when obsolete
      (princ "  This variable is obsolete")
      (if (nth 2 obsolete)
          (princ (format " since %s" (nth 2 obsolete))))
      (princ (cond ((stringp use) (concat ";\n  " use))
		   (use (format-message ";\n  use `%s' instead."
                                        (car obsolete)))
		   (t ".")))
      (terpri))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-alias)
(defun help-fns--var-alias (variable)
  ;; Mention if it's an alias.
  (let ((alias (condition-case nil
                   (indirect-variable variable)
                 (error variable))))
    (unless (eq alias variable)
      (princ (format-message
              "  This variable is an alias for `%s'.\n"
              alias)))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-aliases)
(defun help-fns--var-aliases (variable)
  ;; Mention if it has any aliases.
  (let (aliases alias)
    (mapatoms
     (lambda (sym)
       (when (and (boundp sym)
		  (setq alias (indirect-variable sym))
                  (eq alias variable)
		  (not (eq alias sym)))
	 (push sym aliases)))
     obarray)
    (when aliases
      (princ
       (if (= (length aliases) 1)
           (format-message
            "  This variable has an alias: `%s'.\n" (car aliases))
         (format-message
          "  This variable has the following aliases: %s.\n"
          (mapconcat
           (lambda (sym)
             (format "`%s'" sym))
           aliases ",\n    ")))))))

(add-hook 'help-fns-describe-variable-functions #'help-fns--var-bufferlocal)
(defun help-fns--var-bufferlocal (variable)
  (let ((permanent-local (get variable 'permanent-local))
        (locus (variable-binding-locus variable)))
    ;; Mention if it's a local variable.
    (cond
     ((and (local-variable-if-set-p variable)
	   (or (not (local-variable-p variable))
	       (with-temp-buffer
	         (local-variable-if-set-p variable))))
      (princ "  Automatically becomes ")
      (if permanent-local
	  (princ "permanently "))
      (princ "buffer-local when set.\n"))
     ((not permanent-local))
     ((bufferp locus)
      (princ
       (substitute-command-keys
        "  This variable's buffer-local value is permanent.\n")))
     (t
      (princ (substitute-command-keys
	      "  This variable's value is permanent \
if it is given a local binding.\n"))))))


;; Faces.

;;;###autoload
(defun describe-face (face &optional frame)
  "Display the properties of face FACE on FRAME.
Interactively, FACE defaults to the faces of the character after point
and FRAME defaults to the selected frame.

If the optional argument FRAME is given, report on face FACE in that frame.
If FRAME is t, report on the defaults for face FACE (for new frames).
If FRAME is omitted or nil, use the selected frame."
  (interactive (list (read-face-name "Describe face"
                                     (or (face-at-point t) 'default)
                                     t)))
  (help-setup-xref (list #'describe-face face)
		   (called-interactively-p 'interactive))
  (unless face
    (setq face 'default))
  (if (not (listp face))
      (setq face (list face)))
  (with-help-window (help-buffer)
    (with-current-buffer standard-output
      (dolist (f face (buffer-string))
	(if (stringp f) (setq f (intern f)))
	;; We may get called for anonymous faces (i.e., faces
	;; expressed using prop-value plists).  Those can't be
	;; usefully customized, so ignore them.
	(when (symbolp f)
	  (insert "Face: " (symbol-name f))
	  (if (not (facep f))
	      (insert "   undefined face.\n")
	    (let ((customize-label "customize this face")
		  file-name)
	      (insert (concat " (" (propertize "sample" 'font-lock-face f) ")"))
	      (princ (concat " (" customize-label ")\n"))
	      ;; FIXME not sure how much of this belongs here, and
	      ;; how much in `face-documentation'.  The latter is
	      ;; not used much, but needs to return nil for
	      ;; undocumented faces.
	      (let ((alias (get f 'face-alias))
		    (face f)
		    obsolete)
		(when alias
		  (setq face alias)
		  (insert
		   (format-message
                    "\n  %s is an alias for the face `%s'.\n%s"
                    f alias
                    (if (setq obsolete (get f 'obsolete-face))
                        (format-message
                         "  This face is obsolete%s; use `%s' instead.\n"
                         (if (stringp obsolete)
                             (format " since %s" obsolete)
                           "")
                         alias)
                      ""))))
		(insert "\nDocumentation:\n"
                        (substitute-command-keys
                         (or (face-documentation face)
                             "Not documented as a face."))
			"\n\n"))
	      (with-current-buffer standard-output
		(save-excursion
		  (re-search-backward
		   (concat "\\(" customize-label "\\)") nil t)
		  (help-xref-button 1 'help-customize-face f)))
	      (setq file-name (find-lisp-object-file-name f 'defface))
	      (when file-name
		(princ (substitute-command-keys "Defined in `"))
		(princ (file-name-nondirectory file-name))
		(princ (substitute-command-keys "'"))
		;; Make a hyperlink to the library.
		(save-excursion
		  (re-search-backward
                   (substitute-command-keys "`\\([^`']+\\)'") nil t)
		  (help-xref-button 1 'help-face-def f file-name))
		(princ ".")
		(terpri)
		(terpri))))
	  (terpri)
          (run-hook-with-args 'help-fns-describe-face-functions f frame))))))

(add-hook 'help-fns-describe-face-functions
          #'help-fns--face-custom-version-info)
(defun help-fns--face-custom-version-info (face _frame)
  (when-let ((version-info (describe-variable-custom-version-info face 'face)))
    (insert version-info)
    (terpri)))

(add-hook 'help-fns-describe-face-functions #'help-fns--face-attributes)
(defun help-fns--face-attributes (face frame)
  (let* ((attrs '((:family . "Family")
		  (:foundry . "Foundry")
		  (:width . "Width")
		  (:height . "Height")
		  (:weight . "Weight")
		  (:slant . "Slant")
		  (:foreground . "Foreground")
		  (:distant-foreground . "DistantForeground")
		  (:background . "Background")
		  (:underline . "Underline")
		  (:overline . "Overline")
		  (:strike-through . "Strike-through")
		  (:box . "Box")
		  (:inverse-video . "Inverse")
		  (:stipple . "Stipple")
		  (:font . "Font")
		  (:fontset . "Fontset")
                  (:extend . "Extend")
		  (:inherit . "Inherit")))
	 (max-width (apply #'max (mapcar #'(lambda (x) (length (cdr x)))
					 attrs))))
    (dolist (a attrs)
      (let ((attr (face-attribute face (car a) frame)))
	(insert (make-string (- max-width (length (cdr a))) ?\s)
		(cdr a) ": " (format "%s" attr))
	(if (and (eq (car a) :inherit)
		 (not (eq attr 'unspecified)))
	    ;; Make a hyperlink to the parent face.
	    (save-excursion
	      (re-search-backward ": \\([^:]+\\)" nil t)
	      (help-xref-button 1 'help-face attr)))
	(insert "\n")))
    (terpri)))

(defvar help-xref-stack-item)

;;;###autoload
(defun describe-symbol (symbol &optional buffer frame)
  "Display the full documentation of SYMBOL.
Will show the info of SYMBOL as a function, variable, and/or face.
Optional arguments BUFFER and FRAME specify for which buffer and
frame to show the information about SYMBOL; they default to the
current buffer and the selected frame, respectively."
  (interactive
   (let* ((v-or-f (symbol-at-point))
          (found (if v-or-f (cl-some (lambda (x) (funcall (nth 1 x) v-or-f))
                                     describe-symbol-backends)))
          (v-or-f (if found v-or-f (function-called-at-point)))
          (found (or found v-or-f))
          (enable-recursive-minibuffers t)
          (val (completing-read (if found
				    (format
                                     "Describe symbol (default %s): " v-or-f)
				  "Describe symbol: ")
				#'help--symbol-completion-table
				(lambda (vv)
                                  (cl-some (lambda (x) (funcall (nth 1 x) vv))
                                           describe-symbol-backends))
				t nil nil
				(if found (symbol-name v-or-f)))))
     (list (if (equal val "")
	       v-or-f (intern val)))))
  (if (not (symbolp symbol))
      (user-error "You didn't specify a function or variable"))
  (unless (buffer-live-p buffer) (setq buffer (current-buffer)))
  (unless (frame-live-p frame) (setq frame (selected-frame)))
  (with-current-buffer (help-buffer)
    ;; Push the previous item on the stack before clobbering the output buffer.
    (help-setup-xref nil nil)
    (let* ((docs
            (nreverse
             (delq nil
                   (mapcar (pcase-lambda (`(,name ,testfn ,descfn))
                             (when (funcall testfn symbol)
                               ;; Don't record the current entry in the stack.
                               (setq help-xref-stack-item nil)
                               (cons name
                                     (funcall descfn symbol buffer frame))))
                           describe-symbol-backends))))
           (single (null (cdr docs))))
      (while (cdr docs)
        (goto-char (point-min))
        (let ((inhibit-read-only t)
              (name (caar docs))        ;Name of doc currently at BOB.
              (doc (cdr (cadr docs))))  ;Doc to add at BOB.
          (when doc
            (insert doc)
            (delete-region (point)
                           (progn (skip-chars-backward " \t\n") (point)))
            (insert "\n\n"
                    (eval-when-compile
                      (propertize "\n" 'face
                                  '(:height 0.1 :inverse-video t :extend t)))
                    "\n")
            (when name
              (insert (symbol-name symbol)
                      " is also a " name "." "\n\n"))))
        (setq docs (cdr docs)))
      (unless single
        ;; Don't record the `describe-variable' item in the stack.
        (setq help-xref-stack-item nil)
        (help-setup-xref (list #'describe-symbol symbol) nil))
      (goto-char (point-min)))))

;;;###autoload
(defun describe-syntax (&optional buffer)
  "Describe the syntax specifications in the syntax table of BUFFER.
The descriptions are inserted in a help buffer, which is then displayed.
BUFFER defaults to the current buffer."
  (interactive)
  (setq buffer (or buffer (current-buffer)))
  (help-setup-xref (list #'describe-syntax buffer)
		   (called-interactively-p 'interactive))
  (with-help-window (help-buffer)
    (let ((table (with-current-buffer buffer (syntax-table))))
      (with-current-buffer standard-output
	(describe-vector table 'internal-describe-syntax-value)
	(while (setq table (char-table-parent table))
	  (insert "\nThe parent syntax table is:")
	  (describe-vector table 'internal-describe-syntax-value))))))

(defun help-describe-category-set (value)
  (insert (cond
	   ((null value) "default")
	   ((char-table-p value) "deeper char-table ...")
	   (t (condition-case nil
		  (category-set-mnemonics value)
		(error "invalid"))))))

;;;###autoload
(defun describe-categories (&optional buffer)
  "Describe the category specifications in the current category table.
The descriptions are inserted in a buffer, which is then displayed.
If BUFFER is non-nil, then describe BUFFER's category table instead.
BUFFER should be a buffer or a buffer name."
  (interactive)
  (setq buffer (or buffer (current-buffer)))
  (help-setup-xref (list #'describe-categories buffer)
		   (called-interactively-p 'interactive))
  (with-help-window (help-buffer)
    (let* ((table (with-current-buffer buffer (category-table)))
	   (docs (char-table-extra-slot table 0)))
      (if (or (not (vectorp docs)) (/= (length docs) 95))
	  (error "Invalid first extra slot in this category table\n"))
      (with-current-buffer standard-output
        (setq-default help-button-cache (make-marker))
	(insert "Legend of category mnemonics ")
        (insert-button "(longer descriptions at the bottom)"
                       'action help-button-cache
                       'follow-link t
                       'help-echo "mouse-2, RET: show full legend")
        (insert "\n")
	(let ((pos (point)) (items 0) lines n)
	  (dotimes (i 95)
	    (if (aref docs i) (setq items (1+ items))))
	  (setq lines (1+ (/ (1- items) 4)))
	  (setq n 0)
	  (dotimes (i 95)
	    (let ((elt (aref docs i)))
	      (when elt
		(string-match ".*" elt)
		(setq elt (match-string 0 elt))
		(if (>= (length elt) 17)
		    (setq elt (concat (substring elt 0 14) "...")))
		(if (< (point) (point-max))
		    (move-to-column (* 20 (/ n lines)) t))
		(insert (+ i ?\s) ?: elt)
		(if (< (point) (point-max))
		    (forward-line 1)
		  (insert "\n"))
		(setq n (1+ n))
		(if (= (% n lines) 0)
		    (goto-char pos))))))
	(goto-char (point-max))
	(insert "\n"
		"character(s)\tcategory mnemonics\n"
		"------------\t------------------")
	(describe-vector table 'help-describe-category-set)
        (set-marker help-button-cache (point))
	(insert "Legend of category mnemonics:\n")
	(dotimes (i 95)
	  (let ((elt (aref docs i)))
	    (when elt
	      (if (string-match "\n" elt)
		  (setq elt (substring elt (match-end 0))))
	      (insert (+ i ?\s) ": " elt "\n"))))
	(while (setq table (char-table-parent table))
	  (insert "\nThe parent category table is:")
	  (describe-vector table 'help-describe-category-set))))))


;;; Replacements for old lib-src/ programs.  Don't seem especially useful.

;; Replaces lib-src/digest-doc.c.
;;;###autoload
(defun doc-file-to-man (file)
  "Produce an nroff buffer containing the doc-strings from the DOC file."
  (interactive (list (read-file-name "Name of DOC file: " doc-directory
                                     internal-doc-file-name t)))
  (or (file-readable-p file)
      (error "Cannot read file `%s'" file))
  (pop-to-buffer (generate-new-buffer "*man-doc*"))
  (setq buffer-undo-list t)
  (insert ".TH \"Command Summary for GNU Emacs\"\n"
          ".AU Richard M. Stallman\n")
  (insert-file-contents file)
  (let (notfirst)
    (while (search-forward "\^_" nil 'move)
      (if (= (following-char) ?S)
          (delete-region (1- (point)) (line-end-position))
        (delete-char -1)
        (if notfirst
            (insert "\n.DE\n")
          (setq notfirst t))
        (insert "\n.SH ")
        (insert (if (= (following-char) ?F) "Function " "Variable "))
        (delete-char 1)
        (forward-line 1)
        (insert ".DS L\n"))))
  (insert "\n.DE\n")
  (setq buffer-undo-list nil)
  (nroff-mode))

;; Replaces lib-src/sorted-doc.c.
;;;###autoload
(defun doc-file-to-info (file)
  "Produce a texinfo buffer with sorted doc-strings from the DOC file."
  (interactive (list (read-file-name "Name of DOC file: " doc-directory
                                     internal-doc-file-name t)))
  (or (file-readable-p file)
      (error "Cannot read file `%s'" file))
  (let ((i 0) type name doc alist)
    (with-temp-buffer
      (insert-file-contents file)
      ;; The characters "@{}" need special treatment.
      (while (re-search-forward "[@{}]" nil t)
        (backward-char)
        (insert "@")
        (forward-char 1))
      (goto-char (point-min))
      (while (search-forward "\^_" nil t)
        (when (/= (following-char) ?S)
          (setq type (char-after)
                name (buffer-substring (1+ (point)) (line-end-position))
                doc (buffer-substring (line-beginning-position 2)
                                      (if (search-forward  "\^_" nil 'move)
                                          (1- (point))
                                        (point)))
                alist (cons (list name type doc) alist))
          (backward-char 1))))
    (pop-to-buffer (generate-new-buffer "*info-doc*"))
    (setq buffer-undo-list t)
    ;; Write the output header.
    (insert "\\input texinfo  @c -*-texinfo-*-\n"
            "@setfilename emacsdoc.info\n"
            "@settitle Command Summary for GNU Emacs\n"
            "@finalout\n"
            "\n@node Top\n"
            "@unnumbered Command Summary for GNU Emacs\n\n"
            "@table @asis\n\n"
            "@iftex\n"
            "@global@let@ITEM@item\n"
            "@def@item{@filbreak@vskip5pt@ITEM}\n"
            "@font@tensy cmsy10 scaled @magstephalf\n"
            "@font@teni cmmi10 scaled @magstephalf\n"
            "@def\\{{@tensy@char110}}\n" ; this backslash goes with cmr10
            "@def|{{@tensy@char106}}\n"
            "@def@{{{@tensy@char102}}\n"
            "@def@}{{@tensy@char103}}\n"
            "@def<{{@teni@char62}}\n"
            "@def>{{@teni@char60}}\n"
            "@chardef@@64\n"
            "@catcode43=12\n"
            "@tableindent-0.2in\n"
            "@end iftex\n")
    ;; Sort the array by name; within each name, by type (functions first).
    (setq alist (sort alist (lambda (e1 e2)
                              (if (string-equal (car e1) (car e2))
                                  (<= (cadr e1) (cadr e2))
                                (string-lessp (car e1) (car e2))))))
    ;; Print each function.
    (dolist (e alist)
      (insert "\n@item "
              (if (char-equal (cadr e) ?\F) "Function" "Variable")
              " @code{" (car e) "}\n@display\n"
              (nth 2 e)
              "\n@end display\n")
      ;; Try to avoid a save size overflow in the TeX output routine.
      (if (zerop (setq i (% (1+ i) 100)))
          (insert "\n@end table\n@table @asis\n")))
    (insert "@end table\n"
            "@bye\n")
    (setq buffer-undo-list nil)
    (texinfo-mode)))

(provide 'help-fns)

;;; help-fns.el ends here
