lisp/help-fns.el

   1 ;;; help-fns.el --- Complex help functions
   2
   3 ;; Copyright (C) 1985, 1986, 1993, 1994, 1998, 1999, 2000, 2001,
   4 ;;   2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   5
   6 ;; Maintainer: FSF
   7 ;; Keywords: help, internal
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software; you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation; either version 3, or (at your option)
  14 ;; any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  23 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  24 ;; Boston, MA 02110-1301, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; This file contains those help commands which are complicated, and
  29 ;; which may not be used in every session.  For example
  30 ;; `describe-function' will probably be heavily used when doing elisp
  31 ;; programming, but not if just editing C files.  Simpler help commands
  32 ;; are in help.el
  33
  34 ;;; Code:
  35
  36 (require 'help-mode)
  37
  38 ;; Functions
  39
  40 ;;;###autoload
  41 (defun describe-function (function)
  42   "Display the full documentation of FUNCTION (a symbol)."
  43   (interactive
  44    (let ((fn (function-called-at-point))
  45          (enable-recursive-minibuffers t)
  46          val)
  47      (setq val (completing-read (if fn
  48                                     (format "Describe function (default %s): " fn)
  49                                   "Describe function: ")
  50                                 obarray 'fboundp t nil nil
  51                                 (and fn (symbol-name fn))))
  52      (list (if (equal val "")
  53                fn (intern val)))))
  54   (if (null function)
  55       (message "You didn't specify a function")
  56     (help-setup-xref (list #'describe-function function) (interactive-p))
  57     (save-excursion
  58       (with-help-window (help-buffer)
  59         (prin1 function)
  60         ;; Use " is " instead of a colon so that
  61         ;; it is easier to get out the function name using forward-sexp.
  62         (princ " is ")
  63         (describe-function-1 function)
  64         (with-current-buffer standard-output
  65           ;; Return the text we displayed.
  66           (buffer-string))))))
  67
  68 (defun help-split-fundoc (docstring def)
  69   "Split a function DOCSTRING into the actual doc and the usage info.
  70 Return (USAGE . DOC) or nil if there's no usage info.
  71 DEF is the function whose usage we're looking for in DOCSTRING."
  72   ;; Functions can get the calling sequence at the end of the doc string.
  73   ;; In cases where `function' has been fset to a subr we can't search for
  74   ;; function's name in the doc string so we use `fn' as the anonymous
  75   ;; function name instead.
  76   (when (and docstring (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" docstring))
  77     (cons (format "(%s%s"
  78                   ;; Replace `fn' with the actual function name.
  79                   (if (consp def) "anonymous" def)
  80                   (match-string 1 docstring))
  81           (substring docstring 0 (match-beginning 0)))))
  82
  83 (defun help-add-fundoc-usage (docstring arglist)
  84   "Add the usage info to DOCSTRING.
  85 If DOCSTRING already has a usage info, then just return it unchanged.
  86 The usage info is built from ARGLIST.  DOCSTRING can be nil.
  87 ARGLIST can also be t or a string of the form \"(FUN ARG1 ARG2 ...)\"."
  88   (unless (stringp docstring) (setq docstring "Not documented"))
  89   (if (or (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" docstring) (eq arglist t))
  90       docstring
  91     (concat docstring
  92             (if (string-match "\n?\n\\'" docstring)
  93                 (if (< (- (match-end 0) (match-beginning 0)) 2) "\n" "")
  94               "\n\n")
  95             (if (and (stringp arglist)
  96                      (string-match "\\`([^ ]+\\(.*\\))\\'" arglist))
  97                 (concat "(fn" (match-string 1 arglist) ")")
  98               (format "%S" (help-make-usage 'fn arglist))))))
  99
 100 (defun help-function-arglist (def)
 101   ;; Handle symbols aliased to other symbols.
 102   (if (and (symbolp def) (fboundp def)) (setq def (indirect-function def)))
 103   ;; If definition is a macro, find the function inside it.
 104   (if (eq (car-safe def) 'macro) (setq def (cdr def)))
 105   (cond
 106    ((byte-code-function-p def) (aref def 0))
 107    ((eq (car-safe def) 'lambda) (nth 1 def))
 108    ((and (eq (car-safe def) 'autoload) (not (eq (nth 4 def) 'keymap)))
 109     "[Arg list not available until function definition is loaded.]")
 110    (t t)))
 111
 112 (defun help-make-usage (function arglist)
 113   (cons (if (symbolp function) function 'anonymous)
 114         (mapcar (lambda (arg)
 115                   (if (not (symbolp arg))
 116                       (if (and (consp arg) (symbolp (car arg)))
 117                           ;; CL style default values for optional args.
 118                           (cons (intern (upcase (symbol-name (car arg))))
 119                                 (cdr arg))
 120                         arg)
 121                     (let ((name (symbol-name arg)))
 122                       (if (string-match "\\`&" name) arg
 123                         (intern (upcase name))))))
 124                 arglist)))
 125
 126 ;; Could be this, if we make symbol-file do the work below.
 127 ;; (defun help-C-file-name (subr-or-var kind)
 128 ;;   "Return the name of the C file where SUBR-OR-VAR is defined.
 129 ;; KIND should be `var' for a variable or `subr' for a subroutine."
 130 ;;   (symbol-file (if (symbolp subr-or-var) subr-or-var
 131 ;;               (subr-name subr-or-var))
 132 ;;             (if (eq kind 'var) 'defvar 'defun)))
 133 ;;;###autoload
 134 (defun help-C-file-name (subr-or-var kind)
 135   "Return the name of the C file where SUBR-OR-VAR is defined.
 136 KIND should be `var' for a variable or `subr' for a subroutine."
 137   (let ((docbuf (get-buffer-create " *DOC*"))
 138         (name (if (eq 'var kind)
 139                   (concat "V" (symbol-name subr-or-var))
 140                 (concat "F" (subr-name subr-or-var)))))
 141     (with-current-buffer docbuf
 142       (goto-char (point-min))
 143       (if (eobp)
 144           (insert-file-contents-literally
 145            (expand-file-name internal-doc-file-name doc-directory)))
 146       (let ((file (catch 'loop
 147                     (while t
 148                       (let ((pnt (search-forward (concat "\x1f" name "\n"))))
 149                         (re-search-backward "\x1fS\\(.*\\)")
 150                         (let ((file (match-string 1)))
 151                           (if (member file build-files)
 152                               (throw 'loop file)
 153                             (goto-char pnt))))))))
 154         (if (string-match "\\.\\(o\\|obj\\)\\'" file)
 155             (setq file (replace-match ".c" t t file)))
 156         (if (string-match "\\.c\\'" file)
 157             (concat "src/" file)
 158           file)))))
 159
 160 (defface help-argument-name '((((supports :slant italic)) :inherit italic))
 161   "Face to highlight argument names in *Help* buffers."
 162   :group 'help)
 163
 164 (defun help-default-arg-highlight (arg)
 165   "Default function to highlight arguments in *Help* buffers.
 166 It returns ARG in face `help-argument-name'; ARG is also
 167 downcased if it displays differently than the default
 168 face (according to `face-differs-from-default-p')."
 169   (propertize (if (face-differs-from-default-p 'help-argument-name)
 170                   (downcase arg)
 171                 arg)
 172               'face 'help-argument-name))
 173
 174 (defun help-do-arg-highlight (doc args)
 175   (with-syntax-table (make-syntax-table emacs-lisp-mode-syntax-table)
 176     (modify-syntax-entry ?\- "w")
 177     (dolist (arg args doc)
 178       (setq doc (replace-regexp-in-string
 179                  ;; This is heuristic, but covers all common cases
 180                  ;; except ARG1-ARG2
 181                  (concat "\\<"                   ; beginning of word
 182                          "\\(?:[a-z-]*-\\)?"     ; for xxx-ARG
 183                          "\\("
 184                          (regexp-quote arg)
 185                          "\\)"
 186                          "\\(?:es\\|s\\|th\\)?"  ; for ARGth, ARGs
 187                          "\\(?:-[a-z0-9-]+\\)?"  ; for ARG-xxx, ARG-n
 188                          "\\(?:-[{([<`\"].*?\\)?"; for ARG-{x}, (x), <x>, [x], `x'
 189                          "\\>")                  ; end of word
 190                  (help-default-arg-highlight arg)
 191                  doc t t 1)))))
 192
 193 (defun help-highlight-arguments (usage doc &rest args)
 194   (when usage
 195     (with-temp-buffer
 196       (insert usage)
 197       (goto-char (point-min))
 198       (let ((case-fold-search nil)
 199             (next (not (or args (looking-at "\\["))))
 200             (opt nil))
 201         ;; Make a list of all arguments
 202         (skip-chars-forward "^ ")
 203         (while next
 204           (or opt (not (looking-at " &")) (setq opt t))
 205           (if (not (re-search-forward " \\([\\[(]*\\)\\([^] &)\.]+\\)" nil t))
 206               (setq next nil)
 207             (setq args (cons (match-string 2) args))
 208             (when (and opt (string= (match-string 1) "("))
 209               ;; A pesky CL-style optional argument with default value,
 210               ;; so let's skip over it
 211               (search-backward "(")
 212               (goto-char (scan-sexps (point) 1)))))
 213         ;; Highlight aguments in the USAGE string
 214         (setq usage (help-do-arg-highlight (buffer-string) args))
 215         ;; Highlight arguments in the DOC string
 216         (setq doc (and doc (help-do-arg-highlight doc args))))))
 217   ;; Return value is like the one from help-split-fundoc, but highlighted
 218   (cons usage doc))
 219
 220 ;;;###autoload
 221 (defun describe-simplify-lib-file-name (file)
 222   "Simplify a library name FILE to a relative name, and make it a source file."
 223   (if file
 224       ;; Try converting the absolute file name to a library name.
 225       (let ((libname (file-name-nondirectory file)))
 226         ;; Now convert that back to a file name and see if we get
 227         ;; the original one.  If so, they are equivalent.
 228         (if (equal file (locate-file libname load-path '("")))
 229             (if (string-match "[.]elc\\'" libname)
 230                 (substring libname 0 -1)
 231               libname)
 232           file))))
 233
 234 (defun find-source-lisp-file (file-name)
 235   (let* ((elc-file (locate-file (concat file-name
 236                                  (if (string-match "\\.el" file-name)
 237                                      "c"
 238                                    ".elc"))
 239                                  load-path))
 240          (str (if (and elc-file (file-readable-p elc-file))
 241                   (with-temp-buffer
 242                     (insert-file-contents-literally elc-file nil 0 256)
 243                     (buffer-string))))
 244          (src-file (and str
 245                         (string-match ";;; from file \\(.*\\.el\\)" str)
 246                         (match-string 1 str))))
 247     (if (and src-file (file-readable-p src-file))
 248         src-file
 249       file-name)))
 250
 251 (declare-function ad-get-advice-info "advice" (function))
 252
 253 ;;;###autoload
 254 (defun describe-function-1 (function)
 255   (let* ((advised (and (symbolp function) (featurep 'advice)
 256                        (ad-get-advice-info function)))
 257          ;; If the function is advised, use the symbol that has the
 258          ;; real definition, if that symbol is already set up.
 259          (real-function
 260           (or (and advised
 261                    (cdr (assq 'origname advised))
 262                    (fboundp (cdr (assq 'origname advised)))
 263                    (cdr (assq 'origname advised)))
 264               function))
 265          ;; Get the real definition.
 266          (def (if (symbolp real-function)
 267                   (symbol-function real-function)
 268                 function))
 269          file-name string
 270          (beg (if (commandp def) "an interactive " "a ")))
 271     (setq string
 272           (cond ((or (stringp def)
 273                      (vectorp def))
 274                  "a keyboard macro")
 275                 ((subrp def)
 276                  (if (eq 'unevalled (cdr (subr-arity def)))
 277                      (concat beg "special form")
 278                    (concat beg "built-in function")))
 279                 ((byte-code-function-p def)
 280                  (concat beg "compiled Lisp function"))
 281                 ((symbolp def)
 282                  (while (symbolp (symbol-function def))
 283                    (setq def (symbol-function def)))
 284                  (format "an alias for `%s'" def))
 285                 ((eq (car-safe def) 'lambda)
 286                  (concat beg "Lisp function"))
 287                 ((eq (car-safe def) 'macro)
 288                  "a Lisp macro")
 289                 ((eq (car-safe def) 'autoload)
 290                  (setq file-name (nth 1 def))
 291                  (format "%s autoloaded %s"
 292                          (if (commandp def) "an interactive" "an")
 293                          (if (eq (nth 4 def) 'keymap) "keymap"
 294                            (if (nth 4 def) "Lisp macro" "Lisp function"))
 295                          ))
 296                 ((keymapp def)
 297                  (let ((is-full nil)
 298                        (elts (cdr-safe def)))
 299                    (while elts
 300                      (if (char-table-p (car-safe elts))
 301                          (setq is-full t
 302                                elts nil))
 303                      (setq elts (cdr-safe elts)))
 304                    (if is-full
 305                        "a full keymap"
 306                      "a sparse keymap")))
 307                 (t "")))
 308     (princ string)
 309     (with-current-buffer standard-output
 310       (save-excursion
 311         (save-match-data
 312           (if (re-search-backward "alias for `\\([^`']+\\)'" nil t)
 313               (help-xref-button 1 'help-function def)))))
 314     (or file-name
 315         (setq file-name (symbol-file function 'defun)))
 316     (setq file-name (describe-simplify-lib-file-name file-name))
 317     (when (equal file-name "loaddefs.el")
 318       ;; Find the real def site of the preloaded function.
 319       ;; This is necessary only for defaliases.
 320       (let ((location
 321              (condition-case nil
 322                  (find-function-search-for-symbol function nil "loaddefs.el")
 323                (error nil))))
 324         (when location
 325           (with-current-buffer (car location)
 326             (goto-char (cdr location))
 327             (when (re-search-backward
 328                    "^;;; Generated autoloads from \\(.*\\)" nil t)
 329               (setq file-name (match-string 1)))))))
 330     (when (and (null file-name) (subrp def))
 331       ;; Find the C source file name.
 332       (setq file-name (if (get-buffer " *DOC*")
 333                           (help-C-file-name def 'subr)
 334                         'C-source)))
 335     (when file-name
 336       (princ " in `")
 337       ;; We used to add .el to the file name,
 338       ;; but that's completely wrong when the user used load-file.
 339       (princ (if (eq file-name 'C-source) "C source code" file-name))
 340       (princ "'")
 341       ;; See if lisp files are present where they where installed from.
 342       (if (not (eq file-name 'C-source))
 343           (setq file-name (find-source-lisp-file file-name)))
 344
 345       ;; Make a hyperlink to the library.
 346       (with-current-buffer standard-output
 347         (save-excursion
 348           (re-search-backward "`\\([^`']+\\)'" nil t)
 349           (help-xref-button 1 'help-function-def real-function file-name))))
 350     (princ ".")
 351     (terpri)
 352     (when (commandp function)
 353       (if (and (eq function 'self-insert-command)
 354                (eq (key-binding "a") 'self-insert-command)
 355                (eq (key-binding "b") 'self-insert-command)
 356                (eq (key-binding "c") 'self-insert-command))
 357           (princ "It is bound to many ordinary text characters.\n")
 358         (let* ((remapped (command-remapping function))
 359                (keys (where-is-internal
 360                       (or remapped function) overriding-local-map nil nil))
 361                non-modified-keys)
 362           ;; Which non-control non-meta keys run this command?
 363           (dolist (key keys)
 364             (if (member (event-modifiers (aref key 0)) '(nil (shift)))
 365                 (push key non-modified-keys)))
 366           (when remapped
 367             (princ "It is remapped to `")
 368             (princ (symbol-name remapped))
 369             (princ "'"))
 370
 371           (when keys
 372             (princ (if remapped " which is bound to " "It is bound to "))
 373             ;; If lots of ordinary text characters run this command,
 374             ;; don't mention them one by one.
 375             (if (< (length non-modified-keys) 10)
 376                 (princ (mapconcat 'key-description keys ", "))
 377               (dolist (key non-modified-keys)
 378                 (setq keys (delq key keys)))
 379               (if keys
 380                   (progn
 381                     (princ (mapconcat 'key-description keys ", "))
 382                     (princ ", and many ordinary text characters"))
 383                 (princ "many ordinary text characters"))))
 384           (when (or remapped keys non-modified-keys)
 385             (princ ".")
 386             (terpri)))))
 387     (let* ((arglist (help-function-arglist def))
 388            (doc (documentation function))
 389            (usage (help-split-fundoc doc function)))
 390       (with-current-buffer standard-output
 391         ;; If definition is a keymap, skip arglist note.
 392         (unless (keymapp def)
 393           (let* ((use (cond
 394                         (usage (setq doc (cdr usage)) (car usage))
 395                         ((listp arglist)
 396                          (format "%S" (help-make-usage function arglist)))
 397                         ((stringp arglist) arglist)
 398                         ;; Maybe the arglist is in the docstring of a symbol
 399                         ;; this one is aliased to.
 400                         ((let ((fun real-function))
 401                            (while (and (symbolp fun)
 402                                        (setq fun (symbol-function fun))
 403                                        (not (setq usage (help-split-fundoc
 404                                                          (documentation fun)
 405                                                          function)))))
 406                            usage)
 407                          (car usage))
 408                         ((or (stringp def)
 409                              (vectorp def))
 410                          (format "\nMacro: %s" (format-kbd-macro def)))
 411                         (t "[Missing arglist.  Please make a bug report.]")))
 412                  (high (help-highlight-arguments use doc)))
 413             (let ((fill-begin (point)))
 414               (insert (car high) "\n")
 415               (fill-region fill-begin (point)))
 416             (setq doc (cdr high))))
 417         (let ((obsolete (and
 418                          ;; function might be a lambda construct.
 419                          (symbolp function)
 420                          (get function 'byte-obsolete-info))))
 421           (when obsolete
 422             (princ "\nThis function is obsolete")
 423             (when (nth 2 obsolete)
 424               (insert (format " since %s" (nth 2 obsolete))))
 425             (insert ";\n"
 426                     (if (stringp (car obsolete)) (car obsolete)
 427                       (format "use `%s' instead." (car obsolete)))
 428                     "\n"))
 429           (insert "\n"
 430                   (or doc "Not documented.")))))))
 431
 432 \f
 433 ;; Variables
 434
 435 ;;;###autoload
 436 (defun variable-at-point (&optional any-symbol)
 437   "Return the bound variable symbol found at or before point.
 438 Return 0 if there is no such symbol.
 439 If ANY-SYMBOL is non-nil, don't insist the symbol be bound."
 440   (or (condition-case ()
 441           (with-syntax-table emacs-lisp-mode-syntax-table
 442             (save-excursion
 443               (or (not (zerop (skip-syntax-backward "_w")))
 444                   (eq (char-syntax (following-char)) ?w)
 445                   (eq (char-syntax (following-char)) ?_)
 446                   (forward-sexp -1))
 447               (skip-chars-forward "'")
 448               (let ((obj (read (current-buffer))))
 449                 (and (symbolp obj) (boundp obj) obj))))
 450         (error nil))
 451       (let* ((str (find-tag-default))
 452              (sym (if str (intern-soft str))))
 453         (if (and sym (or any-symbol (boundp sym)))
 454             sym
 455           (save-match-data
 456             (when (and str (string-match "\\`\\W*\\(.*?\\)\\W*\\'" str))
 457               (setq sym (intern-soft (match-string 1 str)))
 458               (and (or any-symbol (boundp sym)) sym)))))
 459       0))
 460
 461 (defun describe-variable-custom-version-info (variable)
 462   (let ((custom-version (get variable 'custom-version))
 463         (cpv (get variable 'custom-package-version))
 464         (output nil))
 465     (if custom-version
 466         (setq output
 467               (format "This variable was introduced, or its default value was changed, in\nversion %s of Emacs.\n"
 468                       custom-version))
 469       (when cpv
 470         (let* ((package (car-safe cpv))
 471                (version (car (cdr-safe cpv)))
 472                (pkg-versions (assq package customize-package-emacs-version-alist))
 473                (emacsv (cdr (assoc version pkg-versions))))
 474           (if (and package version)
 475               (setq output
 476                     (format (concat "This variable was introduced, or its default value was changed, in\nversion %s of the %s package"
 477                                     (if emacsv
 478                                         (format " that is part of Emacs %s" emacsv))
 479                                     ".\n")
 480                             version package))))))
 481     output))
 482
 483 ;;;###autoload
 484 (defun describe-variable (variable &optional buffer frame)
 485   "Display the full documentation of VARIABLE (a symbol).
 486 Returns the documentation as a string, also.
 487 If VARIABLE has a buffer-local value in BUFFER or FRAME
 488 \(default to the current buffer and current frame),
 489 it is displayed along with the global value."
 490   (interactive
 491    (let ((v (variable-at-point))
 492          (enable-recursive-minibuffers t)
 493          val)
 494      (setq val (completing-read (if (symbolp v)
 495                                     (format
 496                                      "Describe variable (default %s): " v)
 497                                   "Describe variable: ")
 498                                 obarray
 499                                 '(lambda (vv)
 500                                    (or (boundp vv)
 501                                        (get vv 'variable-documentation)))
 502                                 t nil nil
 503                                 (if (symbolp v) (symbol-name v))))
 504      (list (if (equal val "")
 505                v (intern val)))))
 506   (unless (buffer-live-p buffer) (setq buffer (current-buffer)))
 507   (unless (frame-live-p frame) (setq frame (selected-frame)))
 508   (if (not (symbolp variable))
 509       (message "You did not specify a variable")
 510     (save-excursion
 511       (let ((valvoid (not (with-current-buffer buffer (boundp variable))))
 512             val val-start-pos locus)
 513         ;; Extract the value before setting up the output buffer,
 514         ;; in case `buffer' *is* the output buffer.
 515         (unless valvoid
 516           (with-selected-frame frame
 517             (with-current-buffer buffer
 518               (setq val (symbol-value variable)
 519                     locus (variable-binding-locus variable)))))
 520         (help-setup-xref (list #'describe-variable variable buffer)
 521                          (interactive-p))
 522         (with-help-window (help-buffer)
 523           (with-current-buffer buffer
 524             (prin1 variable)
 525             ;; Make a hyperlink to the library if appropriate.  (Don't
 526             ;; change the format of the buffer's initial line in case
 527             ;; anything expects the current format.)
 528             (let ((file-name (symbol-file variable 'defvar)))
 529               (setq file-name (describe-simplify-lib-file-name file-name))
 530               (when (equal file-name "loaddefs.el")
 531                 ;; Find the real def site of the preloaded variable.
 532                 (let ((location
 533                        (condition-case nil
 534                            (find-variable-noselect variable file-name)
 535                          (error nil))))
 536                   (when location
 537                     (with-current-buffer (car location)
 538                       (when (cdr location)
 539                         (goto-char (cdr location)))
 540                       (when (re-search-backward
 541                              "^;;; Generated autoloads from \\(.*\\)" nil t)
 542                         (setq file-name (match-string 1)))))))
 543               (when (and (null file-name)
 544                          (integerp (get variable 'variable-documentation)))
 545                 ;; It's a variable not defined in Elisp but in C.
 546                 (setq file-name
 547                       (if (get-buffer " *DOC*")
 548                           (help-C-file-name variable 'var)
 549                         'C-source)))
 550               (if file-name
 551                   (progn
 552                     (princ " is a variable defined in `")
 553                     (princ (if (eq file-name 'C-source) "C source code" file-name))
 554                     (princ "'.\n")
 555                     (with-current-buffer standard-output
 556                       (save-excursion
 557                         (re-search-backward "`\\([^`']+\\)'" nil t)
 558                         (help-xref-button 1 'help-variable-def
 559                                           variable file-name)))
 560                     (if valvoid
 561                         (princ "It is void as a variable.")
 562                       (princ "Its ")))
 563                 (if valvoid
 564                     (princ " is void as a variable.")
 565                   (princ "'s "))))
 566             (if valvoid
 567                 nil
 568               (with-current-buffer standard-output
 569                 (setq val-start-pos (point))
 570                 (princ "value is ")
 571                 (terpri)
 572                 (let ((from (point)))
 573                   (pp val)
 574                   ;; Hyperlinks in variable's value are quite frequently
 575                   ;; inappropriate e.g C-h v <RET> features <RET>
 576                   ;; (help-xref-on-pp from (point))
 577                   (if (< (point) (+ from 20))
 578                       (delete-region (1- from) from)))))
 579             (terpri)
 580
 581             (when locus
 582               (if (bufferp locus)
 583                   (princ (format "%socal in buffer %s; "
 584                                  (if (get variable 'permanent-local)
 585                                      "Permanently l" "L")
 586                                  (buffer-name)))
 587                 (princ (format "It is a frame-local variable; ")))
 588               (if (not (default-boundp variable))
 589                   (princ "globally void")
 590                 (let ((val (default-value variable)))
 591                   (with-current-buffer standard-output
 592                     (princ "global value is ")
 593                     (terpri)
 594                     ;; Fixme: pp can take an age if you happen to
 595                     ;; ask for a very large expression.  We should
 596                     ;; probably print it raw once and check it's a
 597                     ;; sensible size before prettyprinting.  -- fx
 598                     (let ((from (point)))
 599                       (pp val)
 600                       ;; See previous comment for this function.
 601                       ;; (help-xref-on-pp from (point))
 602                       (if (< (point) (+ from 20))
 603                           (delete-region (1- from) from))))))
 604               (terpri))
 605
 606             ;; If the value is large, move it to the end.
 607             (with-current-buffer standard-output
 608               (when (> (count-lines (point-min) (point-max)) 10)
 609                 ;; Note that setting the syntax table like below
 610                 ;; makes forward-sexp move over a `'s' at the end
 611                 ;; of a symbol.
 612                 (set-syntax-table emacs-lisp-mode-syntax-table)
 613                 (goto-char val-start-pos)
 614                 ;; The line below previously read as
 615                 ;; (delete-region (point) (progn (end-of-line) (point)))
 616                 ;; which suppressed display of the buffer local value for
 617                 ;; large values.
 618                 (when (looking-at "value is") (replace-match ""))
 619                 (save-excursion
 620                   (insert "\n\nValue:")
 621                   (set (make-local-variable 'help-button-cache)
 622                        (point-marker)))
 623                 (insert "value is shown ")
 624                 (insert-button "below"
 625                                'action help-button-cache
 626                                'follow-link t
 627                                'help-echo "mouse-2, RET: show value")
 628                 (insert ".\n")))
 629             (terpri)
 630
 631             (let* ((alias (condition-case nil
 632                              (indirect-variable variable)
 633                            (error variable)))
 634                    (obsolete (get variable 'byte-obsolete-variable))
 635                    (safe-var (get variable 'safe-local-variable))
 636                    (doc (or (documentation-property variable 'variable-documentation)
 637                             (documentation-property alias 'variable-documentation)))
 638                    (extra-line nil))
 639               ;; Add a note for variables that have been make-var-buffer-local.
 640               (when (and (local-variable-if-set-p variable)
 641                          (or (not (local-variable-p variable))
 642                              (with-temp-buffer
 643                                (local-variable-if-set-p variable))))
 644                 (setq extra-line t)
 645                 (princ "  Automatically becomes buffer-local when set in any fashion.\n"))
 646
 647               ;; Mention if it's an alias
 648               (unless (eq alias variable)
 649                 (setq extra-line t)
 650                 (princ (format "  This variable is an alias for `%s'.\n" alias)))
 651
 652               (when obsolete
 653                 (setq extra-line t)
 654                 (princ "  This variable is obsolete")
 655                 (if (cdr obsolete) (princ (format " since %s" (cdr obsolete))))
 656                 (princ ";\n  ")
 657                 (princ (if (stringp (car obsolete)) (car obsolete)
 658                          (format "use `%s' instead." (car obsolete))))
 659                 (terpri))
 660               (when safe-var
 661                 (setq extra-line t)
 662                 (princ "  This variable is safe as a file local variable ")
 663                 (princ "if its value\n  satisfies the predicate ")
 664                 (princ (if (byte-code-function-p safe-var)
 665                            "which is byte-compiled expression.\n"
 666                          (format "`%s'.\n" safe-var))))
 667
 668               (if extra-line (terpri))
 669               (princ "Documentation:\n")
 670               (with-current-buffer standard-output
 671                 (insert (or doc "Not documented as a variable."))))
 672             ;; Make a link to customize if this variable can be customized.
 673             (when (custom-variable-p variable)
 674               (let ((customize-label "customize"))
 675                 (terpri)
 676                 (terpri)
 677                 (princ (concat "You can " customize-label " this variable."))
 678                 (with-current-buffer standard-output
 679                   (save-excursion
 680                     (re-search-backward
 681                      (concat "\\(" customize-label "\\)") nil t)
 682                     (help-xref-button 1 'help-customize-variable variable))))
 683               ;; Note variable's version or package version
 684               (let ((output (describe-variable-custom-version-info variable)))
 685                 (when output
 686                   (terpri)
 687                   (terpri)
 688                   (princ output))))
 689
 690             (save-excursion
 691               (set-buffer standard-output)
 692               ;; Return the text we displayed.
 693               (buffer-string))))))))
 694
 695
 696 ;;;###autoload
 697 (defun describe-syntax (&optional buffer)
 698   "Describe the syntax specifications in the syntax table of BUFFER.
 699 The descriptions are inserted in a help buffer, which is then displayed.
 700 BUFFER defaults to the current buffer."
 701   (interactive)
 702   (setq buffer (or buffer (current-buffer)))
 703   (help-setup-xref (list #'describe-syntax buffer) (interactive-p))
 704   (with-help-window (help-buffer)
 705     (let ((table (with-current-buffer buffer (syntax-table))))
 706       (with-current-buffer standard-output
 707         (describe-vector table 'internal-describe-syntax-value)
 708         (while (setq table (char-table-parent table))
 709           (insert "\nThe parent syntax table is:")
 710           (describe-vector table 'internal-describe-syntax-value))))))
 711
 712 (defun help-describe-category-set (value)
 713   (insert (cond
 714            ((null value) "default")
 715            ((char-table-p value) "deeper char-table ...")
 716            (t (condition-case err
 717                   (category-set-mnemonics value)
 718                 (error "invalid"))))))
 719
 720 ;;;###autoload
 721 (defun describe-categories (&optional buffer)
 722   "Describe the category specifications in the current category table.
 723 The descriptions are inserted in a buffer, which is then displayed.
 724 If BUFFER is non-nil, then describe BUFFER's category table instead.
 725 BUFFER should be a buffer or a buffer name."
 726   (interactive)
 727   (setq buffer (or buffer (current-buffer)))
 728   (help-setup-xref (list #'describe-categories buffer) (interactive-p))
 729   (with-help-window (help-buffer)
 730     (let ((table (with-current-buffer buffer (category-table))))
 731       (with-current-buffer standard-output
 732         (describe-vector table 'help-describe-category-set)
 733         (let ((docs (char-table-extra-slot table 0)))
 734           (if (or (not (vectorp docs)) (/= (length docs) 95))
 735               (insert "Invalid first extra slot in this char table\n")
 736             (insert "Meanings of mnemonic characters are:\n")
 737             (dotimes (i 95)
 738               (let ((elt (aref docs i)))
 739                 (when elt
 740                   (insert (+ i ?\s) ": " elt "\n"))))
 741             (while (setq table (char-table-parent table))
 742               (insert "\nThe parent category table is:")
 743               (describe-vector table 'help-describe-category-set))))))))
 744
 745 (provide 'help-fns)
 746
 747 ;; arch-tag: 9e10331c-ae81-4d13-965d-c4819aaab0b3
 748 ;;; help-fns.el ends here