bug#24913: 25.1.50; Emacs accepts undocumented and confusing combinations of &optional and &rest in argument lists

[Philipp Stephani <p.stephani2@gmail.com>]

For example:

(funcall (lambda (&optional &rest &rest &optional x) (list x)) 'a)
=> ((a))

Obviously here the &rest keyword "wins", but I think that's overly
confusing.  Such an argument list is most likely a programmer mistake,
and should signal an error to make the programmer aware of the mistake.



In GNU Emacs 25.1.50.13 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2016-11-09 built on localhost
Repository revision: eb364fddec1431f459166cebb36f09f6b371dd71
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04 LTS

Configured using:
 'configure --with-modules --enable-checking
 --enable-check-lisp-object-type 'CFLAGS=-ggdb3 -O0''

Configured features:
XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
cl-loaddefs pcase cl-lib mail-prsvr mail-utils time-date mule-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment elisp-mode lisp-mode prog-mode register
page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 88939 12159)
 (symbols 48 19888 0)
 (miscs 40 343 148)
 (strings 32 14757 5052)
 (string-bytes 1 440451)
 (vectors 16 12779)
 (vector-slots 8 446082 5011)
 (floats 8 166 60)
 (intervals 56 209 0)
 (buffers 976 24)
 (heap 1024 23753 956))

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