bug#24700: 26.0.50; unimplemented cl-defstruct slot option :type used in Emacs source code

[Gemini Lasswell <gazally@runbox.com>]

The only slot option implemented in Emacs Lisp for cl-defstruct is
:read-only, according to the documentation. However there exists code in
the Emacs source tree which uses the :type option as in Common Lisp. My
(possibly incomplete) search found it in the following files:

emacs-lisp/cl-generic.el
emacs-lisp/cl-preloaded.el
emacs-lisp/eieio-core.el
emacs-lisp/ert.el
erc/erc-backend.el
gnus/nnmaildir.el

The code for cl-defstruct ignores any keyword other than :read-only, but
the problem is that since :type is not included in the edebug spec for
cl-defstruct's slot options, edebug and testcover give errors when asked
to instrument these files. To reproduce:

1. emacs -Q
2. M-x edebug-all-defs RET
3. C-x C-f lisp/emacs-lisp/cl-generic.el RET
4. M-x eval-buffer RET

In GNU Emacs 26.0.50.2 (x86_64-apple-darwin15.6.0, NS appkit-1404.47 Version 10.11.6 (Build 15G1004))
 of 2016-10-14 built on rainbow.local
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Edebugging all definitions is on.
edebug-syntax-error: Invalid read syntax: "Failed matching", ("cl-defstruct" [&or symbolp (gate symbolp &rest [&or symbolp (&or [":conc-name" symbolp] [":constructor" symbolp &optional cl-lambda-list] [":copier" symbolp] [":predicate" symbolp] [":include" symbolp &rest sexp] [":print-function" sexp] [":type" symbolp] [":named"] [":initial-offset" natnump])])] [&optional stringp] &rest &or symbolp (symbolp def-form &optional ":read-only" sexp))
Configured using:
 'configure --with-ns'

Configured features:
JPEG RSVG IMAGEMAGICK NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS
NS

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

Major mode: Emacs-Lisp

Minor modes in effect:
  diff-auto-refine-mode: t
  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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny dired dired-loaddefs
format-spec rfc822 mml mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils cl-macs vc-git diff-mode
easy-mmode map seq byte-opt gv bytecomp byte-compile cl-extra help-mode
cconv edebug easymenu cl-loaddefs pcase cl-lib time-date mule-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/ns-win ns-win ucs-normalize term/common-win 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
term/tty-colors 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
obarray 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 kqueue
cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 214195 19525)
 (symbols 48 21023 0)
 (miscs 40 46 192)
 (strings 32 21113 4927)
 (string-bytes 1 657659)
 (vectors 16 35806)
 (vector-slots 8 677585 4828)
 (floats 8 183 222)
 (intervals 56 396 16)
 (buffers 976 12))