bug#40727: 27.0.91; 'cl-loop ... across ... and' seems broken

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

In Emacs 26:

emacs -Q -batch -l cl-lib -eval '(cl-loop for x across [1 2] and y across [3 4])'

works (i.e. no error), but in Emacs 27 it gives an error

Symbol’s value as variable is void: --cl-vec--

This doesn't happen with "for" instead of "and", and also doesn't happen
with lists and "in".  If it helps, here's the backtrace:

  (length --cl-vec--)
  (let ((--cl-vec-- [1 2]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (x nil) (--cl-vec-- [3 4]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (y nil)) (while (and (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--) (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--)) (cl-psetq x (aref --cl-vec-- --cl-idx--) y (aref --cl-vec-- --cl-idx--))) nil)
  (catch '--cl-block-nil-- (let ((--cl-vec-- [1 2]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (x nil) (--cl-vec-- [3 4]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (y nil)) (while (and (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--) (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--)) (cl-psetq x (aref --cl-vec-- --cl-idx--) y (aref --cl-vec-- --cl-idx--))) nil))
  (cl--block-wrapper (catch '--cl-block-nil-- (let ((--cl-vec-- [1 2]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (x nil) (--cl-vec-- [3 4]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (y nil)) (while (and (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--) (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--)) (cl-psetq x (aref --cl-vec-- --cl-idx--) y (aref --cl-vec-- --cl-idx--))) nil)))
  (cl-block nil (let ((--cl-vec-- [1 2]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (x nil) (--cl-vec-- [3 4]) (--cl-len-- (length --cl-vec--)) (--cl-idx-- -1) (y nil)) (while (and (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--) (< (setq --cl-idx-- (1+ --cl-idx--)) --cl-len--)) (cl-psetq x (aref --cl-vec-- --cl-idx--) y (aref --cl-vec-- --cl-idx--))) nil))
  (cl-loop for x across [1 2] and y across [3 4])
  eval((cl-loop for x across [1 2] and y across [3 4]) t)
  command-line-1(("-f" "toggle-debug-on-error" "-l" "cl-lib" "-eval" "(cl-loop for x across [1 2] and y across [3 4])"))
  command-line()
  normal-top-level()



In GNU Emacs 27.0.91 (build 3, x86_64-pc-linux-gnu, GTK+ Version 3.24.13)
 of 2020-04-20
Repository revision: a1040861f118881004f59866111f64cd0ae03b7a
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux rodete

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

Configured using:
 'configure --enable-checking=all --enable-gtk-deprecation-warnings
 --enable-gcc-warnings=warn-only --enable-check-lisp-object-type
 --with-mailutils --without-pop 'CFLAGS=-O0 -g3' LDFLAGS=-g3'

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK3
X11 XDBE XIM MODULES THREADS PDUMPER GMP

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
  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 rmc dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec epa epg epg-config gnus-util
rmail rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils phst skeleton
derived edmacro kmacro pcase ffap thingatpt url url-proxy url-privacy
url-expand url-methods url-history url-cookie url-domsuf url-util
url-parse auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
password-cache json map url-vars mailcap subr-x rx gnutls puny seq
byte-opt gv bytecomp byte-compile cconv dbus xml cl-loaddefs cl-lib
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer 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 composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
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 threads dbusbind
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 63095 5761)
 (symbols 48 8435 1)
 (strings 32 22388 1823)
 (string-bytes 1 711569)
 (vectors 16 12506)
 (vector-slots 8 174130 5982)
 (floats 8 25 34)
 (intervals 56 201 0)
 (buffers 1000 12))

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