bug#42919: 27.1; Strange byte compile error with `cond' involving cons

[Ikumi Keita <ikumi@ikumi.que.jp>]

I encountered a strange byte compile error with simple elisp code.

[How to reproduce]
1. Save the following file as /tmp/foo.el:
--- /tmp/foo.el ----------------------------
(defun xyz (arg)
  (cond
;   ((member '("image") arg) ; OK
;   ((member '(rel "image") arg) ; OK
;   ((remove '(rel . "image") arg) ; OK
;   ((memq '(rel . "image") arg) ; NG
   ((member '(rel . "image") arg) ; NG
    1)))
--------------------------------------------
2. emacs-27.1 -Q
3. M-x byte-compile-file /tmp/foo.el RET
4. Then byte compile fails with the following error:
Compiling file /tmp/foo.el at Wed Aug 19 03:38:06 2020
Entering directory ‘/tmp/’
foo.el:1:13:Error: Wrong type argument: listp, "image"
in *Compile-Log* buffer. I don't see foo.elc in /tmp after that.
Expected result is that byte compile finishes without error and foo.elc
is generated.

[Additional info]
a. As written in the above code, only cons (rel . "image") causes this
   error. Both lists (rel "image") and ("image") are OK.
b. As written in the above code, both `member' and `memq' fail while
   `remove' succeeds.
c. Emacs 26.3 works as expected.

Regards,
Ikumi Keita


In GNU Emacs 27.1 (build 1, x86_64-unknown-freebsd12.1, GTK+ Version 3.24.20)
 of 2020-08-19 built on freebsd.vmware
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: 12.1-RELEASE-p8

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Compiling /tmp/foo.el... (xyz)
You can run the command ‘byte-compile-file’ with M-x by-c RET
Compiling /tmp/foo.el... (xyz)
Mark set
next-line: End of buffer [2 times]
Mark set
Making completion list...

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS GLIB NOTIFY KQUEUE ACL
GNUTLS LIBXML2 FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
XDBE XIM MODULES THREADS JSON PDUMPER LCMS2 GMP

Important settings:
  value of $EMACSLOADPATH: /home/keita/elisp:
  value of $LANG: C
  locale-coding-system: nil

Major mode: Emacs-Lisp

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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/keita/elisp/reftex-parse hides /home/keita/scr/emacs-27.1/lisp/textmodes/reftex-parse

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search seq gv
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date subr-x cl-loaddefs cl-lib warnings byte-opt compile
comint ansi-color ring bytecomp byte-compile cconv 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 kqueue lcms2 dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 51013 10241)
 (symbols 48 6580 1)
 (strings 32 16915 1623)
 (string-bytes 1 565681)
 (vectors 16 10152)
 (vector-slots 8 141502 12592)
 (floats 8 25 119)
 (intervals 56 304 125)
 (buffers 1000 16))