bug#54797: 27.1; "Old-style backquotes detected!" when there are no backquotes.

[Bruce Mardle via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Short version:
Try to evaluate
'(, foo)
and you'll get (error "Old-style backquotes detected!"), which is
confusing considering that the expression doesn't contain a backquote!


Long version:
My code was evaluating happily yesterday (on what much have been an old
version of Emacs) but came up with that error on 27.1 today.  It turned
out I had "(, " in a few places. They should have been "(* ", (OCR
failure) so I suppose I should thank the error message for helping me find
those... but it's a confusing message when source doesn't contain any
backquotes!
(I spent a while Googling to find out what was happening but only found
cases of people getting the error message whose code *did* contain a
backquote.)






In GNU Emacs 27.1 (build 1, x86_64-pc-cygwin)
 of 2020-10-29 built on moufang2
Repository revision: 14432a33511ec750815c6f3b188f2c0d21b4cb22
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
Quit
Please type y or n, or C-v/M-v to scroll: y
View mode: type C-h for help, h for commands, q to quit.
Mark saved where search started
Mark set
Mark saved where search started
split-window: Attempt to split minibuffer window
command-execute: Command attempted to use minibuffer while in minibuffer
elisp--preceding-sexp: Old-style backquotes detected!
Making completion list...
Quit
Configured using:
 'configure
 --srcdir=/home/kbrown/src/cygpackages/emacs/emacs-27.1-2.x86_64/src/emacs-27.1
 --prefix=/usr --exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc
 --docdir=/usr/share/doc/emacs --htmldir=/usr/share/doc/emacs/html -C
 --with-w32 'CFLAGS=-ggdb -O2 -pipe -Wall -Werror=format-security
 -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong
 --param=ssp-buffer-size=4
 -fdebug-prefix-map=/home/kbrown/src/cygpackages/emacs/emacs-27.1-2.x86_64/build=/usr/src/debug/emacs-27.1-2
 -fdebug-prefix-map=/home/kbrown/src/cygpackages/emacs/emacs-27.1-2.x86_64/src/emacs-27.1=/usr/src/debug/emacs-27.1-2'
 CPPFLAGS= LDFLAGS='


Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GLIB NOTIFY GFILENOTIFY ACL GNUTLS
LIBXML2 HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS XIM MODULES THREADS JSON
PDUMPER LCMS2 GMP


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


Major mode: Lisp Interaction


Minor modes in effect:
  shell-dirtrack-mode: t
  display-time-mode: t
  show-paren-mode: t
  tooltip-mode: t
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  mouse-wheel-mode: t
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  global-font-lock-mode: t
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  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t


Load-path shadows:
/usr/share/emacs/27.1/lisp/woman hides /cygdrive/c/users/bruce/elisp/woman


Features:
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rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils goto-addr noutline outline view
browse-url smerge-mode diff diff-mode easy-mmode shrinkrapt thingatpt
vc-filewise vc-rcs vc vc-dispatcher bookmark text-property-search pp
mule-util jka-compr info cl-print debug backtrace find-func derived
time-date subr-x cl-extra help-fns radix-tree help-mode misearch
multi-isearch shell pcomplete compile comint ansi-color ring cc-mode
cc-fonts easymenu cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine
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cconv avoid time paren cus-start cus-load tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
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timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic cham georgian
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japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
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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
gfilenotify w32 lcms2 multi-tty make-network-process emacs)


Memory information:
((conses 16 145234 17681)
 (symbols 48 12800 1)
 (strings 32 42138 2254)
 (string-bytes 1 1296256)
 (vectors 16 23598)
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