bug#31586: 27.0.50; `frame-title-format' doesn't save match data

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

emacs -Q -eval "(setq frame-title-format '(\"\" (:eval (string-match \".\" \"a\"))))"

Then go to the first character in the scratch buffer (M-<), and run

M-% a RET b RET

The first time you attempt to replace something, Emacs will signal an
error:

perform-replace: Args out of range: #<buffer *scratch*>, 0, 1

Backtrace:

Debugger entered--Lisp error: (args-out-of-range #<buffer *scratch*> 0 1)
  buffer-substring-no-properties(0 1)
  perform-replace("a" "b" t nil nil nil nil nil nil nil nil)
  query-replace("a" "b" nil nil nil nil nil)
  funcall-interactively(query-replace "a" "b" nil nil nil nil nil)
  call-interactively(query-replace nil nil)
  command-execute(query-replace)

Apparently the `string-match' in `frame-title-format' has overwritten
the match data.  This worked in Emacs 24.5.  It breaks the informal
contract for the match data, namely that any code is free to change it,
and code that relies on the match data staying intact needs to protect
it.


In GNU Emacs 27.0.50 (build 69, x86_64-apple-darwin17.4.0, NS appkit-1561.20 Version 10.13.3 (Build 17D102))
 of 2018-05-22 built on p
Repository revision: 02f303d75f876517b7802f787413cbb418203315
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.3

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

Configured using:
 'configure --with-modules --without-pop --with-mailutils
 --enable-gcc-warnings=yes --enable-checking
 --enable-check-lisp-object-type 'CFLAGS=-ggdb3 -O0''

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS
JSON

Important settings:
  value of $LANG: de_DE.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
  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:
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bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
easymenu 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 cl-loaddefs cl-lib sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils time-date elec-pair
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/ns-win ns-win ucs-normalize mule-util term/common-win
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow isearch timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core term/tty-colors frame cl-generic
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korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
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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 204577 6502)
 (symbols 48 20009 1)
 (miscs 40 56 152)
 (strings 32 28860 1923)
 (string-bytes 1 773241)
 (vectors 16 35283)
 (vector-slots 8 721708 13474)
 (floats 8 51 65)
 (intervals 56 210 0)
 (buffers 992 11))