bug#54084: 28.0.91; Regression: can't create empty image buffer

[Corwin Brust]

Under Emacs -Q

1. switch to a new buffer, e.g. C-x b *foo* RET
2. M-x image-mode RET

3. Insert the following text and press C-c C-c

<svg width="400" height="400">
  <rect x="100" y="100" width="200" height="100"
        fill="none" stroke="blue" stroke-width="2"/>
</svg>

In Emacs 27.2 the outline of a rectangle is displayed as an image.

In Emacs 28.0.91 an error is emitted at step 2:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  image-mode()
  funcall-interactively(image-mode)
  command-execute(image-mode record)
  execute-extended-command(nil "image-mode" "image-mod")
  funcall-interactively(execute-extended-command nil "image-mode" "image-mod")
  command-execute(execute-extended-command)

Furthermore, inserting the text and pressing C-c C-c will do nothing
because the error interrupts the mode activation. (A subsequent M-x
image-mode RET after pasting in the snippet works.)

Ergo, it is not possible to create an empty buffer in image-mode, as
was possible in Emacs 27.2 and before.


In GNU Emacs 28.0.91 (build 6, x86_64-w64-mingw32)
 of 2022-02-05 built on AVALON
Repository revision: 821c240075e3b850a61207d18d520126292421ce
Repository branch: emacs-28-nt-dist-build
Windowing system distributor 'Microsoft Corp.', version 10.0.19043
System Description: Microsoft Windows 10 Home (v10.0.2009.19043.1566)

Configured using:
 'configure --with-json --without-dbus --with-native-compilation
 --without-compress-install CFLAGS=-O2'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
XPM ZLIB

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Image[svg]

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-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
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec epa
derived epg rfc6068 epg-config gnus-util rmail rmail-loaddefs
auth-source eieio eieio-core cl-macs eieio-loaddefs password-cache json
map text-property-search seq byte-opt gv bytecomp byte-compile cconv
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-seq help-fns radix-tree time-date subr-x cl-print debug
backtrace help-mode find-func image-mode dired dired-loaddefs exif
cl-loaddefs cl-lib cus-start cus-load iso-transl tooltip eldoc paren
electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
dos-w32 ls-lisp 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 lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax 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 emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads w32notify
w32 lcms2 multi-tty make-network-process native-compile emacs)

Memory information:
((conses 16 87195 11377)
 (symbols 48 8253 0)
 (strings 32 24379 1444)
 (string-bytes 1 764439)
 (vectors 16 14960)
 (vector-slots 8 313276 16186)
 (floats 8 38 231)
 (intervals 56 402 2)
 (buffers 992 13))