bug#53538: 27.2; default-major-mode no longer honored

["George L. Roman" <glroman@gmail.com>]

    % emacs -Q
    C-x b *scratch*
    (setq default-major-mode "text-mode")
    C-x b whatever
    ; Observe "fundamental" mode
    C-f /tmp/foo
    ; Observe "fundamental" mode

    This used to work in 25.1; fails in 26.1, 27.1, and 27.2.


In GNU Emacs 26.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.22.30)
 of 2021-08-09 built on x86-01.mbox.centos.org
Windowing system distributor 'Colin Harrison', version 11.0.70700033
Recent messages:
GNU Emacs 26.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.22.30) of
2021-08-09
Quit
Mark saved where search started
Type "q" in help window to restore its previous buffer.
(New file)
Saving file /tmp/foo...
Wrote /tmp/foo
QKilled /tmp/foo
GNU Emacs 26.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.22.30) of
2021-08-09
Mark activated

Configured using:
 'configure --build=x86_64-redhat-linux-gnu --host=x86_64-redhat-linux-gnu
 --program-prefix= --disable-dependency-tracking --prefix=/usr
 --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/var/lib
 --mandir=/usr/share/man --infodir=/usr/share/info --with-dbus --with-gif
 --with-jpeg --with-png --with-rsvg --with-tiff --with-xft --with-xpm
 --with-x-toolkit=gtk3 --with-gpm=no --with-xwidgets --with-modules
 build_alias=x86_64-redhat-linux-gnu host_alias=x86_64-redhat-linux-gnu
 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g -pipe -Wall -Werror=format-security
 -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions
 -fstack-protector-strong -grecord-gcc-switches
 -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
 'LDFLAGS= -Wl,-z,relro,-z,now -fpie'
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS
LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
MODULES
THREADS XWIDGETS

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

Major mode: Emacs-Lisp

Minor modes in effect:
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  mouse-wheel-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 puny format-spec rfc822 mml
mml-sec epa derived epg gnus-util rmail rmail-loaddefs 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-print help-fns
radix-tree
help-mode misearch multi-isearch dired dired-loaddefs elec-pair time
url-util
finder-inf package easymenu epg-config url-handlers url-parse auth-source
cl-seq eieio eieio-core cl-macs eieio-loaddefs password-cache url-vars seq
byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib time-date
mule-util
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 menu-bar rfn-eshadow isearch timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core term/tty-colors frame
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 minibuffer
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 dbusbind inotify dynamic-setting
system-font-setting font-render-setting xwidget-internal move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 113794 8069)
 (symbols 48 22029 1)
 (miscs 40 82 290)
 (strings 32 33745 1719)
 (string-bytes 1 895894)
 (vectors 16 16587)
 (vector-slots 8 522913 8236)
 (floats 8 62 341)
 (intervals 56 718 42)
 (buffers 992 17))