bug#49692: 26.3; desktop-clear fails becasue of killed buffer

[Sergey Organov <sorganov@gmail.com>]

Starting from 'emacs -Q':

  C-h i
  m libc
  M-x desktop-clear

errors out with:

  Wrong type argument: arrayp, nil

Here is a patch that fixes it:

--8<---------------cut here---------------start------------->8---

Subject: [PATCH] Avoid failing in desktop-clear due to killed buffers

* lisp/desktop.el (desktop-clear): check that buffer is not already
killed before attempting to kill it. A buffer might become killed as
part of regular operation as a side-effect of killing another buffer,
and then attempt to kill it again causes error.
---
 lisp/desktop.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/desktop.el b/lisp/desktop.el
index b9467c87527a..24bb2817aaea 100644
--- a/lisp/desktop.el
+++ b/lisp/desktop.el
@@ -706,7 +706,8 @@ if different)."
                                  "\\)\\'")))
     (dolist (buffer (buffer-list))
       (let ((bufname (buffer-name buffer)))
-       (unless (or (eq (aref bufname 0) ?\s) ;; Don't kill internal buffers
+       (unless (or (null bufname)
+                   (eq (aref bufname 0) ?\s) ;; Don't kill internal buffers
                    (string-match-p preserve-regexp bufname))
          (kill-buffer buffer)))))
   (delete-other-windows)

--8<---------------cut here---------------end--------------->8---


In GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14)
 of 2020-03-26, modified by Debian built on lcy01-amd64-020
System Description:	Ubuntu 20.04.2 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Defining kbd macro...
No keyboard macro defined.
Quit
Setting up indent for shell type bash
Indentation variables are now local.
Indentation setup for shell type bash
Composing main Info directory...done
funcall-interactively: Wrong type argument: arrayp, nil
Making completion list...

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-mEZBk7/emacs-26.3+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: C.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:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
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 sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils desktop frameset cl-loaddefs cl-lib
jka-compr info easymenu sh-script smie executable kmacro term/xterm
xterm time-date elec-pair 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 threads dbusbind inotify 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 116511 7052)
 (symbols 48 21504 1)
 (miscs 40 40 115)
 (strings 32 36315 1226)
 (string-bytes 1 920524)
 (vectors 16 13524)
 (vector-slots 8 476806 9900)
 (floats 8 59 815)
 (intervals 56 278 3)
 (buffers 992 12))