bug#19731: 24.4; /dev/null is deleted by tramp-sh.el

[crocket <crockabiscuit@gmail.com>]

According to https://bbs.archlinux.org/viewtopic.php?pid=1397412#p1397412
, if HISTFILE=/dev/null is set as an environment variable, /dev/null
can be deleted and replaced by a regular file with permission 600.

If I fiddled with magit over tramp sudo method for a while and exited
emacs, I see /dev/null replaced with a regular file with permission
600.

After some inspections, I found HISTFILE=/dev/null in tramp-sh.el.

Could tramp-sh.el be the cause of /dev/null problem?

In GNU Emacs 24.4.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.7)
 of 2015-01-18 on bisson
Windowing system distributor `The X.Org Foundation', version 11.0.11603000
Configured using:
 `configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 --param=ssp-buffer-size=4' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-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
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> C-x C-f <backspace> C-g M-x r e p o r t
<tab> <return>

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

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message idna format-spec
rfc822 mml mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns mail-prsvr mail-utils info easymenu package epg-config
time-date tooltip electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment lisp-mode prog-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer 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 make-network-process dbusbind gfilenotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty emacs)

Memory information:
((conses 16 113852 6530)
 (symbols 48 20679 0)
 (miscs 40 87 124)
 (strings 32 22379 4312)
 (string-bytes 1 542144)
 (vectors 16 12069)
 (vector-slots 8 418986 5747)
 (floats 8 66 65)
 (intervals 56 224 19)
 (buffers 960 12)
 (heap 1024 50731 994))