bug#31497: 27.0.50; vc-hg doesn't separate standard error from standard output

[Philipp Stephani]

Create a Mercurial repository owned by root and add a hgrc file, e.g.:

$ mkdir -p /tmp/hg
$ cd /tmp/hg
$ sudo -s
# hg init
# echo a > a.txt
# hg addremove
# hg commit -m 'commit message'
# touch .hg/hgrc

Then visit a.txt in Emacs as non-root:

$ emacs -Q a.txt

Instead of the revision number, the status line will show
"Hg-not trusting file /tmp/hg/.hg/hgrc ..."

This is because the status line runs something like

$ hg log -l 1 -r . -T '{rev}'

but that outputs

  not trusting file /tmp/hg/.hg/hgrc from untrusted user root, group root
  not trusting file /tmp/hg/.hg/hgrc from untrusted user root, group root

on stderr, and Emacs merges stderr and stdout.  Rather it should ignore
stderr in this case.


In GNU Emacs 27.0.50 (build 27, x86_64-pc-linux-gnu, GTK+ Version 3.22.24)
 of 2018-05-18 built on localhost
Repository revision: f4d9fd3dd45f767eca33fbf1beee40da790fa74e
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Debian GNU/Linux buster/sid

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

Configured using:
 'configure --without-threads --enable-gcc-warnings=warn-only
 --enable-gtk-deprecation-warnings --without-pop --with-mailutils
 --enable-checking --enable-check-lisp-object-type --with-modules
 'CFLAGS=-O0 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY GNUTLS FREETYPE XFT
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 MODULES JSON

Important settings:
  value of $LANG: en_US.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
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
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 move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 95054 11969)
 (symbols 48 20166 1)
 (miscs 40 40 122)
 (strings 32 28302 2388)
 (string-bytes 1 758914)
 (vectors 16 14177)
 (vector-slots 8 499094 14196)
 (floats 8 48 69)
 (intervals 56 222 0)
 (buffers 992 12))

-- 
Google Germany GmbH
Erika-Mann-Straße 33
80636 München

Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado

If you received this communication by mistake, please don’t forward it to
anyone else (it may contain confidential or privileged information), please
erase all copies of it, including all attachments, and please let the sender
know it went to the wrong person.  Thanks.