bug#22481: 25.1.50; vc-hg: emacs "deadlocks" after using hg with huge amounts of ignored files in the repo

[Jan Synacek <jsynacek@redhat.com>]

Steps to reproduce:

1) hg clone https://bitbucket.org/vim-mirror/vim (or any other repo will
do, but I couldn't resist reproducing the issue on this one...)
2) Generate a million files, that will be considered "ignored" in the repo
   $ cd vim
   $ for i in $(seq 1 1000000); do echo ignored > ignored-$i.rej; done
3) Fire up emacs, C-x C-f <the vim repo directory>
   At this point, it will take a while, but that may be a separate issue.
4) Edit any tracked file and save it.
5) C-x v d ENTER
6) Go to a file that's been modified and hit 'v', enter a log message,
   then C-c C-c to commit the change.
7) Hit 'g' to refresh the buffer.
8) Observe the freeze.

Emacs freezes because it's running 'hg status -mardui -C <files>'. The
'-i' is the problem here. Since it takes hg itself a very long time, I'm
not sure if it can be directly fixed in Emacs. But at least a
configuration option that would allow one to disable the "-i" option
would be nice.

Original bugreport: https://bugzilla.redhat.com/show_bug.cgi?id=1232422


In GNU Emacs 25.1.50.2 (x86_64-redhat-linux-gnu, GTK+ Version 3.18.6)
 of 2016-01-28 built on copr-builder-504260318.novalocal
Windowing system distributor 'Fedora Project', version 11.0.11800000
System Description:	Generic release 23 (Generic)

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 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
 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
 -m64 -mtune=generic' LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

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

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: ERC

Minor modes in effect:
  diff-auto-refine-mode: t
  erc-notifications-mode: t
  shell-dirtrack-mode: t
  erc-list-mode: t
  erc-menu-mode: t
  erc-autojoin-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-track-minor-mode: t
  erc-match-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  recentf-mode: t
  override-global-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Loading /home/jsynacek/.emacs.d/recentf...done
Cleaning up the recentf list...done (0 removed)
For information about GNU Emacs and the GNU system, type C-h C-a.
ad-handle-definition: ‘tramp-read-passwd’ got redefined
(redacted for private info)
Mark set
Could not load org-notmuch

Load-path shadows:
/home/jsynacek/.emacs.d/elpa/helm-20160119.417/helm-multi-match hides /home/jsynacek/.emacs.d/elpa/helm-core-20160119.936/helm-multi-match
/home/jsynacek/.emacs.d/elpa/magit-20160119.1409/magit-popup hides /home/jsynacek/.emacs.d/elpa/magit-popup-20160119.1409/magit-popup

Features:
(shadow sort mail-extr emacsbug sendmail notmuch hl-line notmuch-message
notmuch-maildir-fcc notmuch-hello notmuch-tree notmuch-parser
notmuch-show notmuch-print notmuch-crypto notmuch-mua notmuch-address
notmuch-wash diff-mode coolj notmuch-query goto-addr icalendar diary-lib
diary-loaddefs cal-menu calendar cal-loaddefs notmuch-tag crm
notmuch-lib notmuch-version cl message idna rfc822 mml mailabbrev
mail-utils gmm-utils mailheader mm-view mml-smime mml-sec epg smime dig
mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045
ietf-drums erc-desktop-notifications notifications dbus winner
helm-command helm-elisp helm-eval edebug helm-mode helm-files rx
image-dired tramp tramp-compat tramp-loaddefs trampver ucs-normalize
shell dired-aux ffap helm-buffers helm-elscreen helm-tags helm-bookmark
helm-adaptive helm-info bookmark helm-locate helm-external helm-net
browse-url xml url url-proxy url-privacy url-expand url-methods
url-history url-cookie url-domsuf url-util mailcap helm-types private
erc-list erc-menu erc-join erc-ring erc-networks erc-pcomplete pcomplete
erc-track erc-match erc-button erc-fill erc-stamp erc-netsplit
erc-goodies erc erc-backend erc-compat format-spec thingatpt pp
helm-swoop helm-grep helm-regexp helm-plugin helm-utils compile comint
ansi-color ring helm-help helm helm-source eieio-compat helm-multi-match
helm-lib geiser recentf tree-widget wid-edit edmacro kmacro dired-x
dired dired-loaddefs cc-mode cc-fonts cc-guess cc-menus cc-cmds
cc-styles cc-align cc-engine cc-vars cc-defs use-package diminish
bind-key easy-mmode advice finder-inf goto-chg-autoloads
undo-tree-autoloads info package epg-config url-handlers url-parse
auth-source cl-seq eieio byte-opt bytecomp byte-compile cl-extra cconv
eieio-core cl-macs gv eieio-loaddefs gnus-util mm-util help-fns
help-mode easymenu cl-loaddefs pcase cl-lib mail-prsvr password-cache
url-vars paren time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
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 charscript
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 404816 27547)
 (symbols 48 39279 0)
 (miscs 40 147 579)
 (strings 32 78662 12230)
 (string-bytes 1 2409843)
 (vectors 16 58360)
 (vector-slots 8 965773 25031)
 (floats 8 378 279)
 (intervals 56 1052 111)
 (buffers 976 19)
 (heap 1024 47080 3625))

-- 
Jan Synacek
Software Engineer, Red Hat