bug#54606: 27.1; next/previous image command in image-mode triggers tramp connections for all remote dired buffers

[Phil Sainty]

In 27.1 this code is in `image-next-file'.  In master it's now
`image-mode--directory-buffers', but the relevant code looks
the same:

      ;; Find a dired buffer.
      (dolist (buffer (buffer-list))
        (with-current-buffer buffer
          (when (and (derived-mode-p 'dired-mode)
                     (equal (file-truename dir)
                            (file-truename default-directory)))

That call to (file-truename default-directory) for each dired
buffer can cause tramp to spin up for closed connections for
entirely irrelevant dired buffers.

Can we put some guards in there to decide whether or not dir
and default-directory are actually on the same host before
comparing them via file-truename?


-Phil (who is simply testing (not (file-remote-p default-directory))
       as an interim fix)





In GNU Emacs 27.1 (build 2, x86_64-pc-linux-gnu, X toolkit, Xaw scroll 
bars)
 of 2020-08-20 built on mts-devtools
Windowing system distributor 'The X.Org Foundation', version 
11.0.12008000
System Description: Ubuntu 18.04.3 LTS

Recent messages:
Copying /tmp/tramp.XFX7Dz.elcNyCbqo to 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elcNyCbqo...done
Renaming 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elcNyCbqo 
to 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elc...done
Wrote 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elc
Wrote 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.{el,elc}
Making completion list...
Loading 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elc...
Copying 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elc 
to /tmp/tramp.vr7HOL.elc...done
Loading 
/sudo:root@mts-devtools:/usr/local/share/emacs/27.1/lisp/image-mode.elc...done
Hunk already applied
Mark set [2 times]

Configured using:
 'configure --with-x-toolkit=lucid --without-sound'

Configured features:
XPM JPEG TIFF GIF PNG RSVG DBUS GSETTINGS GLIB NOTIFY INOTIFY GNUTLS
LIBXML2 FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS LUCID X11 XDBE
XIM MODULES THREADS PDUMPER LCMS2 GMP

Important settings:
  value of $LC_MONETARY: en_NZ.UTF-8
  value of $LC_NUMERIC: en_NZ.UTF-8
  value of $LC_TIME: en_NZ.UTF-8
  value of $LANG: en_NZ.UTF-8
  locale-coding-system: utf-8

Major mode: Emacs-Lisp

Minor modes in effect:
  hi-lock-mode: t
  global-magit-file-mode: t
  goto-address-prog-mode: t
  elisp-slime-nav-mode: t
  hl-sexp-mode: t
  lexbind-mode: t
  idle-highlight-mode: t
  minibuffer-line-mode: t
  global-edit-server-edit-mode: t
  savehist-mode: t
  magit-wip-before-change-mode: t
  magit-wip-after-apply-mode: t
  magit-wip-after-save-mode: t
  global-git-commit-mode: t
  magit-auto-revert-mode: t
  shell-dirtrack-mode: t
  async-bytecomp-package-mode: t
  my-contextual-help-mode: t
  global-so-long-mode: t
  show-paren-mode: t
  my-visible-bell-mode: t
  cua-mode: t
  global-display-fill-column-indicator-mode: t
  display-fill-column-indicator-mode: t
  minibuffer-depth-indicate-mode: t
  which-key-mode: t
  winner-mode: t
  global-subword-mode: t
  subword-mode: t
  global-hl-line-mode: t
  hl-line-mode: t
  display-time-mode: t
  keep-buffers-mode: t
  fic-mode: t
  my-keys-local-minor-mode: t
  auto-compile-on-load-mode: t
  auto-compile-on-save-mode: t
  auto-compile-mode: t
  url-handler-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/vagrant/.emacs.d/el-get/scratch/el-get hides 
/home/vagrant/.emacs.d/el-get/el-get/el-get
/home/vagrant/.emacs.d/my-lisp/so-long hides 
/usr/local/share/emacs/27.1/lisp/so-long
/home/vagrant/.emacs.d/lisp/python hides 
/usr/local/share/emacs/27.1/lisp/progmodes/python

Features:
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magit-margin magit-mode magit-git magit-section magit-utils crm
magit-popup pcase async-bytecomp async format-spec dash my-text
my-programming my-python so-long my-whitespace ws-trim my-rectangles
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cus-load wid-edit dired-details dired-x highlight-parentheses paren
url-privacy delight delsel cua-base ffap display-fill-column-indicator
mb-depth which-key framemove windmove winner ring cap-words superword
subword hl-line time my-externals .loaddefs windcycle transpose-frame
simple-wiki derived sdcv-mode noutline outline sauron rainbow-mode
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rectangular-region-mode mc-mark-pop mc-mark-more thingatpt
mc-cycle-cursors mc-edit-lines multiple-cursors-core rect mo-git-blame
keep-buffers iedit fic-mode dtrt-indent browse-at-remote vc-git
diff-mode easy-mmode s el-get cl-extra help-mode autoload radix-tree
lisp-mnt cl dired dired-loaddefs my-elpa my-local my-keybindings edmacro
kmacro jka-compr auto-compile packed etags-select-autoloads info
project-local-variables-autoloads advice wtf-autoloads package easymenu
browse-url url-handlers url-parse auth-source cl-seq eieio eieio-core
cl-macs eieio-loaddefs password-cache json subr-x map url-vars seq
byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib 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 tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer 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 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 x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 6395697 774980)
 (symbols 48 99712 1)
 (strings 32 264602 49924)
 (string-bytes 1 13742442)
 (vectors 16 478511)
 (vector-slots 8 5272375 517538)
 (floats 8 2334 4710)
 (intervals 56 1397671 5095)
 (buffers 1000 1327))