bug#38595: 26.3.50; epa-encrypt-file does not work with Tramp

[Benjamin Riefenstahl]

Test scenario where epa-encrypt-file works:

* Create a test file as /tmp/test with any content.
* Call epa-encrypt-file.
* Specify /tmp/test. 
* Push the OK button.
* Message appears: "Encrypting test...wrote test.gpg"

Test scenario that does not work:

* Create a test file as /tmp/test with any content.
* Call epa-encrypt-file.
* Specify /sudo::/tmp/test. 
* Push the OK button.
* A buffer appears with error message:

      Error while encrypting with "/usr/bin/gpg2":

      gpg: can't open '/sudo:root@arrian:/tmp/test': No such file or directory
      gpg: symmetric encryption of '/sudo:root@arrian:/tmp/test' failed: No 
such file or directory

The same happens when I have the file open as /sudo::/tmp/test, so that
Tramp knows the password already.

This is completely reproducable with "emacs -Q".  I first saw this with
an SSH remote (/scp:), where this is of course more important than with
"/sudo:".

-----

In GNU Emacs 26.3.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-10-11 built on arrian
Repository revision: 55dcd32ad2209dc34bfb6b713bf73be9bf4c4cb2
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:     Debian GNU/Linux 10 (buster)

Recent messages:
Tramp: Waiting for prompts from remote shell...done
Tramp: Found remote shell prompt on ‘arrian’
Tramp: Opening connection for root@arrian using sudo...done
Tramp: Inserting ‘/sudo:root@arrian:/tmp/test’...done

Tramp: Checking ‘vc-registered’ for /sudo:root@arrian:/tmp/test...done
Tramp: Inserting ‘/sudo:root@arrian:/tmp/test’...done
Click here or \[abort-recursive-edit] to cancel
Click here or \[exit-recursive-edit] to finish
Encrypting test...
epa-encrypt-file: GPG error: "Encrypt failed", "Exit"
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 LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Info

Minor modes in effect:
  shell-dirtrack-mode: t
  desktop-save-mode: t
  display-time-mode: t
  diff-auto-refine-mode: t
  delete-selection-mode: t
  cua-mode: t
  tooltip-mode: t
  global-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
  blink-cursor-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/benny/.emacs.d/elpa/soap-client-3.1.5/soap-client hides 
/usr/local/share/emacs/26.3.50/lisp/net/soap-client
/home/benny/.emacs.d/elpa/soap-client-3.1.5/soap-inspect hides 
/usr/local/share/emacs/26.3.50/lisp/net/soap-inspect

Features:
(shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec
gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mail-utils edmacro kmacro conf-mode files-x tramp-cache
tramp-sh tramp tramp-compat tramp-loaddefs trampver ucs-normalize shell
pcomplete parse-time format-spec wid-edit epa epg imenu elec-pair
desktop frameset highline benny-calendar-cfg ange-ftp comint ansi-color
ring benny-unicode generic-x cl autoinsert cc-mode cc-fonts cc-guess
cc-menus cc-styles cc-align cc-cmds cc-engine cc-vars cc-defs ps-print
ps-print-loaddefs ps-def lpr advice dired dired-loaddefs derived
benny-x-clipboard disp-table mm-util mail-prsvr time server protbuf
cal-china lunar solar cal-dst cal-bahai cal-islam cal-hebrew holidays
hol-loaddefs vc-git diff-mode easy-mmode vc-fossil diary-lib
diary-loaddefs cal-menu calendar cal-loaddefs delsel cua-base cus-start
cus-load .loaddefs benny-tools autoload radix-tree lisp-mnt finder-inf
info package easymenu epg-config url-handlers url-parse auth-source
cl-seq eieio eieio-core cl-macs eieio-loaddefs password-cache url-vars
seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib time-date
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 313746 13798)
 (symbols 48 31476 2)
 (miscs 40 69 225)
 (strings 32 65435 2858)
 (string-bytes 1 2126620)
 (vectors 16 47039)
 (vector-slots 8 881717 13924)
 (floats 8 844 146)
 (intervals 56 522 78)
 (buffers 992 19))