bug#59090: 29.0.50; unhelpful error message when unable to create PDF thumbnail

[Mike Kupfer]

I have a directory that has a few PDFs--they are magazine downloads
(e.g., IEEE Computer) and apparently have some password protections on
them.

When I try to view the directory using image-dired, I get an image-dired
buffer with some tofu in lieu of the cover thumbnails, plus an error
message in the echo area.  Perhaps that's to be expected, though I'll
note that I do get thumbnails when I browse the directory with a GUI
file browser (e.g., Thunar).

The point of this bug report is that the error message isn't all that
helpful.  I get

  Thumb could not be created for ~/ToRead/a/2022-01/mco202201.issue.pdf:
  exited abnormally with code 1

Looking in *Messages*, I see a bunch of "Cannot find image file"
messages, referring to .jpg files that image-dired apparently expects to
find in ~/.emacs.d/image-dired, but nothing else that appears to be
related to the failure to create the thumbnail.

If I turn on image-dired debugging, I see this line in *Messages*:

  Running convert -size 128x128 
/home/kupfer/ToRead/a/2022-01/mco202201.issue.pdf[0] -resize 128x128> -strip 
jpeg:/home/kupfer/.emacs.d/image-dired/22c69e148696b90d8934e227f0bdedcba4d5314c.jpg

If I run that command by hand, I do get some additional diagnostic
output.  I think image-dired should capture that and report it to the
user.

alto$ convert -size 128x128 /home/kupfer/ToRead/a/2022-01/mco202201.issue.pdf 
-resize "128x128>" -strip 
jpeg:/home/kupfer/.emacs.d/image-dired/22c69e148696b90d8934e227f0bdedcba4d5314c.jpg
convert-im6.q16: attempt to perform an operation not allowed by the security 
policy `PDF' @ error/constitute.c/IsCoderAuthorized/421.
convert-im6.q16: no images defined 
`jpeg:/home/kupfer/.emacs.d/image-dired/22c69e148696b90d8934e227f0bdedcba4d5314c.jpg'
 @ error/convert.c/ConvertImageCommand/3229.

I've reproduced this with "emacs -Q".

The revision hash below includes some changes to MH-E and to the
function move-file-to-trash.  It is based on 8721e87a6ec.

regards,
mike

In GNU Emacs 29.0.50 (build 3, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2022-11-06 built on alto
Repository revision: f749a1dd7875a83e6415d8c512c5659f0f23c834
Repository branch: master-mdk
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure --prefix=/usr/new'

Configured features:
CAIRO FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LIBSELINUX
LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM LUCID ZLIB

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

Major mode: Org

Minor modes in effect:
  shell-dirtrack-mode: t
  delete-selection-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  column-number-mode: t
  auto-fill-function: org-auto-fill-function
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow mh-mime mh-identity mh-letter mh-show goto-addr gnus-cite
emacsbug tabify man display-line-numbers misearch multi-isearch shortdoc
cl-print help-fns radix-tree mule-util apropos image-file
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mml2015 mm-view mml-smime smime gnutls dig gnus-sum shr pixel-fill
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font-lock syntax font-core term/tty-colors frame minibuffer nadvice seq
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cp51932 hebrew greek romanian slovak czech european ethiopic indian
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epa-hook jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button
loaddefs theme-loaddefs faces cus-face macroexp files window
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget keymap hashtable-print-readable backquote threads inotify
dynamic-setting system-font-setting font-render-setting cairo x-toolkit
x multi-tty make-network-process emacs)

Memory information:
((conses 16 415201 40289)
 (symbols 48 26301 0)
 (strings 32 100897 2705)
 (string-bytes 1 3090212)
 (vectors 16 49372)
 (vector-slots 8 551461 39415)
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