bug#69920: 29.2; gnus: article-mode: Toggling MIME inline attachment previews adds superfluous newlines

[Alcor via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

1. Receive an E-Mail message with at least two image attachments (I
tried with two image/png files, sent via SMTP and read via IMAP).

2. Go into the gnus summary buffer and view the received message/article.

3. In the "Attachments: ..." line, click on the attachment to toggle the
inline preview.

4. Click on the attachment button again to hide the inline preview.

5. Repeat steps 3-4 a number of times (e.g. 10-20 times).

6. Observe as newlines keep getting inserted and accumulate under the
preview.

Additionally, the following can be observed:
- Overlays are added to the attachment button, but are never cleaned up
(can be checked with `describe-char' with point on the button).

- If there is more than 1 inline-previewable attachment, clicking on the
button for attachment #1, then #2, then #1, and #2 in that order breaks
the preview state (the inline previews can no longer be hidden). This
may be unrelated, however (please advise if a separate bug should be
opened for this).


In GNU Emacs 29.2 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
 cairo version 1.16.0) of 2024-03-13 built on lcy02-amd64-051
Repository revision: 900dc1b4bf3011e685a1ec7d7ce4dcd0262ec880
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12201001
System Description: Ubuntu 22.04.4 LTS

Configured using:
 'configure --prefix=/snap/emacs/current/usr --with-x-toolkit=gtk3
 --without-xaw3d --with-modules --with-cairo
 --with-native-compilation=aot --without-pgtk --with-xinput2
 --with-tree-sitter --with-json
 'CFLAGS=-isystem/build/emacs/parts/emacs/install/usr/include
 -isystem/build/emacs/parts/emacs/install/usr/include/x86_64-linux-gnu
 -isystem/build/emacs/stage/usr/include -O2'
 'CPPFLAGS=-isystem/build/emacs/parts/emacs/install/usr/include
 -isystem/build/emacs/parts/emacs/install/usr/include/x86_64-linux-gnu
 -isystem/build/emacs/stage/usr/include'
 'LDFLAGS=-L/build/emacs/parts/emacs/install/lib
 -L/build/emacs/parts/emacs/install/usr/lib
 -L/build/emacs/parts/emacs/install/lib/x86_64-linux-gnu
 -L/build/emacs/parts/emacs/install/usr/lib/x86_64-linux-gnu
 -L/build/emacs/stage/usr/lib''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER X11 XDBE XIM XINPUT2 XPM
GTK3 ZLIB

Important settings:
  value of $LANG: de_DE.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Article

Minor modes in effect:
  shell-dirtrack-mode: t
  erc-ring-mode: t
  erc-notifications-mode: t
  erc-netsplit-mode: t
  erc-menu-mode: t
  erc-list-mode: t
  erc-irccontrols-mode: t
  erc-keep-place-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  erc-scrolltobottom-mode: t
  erc-imenu-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-bufbar-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-autojoin-mode: t
  erc-autoaway-mode: t
  recentf-mode: t
  pixel-scroll-precision-mode: t
  minibuffer-depth-indicate-mode: t
  global-whitespace-mode: t
  global-goto-address-mode: t
  goto-address-mode: t
  global-auto-revert-mode: t
  fido-vertical-mode: t
  icomplete-vertical-mode: t
  icomplete-mode: t
  fido-mode: t
  erc-networks-mode: t
  desktop-save-mode: t
  windmove-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Features:
(shadow emacsbug misearch multi-isearch qp descr-text elec-pair
mh-buffers mh-loaddefs gnus-registry registry eieio-base rmailsum rmail
gnus-salt gnus-topic gnus-uu yenc gnus-vm shortdoc help-fns radix-tree
mailalias smtpmail smerge-mode diff diff-mode sort smiley gnus-cite
mm-archive mail-extr textsec uni-scripts idna-mapping ucs-normalize
uni-confusable textsec-check gnus-async gnus-bcklg gnus-ml nndraft nnmh
nnfolder utf-7 rfc2104 network-stream nsm gnus-agent gnus-srvr
gnus-score score-mode nnvirtual gnus-msg nntp gnus-cache
display-line-numbers org-element org-persist org-id org-refile avl-tree
generator oc-basic ol-eww eww url-queue mm-url ol-rmail ol-mhe ol-irc
ol-info ol-gnus nnselect gnus-art mm-uu mml2015 mm-view mml-smime smime
gnutls dig gnus-sum shr pixel-fill kinsoku url-file svg dom gnus-group
gnus-undo gnus-start gnus-dbus gnus-cloud nnimap nnmail mail-source utf7
nnoo gnus-spec gnus-int gnus-range message yank-media puny rfc822 mml
mml-sec epa epg rfc6068 epg-config mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader gnus-win ol-docview
doc-view jka-compr image-mode exif dired dired-loaddefs ol-bibtex bibtex
ol-bbdb ol-w3m ol-doi org-link-doi org ob ob-tangle ob-ref ob-lob
ob-table ob-exp org-macro org-src ob-comint org-pcomplete org-list
org-footnote org-faces org-entities noutline outline ob-emacs-lisp
ob-core ob-eval org-cycle org-table ol org-fold org-fold-core org-keys
oc org-loaddefs find-func cal-menu calendar cal-loaddefs org-version
org-compat org-macs tramp-cache time-stamp tramp-sh tramp tramp-loaddefs
trampver tramp-integration files-x tramp-compat shell parse-time iso8601
disp-table erc-ring erc-desktop-notifications notifications dbus xml
erc-nicks color erc-netsplit erc-menu erc-list erc-goodies erc-imenu
imenu erc-pcomplete pcomplete comint ansi-osc ansi-color erc-button
erc-fill erc-stamp erc-status-sidebar erc-track erc-match erc-join
erc-autoaway leuven-dark-theme recentf tree-widget pixel-scroll cua-base
ring mb-depth whitespace goto-addr thingatpt autorevert filenotify
icomplete erc derived format-spec erc-backend erc-networks easy-mmode
erc-common inline erc-compat pcase compat erc-loaddefs desktop frameset
sendmail rfc2047 rfc2045 ietf-drums gnus nnheader gnus-util
text-property-search time-date mail-utils range mm-util mail-prsvr
cus-edit pp cus-load wid-edit windmove xdg site-start comp comp-cstr
warnings icons rx cl-extra help-mode erc-autoloads info compat-autoloads
markdown-mode-autoloads package browse-url url url-proxy url-privacy
url-expand url-methods url-history url-cookie generate-lisp-file
url-domsuf url-util mailcap url-handlers url-parse auth-source cl-seq
eieio eieio-core cl-macs password-cache json subr-x map byte-opt gv
bytecomp byte-compile url-vars cl-loaddefs cl-lib rmc iso-transl tooltip
cconv eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode 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 lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table 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 dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 735396 84127)
 (symbols 48 46838 24)
 (strings 32 190158 4181)
 (string-bytes 1 5259546)
 (vectors 16 82583)
 (vector-slots 8 2226749 106897)
 (floats 8 679 1292)
 (intervals 56 3126 636)
 (buffers 984 33))