bug#49571: 27.2; many posn event functions return wrong result

[dalanicolai]

- Start emacs (emacs -Q)
- load the following code


(require 'svg)

(define-minor-mode svg-draw-mode
  "Draw svg images using the mouse."
  nil "svg-draw-mode"
  '(([drag-mouse-1] . test)))

(defun svg-create-canvas (width height)
  "Create canvas for drawing svg using the mouse."
  (interactive "nEnter width: \nnEnter height")
  (defvar svg)
  (insert-image (let ((width 800)
                      (height 200))
                  (setq svg (svg-create width height :stroke "black"))
                  (svg-rectangle svg 0 0 width height :fill "white")
                  (svg-image svg)))
  (svg-draw-mode))

(defun test (event)
  (interactive "e")
  ;; (print (format "event-start %s\n" (event-start event)))
  ;; (print (format "event-end %s\n" (event-end event)))
  ;; (print (format "posn-window %s\n" (posn-window event)))
  ;; (print (format "posn-area %s\n" (posn-area event)))
  ;; (print (format "posn-point %s\n" (posn-point event)))
  ;; (print (format "posn-x-y %s\n" (posn-x-y event)))
  ;; (print (format "posn-string %s\n" (posn-string event)))
  (print (format "posn-image %s\n" (posn-image event))))


- Create a "svg canvas" using `M-x svg-create-canvas` (enter a width
and a height)

- Finally click and drag (mouse-1) within the image.

I have included a list of print statements that can be commented in/out
to check the different values. Most of them return wrong values
(e.g. posn-image returns nil while it should return an image
object. posn-point returns a window while it should return a point
etc.)

I have actually tried this in Emacs 27.2 and 28.0.50


In GNU Emacs 27.2 (build 1, x86_64-redhat-linux-gnu, GTK+ Version
3.24.29, cairo version 1.17.4)
 of 2021-06-13 built on buildvm-x86-32.iad2.fedoraproject.org
Windowing system distributor 'The X.Org Foundation', version
11.0.12011000
System Description: Fedora 34 (Workstation Edition)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
Loading /home/dalanicolai/Sync/org/svg/svg-draw-mode.el (source)...done

"posn-image nil
"

Making completion list...
user-error: End of history; no default available

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 --with-xwidgets --with-modules --with-harfbuzz
 --with-cairo --with-json build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu CC=gcc 'CFLAGS=-DMAIL_USE_LOCKF -O2
 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches
 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -Wp,-D_GLIBCXX_ASSERTIONS
 -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-
strong
 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
 LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

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

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

Major mode: Lisp Interaction

Minor modes in effect:
  svg-draw-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-
date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils thingatpt
easy-mmode svg dom xml 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 dynamic-setting system-font-setting
font-render-setting xwidget-internal cairo move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 46476 9688)
 (symbols 48 6283 1)
 (strings 32 16422 2178)
 (string-bytes 1 535143)
 (vectors 16 9620)
 (vector-slots 8 129204 10370)
 (floats 8 20 39)
 (intervals 56 275 0)
 (buffers 1000 12))