bug#45623: 28.0.50; widget-backward sometimes skips one widget

[Mauro Aranda]

Starting from emacs -Q:

1. Eval the following code:
(require 'wid-edit)

(defun test-widget-backward ()
  (interactive)
  (switch-to-buffer "*Widget Test*")
  (kill-all-local-variables)
  (let ((inhibit-read-only t))
    (erase-buffer))
  (remove-overlays)
  (widget-insert "Testing widget movement commands.\n\n")
  (dolist (el '("First" "Second" "Third"))
    (widget-create 'push-button el))
  (widget-insert "\n")
  (goto-char (point-min))
  (use-local-map widget-keymap)
  (widget-setup))

2. C-u 3 C-i to move to the start of the button labeled Third:

3. C-M-i to run the widget-backward command.

Point moves to the start of the button labeled First, not to the
start of the button labeled Second.  I expected point to move to the
start of the button labeled Second.


If instead I use buttons from button.el, moving point with
backward-button (the analogous to widget-backward) behaves as I
expected.


The very first line of widget-move is:
(or (bobp) (> arg 0) (backward-char))

That backward-char moves point from the third button to the second
button before starting to look for the previous widget, so that's the
reason point ends up at the start of the first button.

I don't understand why that call to backward-char is there.  Does anyone
know of a situation where it is useful?


In GNU Emacs 28.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version 3.22.30, cairo 
version 1.15.10)
 of 2021-01-03 built on tbb-desktop
Repository revision: 825b4ec338e82869dc656c7041ab2483b6c22479
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 18.04.5 LTS

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

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

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-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
rfc822 mml easymenu mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map 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 wid-edit
cl-loaddefs cl-lib iso-transl 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
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romanian slovak czech european ethiopic indian cyrillic chinese
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cus-face macroexp files window 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 cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 54440 9138)
 (symbols 48 7084 1)
 (strings 32 19227 1450)
 (string-bytes 1 632153)
 (vectors 16 12046)
 (vector-slots 8 168478 8434)
 (floats 8 23 47)
 (intervals 56 240 0)
 (buffers 984 12))