bug#43612: 28.0.50; Unable to dehighlight region in Customize

[Mauro Aranda]

emacs -Q
M-x customize
Press mouse-1 somewhere in the buffer where there is plain text and
drag.
While dragging, observe that there is no highlighting of the region.
The region used to be highlighted immeadiately.

Release mouse-1: now the region is highlighted.

Click somewhere else in the buffer.  Observe that Emacs highlights the
new region.  Before, a mouse-1 event would dehighlight it and just set
point where the click happened.

This started happening after the refactor in widget-button-click in
8b61e20e4edb9d2f67134bc9f3739f936aafb01c

The reason is that the condition for the when form is evaluating to nil,
skipping all the dispatch of the click when not inside a widget button.
That is, (widget-get button :button-overlay) returns nil here.  I don't
understand why that extra check was added, but this behavior seems
undesirable to me.


In GNU Emacs 28.0.50 (build 71, x86_64-pc-linux-gnu, cairo version 1.15.10)
 of 2020-09-25 built on tbb-desktop
Repository revision: 499848d8407855d8ca24f0c175c602a0f24da074
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 18.04.5 LTS

Configured using:
 'configure --with-x-toolkit=no'

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
GNUTLS LIBXML2 FREETYPE HARFBUZZ ZLIB OLDXMENU 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: Custom

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: (only . t)

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml 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 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 time-date subr-x cus-edit
easymenu cus-start cus-load wid-edit 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 button
loaddefs faces 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 x
multi-tty make-network-process emacs)

Memory information:
((conses 16 72461 7061)
 (symbols 48 8192 1)
 (strings 32 21338 1726)
 (string-bytes 1 670850)
 (vectors 16 12778)
 (vector-slots 8 167810 9017)
 (floats 8 32 53)
 (intervals 56 359 4)
 (buffers 992 12))