bug#50424: 27.2; Tab bar button mouse face not clearing entirely

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: Juri Linkov <juri@linkov.net>,  Alan Third <alan@idiocy.org>,
>   50424@debbugs.gnu.org
> Date: Tue, 07 Sep 2021 21:02:43 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I've fixed tab-bar.el to request the same margin as specified by
> > tab-bar-button-margin, and I also fixed the code in w32term.c and
> > xterm.c which used the corresponding tool-bar values when tab-bar
> > values should have been used.  This improved the situation to some
> > extent, but we still leave behind an artifact when the mouse moves off
> > the tab-bar button: a 1-pixel vertical line.  I think that's because
> > there's no relief definition in the image, but the value of
> > tab-bar-button-relief is non-zero (and xterm.c/w32term.c use that
> > non-zero value when they redraw the buttons).
> 
> Thanks.  Interestingly enough, I don't see a 1-pixel vertical line when
> the highlight is cleared, but it could be an issue with my display.

Try a larger default font, as in

   emacs -Q -fn "Your Font-20"

where "Your Font" is the font you get by default in Emacs.  I only see
the problem clearly when I use such a large font.

Also try "M-x tab-bar-history-mode RET".