bug#33232: `gnus-summary-line-format' padding doesn’t work in gui when there are multiple-column-width characters

[Eli Zaretskii]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Date: Thu, 01 Nov 2018 16:52:32 -0700
> Cc: 33232@debbugs.gnu.org
> 
> >>> Given this (rectangular) excerpt from my bug-gnu-emacs summary:
> >>>> …01-nov…[-> 33224@debbugs.gnu.org        ] bug#33224: `message-simpli…
> >>>> …01-nov…[Noam Postavsky                  ] bug#33225: [debbugs.el] Do…
> >>>> …01-nov…[-> Noam Postavsky               ]  bug#33225: [debbugs.el] D…
> >>>> …01-nov…[積丹尼 Dan Jacobson             ] bug#33226: chromium, firef…
> >>>
> >>> On my system (Debian, with Xorg, i3, GUI Emacs), the last line has its
> >>> “]” sooner than the others.  This is because `gnus-correct-length'
> >>> (along with `char-width') says each of the first three characters is
> >>> two-columns wide: but under GUI, this is untrue, as these three
> >>> collectively form exactely 5 columns (and not six, as would calculate
> >>> `gnus-correct-length').
> >>
> >> Someone just reported something similar on the org list, that
> >> `string-width' doesn't return the actual width occupied by the string,
> >> which you'd think would be the whole point.
> >
> > See Bug#31588, the width of these characters depends on the font, so
> > string-width (which works only on a string) can't give the right answer.
> > Or, from another point of view, it's the font's fault for being too
> > narrow on these characters.
> 
> Yeah, I figured it was probably a font issue, but still it's kind of
> misleading to have a function that *sounds* like it's going to handle
> the font issue, but doesn't.

The only reliable way of getting pixelwise alignment in GUI frames is
to use the :align-to display spec, or other related display property
specs that provide pixelwise width and alignment.