bug#40097: 28.0.50; Preferred font ignored for specific charset

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Tue, 17 Mar 2020 18:35:05 +0200, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Sergey Organov <sorganov@gmail.com>
    >> Cc: 40097@debbugs.gnu.org
    >> Date: Tue, 17 Mar 2020 19:12:33 +0300
    >> 
    >> > Can you show all the fonts on your system that have microsoft-cp1251
    >> > as their registry/encoding?  AFAIK, this is done with xlsfonts.
    >> 
    >> Sure:

    Eli> So there's a single font, Terminus, which supports that charset.  I
    Eli> think you can work around this problem locally by adding that font to
    Eli> face-ignored-fonts.

    Eli> We could perhaps introduce a customizable variable that would allow
    Eli> users who want that to disable the preference of charset-supporting
    Eli> fonts when the text has the 'charset' property.  CC'ing Handa-san who
    Eli> could comment on how important is this feature nowadays.

Ah, now I see where this is coming from: I was looking down in font.c,
but this is a fontset.c feature.

Iʼm not sure how useful it is, I donʼt think fontconfig has any notion
of 'charset' beyond 'does this font support this Unicode character'.

Robert