bug#59347: 29.0.50; `:family` face setting ignored

[Gregory Heytings]

> > With current master, the variable-pitch face is realized as follows:
> >
> > - with 1-3: -ADBO-Source Code 
> > Pro-black-normal-normal-*-29-*-*-*-m-0-iso10646-1, which is a monospace font
> >
> > - with 4: -PfEd-DejaVu Sans-bold-normal-normal-*-29-*-*-*-*-0-iso10646-1, which 
> > is a variable pitch font
> >
> > - with 5: -ADBO-Source Code 
> > Pro-semibold-normal-normal-*-29-*-*-*-m-0-iso10646-1, which is again a 
> > monospace font
> >
> > - with 6: -urw-nimbus sans l-regular-r-normal--29-210-100-100-p-158-iso8859-1, 
> > which is a variable pitch font but without anti-aliasing
> >
> > - with 7: -PfEd-DejaVu Sans-regular-normal-normal-*-29-*-*-*-*-0-iso10646-1, 
> > which is a variable pitch font
> >
> > - with 8-9: -ADBO-Source Code 
> > Pro-light-normal-normal-*-29-*-*-*-m-0-iso10646-1, which is again a monospace 
> > font
> >
> > - with 10-11: -PfEd-DejaVu 
> > Sans-ultralight-normal-normal-*-29-*-*-*-*-0-iso10646-1, which is a variable 
> > pitch font
> >
> > That can't be right.  Only 4, 7, and 10-11 correspond to what is 
> > expected for that face, namely a variable pitch font.
>
> Why do you expect to get a variable pitch font?

The variable-pitch face should use a variable pitch font, shouldn't it? 
Unless there are no such fonts installed on the computer of course, in 
which case it could fall back to a monospace font.

> Emacs tries to find a font from the same family, but if that fails for 
> some reason, all bets are off wrt whether the font we find will be 
> variable-pitch or not.  Or what am I missing?

Why should the weight of the default face influence the font selected for 
the variable-pitch face, to the point that even when variable pitch fonts 
are installed on the computer, they are all flatly rejected because they 
do not explicitly support say the 'semi-bold' weight?  The weight of the 
default face should only influence the weight of the other faces, which is 
what it does with the patch.  With a 'semi-bold' default face, a 'bold' 
variable pitch font is a legitimate candidate for the variable-pitch face.