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

[Gregory Heytings]

> I can see reasons why some users would consider it not just reasonable 
> but "The Right Thing" in their specific situation.  The argument would 
> be as simple as "Which part of `bold` don't you understand?" and would 
> fundamentally be just the same as the argument that we should not use a 
> monospace font when the "sans-serif" family is specified.

This (a user choosing a font for the default face that has no bold and/or 
italic variant) is really an exceptional case, in fact it wasn't easy to 
find one to test that case.  So I think the answer "The font you have 
chosen for the default (or variable-pitch, or...) face has no bold (or 
italic, or...) variant" is more than satisfactory for such exceptional 
cases, and I think that adding more complexity to an already rather 
complex code to handle that exceptional case better is not reasonable. 
Also, I'm pretty sure that with the better solution you suggest, other 
users would complain and ask "why is Emacs using so many different 
fonts?".  Again, this is just my opinion.

Perhaps the most reasonable thing to do here would be to display warnings 
in such cases.