bug#49797: 28.0.50; Setting face to custom fontset doesn't work

[Yuan Fu]

> On Oct 5, 2021, at 12:01 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Tue, 5 Oct 2021 10:31:59 -0700
>> Cc: Kenichi Handa <handa@gnu.org>,
>> 49797@debbugs.gnu.org
>> 
>> Basically, Emacs doesn’t do what it claims to do in the manual, see below 
>> for more explanation.
> 
> It isn't the first time, and the solution could be to fix the docs.

We could, but I think the current behavior is wrong (in the sense that it is 
against what the code is supposed to do, from what I can read). It would be 
worse to ratify and document the wrong behavior.

> 
>> I just want to use different CJK fonts for different faces.
> 
> Why do you need that?  And why specifically for CJK?

Because I only know Chinese? For someone else it could be Arabic characters, 
Japanese hiragana, etc. If you mean why I need more than one font for CJK, it’s 
the same reason for why I need more than one Latin font—because they look 
different and has different use.

> 
>> I think you would agree that, for non-Latin speakers, using different fonts 
>> for different faces (for non-Latin) characters is an important feature.
> 
> No, I don't think I understand why.
> 
> And the usual way to do this is to request a font family or foundry in
> the face spec, not via fontsets.  Doesn't that work for some reason?

Because I want to use different font for different characters for that face, 
isn’t that the whole point of fontsets? Maybe it is easier to understand this 
way:

variable-pitch -> :font "fontset-serif” -> - Latin: Charter
                                           - CJK: Source Han Serif
default -> :font "fontset-default" -> - Latin: SF Mono
                                      - CJK: Source Han Sans

Currently I am unable to use Source Han Serif for CJK characters for 
variable-pitch face (without the ugly solution I mentioned previously).

Yuan